Available P Research Articles

Elevational variation in soil phosphorus pools and controlling factors in alpine areas of Southwest China

As an important life element in the Earth’s ecosystem, soil phosphorus (P) is of great significance to stability and sustainable development of terrestrial ecosystems. However, seasonal variations in different soil P pools and their regulatory mechanisms along elevations are not fully understood. Here, we investigated seasonal variations in soil P pools including total P (TP), available P (AP), inorganic P (IP), organic P (OP), labile P, moderately labile P, and stable P in topsoil (0–15 cm) along different elevations (2600–3900 m) in the Yulong Snow Mountain. The associated drivers including leaf nutrient contents, soil properties, micro-climate, and microbial parameters were also examined. We found that all soil P fractions reached a maximum at mid-elevations (2,900 m and 3,200 m), possibly due to the more active microorganisms and suitable soil climatic conditions for advancing P weathering. Meanwhile, soil AP pool was also observed to be tightly related to the leaf P content along elevations. Unexpectedly, most soil P pools did not show seasonal changes, except for AP showing significantly higher level in the wet season than in the dry season, owing to the high temperature and microbial activity for promoting P release in the wet season. Consequently, we found that microbial P, acid phosphatase and dissolved organic carbon had a stronger influence on different P pools than other soil factors. Moreover, there was a strong interaction of labile P and moderately labile P with soil environments (i.e. soil moisture, temperature, dissolved organic carbon). Collectively, our results revealed the elevational shifts in soil P pools and potential mechanisms in Yulong Mountain, and provided an important theoretical basis for soil P dynamics in response to environments in mountain ecosystems.

Penicillium oxalicum augments soil lead immobilization by affecting indigenous microbial community structure and inorganic phosphate solubilization potential during microbial-induced phosphate precipitation

Phosphate-solubilizing microorganisms (PSMs) are critically important for increasing soil phosphate (P) and decreasing lead (Pb) bioavailability during microbial-induced phosphate precipitation (MIPP). However, their relative contributions to the indigenous soil microbial communities and P-cycling genes during the MIPP process remain unclear. In this study, inoculation of the PSM P. oxalicum in hydroxyapatite-cultured and Pb-contaminated soil increased soil phosphatase activities, available P (AP) concentrations and reduced available Pb levels. Metagenomics revealed a 3.9–44.0% increase in the abundance of P-cycling genes by P. oxalicum inoculation. No P-cycling genes were assigned to Penicillium. While P. oxalicum increased the complexity of microbial community co-occurrence networks, and improved the directly interrelationships between Penicillium and genera containing P-cycling gene. These results suggesting that P. oxalicum obviously positively affected the regulation of indigenous P-cycling functional communities during the MIPP process. Inorganic P solubilization genes (gcd, ppa, and ppx) have been shown to affect soil AP, suggesting that inorganic P solubilization is the major driver of Pb immobilization improvement following P. oxalicum inoculation. These results enhance our understanding of the significant ecological role of PSMs in governing soil P-cycling and alleviating Pb2+ biotoxicity during the MIPP process.

Impact of long-term integrated nutrient management on soil quality and productivity of cotton (Gossypium spp.) + greengram (Vigna radiata) intercropping system in vertisols under semi-arid agroecosystem

Integrated nutrient management has potential to enhance soil quality and sustain agricultural productivity, however, such effects under cotton + greengram intercropping is not well understood in vertisols of Maharashtra, India. Therefore, a field study was conducted during 2016–2017 at the Research field of AICRP for Dryland Agriculture Akola, Maharashtra (India), on an ongoing long-term experiment initiated in 1987–1988 under cotton + greengram (1:1) intercropping system to find out how different nutrient management practices affect the soil quality (SQ) and cotton + greengram productivity. The eight treatments comprised of sole use of organics and chemical fertilizers, integration of organics with chemical fertilizers (INM) to partially substitute nitrogen, and a control treatment. The results after 30th cycle revealed that the partial substitution of N through FYM/gliricidia increased cotton and greengram yield over control. These treatments caused significant improvement in the soil physical and biological properties and also improved the soil fertility status, mainly soil organic carbon (OC) by 53%, available N (AN) by 25%, available P (AP) by 50%, and available K (AK) by 25% over control. The SQ assessment through principal component analysis (PCA) revealed that, in this semi-arid subtropical region, HC, OC, and CO2 evolution can be viewed as important indicators of SQ for cotton + greengram intercropping system. Therefore, we concluded that, INM practice that encourages balanced fertilization must include FYM/gliricidia as part of the nutrient application package in this region to improve soil quality and sustain productivity of cotton + greengram intercropping system.

