Phosphorus activators contribute to legacy phosphorus availability in agricultural soils: A review

Shallow groundwater table fluctuations: A driving force for accelerating the migration and transformation of phosphorus in cropland soil

The accumulation of phosphorus (P) in soil profiles of intensive cropland and the losses caused by runoff and leaching have been widely concerned. However, the loss of soil P due to shallow groundwater table (SGT) fluctuations driven by seasonal changes is often neglected, and the migration and transformation mechanisms of soil P are still unclear. On the basis of the long-term monitoring of cropland soil P accumulation and SGT fluctuations around Erhai Lake, the characteristics of soil P loss driven by SGT fluctuations and the corresponding mechanisms were investigated through a 260-day microcosm experiment. The results revealed that the fluctuations in SGT significantly changed the content and form of P in the soil profile. The soil P loss mainly occurred in dissolved form, mainly involving inorganic P, accounting for 75 %. Compared with those under continuous saturated conditions, soil total P (TP) release during SGT fluctuations significantly increased by 9.5 %, and soil TP storage was reduced by 2 %. SGT fluctuations increased the complexity of microbial networks in the soil profile, stimulated the expression of functional genes for soil P cycling, and promoted soil organic P mineralization. The SGT fluctuations caused an increase in the soil TP loss from cropland to 88.5 kg/ha, which was 70 and 25 times greater than that via leaching and runoff, respectively. These results indicated that SGT fluctuations accelerated the P loss from soil profile of cropland. Therefore, some measures should be comprehensively applied to prevent its loss, such as reducing external P input, improving surface soil P storage capacity and soil P utilization efficiency, reducing surface P leaching into deep soil, and reducing P accumulation in deep soil profiles.

Regulation of iron homeostasis by IMA1 and bHLH104 under phosphate starvation in Arabidopsis

Phosphate (Pi) starvation disrupts iron (Fe) nutrition at phenotypic, physiological, and transcriptional levels. The alteration of Fe homeostasis plays an important role in the adaptive response to Pi starvation. However, utilizing the antagonistic mechanism between P and Fe nutrition to improve adaptation to Pi deficiency in plants still needs to be explored. Here, we constructed inducible and constitutive expression of Fe regulators IMA1 and bHLH104, driven by the CaMV 35S promoter and the promoters of Pi-starvation responsive genes (proIPS1 and proPHT1;4), respectively. The Fe regulators bHLH104 and IMA1 were successfully upregulated in a constitutive and inducible manner under Pi deficiency in these transgenic plants. Regardless of Pi condition, upregulation of bHLH104 and IMA1 had no significant influence on primary root length or root Fe distribution. Nevertheless, the upregulation of bHLH104 and IMA1 induced Fe accumulation in the shoots of transgenic plants, particularly under Pi deficiency. Correspondingly, shoot chlorophyll content increased under Fe deficiency in the transgenic plants. In addition, in situ FeIII distribution revealed that bHLH104 and IMA1 likely interfere with Fe distribution through different pathways. The inducible upregulation of IMA1 significantly led to shoot zinc (Zn) accumulation under Pi deficiency, while the inducible upregulation of bHLH104 resulted in a decrease in shoot Zn and manganese (Mn) contents. The enhancement of Fe and Zn accumulation under the inducible expression of IMA1 under Pi deficiency was attributed to the induction of high expression of key Fe-uptake genes FRO2 and IRT1. The expression of the Zn and Mn uptake genes was also affected in these transgenic plants, which correlated with the changes in Zn and Mn contents. Overall, IMA1 is an excellent candidate for enhancing plant Fe and Zn accumulation and can be specifically induced under conditions of Pi deficiency.

Enhanced cadmium tolerance in perennial ryegrass via exogenous application of Enterobacter hormaechei strain X20

Cadmium (Cd) contamination in soils poses a critical environmental challenge, jeopardizing both agricultural productivity and food safety. The utilization of plant growth-promoting rhizobacteria (PGPR) emerges as a promising strategy for mitigating the adverse effects of heavy metal stress on plant health and development. This study investigates the effectiveness of Enterobacter hormaechei X20 in enhancing Cd tolerance in perennial ryegrass, a species renowned for its phytoremediation potential. Strain X20 demonstrated multiple PGPR traits, including phosphate solubilization, indole-3-acetic acid (IAA) production, and siderophore secretion. Under Cd stress, X20 significantly stimulated plant growth, elevated canopy height, and preserved leaf water content. Additionally, X20 inoculation enhanced Cd uptake and reestablished ion homeostasis by augmenting Fe2+, Cu2+, Zn2+, and Mn2+ levels. It also improved photosynthetic efficiency, particularly by optimizing PSII activity, and strengthened antioxidant defense, alleviating oxidative stress. Metabolomic analysis revealed significant modulations in amino acid and sugar metabolism, marked by increased in serine and glycine levels under Cd stress. Furthermore, fructose and glucose levels rose, while sucrose levels declined, reflecting metabolic reprogramming that facilitates stress adaptation. These findings suggest that Enterobacter hormaechei X20 holds great promise as a bioinoculant for enhancing phytoremediation efficiency and plant resilience in Cd-contaminated soils, providing a sustainable strategy for managing heavy metal pollution in agriculture.

Simultaneous stabilization of cadmium and arsenic in soil by humic acid and mechanically activated phosphate rock

Competition between phosphorus and arsenic limits the application of phosphate materials in soil remediation. However, it is possible to simultaneously stabilize arsenic and cationic metals by sensible use of phosphate's solubility. In this study, ball-milling and humic acid (HA) activated phosphate rock (PR) were used to stabilize cadmium (Cd) and arsenic (As) in soil. After 30 days of treatment with ball-milling and 5 % humic acid-activated phosphate rock (BMP-HA), the leaching concentrations of Cd and As in the soil decreased from 0.12 mg/L and 0.11 mg/L to 0.0086 mg/L and 0.019 mg/L, respectively. The availability of Cd and As was significantly reduced after BMP-HA treatment. The acid-soluble fraction of Cd decreased from 16.30 % to 1.22 %, indicating its transformation into more stable forms. The water-soluble and surface-adsorbed fraction of As decreased to 0.11 %, while the Ca-associated fraction of As increased from 25.87 % to 31.41 %. Ball-milling increased the specific surface area of PR, enhancing the adsorption and surface complexation of Cd. The addition of humic acid facilitated the dissolution of PR. However, the phosphate release rate in BMP-HA was insufficient to activate As. Meanwhile, the released Ca bound with As, further reducing its availability. Overall, BMP-HA proves to be an effective strategy for remediating cadmium and arsenic-contaminated soils.

Temporal shifts in the phosphate mobilising bacterial community reveal contrasting succession patterns in response to different phosphorus sources

BACKGROUND

Phosphate mobilising bacteria (PMB), such as phoD- and pqqC-harbouring bacteria, play a crucial role in mobilising insoluble phosphorus (P) in soil through the secretion of alkaline phosphatase and organic acids.

OBJECTIVES

To evaluate the succession pattern of PMB communities in response to different insoluble P sources.

METHODS

Five P source treatments, including the addition of KH2PO4 (PDP), FePO4 (FEP), Ca3(PO4)2 (TCP), lecithin (LEC), and a negative control, were established in the soil in a microcosmic system. Subsequently, phoD- and pqqC-harbouring bacterial communities were investigated by sequential sampling and high-throughput sequencing. In addition, PMB strains were isolated from these five treatments, and their phosphate mobilising activity was further analysed.

RESULTS

The effect of the insoluble organic P source (LEC) on the succession of PMB communities consistently exceeded that of insoluble inorganic P (Pi) sources (FEP and TCP). A successively enhanced succession and a successively diminishing succession were observed in PMB communities in FEP and TCP, respectively. Furthermore, the soil AP content significantly increased with incubation time in LEC and FEP. Most of the variation in phoD- and pqqC-harbouring bacterial communities was explained by all P fractions, respectively, while Fe-P and stable organic P fractions determined the PMB communities. Insoluble Pi sources, particularly FEP, tended to enrich more high-performance PMB strains for Fe-P.

CONCLUSION

This study firstly reveals the dynamic response of PMB communities to different insoluble P sources at the community level in a short time scale and identifies key PMB taxa that respond to different insoluble P sources, particularly Fe-P. It is also the first to provide community evidence and a feasible method for obtaining high-performance PMB strains for Fe-P in subtropical acidic red soils through directed enrichment culture.

Effect of lignin carbon material on phosphorus solubilisation performance of Bacillus megaterium

Secondary salinisation significantly compromises soil quality because of the over-application of chemical fertilisers. The combined application of biochar and microorganisms enhanced soil physicochemical properties and improved soil remediation efficiency. However, different types of biochar had varying effects on microbial growth and reproduction. A phosphate-solubilising bacterial agent (BM-LPC) was obtained by low-temperature carbonisation/activation lignin-based porous carbon (LPC) in situ culture/adsorption Bacillus megaterium (BM). The maximum soluble phosphorus capacity of BM-LPC was 744.29 mg/L when 1 % LPC was added. This was a 22 % increase compared with BM alone. The maximum adsorption of BM by LPC was 3.66 × 109 colony-forming units (CFU)/g. At 150 days, the viable bacterial count of BM-LPC was 2.09 × 109 CFU/g. The abundances of -OH, -COOH, -NH2, and CO groups on the surface of LPC provided a stable environment for BM, which in turn, enhanced the solubilisation of phosphorus and extended the viability of BM. The findings of this study can help increase the added value of industrial lignin and provide a theoretical basis for soil remediation research.

Bacterial activation level determines Cd(II) immobilization efficiency by calcium-phosphate minerals in soil

Soil mineral properties significantly influence the mobility of Cd(II) within the soil matrix. However, the limited understanding of how microbial metabolism affects mineral structure at the microscale poses challenges for in situ remediation. Here, we designed a model calcium-phosphate system in a urea-rich environment to explore the impact of different microbial activation levels on Cd(II) fixation at mineral interfaces. Findings indicate that bacteria affected the morphological structure of the minerals and the amount of carbonate incorporation (average 5.4 %), thereby enhancing Cd(II) immobilization capacity (up to 9.6 times). This process is influenced by the intensity of bacterial activation, as reflected in their urease activity. Extracellular substances secreted by bacteria are also essential for activating minerals, contributing to a sustained decrease in their surface potential. The introduction of activated minerals in potting experiments markedly stimulated the soil urease activity, promoting the enrichment of functional bacteria and facilitating Cd(II) passivation, thereby reducing Cd(II) uptake by vegetables. An extensive soil survey further corroborated a linkage between soil total phosphorus and urease activity, indirectly emphasizing the universality of phosphate mineral-urease microbial interactions and their critical role in the morphological transformation of Cd(II). Our findings highlight the functional dynamics of urease microorganisms in shaping soil mineral landscapes and regulating heavy metal mobility, with broad implications for soil microscale remediation strategies.

