Soil Phosphorus Cycling Research Articles

Species-dependent phosphorus acquisition strategy modulates soil phosphorus cycle in the subalpine forest of eastern Tibetan Plateau

The availability of phosphorus (P) in soils will ultimately determine forest productivity because of increasing P limitation in terrestrial ecosystems. However, it is still unclear how and to what extent of different plant P-acquisition strategies affect soil P cycling in the subalpine ecosystems. Here, bulk soils (BS) and rhizosphere soils (RS) under Abies fabri and Rhododendron decorum were respectively collected in the early-, mid- and late-growing seasons in a subalpine forest of eastern Tibetan Plateau, and low molecular weight organic acids, microbial biomass P and P fractions were analyzed to decipher the effects of the plants on soil P availability. The P fractions in both BS and RS showed a distinct difference between A. fabri and R. decorum because of their different P acquisition strategies. The ericoid mycorrhiza-associated R. decorum sequestered soil available P through organic P mineralization, while the ectomycorrhizal mycorrhiza-associated A. fabri directly or indirectly acquired both the organic and inorganic P pools. Seasonal variations in soil available P further revealed that the difference in the P acquisition by the two species was closely associated with their growing stages. Inorganic P dissolution by citric acid determined available P supply for A. fabri in the mid-growing season, while organic P mineralization contributed to available P for R. decorum in the early-growing season. Our results indicate that mycorrhizal types and plant growing stages drive plant P acquisition, which results in the coexistence patterns of different species in the same habitat.

Selective logging impacts on soil microbial communities and functioning in Bornean tropical forest.

Rainforests provide vital ecosystem services that are underpinned by plant-soil interactions. The forests of Borneo are globally important reservoirs of biodiversity and carbon, but a significant proportion of the forest that remains after large-scale agricultural conversion has been extensively modified due to timber harvest. We have limited understanding of how selective logging affects ecosystem functions including biogeochemical cycles driven by soil microbes. In this study, we sampled soil from logging gaps and co-located intact lowland dipterocarp rainforest in Borneo. We characterised soil bacterial and fungal communities and physicochemical properties and determined soil functioning in terms of enzyme activity, nutrient supply rates, and microbial heterotrophic respiration. Soil microbial biomass, alpha diversity, and most soil properties and functions were resistant to logging. However, we found logging significantly shifted soil bacterial and fungal community composition, reduced the abundance of ectomycorrhizal fungi, increased the abundance of arbuscular mycorrhizal fungi, and reduced soil inorganic phosphorous concentration and nitrate supply rate, suggesting some downregulation of nutrient cycling. Within gaps, canopy openness was negatively related to ectomycorrhizal abundance and phosphomonoesterase activity and positively related to ammonium supply rate, suggesting control on soil phosphorus and nitrogen cycles via functional shifts in fungal communities. We found some evidence for reduced soil heterotrophic respiration with greater logging disturbance. Overall, our results demonstrate that while many soil microbial community attributes, soil properties, and functions may be resistant to selective logging, logging can significantly impact the composition and abundance of key soil microbial groups linked to the regulation of vital nutrient and carbon cycles in tropical forests.

Assessing the influence of diverse phosphorus sources on bacterial communities and the abundance of phosphorus cycle genes in acidic paddy soils.

The impact of chemical fertilizers on soil microbial communities is well acknowledged. This study assesses the influence of various phosphorus sources on soil bacterial composition, abundance, and Phosphorus Cycle Gene Abundance. Three phosphorus sources (natural phosphate rock, triple super phosphate (TSP), and chemical fertilizer NPK) were field tested following two rice cultivation cycles. Soil samples were subsequently collected and analyzed for bacterial groups and phosphorus cycle genes. Results indicated that the bacterial community composition remained consistent, comprising five main phyla: Firmicutes, Actinobacteria, Proteobacteria, Halobacterota, and Chloroflexia, regardless of fertilizer type. NPK fertilizer significantly reduced the relative abundance of Chloroflexia by 19% and Firmicutes by 16.4%, while increasing Actinobacteria and Proteobacteria by 27.5 and 58.8%, respectively. TSP fertilizer increased Actinobacteria by 27.1% and Halobacterota by 24.8%, but reduced Chloroflexia by 8.6%, Firmicutes by 12.6%, and Proteobacteria by 0.6%. Phosphate rock application resulted in reductions of Chloroflexia by 27.1%, Halobacterota by 22.9%, and Firmicutes by 6.2%, alongside increases in Actinobacteria by 46.6% and Proteobacteria by 23.8%. Combined application of TSP, NPK, and phosphate rock led to increases in Proteobacteria (24-40%) and Actinobacteria (13-39%), and decreases in Chloroflexia (5.2-22%) and Firmicutes (6-12.3%) compared to the control (T0). While the different phosphorus sources did not alter the composition of phosphorus cycle genes, they did modulate their abundance. NPK fertilizer did not significantly affect ppK genes (57-59%) but reduced gcd (100 to 69%), 3-phytase (74 to 34%), appA (91 to 63%), and phoD (83 to 67%). Phosphate rock reduced appA and gcd by 27 and 15%, respectively, while increasing 3-phytase by 19%. TSP decreased ppK and phoD by 42 and 40%, respectively, and gcd and appA by 34 and 56%, respectively. Combined fertilizers reduced appA (49 to 34%), 3-phytase (10 to 0%), and gcd (27 to 6%), while increasing ppK (72 to 100%). Among tested phosphorus sources, natural phosphate rock was best, causing moderate changes in bacterial composition and phosphorus genes, supporting balanced soil microbial activity. These findings highlight the complex interactions between fertilizers and soil microbial communities, underscoring the need for tailored fertilization strategies to maintain soil health and optimize agricultural productivity.

