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.

Insights into enzyme activity and phosphorus conversion during kitchen waste composting utilizing phosphorus-solubilizing bacterial inoculation

The main objective of this research was to investigate the effects of Phosphorus-Solubilizing Bacterial (PSB) inoculant on the bacterial structure and phosphorus transformation during kitchen waste composting. High throughput sequencing, topological roles, and multiple analysis methods were conducted to explain the links between phosphorus fractions, enzyme contents, and microbial community structure and function. The findings indicated that bacterial inoculant improved environmental parameters and increased the concentration of total phosphorus, Olsen phosphorus, citric acid phosphorus, OM decomposition, and bacterial diversity. Network analysis concluded that the inoculation treatment was more complex (nodes and edges) and contained more positive links than the control, implying the inoculation effect. The structural equation model also displayed that pH and enzyme activity directly enhanced the phosphorus conversion and bacterial structure. Overall, these results suggest that bacterial inoculation may considerably increase enzyme activity, thus improving biological phosphorus transformation and nutrient content in composting products.

Response of Wheat Cultivars to Organic and Inorganic Nutrition: Effect on the Yield and Soil Biological Properties

The deterioration of soil biological health is the most important aspect associated with the sustainability of cereal-based food production systems. The application of organic nutrient sources is widely accepted and recommended for sustaining crop productivity and preserving soil fertility. Therefore, a study was carried out to assess the effects of different levels of farmyard manure (FYM10: 10 t ha−1, FYM20: 20 t ha−1, FYM30: 30 t ha−1), including inorganic fertilizer (NPK) on the soil and the biological properties of five high-yielding wheat cultivars (HD 2967, DPW 621-50, PBW 550, and WH 1105) over a three-year period (2014–2015 to 2016–2017). The results showed that the application of NPK produced significantly higher yields compared to different levels of FYM and the control during all the study years. The continuous addition of a higher rate of FYM at 30 t ha−1 was found to be beneficial in terms of enhancing crop yield gain, thereby bridging the yield gap to only 7.2% in the third year; the gap was 69.1% in the first year with NPK application. The microbial population and microbial biomass carbon were significantly higher in the FYM treatments compared to the NPK treatment. The activities of different soil enzymes were observed to be significantly maximum in the FYM30 treatment. Similarly, the addition of FYM significantly improved the soil respiration and microbial activity over the NPK and control treatments. Based on the principal component analysis, fluorescein diacetate, bacteria, fungi, and actinomycetes were observed as sensitive biological parameters for the assessing of soil biological health. The soil biological index (SBI) determined with the sensitive parameters was in the decreasing order of FYM30 (0.70), FYM20 (0.61), FYM10 (0.55), NPK (0.18), and control (0.15). Considering both the SBI and the sustainability yield index together, the performance of WH 1105 was found to be better compared to the rest of the wheat cultivars. Our results conclude that the application of FYM in the long run increases the crop yield (24.3 to 38.9%) and improves the soil biological process, leading to the improved biological index of the soil.

The Promotive Effect of Cyanobacteria and Chlorella sp. Foliar Biofertilization on Growth and Metabolic Activities of Willow (Salix viminalis L.) Plants as Feedstock Production, Solid Biofuel and Biochar as C Carrier for Fertilizers via Torrefaction Process