Altered microbial P cycling genes drive P availability in soil after afforestation

Soil Phosphorous (P) availability is a limiting factor for plant growth and regulates biological metabolism in plantation ecosystems. The effect of variations in soil microbial P cycling potential on the availability of soil P during succession in plantation ecosystems is unclear. In this study, a metagenomics approach was used to explore variations in the composition and diversity of microbial P genes along a 45-year recovery sequence of Robinia pseudoacacia on the Loess Plateau, as well soil properties were measured. Our results showed that the diversity of P cycling genes (inorganic P solubilization and organic P mineralization genes) increased significantly after afforestation, and the community composition showed clear differences. The gcd and ppx genes were dominant in inorganic P transformation, whereas phnM gene dominated the transformation of organic P. The abundance of genes involved in inorganic P solubilization and organic P mineralization was significantly positively correlated with P availability, particularly for phnM, gcd, ppx, and phnI genes, corresponding to the phyla Gemmatimonadetes, Acidobacteria, Bacteroidetes, and Planctomycetes. The critical drivers of the microbial main genes of soil P cycling were available P (AP) and total N (TN) in soil. Overall, these findings highlight afforestation-induced increases in microbial P cycling genes enhanced soil P availability. and help to better understand how microbial growth metabolism caused by vegetation restoration in ecologically fragile areas affects the soil P cycling.

Response of soil bacterial communities in wheat rhizosphere to straw mulching and N fertilization.

Straw mulching and N fertilization are effective in augmenting crop yields. Since their combined effects on wheat rhizosphere bacterial communities remain largely unknown, our aim was to assess how the bacterial communities respond to these agricultural measures. We studied wheat rhizosphere microbiomes in a split-plot design experiment with maize straw mulching (0 and 8,000 kg straw ha-1) as the main-plot treatment and N fertilization (0, 120 and 180 kg N ha-1) as the sub-plot treatment. Bacterial communities in the rhizosphere were analyzed using 16S rRNA gene amplicon sequencing and quantitative PCR. Most of the differences in soil physicochemical properties and rhizosphere bacterial communities were detected between the straw mulching (SM) and no straw mulching (NSM) treatments. The contents of soil organic C (SOC), total N (TN), NH4 +-N, available N (AN), available P (AP) and available K (AK) were higher with than without mulching. Straw mulching led to greater abundance, diversity and richness of the rhizosphere bacterial communities. The differences in bacterial community composition were related to differences in soil temperature and SOC, AP and AK contents. Straw mulching altered the soil physiochemical properties, leading to greater bacterial diversity and richness of the rhizosphere bacterial communities, likely mostly due to the increase in SOC content that provided an effective C source for the bacteria. The relative abundance of Proteobacteria was high in all treatments and most of the differentially abundant OTUs were proteobacterial. Multiple OTUs assigned to Acidobacteria, Chloroflexi and Actinobacteria were enriched in the SM treatment. Putative plant growth promoters were enriched both in the SM and NSM treatments. These findings indicate potential strategies for the agricultural management of soil microbiomes.

Effects of on- and off-year management practices on the soil organic C fractions and microbial community in a Moso bamboo (Phyllostachys edulis) forest in subtropical China.