Soil phosphorus cycling across a 100-year deforestation chronosequence in the Amazon rainforest.

Deforestation of tropical rainforests is a major land use change that alters terrestrial biogeochemical cycling at local to global scales. Deforestation and subsequent reforestation are likely to impact soil phosphorus (P) cycling, which in P-limited ecosystems such as the Amazon basin has implications for long-term productivity. We used a 100-year replicated observational chronosequence of primary forest conversion to pasture, as well as a 13-year-old secondary forest, to test land use change and duration effects on soil P dynamics in the Amazon basin. By combining sequential extraction and P K-edge X-ray absorption near edge structure (XANES) spectroscopy with soil phosphatase activity assays, we assessed pools and process rates of P cycling in surface soils (0-10 cm depth). Deforestation caused increases in total P (135-398 mg kg-1 ), total organic P (Po ) (19-168 mg kg-1 ), and total inorganic P (Pi ) (30-113 mg kg-1 ) fractions in surface soils with pasture age, with concomitant increases in Pi fractions corroborated by sequential fractionation and XANES spectroscopy. Soil non-labile Po (10-148 mg kg-1 ) increased disproportionately compared to labile Po (from 4-5 to 7-13 mg kg-1 ). Soil phosphomonoesterase and phosphodiesterase binding affinity (Km ) decreased while the specificity constant (Ka ) increased by 83%-159% in 39-100y pastures. Soil P pools and process rates reverted to magnitudes similar to primary forests within 13 years of pasture abandonment. However, the relatively short but representative pre-abandonment pasture duration of our secondary forest may not have entailed significant deforestation effects on soil P cycling, highlighting the need to consider both pasture duration and reforestation age in evaluations of Amazon land use legacies. Although the space-for-time substitution design can entail variation in the initial soil P pools due to atmospheric P deposition, soil properties, and/or primary forest growth, the trend of P pools and process rates with pasture age still provides valuable insights.

Mixture enhances microbial network complexity of soil carbon, nitrogen and phosphorus cycling in Eucalyptus plantations

Mixed-species plantations have the potential to promote soil nutrient cycling, productivity, and ecosystem function. However, the microbial mechanisms underlying the mixing effect in different stand types remain poorly understood. We studied the effect of mixtures with either one of the three N2-fixing or one of the three non-N2-fixing tree species on Eucalyptus growth. Furthermore, we employed metagenomics to investigate co-occurrence networks of soil microbial community, and carbon (C), nitrogen (N), and phosphorus (P)-transformation gene in the Eucalyptus rhizosphere and bulk soil of the monospecific or mixed Eucalyptus plantations. Mixing with either N2-fixing or non–N2-fixing species can promote the network complexity rather than diversity of soil microbial community. Mixture always significantly increased Eucalyptus growth and the network complexity and stability of C, N, and P-transformation genes, but decreased their gene abundance, suggesting a trade-off between functionality and abundance stimulated by mixed-species afforestation. The positive mixing effects on Eucalyptus growth were related with the interactions between C, N, and P cycling, depending on N2-fixing functional traits. Mixtures of N2-fixing trees intensively promoted correlations between Eucalyptus growth and N and P functional genes, while non-N2-fixing trees extensively stimulated the significant correlations with both C, N, and P genes and soil total P. Our findings highlight the importance of rapid responses of soil functional microbes for nutrient cycling, for favoring productivity in mixed-species forest plantations.