The effect of foliar application of Cyanobacteria and Chlorella sp. monocultures on physiological activity, element composition, development and biomass weight of basket willow (Salix viminalis L.) and the possibility to prepare biofuel from it in the fortification process was studied. Triple foliar plant spraying with non-sonicated monocultures of Cyanobacteria (Anabaena sp. PCC 7120, Microcystis aeruginosa MKR 0105) and Chlorella sp. exhibited a considerably progressive impact on metabolic activity and development of plants. This biofertilization increased cytomembrane impermeability, the amount of chlorophyll in plants, photosynthesis productivity and transpiration, as well as degree of stomatal opening associated with a decreased concentration of intercellular CO2, in comparison to control (treatments with water, Bio-Algeen S90 or with environmental sample). The applied strains markedly increased the element content (N, P, K) in shoots and the productivity of crucial growth enzymes: alkaline or acid phosphorylase, total dehydrogenases, RNase and nitrate reductase. Treatments did not affect energy properties of the burnt plants. These physiological events were associated with the improved growth of willow plants, namely height, length and amount of all shoots and their freshly harvested dry mass, which were increased by over 25% compared to the controls. The effectiveness of these treatments depended on applied monoculture. The plant spraying with Microcystis aeruginosa MKR 0105 was a little more effective than treatment with Chlorella sp. and Anabaena sp. or the environmental sample. The research demonstrate that the studied Cyanobacteria and Chlorella sp. monocultures have prospective and useful potential in production of Salix viminalis L., which is the basic energy plant around the word. In this work, a special batch reactor was used to produce torrefaction material in an inert atmosphere: nitrogen, thermogravimetric analysis and DTA analysis, like Fourier-transform infrared spectroscopy. The combustion process of Salix viminalis L. with TG-MS analysis was conducted as well as study on a willow torrefaction process, obtaining 30% mass reduction with energy loss close to 10%. Comparing our research results to other types of biomasses, the isothermal temperature of 245 °C during thermo-chemical conversion of willow for the carbonized solid biofuel production from Salix viminalis L. biomass fertilized with Cyanobacteria and Chlorella sp. is relatively low. At the end, a SEM-EDS analysis of ash from torrefied Salix viminalis L. after carbonization process was conducted.

The wheat growth-promoting traits of Ochrobactrum and Pantoea species, responsible for solubilization of different P sources, are ensured by genes encoding enzymes of multiple P-releasing pathways

Production and release of organic acids and phosphatase enzymes by microbes are important for inorganic and organic phosphorus cycling in soil. The presence of microorganisms with corresponding traits in the plant rhizosphere lead to improved plant P uptake and ultimately growth promotion. We studied the potential of two rhizosphere-competent strains, Pantoea sp. MR1 and Ochrobactrum sp. SSR, for solubilization of different organic and inorganic P sources in vitro. In a pot experiment we further revealed the impact of the two strains on wheat seedling performance in soil amended with either phytate, rock phosphate or K₂HPO₄ as solely P source. To directly link P-solubilizing activity to the strain-specific genetic potential, we designed novel primers for glucose dehydrogenase (gcd), phosphatase (pho) and phytase (phy) genes, which are related to the organic and inorganic P solubilization potential. Quantitative tracing of these functional genes in the inoculated soils of the conducted pot experiment further allowed to compare strain abundances in the soil in dependency on the present P source. We observed strain- and P source-dependent patterns of the P solubilization in vitro as well as in the pot experiment, whereby P release, particularly from phytate, was linked to the strain abundance. We further revealed that the activity of microbial phosphatases is determined by the interplay between functional gene abundance, available soil P, and substrate availability. Moreover, positive impacts of microbial seed inoculation on wheat root architecture and aboveground growth parameters were observed. Our results suggest that screening for rhizosphere-competent strains with gcd, pho and phy genes may help to identify new microbial taxa that are able to solubilize and mineralize inorganic as well as organic bound P. Subsequently, the targeted use of corresponding strains may improve P availability in agricultural soils and consequently reduce fertilizer application.

Phosphorus release during alkaline treatment of waste activated sludge from wastewater treatment plants with Al salt enhanced phosphorus removal: Speciation and mechanism clarification

Chemical phosphorus removal (CPR) is being increasingly adopted in wastewater treatment plants (WWTPs) to enhance P elimination to comply with stringent discharge limits. However, strategies to recover P enriched in the produced waste activated sludge (WAS) are not well developed. In this study, we investigated the release of P in WAS from three WWTPs employing Al salt enhanced CPR by alkaline treatment. We also monitored P mobilization by tracking the dynamics of P fractions and species, the dissolution of major metals, and sludge cell integrities as pH was altered. The level of aqueous total phosphorus (TP_aq) in the sludge increased significantly to >200 mg/L (from <11 mg/L in the raw sludge) as the pH was increased to 12, with the majority being PO₄-P_aq especially at high pHs. The dominance of non-apatite inorganic phosphorus (NAIP) in the sludge-P, a good correlation observed between aqueous PO₄-P and aqueous Al, and the reversibility of P mobilization all suggest that the dissolution of Al-bound P was largely responsible for the sludge-P release. Sludge cell integrity, on the other hand, was not closely correlated with TP_aq concentrations. Although the level of TP released in this study is among the highest, a more efficient strategy still needs to be developed to further enhance sludge-P release when TP content in the sludge mixture (TP_mx) is considered (TP_mx was >800 mg/L in this work).

