Depth-dependent influence of biochar application on the abundance and community structure of diazotrophic under sugarcane growth

How binomial (traditional rainfed olive grove-Crocus sativus) crops impact the soil bacterial community and enhance microbial capacities

Intercropping can favour the yield of the main crop. However, because of the potential competition among woody crops, this system is rarely used by farmers. To increase knowledge about the intercropping system, we have explored three different combinations of alley cropping in rainfed olive groves compared to conventional management (CP): (i) Crocus sativus (D-S); (ii) Vicia sativa/Avena sativa in annual rotation (D-O); and (iii) Lavandula x intermedia (D-L). Different soil chemical properties were analyzed to evaluate the effects of alley cropping, while 16S rRNA amplification and enzymatic activities were determined to study the changes that occurred in soil microbial communities and activity. In addition, the influence of intercropping on the potential functionality of the soil microbial community was measured. Data revealed that the intercropping systems highly affected the microbial community and soil properties. The D-S cropping system increased soil total organic carbon and total nitrogen that were correlated with the bacterial community, indicating that both parameters were the main drivers shaping the structure of the bacterial community. The D-S soil cropping system had significantly higher relative abundances of the phyla Bacteroidetes, Proteobacteria, and Patescibacteria compared to the other systems and the genera Adhaeribacter, Arthrobacter, Rubellimicrobium, and Ramlibacter, related to C and N functions. D-S soil was also related to the highest relative abundances of Pseudoarthrobacter and Haliangium, associated with the plant growth-promoting effect, antifungal activity, and a potential P solubilizer. A potentially increase of C fixation and N fixation in soils was also observed in the D-S cropping system. These positive changes were related to the cessation of tillage and the development of a spontaneous cover crop, which increased soil protection. Thus, management practices that contribute to increasing soil cover should be encouraged to improve soil functionality.

Plant growth and stress-regulating metabolite response to biochar utilization boost crop traits and soil health

Introduction

The utilization of biochar (BC) as a soil amendment in agriculture has gained significant traction among many farmers and researchers, primarily due to its eco-friendly role in boosting crop output. However, the performance of specific metabolites (e.g., zeatin, melatonin, sucrose, and phenyllactic acid) in the various tissues of sugarcane plant (leaf, stem, and root) and rhizosphere soil-deemed plant growth and stress regulators in a long-term BC-amended field remains poorly understood. Additionally, literature on the shift in soil attributes and crop growth triggered by the strong response of these bioactive compounds to longterm BC utilization remains undocumented.

Methods

Metabolome integrated with highthroughput sequencing analyses were conducted to identify and quantify the performance of plant growth and stress-regulating metabolites in a long-term BC-amended field. Additionally, we investigated how the response of these compounds to BC-treated soil influences crop traits and soil biochemical properties.

Results

We also identified and quantified the performance of pathogenic bacteria and unraveled the association between these compounds and potential plant growth-promoting bacteria. The BC-supplemented soil significantly boosted the crop traits, including brix, sucrose content, and chlorophyll, as well as soil nutrients, such as soil total nitrogen (TN), ammonium (NH4 +-N), and nitrate (NO3 --N). We also noticed that metabolite-deemed plant growth and stress regulators, including melatonin and phenyllactic acid, were enriched considerably in the stem and root tissues of the BC-amended soil. Zeatin in the leaf, stem, and root tissues exhibited the same trend, followed by sucrose in the leaf tissue of the BC-treated soil, implying that the strong response of these compounds to BC utilization contributed to the promotion of crop traits and soil quality. Pathogenic bacteria belonging to Proteobacteria and Acidobacteria were suppressed under the BC-supplemented soil, especially in the root tissue and rhizosphere soil, whereas plant growth-regulating bacteria, mainly Bradyrhizobium, responded strongly and positively to several metabolites.

Discussion

Our finding provides valuable information for agronomists, farmers, and environmentalists to make informed decisions about crop production, land use, and soil management practices. Proper soil assessment and understanding of the interaction between the attributes of soil, BC, and metabolites are essential for promoting sustainable agriculture practices and land conservation.