Natural variation in the GmVPE1 promoter contributes to phosphorus re-translocation to seeds and improves soybean yield

Phosphorus (P) is an essential yet frequently deficient plant nutrient. Optimizing P distribution and recycling between tissues is vital for improving P utilization efficiency (PUE). Yet, the mechanisms underlying the transport and re-translocation of P within plants remain unclear. Here, wide-ranging natural diversity in seed P allocation and positive correlations among yield traits were found using 190 soybean accessions in field trials. Among them, the P-efficient genotype BX10 outperformed BD2 in assessments of PUE that were largely explained through differences in P redistribution from pods to seeds under low P stress. Pods of BX10 were therefore subjected to transcriptome analysis, and GmVPE1 was identified as a vacuolar Pi transporter to investigate further. Importantly, significant DNA polymorphism in GmVPE1 promoter regions was remarkably associated with seed weight among soybean accessions grown on P-deficient soils. Further analyses suggested that mRNA abundance of GmVPE1 in haplotype 2 (Hap) is significantly higher than that GmVPE1Hap1. GmVPE1 was highly upregulated by P deficiency and preferentially expressed in pods, seeds, and seed coats, which was consistent with GUS staining using transgenic soybean plants carrying pGmVPE1Hap2::GUS. Near-isogenic lines carrying the GmVPE1Hap2 allele, along with stable transgenic soybeans overexpressing GmVPE1 in a GmVPE1Hap1 background, had increases in PUE, more seed setting, and greater yields in both greenhouse and field trials than control plants. In summary, natural variation among GmVPE1 alleles determines genetic expression and subsequent P re-translocation phenotypes, which impacts PUE and yield, and thereby makes this an important genetic resource for soybean molecular breeding.

Mechanisms of microplastic generation from polymer-coated controlled-release fertilizers (PC-CRFs)

Polymer-coated controlled-release fertilizers (PC-CRFs) are valued for nutrient efficiency, but concerns remain about the long-term impacts of their plastic coatings on soil health. This study investigates the physicochemical characteristics of two commercially available PC-CRFs, type A and B, and their changes during nutrient release. Accelerated nutrient release experiments were conducted for 25 d in ultrapure water (free water) and saturated soil with five wet-dry cycles. Total phosphorus and total nitrogen release were measured, with lower concentrations found in soil column effluent compared to water. Additionally, studying microplastic (MP) release from type A PC-CRFs during nutrient release showed that a significantly greater number of MPs were released in the soil column than in water. The results also indicated a preferential migration of smaller MPs to the deeper layers of the soil column. Microscopic pores and cracks were observed through surface morphology analysis, likely caused by osmotic pressure during nutrient release, potentially contributing to MP generation. Mechanical degradation of the type A PC-CRF microcapsules was assessed through surface wear and shear tests to simulate the forces exerted by soil particles and agricultural machinery. Our results showed that longer surface wear duration increased the number of generated MPs, while higher loading in surface wear experiments resulted in a larger median diameter of the MPs.

Reduce the application of phosphorus fertilizer in peanut fields and improve its efficiency by using iron modified biochar to adsorb phosphorus recovery products

Introduction

To address the scarcity of agricultural phosphorus (P) fertilizers and reduce phosphorus accumulation in wastewater, this study employed iron-modified biochar (Fe-B) to adsorb phosphorus from water. The phosphorus-loaded iron-modified biochar (Fe-BP) was subsequently applied to peanut fields. Batch experiments were conducted to determine the optimal adsorption parameters and mechanism of Fe-B for phosphate ions (PO4 3-).

Methods

The field experiment utilized a randomized complete block design, comprising the following treatments: no biochar and no P fertilizer (B0P0), no biochar with conventional phosphate fertilizer (B0P1, CK, P2O5 at 144 kg ha-1), biochar with CK (B1P1), Fe-B with CK (FeB-P1), phosphorus-loaded Fe-B with CK (FeBP-P1), and phosphorus-loaded Fe-B with two-thirds CK (FeBP-P2, P2O5 at 96 kg ha-1).

Results

The results demonstrated that the biochar dosage of 0.05 g (2 g L-1) results in a phosphate removal rate exceeding 80%. Optimal adsorption efficiency occurs within a pH range of 6-9, with a sharp decline observed at pH values above 10. The presence of NO3 -, Cl-, and SO4 2- does not significantly affect the phosphate adsorption capacity of Fe-B, unlike HCO3 - and CO3 2-, which reduce it. After the fifth desorption and recycling process, the adsorption capacity of the biochar decreased to 24%. The peanut yield in the FeB-P1 treatment was 50.8% higher than that in the FeBP-P2 treatment. While the phosphorus recovery efficiency (REP) does not significantly differ between FeBP-P2 and B1P1 treatments, both are superior to B0P1. Moreover, FeBP-P2 facilitated the available phosphorus concentration in the root zone.

Discussion

Overall, phosphorus-loaded iron-modified biochar reduced the required amount of phosphorus fertilizer, maintain peanut yield, and enhanced phosphorus fertilizer utilization efficiency.

Multiomics dissection of Brassica napus L. lateral roots and endophytes interactions under phosphorus starvation

Many plants associate with endophytic microbes that improve root phosphorus (P) uptake. Understanding the interactions between roots and endophytes can enable efforts to improve P utilization. Here, we characterize the interactions between lateral roots of endophytes in a core collection of 50 rapeseed (Brassica napus L.) genotypes with differing sensitivities to low P conditions. With the correlation analysis result between bacterial abundance and plant physiological indices of rapeseeds, and inoculation experiments on plates and soil, we identify one Flavobacterium strain (C2) that significantly alleviates the P deficiency phenotype of rapeseeds. The underlying mechanisms are explored by performing the weighted gene coexpression network analysis (WGCNA), and conducting genome-wide association studies (GWAS) using Flavobacterium abundance as a quantitative trait. Under P-limited conditions, C2 regulates fatty acid and lipid metabolic pathways. For example, C2 improves metabolism of linoleic acid, which mediates root suberin biosynthesis, and enhances P uptake efficiency. In addition, C2 suppresses root jasmonic acid biosynthesis, which depends on α-linolenic acid metabolism, improving C2 colonization and activating P uptake. This study demonstrates that adjusting the endophyte composition can modulate P uptake in B. napus plants, providing a basis for developing agricultural microbial agents.

Combined use of arbuscular mycorrhizal fungi and alkaline lignin enhance phosphorus nutrition and alleviate cadmium stress in lettuce (Lactuca sativa L.)

The excessive application of phosphorus (P) fertiliser and its poor utilisation efficiency have led to significant amounts of P being retained in agricultural soils in unavailable forms. The application of alkaline lignin to soil and its inoculation with arbuscular mycorrhizal fungi (AMF) have both been shown to improve plant P nutrition. However, their combined effects on soil P transformation remain unclear, particularly in cadmium (Cd)-contaminated soils. A potting experiment was conducted to examine the combined effects of AMF and alkaline lignin on soil P and Cd bioavailability and on the uptake of P and Cd by lettuce (Lactuca sativa L.) that were grown for 56 d in a growth chamber. Combined AMF and alkaline lignin treatment increased soil P availability and alkaline phosphatase activity. It furthermore increased bioavailable Cd concentrations of rhizosphere and bulk soils by 48 % and 72 %, respectively, and the Cd concentration in roots by 85 %, but the Cd concentration was not affected in the edible parts (shoots) of the lettuce. Moreover, the combined treatment increased shoot biomass by 26-70 % and root biomass by 99-164 %. Our findings suggested that the combined use of AMF and alkaline lignin mobilised both P and Cd in soil but did not increase the accumulation of Cd in the shoots of plants growing in Cd-contaminated soils, these results would provide guideline for increasing Cd tolerance of plants and their yield.

Soil P-stimulating bacterial communities: response and effect assessment of long-term fertilizer and rhizobium inoculant application

BACKGROUND

Phosphorus (P) plays a vital role in plant growth. The pqqC and phoD genes serve as molecular markers for inorganic and organic P breakdown, respectively. However, the understanding of how P-mobilizing bacteria in soil respond to long-term fertilization and rhizobium application is limited. Herein, soil that had been treated with fertilizer and rhizobium for 10 years was collected to investigate the characteristics of P-mobilizing bacterial communities. Five treatments were included: no fertilization (CK), phosphorus fertilizer (P), urea + potassium fertilizer (NK), NPK, and PK + Bradyrhizobium japonicum 5821 (PK + R).

RESULTS

The soybean nodule dry weight was highest in the P treatment (1.93 g), while the soybean yield peaked in the PK + R treatment (3025.33 kg ha- 1). The abundance of the pqqC gene increased in the rhizosphere soil at the flowering-podding stage and in the bulk soil at the maturity stage under the P treatment, while its abundance increased in the bulk soil at the flowering-podding stage and in the rhizosphere soil at the maturity stage under the PK + R treatment. The abundance of the phoD gene was enhanced in the bulk soil at the flowering-podding stage under the PK + R treatment. The Shannon and Ace indexes of pqqC- and phoD-harboring bacteria were higher in the rhizosphere soil at maturity under the PK + R treatment compared to other treatments. Furthermore, a comprehensive analysis of the neutral community model and co-occurrence pattern demonstrated that the application of P fertilizer alone led to an increase in the distribution and dynamic movement of pqqC-harboring bacteria, but resulted in a decrease in complexity of network structure. On the other hand, rhizobium inoculation enhanced the distribution and dynamic movement of phoD-harboring bacteria, as well as the stability and complexity of the network structure. Pseudomonas and Nitrobacter, as well as Steptomyces, Stella, and Nonomuraea, may be crucial genera regulating the composition and function of pqqC- and phoD-harboring communities, respectively.

CONCLUSIONS

These findings affirm the crucial role of fertilization and rhizobium inoculation in regulating pqqC- and phoD-harboring bacterial communities, and highlight the significance of long-term phosphate-only fertilization and rhizobium inoculation in enhancing dissolved inorganic phosphorus and mineralized organophosphorus, respectively.