Colloidally Confined Crystallization of Highly Efficient Ammonium Phosphomolybdate Catalysts

Nanodroplets in inverse miniemulsions provide a colloidal confinement for the crystallization of ammonium phosphomolybdate (APM), influencing the resulting particle size. The effects of the space confinement are investigated by comparing the crystallization of analogous materials both in miniemulsion and in bulk solution. Both routes result in particles with a rhombododecahedral morphology, but the ones produced in miniemulsion have sizes between 40 and 90 nm, 3 orders of magnitude smaller than the ones obtained in bulk solution. The catalytic activity of the materials is studied by taking the epoxidation of cis-cyclooctene as a model reaction. The miniemulsion route yields APM particles catalytically much more active than analogous samples produced in bulk solution, which can be explained by their higher dispersibility in organic solvents, their higher surface area, and their higher porosity. Inorganic phosphate salt precursors are compared with organic phosphate sources. APM nanoparticles prepared in miniemulsion from d-glucose-6-phosphate and O-phospho-dl-serine yield a conversion in the epoxidation reaction of more than 90% after only 1 h, compared to 30% for materials prepared in bulk solution. In addition, the catalysts prepared in miniemulsion display a promising recyclability.

Phylogenetic-scale disparities in the soil microbial diversity-ecosystem functioning relationship

The historical conditions under which bacterial lineages evolve determine their functional traits, and consequently their contribution to ecosystem functions (EFs). Under significant trait conservatism, which is common in prokaryotes, phylogeny may track the evolutionary history of species and predict their functionality. Productive communities can arise from: (i) the coexistence of functional, and therefore phylogenetically distant lineages, producing high EF rates at large phylogenetic diversity (PD); (ii) the dominance of productive lineages that outcompete other clades, generating high EF at low PD. Community composition will modulate the PD-EF relationship: The effects of anciently divergent lineages, whose deeply conserved functions determine the occupancy of major niches, may differ from that of recently divergent lineages showing adaptations to current conditions. We hypothesized that, in our model Mediterranean ecosystem, EF can be explained both by competitive superiority of ancient lineages and functional complementarity of recent lineages. To test this hypothesis, we sequenced a phylogenetic marker targeting bacteria across 28 soil plots and quantified EF related to microbial productivity, decomposition and nutrient cycling. Plots accumulating recently divergent lineages consistently showed higher EF levels that were slightly modified by the accumulation of ancient lineages. We discuss the assembly processes behind these phylogenetic-scale disparities and the final outcome in terms of ecosystem functioning.

The Interaction between Arbuscular Mycorrhizal Fungi and Endophytic Bacteria Enhances Plant Growth of Acacia gerrardii under Salt Stress

Microbes living symbiotically in plant tissues mutually cooperate with each other by providing nutrients for proliferation of the partner organism and have a beneficial effect on plant growth. However, few studies thus far have examined the interactive effect of endophytic bacteria and arbuscular mycorrhizal fungi (AMF) in hostile conditions and their potential to improve plant stress tolerance. In this study, we investigated how the synergistic interactions of endophytic bacteria and AMF affect plant growth, nodulation, nutrient acquisition and stress tolerance of Acacia gerrardii under salt stress. Plant growth varied between the treatments with both single inoculants and was higher in plants inoculated with the endophytic B. subtilis strain than with AMF. Co-inoculated A. gerrardii had a significantly greater shoot and root dry weight, nodule number, and leghemoglobin content than those inoculated with AMF or B. subtilis alone under salt stress. The endophytic B. subtilis could alleviate the adverse effect of salt on AMF colonization. The differences in nitrate and nitrite reductase and nitrogenase activities between uninoculated plants and those inoculated with AMF and B. subtilis together under stress were significant. Both inoculation treatments, either B. subtilis alone or combined with AMF, enhanced the N, P, K, Mg, and Ca contents and phosphatase activities in salt-stressed A. gerrardii tissues and reduced Na and Cl concentration, thereby protecting salt-stressed plants from ionic and osmotic stress-induced changes. In conclusion, our results indicate that endophytic bacteria and AMF contribute to a tripartite mutualistic symbiosis in A. gerrardii and are coordinately involved in the plant adaptation to salt stress tolerance.