Free-living bacteria stimulate sugarcane growth traits and edaphic factors along soil depth gradients under contrasting fertilization

Free-living bacterial community and abundance have been investigated extensively under different soil management practices. However, little is known about their nitrogen (N) fixation abilities, and how their contributions to N budgets impact plant growth, yield, and carbon (C) and N cycling enzymes in a long-term consecutive sugarcane monoculture farming system, under contrasting amendments, along different soil horizons. Here, nifH gene amplicon was used to investigate diazotrophs bacterial community and abundance by leveraging high-throughput sequencing (HTS). Moreover, edaphic factors in three soil depths (0-20, 20-40, and 40-60 cm) under control (CK), organic matter (OM), biochar (BC), and filter mud (FM) amended soils were investigated. Our analysis revealed that β-glucosidase activity, acid phosphatase activity, ammonium (NH₄⁺-N), nitrate (NO₃^-N), total carbon (TC), total nitrogen (TN), and available potassium (AK) were considerably high in 0-20 cm in all the treatments. We also detected a significantly high proportion of Proteobacteria and Geobacter in the entire sample, including Anabaena and Enterobacter in 0-20 cm soil depth under the BC and FM amended soils, which we believed were worthy of promoting edaphic factors and sugarcane traits. This phenomenon was further reinforced by network analysis, where diazotrophs bacteria belonging to Proteobacteria exhibited strong and positive associations soil electrical conductivity (EC), soil organic matter content (SOM) available phosphorus (AP), TN, followed by NH4⁺-N and NO₃^-N, a pattern that was further validated by Mantel test and Pearson's correlation coefficients analyses. Furthermore, some potential N-fixing bacteria, including Burkholderia, Azotobacter, Anabaena, and Enterobacter exhibited a strong and positive association with sugarcane agronomic traits, namely, sugarcane stalk, ratoon weight, and chlorophyll content. Taken together, our findings are likely to broaden our understanding of free-living bacteria N-fixation abilities, and how their contributions to key soil nutrients such as N budgets impact plant growth and yield, including C and N cycling enzymes in a long-term consecutive sugarcane monoculture farming system, under contrasting amendments, along different soil horizons.

Optimising water holding capacity and hydrophobicity of biochar for soil amendment - A review

Biochar is a product of the thermal treatment of biomass, and it can be used for enhancing soil health and productivity, soil carbon sequestration, absorbance of pollutants from water and soil, and promoting environmental sustainability. Extensive research has been done on applications of biochar to enhance the Water Holding Capacity (WHC) of biochar amended soil. However, a comprehensive road map of biochar optimised for enhanced WHC, and reduced hydrophobicity is not yet published. This review is the first to provide not only quantitative information on the impacts of biochar properties in WHC and hydrophobicity, but also a road map to optimise biochar for enhanced WHC when applied as a soil amendment. The review shows that straw or grass-derived biochar (at 500-600 °C) increases the WHC of soil if applied at 1 to 3 % in the soil. It is clear from the review that soil of varying texture requires different particle sizes of biochar to enhance the WHC and reduce hydrophobicity. Furthermore, the review concludes that ageing biochar for at least a year with enhanced oxidation is recommended for improving the WHC and reducing hydrophobicity compared to using biochar immediately after production. Additionally, while producing biochar a residence time of 1 to 2 h is recommended to reduce the biochar's hydrophobicity. Finally, a road map for optimising biochar is presented as a schematic that can be a resource for making decisions during biochar production for soil amendment.

Niche differentiation modulates metabolites abundance and composition in silicon fertilizer amended soil during sugarcane growth

BACKGROUND

As one of the vital crops globally, sugarcane (Saccharum officinarum L.) has been one of model crops for conducting metabolome research. Although many studies have focused on understanding bioactive components in specific sugarcane tissues, crucial questions have been left unanswered about the response of metabolites to niche differentiation such as different sugarcane tissues (leaf, stem and root), and soil regions (rhizosphere and bulk) under silicon (Si) amended soils. Here, nontargeted metabolite profiling method was leveraged to assess the similarities and differences in the abundance and community composition of metabolites in the different sugarcane and soil compartments. Identify the compartment-specific expression patterns of metabolites, and their association with cane agronomic traits and edaphic factors. We also investigated the response of sugarcane agronomic traits and edaphic factors to Si amended soil.