Relationships between soil test phosphorus and county-level agricultural surplus phosphorus

National nutrient inventories provide surplus phosphorus (P) estimates derived from county-scale mass balance calculations using P inputs from manure and fertilizer sales and P outputs from crop yield data. Although bioavailable P and surplus P are often correlated at the field scale, few studies have investigated the relationship between measured soil P concentrations of large-scale soil testing programs and inventory-based surplus P estimates. In this study, we assessed the relationship between national surplus P data from the NuGIS dataset and laboratory-measured soil test phosphorus (STP) at the county scale for Arkansas, North Carolina, and Oklahoma. For optimal periods of surplus P aggregation, surplus P was positively correlated with STP based on both Pearson (Arkansas: r = 0.65, North Carolina: r = 0.45, Oklahoma: r = 0.52) and Spearman correlation coefficients (Arkansas: ρ = 0.57, North Carolina: ρ = 0.28, and Oklahoma: ρ = 0.66). Based on Pearson correlations, the optimal surplus P aggregation periods were 10, 30, and 4 years for AR, NC, and OK, respectively. On average, STP was more strongly correlated with surplus P than with individual P inventory components (fertilizer, manure, and crop removal), except in North Carolina. In Arkansas and North Carolina, manure P was positively correlated with STP, and fertilizer P was negatively correlated with STP. Altogether, results suggest that surplus P moderately correlates with STP concentrations, but aggregation period and location-specific factors influence the strength of the relationship.

Unearthing the soil-bacteria nexus to enhance potassium bioavailability for global sustainable agriculture: A mechanistic preview

Established as a plant macronutrient, potassium (K) substantially bestows plant growth and thus, global food production. It is absorbed by plants as potassium cation (K+) from soil solution, which is enriched through slow-release from soil minerals or addition of soluble fertilizers. Contribution of bioavailable K+ from soil is usually insignificant (< 2 %), although the earth's crust is rich in K-bearing minerals. However, K is fixed largely in interlayer spaces of K-bearing minerals, which can be released by K-solubilizing bacteria (KSB) such as Bacillus, Pseudomonas, Enterobacter, and Acidithiobacillus. The underlying mechanisms of K dissolution by KSB include acidolysis, ion exchange reactions, chelation, complexolysis, and release of various organic and inorganic acids such as citric, oxalic, acetic, gluconic, and tartaric acids. These acids cause disintegration of K-bearing minerals and bring K+ into soil solution that becomes available to the plants. Current literature review updates the scientific information about microbial species, factors, and mechanisms governing the bio-intrusion of K-bearing minerals. Moreover, it explores the potential of KSB not only for K-solubilization but also to enhance bioavailability of phosphorus, nitrogen, and micronutrients, as well as its other beneficial impact on plant growth. Thus, in the context of sustainable agricultural production and global food security, utilization of KSB may facilitate plant nutrient availability, conserve natural resources, and reduce environmental impacts caused by chemical fertilizers.

Hydrogeochemical evolution and heavy metal characterization of groundwater from southwestern, Nigeria: An integrated assessment using spatial, indexical, irrigation, chemometric, and health risk models

This study examines the hydrogeochemical and heavy metal parameters of groundwater in Ojo District to determine its suitability for use, potential sources, and human health implications. Ten groundwater samples were assessed, and hydrogeochemical modelling was performed via the Aquachem software. The chemical ions were in the following order: EC > (107.78-448.65 μS/cm) > TDS (182.02-320.77 mg/l) > TH (46.22-182.45 mg/l) > pH (5.55-6.35); HCO3 - (64.13-125.82 mg/l) > Na+ (36.87-96.49 mg/l) > Ca2+ (47.65-58.88 mg/l) > SO4 2- (19.94-53.67) > NO3 - (15.55-44.25 mg/l) > Cl- (20.43-27.16 mg/l) > Mg2+ (11.09-16.87 mg/l) and K+ (2.55-7.86 mg/l). The concentrations of heavy metals in groundwater were in the range of: Fe (0.11-0.27 mg/l) > Mn (0.003-0.16 mg/l) > Ni (0.05-0.12 mg/l) > Zn (0.003-0.05 mg/l) > Pb (0.001-0.03 mg/l) > As (0.001-0.005 mg/l) > Cr (0.002-0.005 mg/l) > Cd (0.001-0.003 mg/l) and Cu (0.001-0.0002 mg/l), with Pb, Mn, and Ni exceeding their allowable limits. The Schoeller and Gibbs plots revealed that the major mechanisms controlling the aquifer groundwater in Ojo region are geological rock weathering and mineralization, with a minimal influence of saltwater intrusion. The piper trilinear diagram also revealed that none of the cation was dominant while the anions were strongly dominated by HCO3 - (weak acids). The hydrogeochemical facies which describes the geochemical characteristics of the groundwater were classified into 3 types; "Ca2+-Mg+-HCO3 - (65 %)", "mixing zones (30 %)", and "Na+-K+-Cl--HCO3 - (5 %)". The hydrogeochemical modelling revealed that the groundwater is characterized by forward cation exchange, while rock-water interactions (silicate dissolution) were heavily involved in the geochemical processes. The single pollution index showed that Pb, Ni, and Mn contributed significantly to contamination, and the multi-pollution indices showed that the groundwater was slightly-moderately polluted. The integrated groundwater quality index revealed that only 10 % were clean, 50 % were poor or moderately unclean, 30 % were highly unclean, and only 10 % were extremely unclean (unfit for utilization). The water pollution index showed that 70 % of the groundwater was good. The irrigation indices suggest that the groundwater would enhance soil quality and support plant growth. Multivariate analysis revealed that the groundwater is being influenced by geogenic factors and anthropogenic activities. The health risk assessment (Hazard Quotient and Hazard Index) showed that exposure of adults to the investigated groundwaters could result in noncarcinogenic adverse effects. The cancer risk values also exceeded the minimum limit (1.0 x 10-6) and thresholds (1.0 x 10-4) for adults, indicating the carcinogenic potential of the groundwater.

Halotolerant phosphate solubilizing bacteria isolated from arid area in Tunisia improve P status and photosynthetic activity of cultivated barley under P shortage

Forty-seven (47) bacterial strains were isolated from soil of Gabes (an arid region in southern Tunisia) and were screened for their ability to produce Indole-3-Acetic Acid (IAA) and to solubilize phosphate (P). The characterization and molecular identification of the most successful P-solubilizing bacteria (PSB) were then carried out. When grown on suitable artificial media, the most salt-tolerant strains also showed the highest P solubilization capacity (up to 126.8 μg ml-1 of released phosphorus after 7 day incubation) and the strongest ability to produce IAA (up to 101.86 μg ml-1 after 3 day incubation). Overall, bacterial isolates displayed a different tolerance to varying pH, temperatures, and salinity. The molecular identification revealed that 11 strains belonged to three genera: Bacillus, Pseudomonas and Mesorhizobium. Inoculation of barley with P-solubilizing bacteria under tricalcium phosphate-induced P shortage significantly improved plant growth (biomass, shoot height, and root length) together with increasing total chlorophyll contents and photosynthetic activity. This was concomitant with (i) higher P uptake and translocation and (ii) increased phosphorus absorption and utilization efficiencies (PAE and PUE), which is indicative of a better plant P nutrition under P scarcity. Taken together, we provide strong arguments showing that bacteria native to extreme environments display PSB potential making them promising candidates to mitigate low Pi availability for crop plants.

Phosphorus-loaded coconut biochar: A novel strategy for cadmium remediation and soil fertility enhancement

The management of cadmium (Cd) contamination in soils poses a significant environmental challenge. This study investigates the effectiveness of phosphorus (P)-loaded coconut biochar, synthesized at various pyrolysis temperatures (450°C, 500°C, 550°C, and 600°C), in immobilizing Cd and enhancing P availability in soil environments. The biochar underwent a series of treatments including activation and P enrichment, followed by incubation trials to evaluate its performance in Cd immobilization and P bioavailability enhancement across varying soil concentrations (0.5 %, 1.0 %, and 2.0 %) over time periods of 15, 30, and 45 days. Remediation progress was monitored using phytotoxicity assessments with radish (Raphanus sativus) root length as a bioindicator, supplemented by urease activity analyses. Notably, the activation process increased the P loading capacity of biochar produced at 450°C, 500°C, and 550°C by 54.6 %, 72.4 %, and 51.8 %, respectively, while reducing the P retention capacity of biochar prepared at 600°C by 31.0 %. The biochar activated at 550°C presented the highest efficiency in remediating Cd-contaminated soils. Key findings indicate that the enhanced specific surface area and oxygenated functional group content of the activated biochar facilitated Cd adsorption and P uptake. The P-loaded biochar exhibited a substantial adsorption capacity for Cd, particularly effective at lower concentrations, rendering it highly suitable for soil remediation purposes. Additionally, the study revealed that the application of biochar led to an increase in soil pH, resulting in precipitation of Cd as hydroxide species and formation of insoluble complexes with phosphate ions, thereby reducing its bioavailability. In summary, incorporating P-loaded biochar into soil significantly improved soil quality and enhanced Cd passivation in contaminated soils. The utilization of biochar produced at 550°C, which exhibited optimal performance, suggests a practical and sustainable approach for soil remediation. Future research endeavors should prioritize the refinement of the biochar production process to enhance cost-effectiveness while maintaining high P loading efficiency.

The role of proton excreted by Advenella kashmirensis DF12 during ammonium assimilation in phosphate solubilization

Phosphate-solubilizing bacteria (PSB) can solubilize soil fixed phosphorus (P) to plant available forms. In previous studies, the mechanisms of inorganic phosphate solubilization by PSB mostly focused on the acidolysis of organic acids. Here we screened a highly efficient PSB, Advenella kashmirensis DF12, with the maximum P solubilization of 590 mg L- 1 at 6 days. In addition to its P solubilizing ability, DF12 also showed a tolerance to pH from 5 to 10 and a nitrogen fixation potential. The multiple functions of DF12 and its wide adaptability to various environmental conditions make it a promising biofertilizer candidate. The combined analysis of extracellular metabolites and intracellular metabolome data revealed that the production of organic acid (mainly gluconic acid) is not the only mechanism of P solubilized by DF12, the solubilized P content was not correlated with the gluconic acid concentration but was in a highly significant positive correlation with proton concentration, extrusion of proton during NH4+ assimilation plays a key role in phosphate solubilization. Moreover, the contribution of NH4+ assimilation to phosphorus solubilization is generally present in PSB. Therefore, we proposed that applying ammonium fertilizer in P-deficient soil is more appropriate, it can not only supplement nitrogen fertilizer, but also enhance P use efficiency, which contributes to worldwide fertilizer use reduction and efficiency improvement.