On- and off-year management practices are usually adopted in Moso bamboo (Phyllostachys edulis) forests to achieve higher productivity. However, little is known about the effects of these management practices on soil C sequestration and microbial community structure. In the present study, soil nutrient content, organic C fractions, and bacterial and fungal communities were comparatively investigated in on- and off-year bamboo stands. The results showed that soil organic C (SOC), alkali-hydrolyzable N (AN), and available P (AP) in the on-year were significantly lower (p ≤ 0.05) than those in the off-year. Among the different soil organic C fractions, easily oxidizable organic C (EOC), microbial biomass C (MBC), Ca-bound SOC (Ca-SOC), and Fe/Al-bound SOC (Fe/Al-SOC) also had significantly higher contents in the off-year than in the on-year, with MBC and EOC decreasing by 56.3% and 24.5%, respectively, indicating that both active and passive soil organic C pools increased in the off-year. However, the alpha diversities of both soil bacteria and fungi were significantly lower in the off-year soils than in the on-year soils. The bacterial taxa Actinobacteria, Planctomycetes, WPS-2, Acidothermus, Candidatus_Solibacter, Burkholderia-Caballeronia-Paraburkholderia, and Candidatus_Xiphinematobacter were increased in off-year soils relative to on-year soils. Meanwhile, fungal taxa Ascomycota, Mortierella, Hypocrea, Cryptococcus, Clitopilus, and Ceratocystis were significantly increased in on-year soils. Soil pH, SOC, AP, MBC, EOC, and Ca-SOC were significantly correlated with bacterial and fungal communities, with soil pH being the most important driving factor for the shift in bacterial and fungal communities. Our findings showed that the studied bamboo forest possessed an inherent restorative ability in the off-year, which can reverse the soil nutrient and C depletion in the on-years and ensure soil fertility in the long term.

PhoD-harboring bacterial community composition dominates organic P mineralization under long-term P fertilization in acid purple soil.

A better understanding of the regulatory role of microorganisms on soil phosphorous (P) mobilization is critical for developing sustainable fertilization practices and reducing P resource scarcity. The phoD genes regulate soil organic P (Po) mobilization. Based on the long-term P application experiments in acid purple soil of maize system in Southwest China (started in 2010), the experiment included five P levels: 0, 16, 33, 49, and 65.5 kg P hm-2 (P0, P16, P33, P49, and P65.5, respectively). The molecular speciation of organic P in soil was determined by 31P-nuclear magnetic resonance (NMR), high-throughput sequencing technology, and real-time qPCR were used to analyze the bacterial community and abundance of phoD-harboring bacterial genes, exploring the bacterial community and abundance characteristics of phoD gene and its relationship with the forms of Po and alkaline phosphatase (ALP) activity in the soil. The results showed that the orthophosphate monoesters (OM) were the main Po speciation and varied by P fertilization in acid purple soil. ALP activity decreased as P fertilization increased. Co-occurrence network analysis identified the overall network under five P fertilizations. The keystone taxon base on the network showed that Collimonas, Roseateles, Mesorhizobium, and Cellulomonas positively correlated with both OM and Po. The random forest showed that Cellulomonas, Roseateles, and Rhodoplanes were the key predictors for ALP activity. The keystone taxon was a more important predictor than the dominant taxon for ALP, OM, and Po. The structural equation model (SEM) showed that soil organic matter (SOM), available P (AP), and OM were the main factors influencing the ALP by reshaping phoD-harboring bacteria alpha diversity, community composition, and phoD abundance. The phoD-harboring bacterial community composition especially the keystone taxon rather than alpha diversity and abundance dominated the ALP activity, which could promote P utilization over an intensive agroecosystem. These findings improve the understanding of how long-term gradient fertilization influences the community composition and function of P-solubilizing microorganisms in acid purple soil.

Metagenomic insights into the effects of organic and inorganic agricultural managements on soil phosphorus cycling