RESULTS

We found that Si fertilizer exhibited the advantages of overwhelmingly promoting the height and theoretical production of cane, and profoundly increased soil Si content by 24.8 and 27.0%, while soil available potassium (AK) was enhanced by 3.07 and 2.67 folds in the bulk and rhizosphere soils, respectively. It was also noticed that available phosphorus (AP) in the rhizosphere soil tremendously increased by 105.5%. We detected 339 metabolites in 30 samples using LC-MS/MS analyses, 161 of which were classified and annotated, including organooxygen compounds (19.9%), carboxylic acids and derivatives (15.5%), fatty acyls (15.5%), flavonoids (4.4%), phenols (4.4%), and benzene and substituted derivatives (3.7%). In addition, the total percentages covered by these core metabolites in each compartment ranged from 94.0% (bulk soil) to 93.4% (rhizosphere soil), followed by 87.4% (leaf), 81.0% (root) and 80.5% (stem), suggesting that these bioactive compounds may have migrated from the belowground tissues and gradually filtered in various aboveground niches of the plant. We also observed that the variations and enrichment of metabolites abundance and community were compartment-specific. Furthermore, some key bioactive compounds were markedly associated with plant growth parameters and soil edaphic.

CONCLUSION

Taken together, we hypothesized that Si utilization can exhibit the advantage of enhancing edaphic factors and cane agronomic traits, and variations in metabolites community are tissue-specific.

Silicon fertilizer mediated structural variation and niche differentiation in the rhizosphere and endosphere bacterial microbiome and metabolites of sugarcane

The microbiomes of plant are potential determinants of plant growth, productivity, and health. They provide plants with a plethora of functional capacities, namely, phytopathogens suppression, access to low-abundance nutrients, and resistance to environmental stressors. However, a comprehensive insight into the structural compositions of the bacterial abundance, diversity, richness, and function colonizing various microenvironments of plants, and specifically their association with bioactive compounds and soil edaphic factors under silicon (Si) amendment remains largely inconclusive. Here, high-throughput sequencing technology and nontargeted metabolite profiling method were adopted to test the hypotheses regarding microbiome niche abundance, diversity, richness, function, and their association with bioactive compounds and soil edaphic factors within different ecological niches (leaf, stem, root, rhizosphere, and bulk soils) under Si amendment during cane growth were we addressed. Our results demonstrated that Si correspondingly increased sugarcane theoretical production and yield, and remarkably enhanced soil nutrient status, especially Si, AP, and AK. It was also observed that bacterial diversity demonstrated tissue-dependent distribution patterns, with the bulk soil, rhizosphere soil, and root endosphere revealing the highest amount of bacterial diversity compared with the stem and leaf tissues. Moreover, Si exhibited the advantage of considerably promoting bacterial abundance in the various plant compartments. Co-occurrence interactions demonstrated that Si application has the potential to increase bacterial diversity maintenance, coexistence, and plant–soil systems bacteria connections, thereby increasing the functional diversity in the various plant tissues, which, in turn, could trigger positive growth effects in plants. Network analysis further revealed that metabolite profiles exhibited a strong association with bacterial community structures. It was also revealed that Si content had a considerable positive association with bacterial structures. Our findings suggest that the dynamic changes in microbe’s community composition in different plant and soil compartments were compartment-specific. Our study provides comprehensive empirical evidence of the significance of Si in agriculture and illuminated on differential metabolite profiles and soil microbe’s relationship.

Biochar Application Increases Labile Carbon and Inorganic Nitrogen Supply in a Continuous Monocropping Soil

Biochar is an effective method for increasing soil carbon (C) sequestration and nitrogen (N) supply under continuous monocropping. To investigate the impact of biochar placement methods on soil C and N, a one-year field experiment with five treatments was conducted including control, mineral fertilizers only (F), biochar hole placement (BFH; biochar applied to the soil layer at 5–10 cm) + F, biochar band placement (BFB; biochar applied to the soil layer at 15–20 cm) + F, and biochar band and hole placement + F (BFBH). The results showed that, regardless of the placement method, biochar application increased soil total organic C (TOC) and C pool management index by 6.9–39.7% and 4.1–36.1%, respectively, especially for dissolved organic C (DOC; 6.9–51.3%), readily oxidizable C (ROC; 2.4–46.4%), and microbial biomass C (MBC; 10.4–41.7%). Single biochar placement methods significantly influenced DOC, MBC, and ROC contents of both soil layers in the rank order of BFH ≈ BFBH > BFB at 0–15 cm and BFB ≈ BFBH > BFH at 15–30 cm. Soil TN and microbial biomass N (MBN) mainly accumulated at the site of biochar placement. The increased soil TOC:TN and MBC:N ratios under biochar treatments promoted inorganic N immobilization and reduced the loss of ammonium N and nitrate N (NO3−-N) through leaching at the early stage of tobacco growth. Biochar-adsorbed N was remobilized at a later period (vigorous growth stage and maturity), possibly causing the slow decrease in NO3−-N content. Additionally, soil C and N pools were significantly influenced by the main effects of soil layer and growth stage. Overall, biochar application increased soil C and N pools and inorganic N supply through N remobilization. However, the increased labile organic C content and microbial activity may prevent C sequestration in biochar-amended soils.