Isolation and identification of plant growth-promoting rhizobacteria from Spinifex littoreus in Parangkusumo Coastal Sand Dunes, Indonesia

Utilizing coastal land for agriculture presents challenges such as low water content, high soil salinity, and low organic compound content. To support plant growth under these conditions, biofertilizers composed of plant growth promoting Rhizobacteria (PGPR), especially those inhabiting coastal areas, are needed. The Parangkusumo sand dunes on the southern coast of Java, Indonesia, is a unique coastal ecosystem characterized by arid conditions, high temperatures, and high soil salinity. To date, no studies have reported the isolation of PGPR from this ecosystem. This study is the first to isolate and identify PGPR associated with Spinifex littoreus, a dominant plant species in the Parangkusumo sand dunes, which are adapted to the harsh condition of Parangkusumo sand dunes. Ten rhizobacterial isolates were obtained, with five identified as members of the Bacillaceae family. All isolates demonstrated phosphate solubilization activity, while seven exhibited cellulolytic activity. One isolate, Priestia aryabhattai strain 2, notably showed phosphate solubilization and nitrogen fixation activities. The findings of this PGPR activity screening offer valuable insights for developing biofertilizers tailored for coastal agricultural applications.

Effects of calcium phosphate and phosphorus-dissolving bacteria on microbial structure and function during Torreya Grandis branch waste composting

BACKGROUND BURKHOLDERIA: is a phosphorus solubilizing microorganism discovered in recent years, which can dissolve insoluble phosphorus compounds into soluble phosphorus. To investigate the effects of Burkholderia and calcium phosphate on the composting of Torreya grandis branches and leaves, as well as to explain the nutritional and metabolic markers related to the composting process.

METHODS

In this study, we employed amplicon sequencing and untargeted metabolomics analysis to examine the interplay among phosphorus (P) components, microbial communities, and metabolites during T. grandis branch and leaf waste composting that underwent treatment with calcium phosphate and phosphate-solubilizing bacteria (Burkholderia). There were four composting treatments, 10% calcium phosphate (CaP) or 5 ml/kg (1 × 108/ml Burkholderia) microbial inoculum (WJP) or both (CaP + WJP), and the control group (CK).

RESULTS

The results indicated that Burkholderia inoculation and calcium phosphate treatment affected the phosphorus composition, pH, EC, and nitrogen content. Furthermore, these treatments significantly affected the diversity and structure of bacterial and fungal communities, altering microbial and metabolite interactions. The differential metabolites associated with lipids and organic acids and derivatives treated with calcium phosphate treatment are twice as high as those treated with Burkholderia in both 21d and 42d. The results suggest that calcium phosphate treatment alters the formation of some biological macromolecules.

CONCLUSION

Both Burkholderia inoculation and calcium phosphate treatment affected the phosphorus composition, nitrogen content and metabolites of T. grandis branch and leaf waste compost.These results extend our comprehension of the coupling of matter transformation and community succession in composting with the addition of calcium phosphate and phosphate-solubilizing bacteria.

Differential responses of soil phosphorus fractions to varied nitrogen compound additions in a meadow steppe

Nitrogen (N) addition can greatly influence soil inorganic phosphorus (Pi) and organic phosphorus (Po) transformations. However, whether and how the N compound forms may differentially affect the soil P fractions remain unclear. Here, we investigated the responses of soil Pi (labile Pi, moderately-occluded Pi, and recalcitrant Pi) and Po fractions (labile Po and stable Po) to varying addition rates of three N compounds ((NH4)2SO4, NH4NO3, and urea) in a meadow steppe in northern China. Our studies revealed that with increasing N addition rate, soil labile and moderately-occluded Pi increased, accompanied by decreases in soil recalcitrant Pi. This shift was attributed to N-induced soil acidification, which accelerated the conversion of recalcitrant Pi into labile and moderately-occluded Pi. Soil labile Po decreased with increasing rate of N addition, whilst soil stable Po was not affected. Regardless of the compound forms, N addition increased soil Olsen-P, suggesting a potential alleviation of P limitation in this grassland ecosystem. The effect of N addition on soil labile Pi was significantly greater with addition of urea than with addition of either (NH4)2SO4 or NH4NO3, indicating that urea was more efficient in enhancing soil P availability. Addition of (NH4)2SO4 imposed a more pronounced positive effect on soil moderately-occluded Pi than the addition of either NH4NO3 or urea, mainly due to the greater mobilization of recalcitrant Pi as a result of higher soil acidification strength of (NH4)2SO4. These findings underscore the importance of considering the distinct effects of different N compounds when studying grassland soil P dynamics and availability in response to N addition.

How do high phosphate concentrations affect soil microbial communities after a century of ecosystem self-reclamation?

The use of rock phosphate (RP) instead of soluble phosphate fertilizers is preferred for the development of more sustainable agriculture. However, the impact of high concentrations in RP on bacterial and fungal communities remains poorly documented. Thus, next-generation sequencing was used to characterize bacterial and fungal communities in the soils and roots of four plant species growing naturally in a self-restored ecosystem, on former open-pit phosphate mines where past exploitation generated locally a substantial phosphate enrichment of the soil. Our results show that bacterial communities are dominated by Actinobacteria and Proteobacteria phyla, while the Ascomycota and Basidiomycota phyla predominate in the fungal community. The alpha and beta diversities of both bacterial and fungal communities differ significantly between the root and soil compartments but are not significantly affected by RP inputs. However, Amplicon Sequence Variants (ASVs) indicative of RP-enriched soils have been identified; among them are bacteria representative of Streptomyces, Bacillus, Mycobacterium or Agromyces. Implications of these results open new ways of reflection to understand the microbial response following RP-inputs and long-term soil restoration, as well as to formulate microbial-based bioinoculants for sustainable agriculture applications based on microorganisms better adapted to high concentrations of RP.

Phosphorus dynamics in volcanic soils of Weizhou Island, China: implications for environmental and agricultural applications

The dynamics of phosphorus are intricately governed by geological and ecological processes. Examining phosphorus dynamics in volcanic islands can enhance our comprehension of its behavior within such unique geological systems. However, research on phosphorus dynamics in volcanic islands remains limited. We investigated the phosphorus content of volcaniclastic rocks and basalt soils from Weizhou Island, China, to understand the influencing factors on phosphorus dynamics. The results indicate that in the volcaniclastic profile, phosphorus concentrates at 20-40 cm (17 mg/kg), decreases at 40-60 cm (11.9 mg/kg), and increases at 80-200 cm up to 46.4 mg/kg proximate to the bedrock, for the basalt profile, phosphorus content increases from the surface (80.2 mg/kg) towards the bedrock (83.9 mg/kg). The differences in phosphorus distribution between volcaniclastic rocks and basalts reflect the influence of parent material, rock weathering degree, carbonate content, topographic elevation, sea level changes, and geological activities. A strong positive correlation (R = 0.96907) between total and available phosphorus has been observed, suggesting that total phosphorus content effectively predicts available phosphorus content. Volcaniclastic rocks in wharves and high-elevation areas show low total phosphorus, while forest land with dense vegetation and neutral to alkaline soil supports higher total phosphorus due to enhanced bioavailability for plant absorption and utilization. Overall, the basalt soil of the volcanic island Weizhou Island demonstrates superior long-term fertility compared to the volcaniclastic soil. Despite its low total phosphorus content, it mainly exists in a highly bioavailable form, facilitating plant absorption, which is crucial for enhancing agricultural yields and ecosystem restoration on volcanic islands.

Soil phosphorus fractionations as affected by cropping systems in the central mid-hills region of Nepal

Soil plays a critical role as the primary reservoir of phosphorus (P) in terrestrial ecosystems. Sequential fractionation has been extensively utilized to gain insights into the characteristics and dynamics of soil P. However, there is a knowledge gap regarding the different P pools in Nepalese soils. Therefore, this study aimed to investigate the impact of cropping systems on soil P fractions in the central mid-hills of Nepal. The study focused on four cropping systems: vegetable, fruit, rice, and maize-based systems, which exhibited variations in nutrient management, topography, and cropping intensity. A total of 240 soil samples (60 samples from each cropping system) were collected from multiple sites within the central mid-hill region. Standard analytical methods were used to determine the general parameters of the soils, while the sequential fractionation method was employed to assess the organic and inorganic P pools. The results indicated that the effect of cropping systems on soil pH, calcium carbonate (CaCO3) content, and the proportion of sand, silt, and clay was not statistically significant in terms of general parameters. However, significant differences were observed among the different cropping systems in organic matter (OM), electrical conductivity (EC), cation exchange capacity (CEC), and available phosphorus. Similarly, in terms of inorganic phosphorus fractions, loosely bound P (LB-P), aluminum bound P (Al-P), iron bound P (Fe-P), and reductant soluble P (RS-P) were significantly affected, while calcium bound P (Ca-P) did not show a significant difference. Furthermore, in terms of organic phosphorus fractions, labile organic P (L-Po), fluvic acid organic P (FA-Po), and non-labile organic P (NL-Po) exhibited significant differences, whereas moderately labile organic P (ML-Po) and humic acid organic P (HA-Po) did not show a significant difference. Additionally, reductant soluble P showed a significant difference, while total P did not differ significantly. The vegetable-based system exhibited higher levels of the majority of P fractions, followed by the fruit-based, maize-based, and rice-based systems. These findings emphasize the importance of considering cropping systems and their response to different phosphorus pools, as this knowledge can contribute to the development of improved soil phosphorus management strategies and promote sustainable agricultural practices in the region.

Humic acid enhances the co-transport of colloids and phosphorus in saturated porous media

Phosphorus (P) has been widely recognized as a substance that is difficult to transport due to its tendency to become easily fixed in the soil. However, many reports demonstrate that groundwater P pollution is rising in humus-rich areas. Research is urgently needed to confirm (or reject) the hypothesis that increased P pollution is related to humus, as there is currently limited quantitative research on this topic. In this study, we conducted a series of batch equilibrium adsorption-desorption experiments and column experiments to quantify the effects of montmorillonite colloids (MCs) and humic acids (HCs, the main components of humus) on the P transport behavior. The results indicate that P's adsorption and desorption behavior on MCs can be well simulated using the Langmuir and Temkin models (R2 > 0.91). Compared to the non-HC treatments, HCs significantly increased MCs' P adsorption and desorption capacity 5.18 and 7.21 times, respectively. Moreover, HCs facilitated the transport ability of the MC-P mixture through the saturated quartz sand column. In a 0.1 M NaCl solution, the MC-P mixture is nearly completely adsorbed on the surface of quartz sand, with a penetration rate of only 0.5%. In contrast, the HC-MC-P mixture can evidently penetrate further at a rate of 26.1%. The transport parameters fitted using HYDRUS-1D further indicated that the presence of humic acids significantly decreased the deposition coefficients of colloids, thereby enhancing the co-transport of colloids and P through the quartz sand porous medium. The potential mechanism of P pollution in humus-rich areas is likely enhanced by the formation of an HC-colloid-P mixture, which greatly increases the adsorption amount of P on colloids and enhances the electrostatic and spatial repulsion between colloids as well as between colloids and quartz sand. It reduces the aggregation and adsorption of colloids, ultimately transferring P into groundwater through colloid-facilitated co-transport. The findings of this study clarified the relationship between the transport of P, colloids, and HCs, which provides a theoretical basis for explaining the P pollution mechanism in humus-rich areas.