Microbes play important roles in regulating soil phosphorus (P) cycling in agroecosystems. However, little is known about how P-cycling microbes respond to organic and inorganic agricultural managements in terms of their functional and phylogenetic traits. Here, metagenomics was used to determine effects of P-cycling functional genes and taxa on soil P availability in a forage (Broussonetia papyrifera) monoculture ecosystem under organic (inoculating arbuscular mycohrrizal fungi (AMF) and intercropping legume (Medicago sativa)) and inorganic (adding chemical nitrogen (N) and P fertilizers) managements. The results showed that soil available P (AP) in plots with both legume and AMF addition was increased by 54.3 % compared with the control and was1.6–2.4 times higher than in plots with N or P fertilization. The abundance of ppa involved in inorganic-P solubilization was significantly increased after adding both legume and AMF compared with P-addition treatment. Soil alkaline phosphatase activity increased with P fertilizer addition and was positively correlated with soil AP. The abundances of phoA and phnI involved in organic-P mineralization were significantly higher under P fertilization treatment than under N fertilization treatment. Soil total N and AP were the key drivers on interactions among P-transportation genes, organic-P mineralization genes and taxa related to P-transportation. Overall, organic agricultural management increases soil P availability by increasing the potential of inorganic-P solubilization, while inorganic agricultural management regulates P availability via altering the potential of organic-P mineralization. These findings could provide a better understanding of the mechanisms that drive soil P availability under organic and inorganic agricultural managements.

Cotton-maize intercropping increases rhizosphere soil phosphorus bioavailability by regulating key phosphorus cycling genes in northwest China

Intercropping is widely used as an important means to promote crop productivity; but the underpinning mechanisms of rhizosphere soil microbial processes in shaping soil phosphorus (P) bioavailability under cotton-based intercropping systems have not been investigated in arid northwest China. Therefore, taking cotton-maize intercropping as an example, biologically based P (BBP) and metagenomics methods were used to investigate changes of soil P bioavailability, microbial community and functional P-cycling genes in the rhizosphere. Three treatments were cotton monoculture, maize monoculture and cotton-maize intercropping. We found that rhizosphere soils from cotton-maize intercropping exhibited higher soil organic matter (SOM), available P (AP), and alkaline phosphatase (ALP) than those of crop monocultures (p < 0.05). The change of bioavailable-P fractions in the order HCl-P > Citrate-P > Enzyme-P > CaCl2-P, and higher mount of CaCl2-P, Citrate-P and Enzyme-P were observed in soil samples from cotton-maize intercropping. These results indicated that P bioavailability were improved after two crops intercropping. The dominate soil microbial community from all treatments belonged to the phyla Proteobacteria, Actinobacteria, Acidobacteria, Chloroflexi and Gemmatimonadetes. In addition, we observed that the expression of functional genes which involved in soil microbial inorganic phosphate transportation (phoR), inorganic phosphate solubilization (phoD, glpA, glpK, glpQ), phosphate ester mineralization (gcd, ppk, ppx), and phosphate ester mineralization (pstABC, pit) were also up-regulated in cotton-maize intercropping (p < 0.05). Redundancy analysis showed that SOM, CaCl2-P and AP significantly correlated genes gcd, ppx, pstABC, pit, and phoD, suggesting that SOM, CaCl2-P and available P are important factors in influencing expression of these P-cycling functional genes. It is concluded that cotton-maize intercropping increased P bioavailability via changing rhizosphere soil microbial composition and functional genes.

Characteristics of Organic Phosphorus Pool in Soil of Typical Agriculture Systems in South China

Organic phosphorus (P) is an important potential source of plant P nutrition in agro-ecosystems. It was hypothesized that the soil organic P pools were distinguished one from another by different land-utilization patterns. A total of 38 sites were sampled, to clarify the organic P pool and its distribution in paddy fields, vegetable fields, and orchards. Soil organic P fractions, including labile organic P (LOP), moderately labile organic P (MLOP), moderately resistant organic P (MROP) and highly resistant organic P (HROP) were examined. Results showed that the soil total P (TP) and available P (AP) concentration have enhanced by 138% and 1559%, respectively, over the last four decades. The soil total organic P (TOP) accounted for 21.4% of the TP pool. Soil MLOP dominated the organic P reservoir, irrespective of land-planting pattern. Soil organic P fractions ranked as MLOP &gt; MROP &gt; HROP &gt; LOP. The highest accumulations of TP, AP and TOP were in the vegetable fields, followed by orchards and paddy fields. The vegetable fields had higher LOP and MLOP levels than those of the paddy fields and orchards, whereas the paddy fields exhibited higher concentrations of MROP, and HROP. Soil pH, organic matter and available nitrogen all contributed to the buildup of the organic P pool. It was suggested that soil organic P should be considered preferentially in the management of the plant P nutrient in regional planting systems.