Sugarcane–Peanut Intercropping System Enhances Bacteria Abundance, Diversity, and Sugarcane Parameters in Rhizospheric and Bulk Soils

Sugarcane–legume intercropping systems can effectively control pests and diseases as well as improve the fertility and health of farmland soil. However, little is known about the response of bacterial abundance, diversity, and community composition in the rhizosphere and non-rhizosphere soils under the sugarcane–peanut farming system. A field experiment was conducted with two treatments: sugarcane monoculture and sugarcane–peanut intercropping to examine the response of sugarcane parameters and edaphic factors. We also deciphered bacterial abundance, diversity, and community composition in the root endosphere, rhizosphere, and bulk soil by leveraging Illumina sequencing to conduct the molecular characterization of the 16S rRNA gene and nitrogenase (nifH) gene. We observed that sugarcane–peanut intercropping exhibited the advantages of tremendously increasing cane stalk height, stalk weight, and millable stalk number/20 m, and edaphic factors, namely, pH (1.13 and 1.93), and available phosphorus exhibited a fourfold and sixfold increase (4.66 and 6.56), particularly in the rhizosphere and bulk soils, respectively. Our result also showed that the sugarcane–peanut intercropping system significantly increased the bacterial richness of the 16S rRNA gene sequencing data by 13.80 and 9.28% in the bulk soil and rhizosphere soil relative to those in the monocropping sugarcane system, respectively. At the same time, sugarcane intercropping with peanuts significantly increased the Shannon diversity of nitrogen-fixing bacteria in the sugarcane rhizosphere soil. Moreover, most edaphic factors exhibited a positive regularity effect on bacterial community composition under the intercropping system. A linear discriminant analysis with effect size analysis of the 16S rRNA sequencing data revealed that bacteria in the root endosphere of the intercropped cane proliferated profoundly, primarily occupied by Devosia, Rhizobiales, Myxococcales, Allorhizobium-Neorhizobium-Pararhizobium-Rhizobium, Bradyrhizobium, and Sphingomonas. In conclusion, our findings demonstrated that sugarcane–peanut intercropping can enhance edaphic factors, sugarcane parameters, and bacterial abundance and diversity without causing adverse impacts on crop production and soil.

Filtered mud improves sugarcane growth and modifies the functional abundance and structure of soil microbial populations

BACKGROUND

Exploring high-quality organic amendments has been a focus of sustainable agriculture. Filtered mud (FM), a sugar factory waste derived from sugarcane stems, could be an alternative organic amendment for sugarcane production. However, the effects of its application proportions on soil fertility, nutrient cycling, structure of soil bacterial and fungal communities, and the growth of sugarcane in clay-loam soils remain unexplored.

METHODS

Three application proportions of FM: (FM1-(FM: Soil at 1:4), FM2-(FM: Soil at 2:3), and FM3-(FM: Soil at 3:2)) were evaluated on sugarcane growth and soil nutrient cycling. High throughput sequencing was also employed to explore soil microbial dynamics.

RESULTS

We observed that FM generally increased the soil's nutritional properties while improving NO₃ ^- retention compared to the control, resulting in increased growth parameters of sugarcane. Specifically, FM1 increased the concentration of NH₄ ⁺-N, the N fraction preferably taken up by sugarcane, which was associated with an increase in the plant height, and more improved growth properties, among other treatments. An increase in the proportion of FM also increased the activity of soil nutrient cycling enzymes; urease, phosphatase, and β-glucosidase. High throughput sequencing revealed that FM reduced the diversity of soil bacteria while having insignificant effects on fungal diversity. Although increasing FM rates reduced the relative abundance of the phyla Proteobacteria, its class members, the Gammaproteobacteria and Betaproteobacteria containing some N-cycling related genera, were stimulated. Also, FM stimulated the abundance of beneficial and lignocellulose degrading organisms. These included the bacterial phyla Actinobacteria, Bacteroidetes, Acidobacteria, Chloroflexi, and the fungal phylum Ascomycota. The distribution of the soil microbial community under FM rates was regulated by the changes in soil pH and the availability of soil nutrients. Since FM1 showed more promise in improving the growth properties of sugarcane, it could be more economical and sustainable for sugarcane production in clay-loam soils.