Effect of a Bacillus velezensis and Lysinibacillus fusiformis-based biofertilizer on phosphorus acquisition and grain yield of soybean

Introduction

Phosphate-solubilizing bacteria that function through acidification (organic acid synthesis) or mineralization (production of enzymes such as phytase and phosphatases) have been explored as a biotechnological alternative to enhance plant access to phosphorus (P) retained in organic and inorganic forms in agricultural soils. This study tested the hypothesis that applying a biofertilizer composed of a recognized phosphate-solubilizing bacterium (Bacillus velezensis - endophytic strain BVPS01) and an underexplored plant growth-promoting bacterium (Lysinibacillus fusiformis - endophytic strain BVPS02) would improve the growth and grain yield of Glycine max L. plants.

Methods

Initial in vitro tests assessed the functional traits of these bacteria, and a mix of strains BVPS01 and BVPS02 was produced and tested under field conditions to evaluate its agronomic efficiency.

Results

The results confirmed the hypothesis that the tested biofertilizer enhances the agronomic performance of G. max plants in the field. The B. velezensis strain (BVPS01) was found to be more effective than the L. fusiformis strain (BVPS02) in solubilizing phosphates via the phosphatase enzyme production pathway, indicated by the expression of the phoC and phoD genes. In contrast, L. fusiformis was more effective in solubilizing phosphates through organic acid and phytase-related pathways, in addition to synthesizing indole-3-acetic acid and increasing the mitotic index in the root meristem of G. max plants. These strains exhibited biological compatibility, and the formulated product based on these rhizobacteria enhanced root development and increased the number of nodules and flowers, positively affecting 1000-grain weight, grain yield, and grain P content.

Discussion

Thus, the tested biofertilizer demonstrated potential to improve root growth and increase both the yield and quality of soybean crops, making it a sustainable and low-cost strategy.

Shallow groundwater table fluctuations promote the accumulation and loss of phosphorus from surface soil to deeper soil in croplands around plateau lakes in Southwest China

The continuous excessive application of phosphorus (P) fertilizers in intensive agricultural production leads to a large accumulation of P in surface soils, increasing the risk of soil P loss by runoff and leaching. However, there are few studies on the accumulation and loss of P from surface soil to deep soil profiles driven by shallow groundwater table (SGT) fluctuations. This study used the intensive cropland around 7 plateau lakes in Yunnan Province as an example and conducted in situ monitoring of P storage in the soil profile and SGT during the rainy season (RS) and dry season (DS) as well as simulation experiments on soil P loss. The aim was to study the spatiotemporal variation in P accumulation in the soil profile of cropland driven by SGT fluctuations in the RS and DS and estimate the P loss in the soil profile driven by SGT fluctuations. The results showed that fluctuations in the SGT promoted P accumulation from the surface soil to deeper soil. The proportions of P stored in various forms in the 30-60 cm and 60-100 cm soil layers in the RS were greater than those in the DS, while the average proportion in the 0-30 cm soil layer in the DS was as high as 48%. Compared with those in the DS, the maximum decreases in the proportion of P stored as TP and Olsen-P in the 0-100 cm soil layer in the RS were 16% and 58%, respectively, due to the rise in the SGT (SGT <30 cm), while the soil TP storage decreased by only 1% when the SGT was maintained at 60-100 cm. The critical thresholds for soil Olsen-P and TP gradually decreased with increasing soil depth, and the risk of P loss in deeper soil increased. The loss of soil P was increased by fluctuations in the SGT. Based on the cropland area around the 7 plateau lakes, P storage, and SGT fluctuations, the average loss intensity and loss amount of TP in the 0-100 cm soil layer around the 7 plateau lakes were estimated to be 25 kg/ha and 56 t, respectively. Therefore, reducing exogenous P inputs, improving soil endogenous P utilization efficiency and maintaining deep soil P retention are the basic strategies for preventing and controlling P accumulation and loss in deep soil caused by SGT fluctuations.

Effect of AMF Inoculation on Reducing Excessive Fertilizer Use

Excessive use of chemical fertilizer is a global concern. Arbuscular mycorrhizal fungi (AMF) are considered a potential solution due to their symbiotic association with crops. This study assessed AMF's effects on maize yield, fertilizer efficiency, plant traits, and soil nutrients under different reduced-fertilizer regimes in medium-low fertility fields. We found that phosphorus supplementation after a 30% fertilizer reduction enhanced AMF's positive impact on grain yield, increasing it by 3.47% with pure chemical fertilizers and 6.65% with mixed fertilizers. The AMF inoculation did not significantly affect the nitrogen and phosphorus fertilizer use efficiency, but significantly increased root colonization and soil mycelium density. Mixed fertilizer treatments with phosphorus supplementation after fertilizer reduction showed greater mycorrhizal effects on plant traits and soil nutrient contents compared to chemical fertilizer treatments. This study highlights that AMF inoculation, closely linked to fertilization regimes, can effectively reduce fertilizer use while sustaining or enhancing maize yields.

How a Long-Term Cover Crop Cultivation Impacts Soil Phosphorus Availability in a No-Tillage System?

The growth of cover crops can contribute to the increase in phosphorus content at depth by root decomposition. The aim of this work was to verify the effect of cover crops on soil phosphorus availability and use by successive plants, and the accumulation of soil P in a no-tillage system conducted for 14 years. This research was carried out during the 2016/2017 and 2017/2018 crop seasons, whose treatments have been installed and maintained since 2003. The experimental design was a randomized block design, and the plots consisted of spring crops: pearl millet, forage sorghum, sunn hemp, and additionally, a fallow/chiseling area. The evaluation of available P was determined by P fractionation. In general, in the two years of evaluation, the accumulation of P in the shoot dry matter was higher in sunn hemp growth, on average 25% higher than pearl millet in 2016 and 40% higher than sorghum in 2017. The highest contents of labile inorganic P were in the sorghum-soybean and fallow/chiseling-soybean successions, with values higher than 50 mg kg-1 of P in the 0-0.1 m soil layer. However, in the other layers analyzed, the cover crops obtained higher availability of labile inorganic P. The systems using cover crops recovered 100% of the P fertilized in soybean.

Selenium-Mediated Shaping of Citrus Rhizobiome for Promotion in Root Growth and Soil Phosphorus Activation

Selenium (Se) has been widely reported to affect plant growth, nutrient cycling, and the rhizobiome. However, how Se shapes the rhizobiome and interacts with plants remains largely elusive. Pot and hydroponic experiments were employed to elucidate the regulatory mechanism of Se in the citrus rhizobiome. Compared to the control, soil Se application significantly increased the root biomass (34.7%) and markedly reduced rhizosphere HCl-P, H2O-P, NaHCO3-IP, and residual-P of citrus, which were related to the variation of citrus rhizobiome. Se primarily enriched Proteobacteria and Actinobacteria as well as the phosphorus (P) functional genes phod and pqqc. Further study revealed that Se altered the metabolite profile of root exudate, particularly enhancing the abundance of l-cyclopentylglycine, cycloleucine, l-proline, l-pipecolic acid, and inositol, which played a key role in reshaping the citrus rhizobiome. These metabolites could serve as both nutrient sources and signaling molecules, thus supporting the growth or chemotaxis of the functional microbes. These bacterial taxa have the potential to solubilize P or stimulate plant growth. These findings provide a novel mechanistic understanding of the intriguing interactions between Se, root exudate, and rhizosphere microbiomes, and demonstrate the potential for utilizing Se to regulate rhizobiome function and enhance soil P utilization in citrus cultivation.

Enhancing Maize Yield and Quality with Metal-Based Nanoparticles without Translocation Risks: A Brief Field Study

Our previous studies have shown physiological and yield intensification of selected crops with the application of nanoparticles (NPs). However, the impact on the quantitative, qualitative, and yield parameters of maize (Zea mays L.) in field conditions remains highly debated. This study aimed to evaluate the effects of zinc oxide (ZnO-NPs), gold NPs anchored to meso-biosilica (Au-NP-bioSi), and titanium dioxide (TiO2-NPs) as biological stimulants under field conditions during the vegetation season of 2021 in the Central European region. The study assessed the effects on the number of plants, yield, yield components, and nutritional quality, including mineral nutrients, starch, and crude protein levels. The potential translocation of these chemically-physically stable NPs, which could pose a hazard, was also investigated. The results indicate that Au-NP-bioSi and ZnO-NPs-treatments were the most beneficial for yield and yield components at a statistically significant level. Mineral nutrient outcomes were varied, with the NP-free variant performing the best for phosphorus-levels, while Au-NP-bioSi and ZnO-NPs were optimal for crude protein. Starch content was comparable across the TiO2-NPs, Au-NP-bioSi, and control variants. Importantly, we observed no hazardous translocation of NPs or negative impacts on maize grain quality. This supports the hypothesis that NPs can serve as an effective tool for precise and sustainable agriculture.

Trichoderma viride improves phosphorus uptake and the growth of Chloris virgata under phosphorus-deficient conditions

Introduction

Phosphorus (P) readily forms insoluble complexes in soil, thereby inhibiting the absorption and utilization of this essential nutrient by plants. Phosphorus deficiency can significantly impede the growth of forage grass. While Trichoderma viride (T. viride) has been recognized for promoting the assimilation of otherwise unobtainable nutrients, its impact on P uptake remains understudied. Consequently, it is imperative to gain a more comprehensive insight into the role of T. viride in facilitating the uptake and utilization of insoluble P in forage grass.