Long-term high-P fertilizer input shifts soil P cycle genes and microorganism communities in dryland wheat production systems

Phosphorus (P) fertilizer input influences crop yield, soil P cycling, and phosphate-solubilizing microorganism (PSM) communities, which play a key role in obtaining soil available phosphorus. However, the responses of soil P cycle genes and PSM communities to long-term high-P fertilizer application are less known in the Chinese Loess Plateau. In this study, metagenomics was used to explore the shifts in the abundance and compositions of soil P cycle genes and PSM communities at a long-term (14 years) trial site with four P fertilization rates. Long-term high-P (200 kg P2O5 ha−1 year−1) inputs resulted in a decrease in the abundance of the P-starvation response genes (phoR and phoP), the high-affinity phosphate-specific transporter (pst), the inorganic P-solubilization, and organic P-mineralization genes (gcd, pqq, and phoD). Long-term P inputs increased the abundance of phosphate-solubilizing bacteria but decreased the abundance of phosphate-solubilizing fungi and weakened the relationship of relevant key soil P genes. Soil total P, inorganic P, available P (AP), dissolved organic C contents, and alkaline phosphatase (ALP) activity were significantly related to soil P cycle genes and PSM community structure. In conclusion, the changes in soil P cycle genes and microbial P solubilization capacity under long-term P input conditions were mainly regulated by soil AP content and ALP activity, while long-term high-P inputs increased soil mineral P immobilization by altering the expression of soil P cycle genes and the PSM functional profiles. These consequences provide a new view for the study of soil P cycles in agricultural ecosystems with P inputs.

The spatio-temporal change in soil P and P-solubilizing bacteria under clover mulching in apple orchards of Loess Plateau.

Cover crop is an effective practice for improving soil quality and increase soil nutrients. However, the spatio-temporal change of soil phosphorus (P) components and P-solubilizing microorganisms in the process of grass succession is not evident. Here, we studied the variation of soil P components and P-solubilizing bacteria at 0-60cm soil layer under clean tillage (CT) and white clover (WC, Trifolium repens L.) grown for 5, 9, and 14 years in an apple test station on the Loess Plateau, China. This study suggested that clover cover could effectively increase the total P, available P (AP), microbial P, organic P (Po), and inorganic P (Al-P, Ca2-P, Ca8-P and Fe-P) in topsoil (0-20cm) and AP, Po and inorganic P at 20-40cm soil layer to improve the soil P bioavailability. The effects of WC living mulch on the soil P forms were more significant with the increase in grass growing years, but this effect was difficult to extend to deep soil. In addition, the WC treatments were beneficial to the growth of P-solubilizing microorganisms in surface soil and improved the alkaline phosphatase activity at 0-40cm soil layer, mainly including Bacillus, Bradyrhizobium, Nocardioides, Sphingomonas and Streptomyces. This study provided a perspective on the dynamic changes of soil P forms and P-solubilizing microorganisms and under long-term cover crop.

Long-term fertilization has different impacts on bacterial communities and phosphorus forms in sugarcane rhizosphere and bulk soils under low-P stress.

The application of phosphorus (P) fertilizer effectively improves soil P availability, but it also affects soil microbial communities. However, the responses of soil bacterial communities and P forms to long-term P fertilization, and the relationships of bacterial communities with soil P forms remain unclear in P-deficient field. In this study, the impacts of different P fertilization treatments (chemical nitrogen and potassium (NK); chemical N, P and K (NPK); and NPK plus straw (NPKS)) on the bacterial communities and P forms in sugarcane rhizosphere (RS) and bulk soils (BS) were evaluated. Compared with the NK, the NPK and NPKS treatments significantly (P<0.05) increased the yield and quality characters of sugarcane, especially under NPKS. Additionally, P fertilization significantly increased the available P (AP), soluble inorganic P (Pi) and retained Pi in both the RS and BS, but they significantly increased the Chao1 and Shannon index only in the BS; and almost all these indices were significantly higher in the RS than in the BS. The bacterial community compositions were also significantly altered by P fertilization, with major changes in the RS and minor changes in the BS. The bacterial genera that were enriched in the sugarcane rhizosphere mainly included Bradyrhizobium, Rhodanobacter, Pseudolabrys, Conexibacter, and Burkholderia-Caballeronia-Paraburkholderia, some of which potentially promote the plant growth. Compared to NK, functional groups involved in the cycling of carbon, N, and sulfur significantly increased or decreased with fertilizer P application. Moreover, the relative abundances of many bacterial species were significantly correlated with the soil P forms. In conclusion, long-term P fertilization altered bacterial structure and functions in P-deficient sugarcane soil, which could help the soil P cycling and suppling. The results provide useful information to stimulate the power of the microbes by fertilization measures to improve soil nutrients and crop production.