Methods

This research explored the influence of T. viride inoculation on P absorption and the growth of Chloris virgata (C. virgata) across various P sources. We treated plants with control P (P), tricalcium phosphate (TCP), calcium phytate (PHY), and low P (LP), with and without T. viride inoculation (P+T, TCP+T, PHY+T, LP+T). We analyzed photosynthesis parameters, growth indices, pigment accumulation, P content, leaf acid phosphatase activity.

Results

Results demonstrated that T. viride inoculation alleviated inhibition of photosynthesis, reduced leaf acid phosphatase activity, and enhanced growth of C. virgata in the presence of insoluble P sources. Additionally, T. viride inoculation enabled the plants to extract more available P from insoluble P sources, as evidenced by a substantial increase in P content: shoot P content surged by 58.23 to 59.08%, and root P content rose by 55.13 to 55.2%. Biomass P-use efficiency (PUE) declined by 38% upon inoculation with T. viride compared to the non-inoculated insoluble P sources, paralleled by a reduction in photosynthetic P-use efficiency (PPUE) by 26 to 29%. Inoculation under insoluble P sources further triggered a lower allocation to root biomass (25 to 26%) and a higher investment in shoot biomass (74 to 75%). However, its application under low P condition curtailed the growth of C. virgata.

Discussion

Our results suggest that T. viride inoculation represents an innovative approach for plants to acquire available P from insoluble P sources, thereby promoting growth amid environmental P limitations. This insight is crucial for comprehending the synergy among forage grass, P, and T. viride.

The halotolerant exopolysaccharide-producing Rhizobium azibense increases the salt tolerance mechanism in Phaseolus vulgaris (L.) by improving growth, ion homeostasis, and antioxidant defensive enzymes

Globally, agricultural productivity is facing a serious problem due to soil salinity which often causes osmotic, ionic, and redox imbalances in plants. Applying halotolerant rhizobacterial inoculants having multifarious growth-regulating traits is thought to be an effective and advantageous approach to overcome salinity stress. Here, salt-tolerant (tolerating 300 mM NaCl), exopolysaccharide (EPS) producing Rhizobium azibense SR-26 (accession no. MG063740) was assessed for salt alleviation potential by inoculating Phaseolus vulgaris (L.) plants raised under varying NaCl regimes. The metabolically active cells of strain SR-26 produced a significant amount of phytohormones (indole-3-acetic acid, gibberellic acid, and cytokinin), ACC deaminase, ammonia, and siderophore under salt stress. Increasing NaCl concentration variably affected the EPS produced by SR-26. The P-solubilization activity of the SR-26 strain was positively impacted by NaCl, as demonstrated by OD shift in NaCl-treated/untreated NBRIP medium. The detrimental effect of NaCl on plants was lowered by inoculation of halotolerant strain SR-26. Following soil inoculation, R. azibense significantly (p ≤ 0.05) enhanced seed germination (10%), root (19%) shoot (23%) biomass, leaf area (18%), total chlorophyll (21%), and carotenoid content (32%) of P. vulgaris raised in soil added with 40 mM NaCl concentration. Furthermore, strain SR-26 modulated the relative leaf water content (RLWC), proline, total soluble protein (TSP), and sugar (TSS) of salt-exposed plants. Moreover, R. azibense inoculation lowered the concentrations of oxidative stress biomarkers; MDA (29%), H2O2 content (24%), electrolyte leakage (31%), membrane stability (36%) and Na+ ion uptake (28%) when applied to 40 mM NaCl-treated plants. Further, R. azibense increases the salt tolerance mechanism of P. vulgaris by upregulating the antioxidant defensive responses. Summarily, it is reasonable to propose that EPS-synthesizing halotolerant R. azibense SR-26 should be applied as the most cost-effective option for increasing the yields of legume crops specifically P. vulgaris in salinity-challenged soil systems.

Study on vertical variation characteristics of soil phosphorus adsorption and desorption in black soil region of Northeast China

The adsorption and desorption of phosphorus (P) in soil constitute a crucial internal cycle that is closely associated with soil fertility, exerting direct influence on the quantity, form, and availability of P within the soil. The vertical spatial variation characteristics of soil adsorption and desorption were investigated for the 0-100 cm soil layer in the northeast black soil region in this study. The maximum adsorption capacity (Qmax) and maximum adsorption buffer capacity (MBC) of black soil in the study area ranged from 313.8 to 411.9 mg kg-1 and from 3.1 to 28.8 L kg-1, respectively, within the soil layer of 0-100 cm depth, exhibiting an increasing trend with greater soil depth. The degree of P adsorption saturation (DPS) exhibited a contrasting trend with the variations in Qmax and MBC, ranging from 3.8% to 21.6%. The maximum desorption capacity (Dmax) and desorption rate (Dr) of soil P ranged from 112.8 to 215.7 mg kg-1 and 32.1% to 52.5%, respectively, while the readily desorbable P (RDP) in soil was within the range of 1.02 to 3.35 mg kg-1. Both Dmax, Dr, and RDP exhibited a decreasing trend with increasing soil depth before showing an upward trend. These research findings not only provide essential background data for the systematic investigation of soil P in the black soil region but also serve as a valuable reference for assessing soil quality in this area.

Biochar-nanoparticle combinations enhance the biogeochemical recovery of a post-mining soil

Here we addressed the capacity of distinct amendments to reduce arsenic (As), copper (Cu), selenium (Se) and zinc (Zn) associated risks and improve the biogeochemical functions of post-mining soil. To this, we examined nanoparticles (NPs) and/or biochar effects, combined with phytostabilization using Lolium perenne L. Soil samples were taken in a former metal mine surroundings. Ryegrass seeds were sown in pots containing different combinations of NPs (zero-valent iron (nZVI) or hydroxyapatite (nH)) (0 and 2 %), and biochar (0, 3 and 5 %). Plants were grown for 45 days and the plant yield and element accumulation were evaluated, also soil properties (element distribution within the soil fractions, fertility, and enzymatic activities associated with microbiota functionality and nutrient cycling) were determined. Results showed biochar-treated soil had a higher pH, and much higher organic carbon (C) content than control soil and NP-treated soils, and it revealed increased labile C, total N, and available P concentrations. Soil treatment with NP-biochar combinations increased exchangeable non-acid cation concentrations and reduced exchangeable Na%, improved soil fertility, reduced sodicity risk, and increased ryegrass biomass. Enzymatic activities, particularly dehydrogenase and glucosidase, increased upon the addition of biochar, and this effect was fostered by NPs. Most treatments led to a significant reduction of metal(loid)s contents in biomass, mitigating contamination risks. The two different NPs had similar effects in many parameters, nH outperformed nZVI in terms of increased nutrients, C content, and enzymatic activities. On the basis of our results, combined biochar-NP amendments use, specially nH, emerges as a potential post-mining soil restoration strategy.

Microbial diversity and keystone species drive soil nutrient cycling and multifunctionality following mangrove restoration

Vegetation restoration exerts transformative effects on nutrient cycling, microbial communities, and ecosystem functions. While extensive research has been conducted on the significance of mangroves and their restoration efforts, the effectiveness of mangrove restoration in enhancing soil multifunctionality in degraded coastal wetlands remains unclear. Herein, we carried out a field experiment to explore the impacts of mangrove restoration and its chronosequence on soil microbial communities, keystone species, and soil multifunctionality, using unrestored aquaculture ponds as controls. The results revealed that mangrove restoration enhanced soil multifunctionality, with these positive effects progressively amplifying over the restoration chronosequence. Furthermore, mangrove restoration led to a substantial increase in microbial diversity and a reshaping of microbial community composition, increasing the relative abundance of dominant phyla such as Nitrospirae, Deferribacteres, and Fusobacteria. Soil multifunctionality exhibited positive correlations with microbial diversity, suggesting a link between variations in microbial diversity and soil multifunctionality. Metagenomic screening demonstrated that mangrove restoration resulted in a simultaneous increase in the abundance of nitrogen (N) related genes, such as N fixation (nirD/H/K), nitrification (pmoA-amoA/B/C), and denitrification (nirK, norB/C, narG/H, napA/B), as well as phosphorus (P)-related genes, including organic P mineralization (phnX/W, phoA/D/G, phnJ/N/P), inorganic P solubilization (gcd, ppx-gppA), and transporters (phnC/D/E, pstA/B/C/S)). The relationship between the abundance of keystone species (such as phnC/D/E) and restoration-induced changes in soil multifunctionality indicates that mangrove restoration enhances soil multifunctionality through an increase in the abundance of keystone species associated with N and P cycles. Additionally, it was observed that changes in microbial community and multifunctionality were largely associated with shifts in soil salinity. These findings demonstrate that mangrove restoration positively influences soil multifunctionality and shapes nutrient dynamics, microbial communities, and overall ecosystem resilience. As global efforts continue to focus on ecosystem restoration, understanding the complexity of mangrove-soil interactions is critical for effective nutrient management and mangrove conservation.

Microbial Consortia: Promising Tool as Plant Bioinoculants for Agricultural Sustainability

In the present scenario, growing population demands more food, resulting in the need for sustainable agriculture. Numerous approaches are explored in response to dangers and obstacles to sustainable agriculture. A viable approach is to be exploiting microbial consortium, which generate diverse biostimulants with growth-promoting characteristics for plants. These bioinoculants play an indispensable role in optimizing nutrient uptake efficiency mitigating environmental stress. Plant productivity is mostly determined by the microbial associations that exist at the rhizospheric region of plants. The engineered consortium with multifunctional attributes can be effectively employed to improve crop growth efficacy. A number of approaches have been employed to identify the efficient consortia for plant growth and enhanced crop productivity. Various plant growth-promoting (PGP) microbes with host growth-supporting characteristics were investigated to see if they might work cohesively and provide a cumulative effect for improved growth and crop yield. The effective microbial consortia should be assessed using compatibility tests, pot experimentation techniques, generation time, a novel and quick plant bioassay, and sensitivity to external stimuli (temperature, pH). The mixture of two or more microbial strains found in the root microbiome stimulates plant growth and development. The present review deals with mechanism, formulation, inoculation process, commercialization, and applications of microbial consortia as plant bioinoculants for agricultural sustainability.

Influence of planting dates and fertilizer modules on yield of chrysanthemum and soil health

BACKGROUND

Optimum planting date and appropriate fertilizer module are essential facets of chrysanthemum cultivation, to enhance quality yield, and improve soil health. A field-based study was undertaken over multiple growing seasons in 2022 and 2023, where six different planting dates, viz., P1:June 15, P2:June 30, P3:July 15, P4:July 30, P5:August 15 and P6:August 30 and two fertilizer modules, FM1:Jeevamrit @ 30 ml plant-1 and FM2:NPK @ 30 g m-2 were systematically examined using a Randomized Block Design (factorial), replicated thrice.