N addition alters growth, non-structural carbohydrates, and C:N:P stoichiometry of Reaumuriasoongorica seedlings in Northwest China

Reaumuria soongorica is an important biological barrier for ecological protection in the Gobi Desert in northwestern China, where soil nitrogen availability is low. N deposition has recently increased significantly in Gobi Desert, and the responses of R. soongorica to N enrichment may become a problem for ecological restoration and protection. However, little is known about the effects of N addition on the biomass, non-structural carbohydrates (NSC), and carbon:nitrogen:phosphorus (C:N:P) stoichiometry of R. soongorica in this region. Here, we examined changes in biomass, NSC and C:N:P ratios of different organs of R. soongorica seedlings in four N addition treatments: 0 (N0), 4.6 (N1), 9.2 (N2), and 13.8 (N3) g m−2 year−1. N addition up to 9.2 g m−2 year−1 significantly increased the biomass of different organs, simultaneously increasing the belowground: aboveground ratio of R. soongorica seedlings. Root NSC concentrations significantly increased under all N addition treatments, but leaf and stem NSC concentrations only increased under the N1 and N2 addition treatments. Nitrogen addition enhanced the soluble sugar concentrations (SSC) of leaves and roots, and reduced starch concentrations (SC) of all organs. Stem and root N concentrations significantly increased under the N2 and N3 treatments, and leaf N concentrations only increased under the N3 treatment, but N addition had no significant effect on plant C and P concentrations. Leaf and stem C:N ratios decreased significantly under the N2 and N3 treatments, but root C:N decreased significantly in all N addition treatments. The N3 treatment significantly increased the N:P ratio of all organs. N addition significantly enhanced available N (AN), available P (AP) and total phosphorus (TP) in rhizosphere soil. Our results suggest that N addition alters the biomass, NSC, N concentrations, C:N and N:P ratios of all plant organs, but roots responded more strongly than stems or leaves to N addition, potentially allowing the plants to absorb more water from the arid soil in this region ensuring the survival of R. soongorica seedlings. Rhizosphere soil AP, AN and TP concentrations were important factors affecting the NSC concentrations and stoichiometric characteristics of R. soongorica.

Influence of carbon-to-phosphorus ratios on phosphorus fractions transformation and bacterial community succession in phosphorus-enriched composting

This study aims to assess the effect of different carbon-to-phosphorus (C:P) ratios on phosphorus (P) fractions transformation, bacterial community succession and microbial P-solubilizing function in kitchen waste composting with rock phosphate (RP) amendment and phosphate-solubilizing bacteria (PSB) inoculation. Results indicated that initial C:P ratio at 50 enhanced organic carbon degradation, available P (AP) accumulation, the amount of PSB and pqqC gene abundance in composting but higher C:P ratio increased microbial biomass phosphorus (MBP) content. Redundancy analysis showed C:P ratios, PSB amount and pqqC gene abundance greatly affected bacterial community diversity and composition. Network analysis indicated that lower C:P ratio enhanced the interaction frequency in core bacterial network for AP transformation. Variance partitioning analysis abiotic factors contributed more to MBP and AP conversion. The study revealed that C:P ratio could directly drive PSB to regulate P fractions and the accumulation of MBP or AP in P-enriched composting.

Long-term phosphorus addition inhibits phosphorus transformations involved in soil arbuscular mycorrhizal fungi and acid phosphatase in two tropical rainforests

Increasing atmospheric nitrogen (N) and phosphorus (P) deposition affect soil nutrient availability and biogeochemical cycles, yet the impacts on the regulatory processes of soil P in P-poor tropical rainforests are not well understood. Based on a ten-year N and P addition experiment in primary and secondary rainforests in Hainan, China, we investigated the effects of N and P additions on four soil P fractions, acid phosphatase (ACP) activity, kinetic characteristics and arbuscular mycorrhizal (AM) diversity. Our results showed that P addition significantly increased soil available P (AP), but had no significant effects on microbial P and microbial N:P ratio in both rainforests. Late-successional primary rainforest had higher microbial P and lower N:P ratio compared to early-successional secondary rainforest, suggesting that forest succession would not aggravate microbial P limitation. Plants and microorganisms accessed most inorganic P by releasing hydrion and organic acids to mobilize soil P, whereas inorganic P accessed by root interception and organic P readily mineralized by ACP and phytase enzymes were relatively low. In the primary rainforest, ACP and kinetic parameters were significantly increased under low N addition, while P addition remarkedly declined ACP activity and AM diversity in both rainforests. Additionally, CaCl2 extractable P, citrate extractable P, and HCl extractable P in the two forests were significantly positively associated with soil AP, but negatively associated with ACP activity, kinetic parameters and AM diversity. Therefore, the transformations of organic P were inhibited after the exogenous addition of inorganic P. Overall, our study evaluates the soil P acquisition strategies and regulatory processes in tropical rainforests with different successional stages, which can be used to predict the effects of long-term N and P deposition on soil P cycling in P-poor tropical rainforests.

Insight into evolution of chemical structure and mineralogy to reveal the mechanism of temperature-dependent phosphorus release from hydrochars

Shrimp shell (SS) is sustainable biomass with abundant minerals and developable phosphorus (P) resource. Hydrothermal carbonization of SS can solve the shortage of P resources and the utilization of waste. However, few studies on the application of SS hydrochar as fertilizer have been conducted. Having an insight into the evolution of chemical structure and mineralogy could understand the mechanism of P release. In this study, Olsen method was employed to determine the available P (AP) release, and the temperature-dependent evolution of crystalline phase, carbon skeleton structures and surface functionalities were characterized by XRD, XPS, FTIR and TG. The results of AP release from SS hydrochar showed the following temperature (120−280 °C in 20 °C intervals) dependence: 120 °C derived hydrochars (2.30 mg/g) >feedstock (1.51 mg/g) > 160−280 °C derived hydrochars. In addition, AP dissolution kinetic data were well fitted to pseudo-second-order equation (R2 >0.999). Two-dimensional correlation spectroscopy revealed that phosphate crystallinity degree was negatively corresponding to release behavior. Meanwhile, calcite crystal growth and the transformation of P species influence the P bioavailability of SS hydrochar. Therefore, hydrochar with lower phosphate crystalline could benefit the P fertilizing efficiency.

Phosphorus status and adsorption characteristics of perennial vegetable-cultivated soils in South China.

Phosphorus (P) is an essential element for crop production and a key source of nonpoint pollution in agroecosystems. In this study, we sought to analyze P levels and the factors affecting soil P availability, via P adsorption, in a typical field system that is characterized by the year-round cultivation of vegetables. A total of 190 sites were sampled from vegetable fields in Guangdong Province, South China. Within the research area, average concentrations of 124.49 mg P kg-1 and 1.55 g P kg-1 were recorded for available P (AP) and total P (TP), respectively, which are 8.53- and 1.78-fold higher, respectively, than the corresponding values recorded in 1980. The determined P adsorption maximum (Qm) averaged at 488.38 mg kg-1, which represents a reduction of 16% compared to the values obtained four decades ago. Accumulations of both TP and AP were found to be negatively correlated with the soil’s maximum adsorption buffering capacity (MBC), although no significant correlations with the soil binding energies (k) and Qm, were seen. However, soil pH was found to be significantly correlated with k and Qm. Furthermore, both free Mn oxides (Mnd) and silt concentrations in the soil were found to contribute to explaining the variations in Qm. Collectively, the findings of this study provide evidence to indicate that there has been an excessive accumulation of P in the perennial vegetable fields of Guangdong Province over the past four decades, which may have had negative effects on the P supply potential of the soil by reducing the maximum adsorption buffering capacity.