RESULTS

P6 planting resulted in early bud formation (44.03 days) and harvesting stage (90.78 days). Maximum plant height (79.44 cm), plant spread (34.04 cm), cut stem length (68.40 cm), flower diameter (7.83 cm), stem strength (19.38˚), vase life (14.90 days), flowering duration (24.08 days), available soil N (314 kg ha-1), available P (37 kg ha-1), available K (347 kg ha-1), bacterial count (124.87 × 107 cfu g-1 soil), actinomycetes count (60.72 × 102 cfu g-1 soil), fungal count (30.95 × 102 cfu g-1 soil), microbial biomass (48.79 µg g-1 soil), dehydrogenase enzyme (3.64 mg TPF h-1 g-1 soil) and phosphatase enzyme (23.79 mol PNP h-1 g-1 soil) was recorded in P1 planting. Among the fertilization module, minimum days to bud formation (74.94 days) and days to reach the harvesting stage (120.95 days) were recorded with the application of NPK @30 g m-2. However, maximum plant height (60.62 cm), plant spread (23.10 cm), number of cut stems m-2 (43.88), cut stem length (51.34 cm), flower diameter (6.92 cm), stem strength (21.24˚), flowering duration (21.75 days), available soil N (317 kg ha-1), available P (37 kg ha-1) and available K (349 kg ha-1) were also recorded with the application of NPK @300 kg ha-1. Maximum vase life (13.87 days), OC (1.13%), bacterial count (131.65 × 107 cfu g-1 soil), actinomycetes count (60.89 × 102 cfu g-1 soil), fungal count (31.11 × 102 cfu g-1 soil), microbial biomass (51.27 µg g-1 soil), dehydrogenase enzyme (3.77 mg TPF h-1 g-1 soil) and phosphatase enzyme (21.72 mol PNP h-1 g-1 soil) were observed with the application of Jeevamrit @ 30 ml plant-1.

CONCLUSION

Early planting (P1) and inorganic fertilization (NPK @ 30 g m-2) resulted in improved yield and soil macronutrient content. The soil microbial population and enzymatic activity were improved with the jeevamrit application. This approach highlights the potential for improved yield and soil health in chrysanthemum cultivation, promoting a more eco-friendly and economically viable agricultural model.

Ammonium addition reduces phosphorus leaching in a long-term mineral or organic fertilized calcareous soil during flooding conditions

Organic amendment substitutes mineral fertilizers has been proven to increase the organic matter content of soils, which in turn may induce phosphorus (P) mobilization by triggering the redox reaction. However, under flooded conditions according to local agricultural practices, as one of the factors restricting the decomposition of organic matter, the role ammonium plays in P transformation and leaching from soils with different organic matter remains unclear. To address the knowledge gap, the calcareous soils were collected from a long-term field trial (>13 years) containing two treatments with equal P inputs: a long-term mineral fertilization and a long-term organic amendment. Both long-term mineral fertilized soil and long-term organic amended soil were split into ammonium applications or no ammonium applications. A series of column devices were deployed to create flooded conditions and monitor the P leaching from the collected soils. The K-edge X-ray absorption near-edge structure and sequential extraction method were employed jointly to detect soil P fractions and speciation, and the P sorption/desorption characteristics of soil were evaluated by Langmuir fitting. The results showed a reduction of cumulative leached P from soils by 33.2%-43.3% after ammonium addition, regardless of previous long-term mineral fertilization or organic amendment history. A significant enhancement of soil labile P pool (indicated by the H2O-P fraction and NaHCO3-P fraction) after ammonium addition results in the reduction in soil P leaching. The reduced P sorption capacity coupled with the transformation from hydroxyapatite to β-tricalcium phosphate indicated that the phosphate retention is attributed to the precipitation formation rather than phosphate sorption by soil. The present study highlights that the ammonium addition could affect the phosphate precipitation transformation. This may be attributed to the effect of ammonium addition on the calcium and magnesium ion content and molar ratio in this soil, thereby regulating the form of soil phosphate precipitation. The mechanisms revealed in this study can support developing optimized agricultural management practices to alleviate soil P loss.

Efficacy of DAP coated with bacterial strains and their metabolites for soil phosphorus availability and maize growth

Phosphorus (P) use efficiency in alkaline/calcareous soils is only 20% due to precipitation of P2O5 with calcium and magnesium. However, coating Diammonium Phosphate (DAP) with phosphorus solubilizing bacteria (PSB) is more appropriate to increase fertilizer use efficiency. Therefore, with the aim to use inorganic fertilizers more effectively present study was conducted to investigate comparative effect of coated DAP with PSB strains Bacillus subtilis ZE15 (MN003400), Bacillus subtilis ZR3 (MN007185), Bacillus megaterium ZE32 (MN003401) and Bacillus megaterium ZR19 (MN007186) and their extracted metabolites with uncoated DAP under axenic conditions. Gene sequencing was done against various sources of phosphorus to analyze genes responsible for phosphatase activity. Alkaline phosphatase (ALP) gene amplicon of 380bp from all tested strains was showed in 1% w/v gel. Release pattern of P was also improved with coated fertilizer. The results showed that coated phosphatic fertilizer enhanced shoot dry weight by 43 and 46% under bacterial and metabolites coating respectively. Shoot and root length up to 44 and 42% with metabolites coated DAP and 41% with bacterial coated DAP. Physiological attributes also showed significant improvement with coated DAP over conventional. The results supported the application of coated DAP as a useful medium to raise crop yield even at lower application rates i.e., 50 and 75% DAP than non-coated 100% DAP application which advocated this coating technique a promising approach for advancing circular economy and sustainable development in modern agriculture.

Bacillus subtilis promotes plant phosphorus (P) acquisition through P solubilization and stimulation of root and root hair growth

Bacteria can be applied as biofertilizers to improve crop growth in phosphorus (P)-limited conditions. However, their mode of action in a soil environment is still elusive. We used the strain ALC_02 as a case study to elucidate how Bacillus subtilis affects dwarf tomato cultivated in soil-filled rhizoboxes over time. ALC_02 improved plant P acquisition by increasing the size and P content of P-limited plants. We assessed three possible mechanisms, namely root growth stimulation, root hair elongation, and solubilization of soil P. ALC_02 produced auxin, and inoculation with ALC_02 promoted root growth. ALC_02 promoted root hair elongation as the earliest observed response and colonized root hairs specifically. Root and root hair growth stimulation was associated with a subsequent increase in plant P content, indicating that a better soil exploration by the root system improved plant P acquisition. Furthermore, ALC_02 affected the plant-available P content in sterilized soil differently over time and released P from native P pools in the soil. Collectively, ALC_02 exhibited all three mechanisms in a soil environment. To our knowledge, bacterial P biofertilizers have not been reported to colonize and elongate root hairs in the soil so far, and we propose that these traits contribute to the overall effect of ALC_02. The knowledge gained in this research can be applied in the future quest for bacterial P biofertilizers, where we recommend assessing all three parameters, not only root growth and P solubilization, but also root hair elongation. This will ultimately support the development of sustainable agricultural practices.

Impact of Modifications from Potassium Hydroxide on Porous Semi-IPN Hydrogel Properties and Its Application in Cultivation

This study synthesized and modified a semi-interpenetrating polymer network hydrogel from polyacrylamide, N,N'-dimethylacrylamide, and maleic acid in a potassium hydroxide solution. The chemical composition, interior morphology, thermal properties, mechanical characteristics, and swelling behaviors of the initial hydrogel (SH) and modified hydrogel (SB) in water, salt solutions, and buffer solutions were investigated. Hydrogels were used as phosphate fertilizer (PF) carriers and applied in farming techniques by evaluating their impact on soil properties and the growth of mustard greens. Fourier-transform infrared spectra confirmed the chemical composition of SH, SB, and PF-adsorbed hydrogels. Scanning electron microscopy images revealed that modification increased the largest pore size from 817 to 1513 µm for SH and SB hydrogels, respectively. After modification, the hydrogels had positive changes in the swelling ratio, swelling kinetics, thermal properties, mechanical and rheological properties, PF absorption, and PF release. The modification also increased the maximum amount of PF loaded into the hydrogel from 710.8 mg/g to 770.9 mg/g, while the maximum % release of PF slightly increased from 84.42% to 85.80%. In addition, to evaluate the PF release mechanism and the factors that influence this process, four kinetic models were applied to confirm the best-fit model, which included zero-order, first-order, Higuchi, and Korsmeyer-Peppas. In addition, after six cycles of absorption and release in the soil, the hydrogels retained their original shapes, causing no alkalinization or acidification. At the same time, the moisture content was higher as SB was used. Finally, modifying the hydrogel increased the mustard greens' lifespan from 20 to 32 days. These results showed the potential applications of modified semi-IPN hydrogel materials in cultivation.

Comparison of bio-beads combined with Pseudomonas edaphica and three phosphate materials for lead immobilization: Performance, mechanism and plant growth

Phosphate materials (PMs) combine with phosphate solubilizing bacteria play an essential roles in lead (Pb) immobilization, but their resulting ability to reduce Pb bioavailability may vary depending on PMs used. In this study, Pseudomonas edaphica GAU-665 and three PMs: tricalcium phosphate, calcium phytate and nano-hydroxyapatite were respectively encapsulated into bio-beads by sodium alginate, which immobilization efficiency of Pb2+ were 99.11%, 97.76% and 99.02% at initial Pb2+ concentration of 200 mg L-1, respectively. The Pb2+ immobilization performance of bio-beads under different conditions and their organic acids secreted were examined. Most Pb2+ was immobilized by bio-beads through combined functions of adsorption, precipitation, ion exchange and biomineralization, accompanied by the formation of more stable compounds such as Pb3(PO4)2, Pb5(PO4)3OH and Pb5(PO4)3Cl. Meanwhile, pot experimental results indicated that the inoculation of CPhy (calcium phytate) bio-beads with PSB have highest biomass and root growth of oat (Avena sativa L.) in Pb-stressed compared with CK, which increased the content of chlorophyll b (167.51%) in shoot. In addition, the CPhy bio-beads enhance the peroxidase, catalase activities and reduce the malondialdehyde content to alleviating lead physiological toxicity in oat, which reductions the Pb accumulation in shoot (52.06%) and root (81.04%), and increased the residual fraction of Pb by 165.80% in soil. These findings suggest the bio-beads combined with P. edaphica GAU-665 and calcium phytate is an efficient Pb immobilization material and provided feasible way to improve safety agricultural production and Pb-contaminated soil remediation.