Manure applications combined with chemical fertilizer improves soil functionality, microbial biomass and rice production in a paddy field

AbstractThe current farming system is highly reliant on synthetic fertilizers, which adversely affect soil quality, the environment, and crop production. Improving crop productivity on a sustainable basis is a challenging issue in the current agricultural system. To address this issue, we assumed that the combined use of manure and chemical fertilizers (CF) could improve rice (Oryza sativa L.) grain yield and soil properties without the expense of the environment. Therefore, a 2‐yr field experiment was conducted to explore optimal fertilizer management strategies using a combination of CF and organic fertilizer in the form of cattle manure (CM) or poultry manure (PM). Manure was added at two levels and soil microbial biomass production, enzyme activities, nutrient content, as well as grain yield of rice were measured. The study consisted of six treatments: no N fertilizer control, 100% chemical fertilizer (Pos‐Con), 60% cattle manure + 40% chemical fertilizer (High‐CM), 30% cattle manure + 70% chemical fertilizer, 60% poultry manure + 40% chemical fertilizer, and 30% poultry manure + 70% chemical fertilizer. Results showed that the addition of manure significantly increased soil enzymatic activities such as soil invertase, acid phosphatase (POH), urease, catalase (CAT), β‐glucosidase, and cellulase as compared to sole CF application. Similarly, the combined fertilizers application led to significant increases in soil microbial biomass C (MBC), microbial biomass N (MBN), soil pH, soil organic C (SOC), total N, available N (AN), available P (AP), and rice yield. Average increases in soil MBC, MBN, SOC AN, and AP in the 0‐to‐20‐cm soil depth were 62.2, 54.5, 29.2, 17.4, and 19.8%, respectively, across the years in the High‐CM treatment compared with the Pos‐Con. In addition, the linear regression analysis showed that soil enzymatic activities were highly positively correlated with soil MBC and MBN. The principal component analysis and linear regression analyses showed that the increased soil enzyme activities and microbial biomass production played a key role in the higher grain yield of rice. Overall, the results of this study demonstrate that the combined use of synthetic fertilizer and organic fertilizer in paddy fields could be beneficial for the farmers in southern China by improving soil functionality and yield of rice on a sustainable basis.

Organic and Inorganic Amendments Shape Bacterial Indicator Communities That Can, In Turn, Promote Rice Yield.

The dynamic patterns of the belowground microbial communities and their corresponding metabolic functions, when exposed to various environmental disturbances, are important for the understanding and development of sustainable agricultural systems. In this study, a two-year field experiment with soils subjected to: chemical fertilization (F), mushroom residues (MR), combined application of chemical fertilizers and mushroom residues (MRF), and no-fertilization (CK) was conducted to evaluate the effect of fertilization on the soil bacterial taxonomic and functional compositions as well as on the rice yield. The highest rice yield was obtained under MRF. Soil microbial properties (microbial biomass carbon (MBC), microbial biomass nitrogen (MBN), urease, invertase, acid phosphatase, and soil dehydrogenase activities) reflected the rice yield better than soil chemical characteristics (soil organic matter (SOM), total N (TN), total K (TK), available P (AP), available K (AK), and pH). Although the dominant bacterial phyla were not significantly different among fertilizations, 10 bacterial indicator taxa that mainly belonged to Actinobacteria (Nocardioides, Marmoricola, Tetrasphaera, and unclassified Intrasporangiaceae) with functions of xenobiotic biodegradation and metabolism and amino acid and nucleotide metabolism were found to strongly respond to MRF. Random Forest (RF) modeling further revealed that these 10 bacterial indicator taxa act as drivers for soil dehydrogenase, acid phosphatase, pH, TK, and C/N cycling, which directly and/or indirectly determine the rice yield. Our study demonstrated the explicit links between bacterial indicator communities, community function, soil nutrient cycling, and crop yield under organic and inorganic amendments, and highlighted the advantages of the combined chemical and organic fertilization in agroecosystems.