Soil phosphorus transformation and plant uptake driven by phosphate-solubilizing microorganisms

Phosphorus (P) is an important nutrient for plants, and a lack of available P greatly limits plant growth and development. Phosphate-solubilizing microorganisms (PSMs) significantly enhance the ability of plants to absorb and utilize P, which is important for improving plant nutrient turnover and yield. This article summarizes and analyzes how PSMs promote the absorption and utilization of P nutrients by plants from four perspectives: the types and functions of PSMs, phosphate-solubilizing mechanisms, main functional genes, and the impact of complex inoculation of PSMs on plant P acquisition. This article reviews the physiological and molecular mechanisms of phosphorus solubilization and growth promotion by PSMs, with a focus on analyzing the impact of PSMs on soil microbial communities and its interaction with root exudates. In order to better understand the ability of PSMs and their role in soil P transformation and to provide prospects for research on PSMs promoting plant P absorption. PSMs mainly activate insoluble P through the secretion of organic acids, phosphatase production, and mycorrhizal symbiosis, mycorrhizal symbiosis indirectly activates P via carbon exchange. PSMs can secrete organic acids and produce phosphatase, which plays a crucial role in soil P cycling, and related genes are involved in regulating the P-solubilization ability. This article reviews the mechanisms by which microorganisms promote plant uptake of soil P, which is of great significance for a deeper understanding of PSM-mediated soil P cycling, plant P uptake and utilization, and for improving the efficiency of P utilization in agriculture.

Manure derived hydrochar reduced phosphorus loss risk via an alteration of phosphorus fractions and diversified microbial community in rice paddy soil

Phosphorus (P) loss caused by the irrational use of manure organic fertilizer has become a worldwide environmental problem, which has caused a potential threat to water safety and intensified agricultural non-point source pollution. Hydrothermal carbonization is method with a low-energy consumption and high efficiency to deal with environmental problems. Application of pig manure-derived hydrochar (PMH) to soil exhibited potential of sustainable development compared with the pristine pig manure (PM). However, the effects of PMH on the distribution of P among the fractions/forms and the interaction between microorganisms and P forms and its relevance to the potential loss of P in paddy fields has not been clarified. Therefore, in this study, a soil column experiment was conducted using the untreated soil (control), and the PM, PMH1 (PMH derived at 180 °C), and PMH2 (PMH derived at 260 °C) treated soils (at the dose of 0.05 %) and rice was cultivated to investigate the effects of PM and PMH on the P fractions, mobilization, ad potential loss via the induced changes on soil microbial community after a complete growing season of rice. The trend of P utilization was evaluated by P speciation via continuous extraction and 31P NMR. The addition of PMH reduced the proportion of residual P in soil by 23.8-26.3 %, and increased the proportion of HCl-P and orthophosphate by 116.2-158.6 % and 6.1-6.8 % compared to PM. The abundance of gcd gene developed after the application of PMH2, which enhanced the mobile forms of soil P utilization via secreting gluconic acid. The network diagram analysis concluded that the changes in various P forms were mainly related to Proteobacteria, Bacteroides, Firmicutes and Acidobacteria. The results illustrated that PMH mitigate the potential risk of P loss more than PM by altering P fractions and affecting soil microbial community.

Understanding phosphorus mobilization mechanisms in acidic soil amended with calcium-silicon-magnesium-potassium fertilizer

Calcium-silicon-magnesium-potassium fertilizer (CSMP) is usually used as an amendment to counteract soil acidification caused by historical excessive nitrogen (N) applications. However, the impact of CSMP addition on phosphorus (P) mobilization in acidic soils and the related mechanisms are not fully understood. Specifically, a knowledge gap exists with regards to changes in soil extracellular enzymes that contribute to P release. Such a knowledge gap was investigated by an incubation study with four treatments: i) initial soil (Control), ii) urea (60 mg kg-1) addition (U); iii) CSMP (1%) addition (CSMP) and iv) urea (60 mg kg-1) and CSMP (1%) additions (U + CSMP). Phosphorus mobilization induced by different processes was distinguished by biologically based P extraction. The Langmuir equation, K edge X-ray absorption near-edge structure spectroscopy, and ecoenzyme vector analysis according to the extracellular enzyme activity stoichiometry were deployed to investigate soil P sorption intensity, precipitation species, and microbial-driven turnover of organophosphorus. Results showed that CaCl2 extractable P (or citric acid extractable P) content increased by 63.4% (or 39.2%) in the soil with CSMP addition, compared with the study control. The accelerated mobilization of aluminum (Al)/iron (Fe)-bound P after CSMP addition, indicated by the reduction of the sum of FePO4·2H2O and AlPO4 proportion, contributed to this increase. The decrease of P sorption capacity can also be responsible for it. The CSMP addition increased enzyme extractable P in the soil nearly 7-fold and mitigated the limitations of carbon (C) and P for soil microorganisms (indicated by the enzyme stoichiometry and ecoenzyme vector analysis), suggesting that microbial turnover processes also contribute to P mobilization in amended acidic soil. These findings indicate that the P mobilization in CSMP amended acidic soil not only attributed to both decreasing P sorption capacity and dissolving phosphate precipitation, but also to the increase of the microbial turnover of the organophosphorus pool.

Degradation of agricultural waste is dependent on chemical fertilizers in long-term paddy-dry rotation field

The practice of returning straw to agricultural fields is a globally employed technique. Such agricultural fields also receive a significant amount of nitrogen (N) and phosphorus (P) fertilizers, because these two macronutrients are essential for plant growth and development. However, the consequences of such macronutrients input on straw decomposition, soil dissolved organic matter (DOM), key microbes, and lignocellulolytic enzymes are still unclear. In a similar aim, we designed a long-term straw returning study without and with different N and P nutrient supplementation: CK (N0P0), T1 (N120P0), T2 (N120P60), T3 (N120P90), T4 (N120P120), T5 (N0P90), T6 (N60P90), and T7 (N180P90), and evaluated their impact on rice and oilseed rape yield, soil DOM, enzymes, lignocellulose content, microbial diversity, and composition. We found straw returning improved overall yield in all treatments and T7 showed the highest yield for oilseed rape (30.31-38.87 g/plant) and rice (9.14-9.91 t/ha) during five-years of study. The fertilizer application showed a significant impact on soil physicochemical properties, such as water holding capacity and soil porosity decreased, and bulk density increased in fertilized treatments, as compared to CK. Similarly, significantly low OM, cellulose, hemicellulose, and lignin content were found in T7, T4, T3, and T2, while high values were found in CK and T5, respectively. The fluorescence excitation-emission matrix spectra of DOM of different treatments revealed that T3, T7, T4, and T6 showed high peak M (microbial by-products), peak A and peak C (humic acid-like) as compared to others. The microbial composition was also distinctive in each treatment and a high relative abundance of Chloroflexi, Actinobacteriota, Ascomycota, and Basidiomycota were found in T2 and T3 treatments, respectively. These findings indicate that the decomposition of straw in the agricultural field was dependent on nutrients input, which facilitated key microbial growth and impacted positively on lignocellulolytic enzymes, which further aided the breakdown of all components of straw in the field efficiently. On the other hand, high input of chemical based fertilizers to soil can lead to several environmental issues, such as nutrient imbalance, nutrient runoff, soil pH change and changes in microbial activities. Keeping that in consideration, we recommend moderate fertilizer dosage (N120P90) in such fields to achieve higher decomposition of crop straw with a small yield compromise.

Parameter evaluation for developing phosphate-solubilizing Bacillus inoculants

Bacterial inoculants have been used in agriculture to improve plant performance. However, laboratory and field requirements must be completed before a candidate can be employed as an inoculant. Therefore, this study aimed to evaluate the parameters for inoculant formulation and the potential of Bacillus subtilis (B70) and B. pumilus (B32) to improve phosphorus availability in maize (Zea mays L.) crops. In vitro experiments assessed the bacterial ability to solubilize and mineralize phosphate, their adherence to roots, and shelf life in cassava starch (CS), carboxymethyl cellulose (CMC), peat, and activated charcoal (AC) stored at 4 °C and room temperature for 6 months. A field experiment evaluated the effectiveness of strains to increase the P availability to plants growing with rock phosphate (RP) and a mixture of RP and triple superphosphate (TS) and their contribution to improving maize yield and P accumulation in grains. The B70 was outstanding in solubilizing RP and phytate mineralization and more stable in carriers and storage conditions than B32. However, root adherence was more noticeable in B32. Among carriers, AC was the most effective for preserving viable cell counts, closely similar to those of the initial inoculum of both strains. Maize productivity using the mixture RPTS was similar for B70 and B32. The best combination was B70 with RP, which improved the maize yield (6532 kg ha-1) and P accumulation in grains (15.95 kg ha-1). Our results indicated that the inoculant formulation with AC carrier and B70 is a feasible strategy for improving phosphorus mobilization in the soil and maize productivity.

Isolation and Identification of Acer truncatum Endophytic Fungus Talaromyces verruculosus and Evaluation of Its Effects on Insoluble Phosphorus Absorption Capacity and Growth of Cucumber Seedlings

The symbiosis between endophytic fungi and plants can promote the absorption of potassium, nitrogen, phosphorus, and other nutrients by plants. Phosphorus is one of the indispensable nutrient elements for plant growth and development. However, the content of available phosphorus in soil is very low, which limits the growth of plants. Phosphorus-soluble microorganisms can improve the utilization rate of insoluble phosphorus. In this study, Talaromyces verruculosus (T. verruculosus), a potential phosphorus-soluble fungus, was isolated from Acer truncatum, a plant with strong stress resistance, and its phosphorus-soluble ability in relation to cucumber seedlings under different treatment conditions was determined. In addition, the morphological, physiological, and biochemical indexes of the cucumber seedlings were assessed. The results show that T. verruculosus could solubilize tricalcium phosphate (TCP) and lecithin, and the solubilization effect of lecithin was higher than that of TCP. After the application of T. verruclosus, the leaf photosynthetic index increased significantly. The photosynthetic system damage caused by low phosphorus stress was alleviated, and the root morphological indexes of cucumber seedlings were increased. The plant height, stem diameter, and leaf area of cucumber seedlings treated with T. verruculosus were also significantly higher than those without treatment. Therefore, it was shown that T. verruculosus is a beneficial endophytic fungus that can promote plant growth and improve plant stress resistance. This study will provide a useful reference for further research on endophytic fungi to promote growth and improve plant stress resistance.