The multifunctionality of soil aggregates is related to the complexity of aggregate microbial community during afforestation

The multifunctionality of soil ecosystems depends on the soil structure and microenvironment because soil is a multi-structured, interconnected system. However, how the microenvironments of different aggregate affect the soil microbial community and soil multifunctionality remains unknown, which hinders our ability to understand the sustainability of afforestation ecosystems. To address this, we investigated three paired afforestation sequences accosted 629.3 km on the Loess Plateau, China. Our results showed that afforestation significantly increased the stability of soil aggregates and the macroaggregates increased soil multifunctionality, including carbon, nitrogen, and phosphorus cycle functions. In addition, soil enzyme (BG, PO, LAP, and NAG) activities were enhanced by the soil aggregate size, which played a major role in supporting soil multifunctionality. This change was directly affected by soil aggregate size or indirectly affected by the complexity of bacterial co-network and was regulated by carbon restriction and the abundance of core species. In addition, macroaggregate increased the complexity of soil bacterial communities and afforestation enhanced the complexity crossed aggregates with different sizes and consequently affected soil multifunctionality during afforestation. Therefore, the responses of soil microbes in different soil aggregates to afforestation should be considered when assessing the sustainability of afforestation, as different soil structures have varied response to forest ecosystems in semiarid and arid climates.

Main sources of soil phosphorus and their seasonal changes across different vegetation restoration stages in karst region of southwest China

Investigating the main sources of soil phosphorus and their seasonal variations across different vegetation restoration stages in karst region of southwest China can deepen our understanding of soil phosphorus cycling during vegetation restoration, and provide scientific reference for the controlling of rocky desertification. Taking the typical karst ecosystems at different vegetation restoration stages in Guilin, Guangxi as the research objects, we conducted a one-year field experiment with three treatments: vegetation restoration for about 10 years (R10), 30 years (R30) and 50 years (R50). We collected rainfall based on precipitation frequency, as well as soil, fresh litter and root samples in each season to measure the concentrations of total phosphorus (TP) in rainfall, the contents of TP and available phosphorus (AP) in soil, and the contents of TP in fresh litter and roots. In combination with litter phosphorus storage and soil microbial biomass phosphorus (MBP), we analyzed the contributions of phosphorus input to soil from different phosphorus sources. The results showed that soil TP content increased initially and then decreased with vegetation restoration, with a seasonal pattern of autumn > summer > spring > winter. Soil AP content was low in all treatments, with higher levels in summer and winter than in spring and autumn. Soil MBP content increased with vegetation restoration, with a seasonal variation pattern of spring >autumn > summer > winter. The annual phosphorus input from rainfall was 0.78 kg·hm-2 with the highest value in spring. The annual phosphorus input from fresh litter in the R10, R30, and R50 treatments was 2.42, 10.64 and 5.03 kg·hm-2. Phosphorus storage in litter was 1.23, 5.32 and 3.45 kg·hm-2. The annual phosphorus input from plant roots was 5.18, 12.65, and 5.96 kg·hm-2, respectively. The highest levels of the above parameters always occurred in the R30 treatment. There was a significant positive correlation between soil TP content and plant root phosphorus input, and a significant negative correlation between soil AP content and rainfall phosphorus input. In summary, the contribution of phosphorus input from different sources to soil phosphorus pool varied across different vegetation restoration stages in the karst region of southwest China. Roots are the main source of soil phosphorus, followed by litters. Phosphorus entering the soil through wet deposition is very limited. Soil microorganisms also contribute to soil phosphorus reserve.

Long-term organic fertilization reshapes the communities of bacteria and fungi and enhances the activities of C- and P-cycling enzymes in calcareous alluvial soil

Soil microbial communities and extracellular enzymes are pivotal in governing the dynamics of soil carbon (C) and phosphorus (P) cycling. Nevertheless, comprehending the underlying regulatory factors and intricate interactions among these vital indicators remains an inadequately explored aspect, especially within the scenario of long-term fertilization. Long-term fertilization experiments were conducted on calcareous alluvial soil. The five fertilization regimes selected were as follows: without fertilization treatment (CK); inorganic NK fertilization treatment (NK); inorganic NPK fertilization treatment (NPK); organic fertilization treatment (M); and combined inorganic NPK with organic fertilization treatment (NPKM). The soil physicochemical properties, β-glucosidase (BG), and alkaline phosphomonoesterase (ALP) activities were determined, together with microbial (bacterial and fungal) community DNA sequences and subsequent bioinformatics analysis after 38 years of different fertilization. The results showed that the content of soil organic carbon (SOC) and available P and the activities of BG and ALP were the highest after M and NPKM treatments, which were 79–104 %, 26–36 times, 161–171 %, and 75–91 % higher than CK, respectively. Hierarchical clustering analysis showed that the bacterial and fungal community structures in M and NPKM treatments were similar, but the community structures in non-organic fertilization treatments (CK, NK, and NPK) were significantly different from those in organic fertilization treatments. The indicator species and correlation analysis combined revealed that most indicator species in organic fertilizer treatments were significantly positively correlated with soil BG and ALP, while most indicator species in non-organic fertilizer (CK and NK) treatments were significantly negatively correlated with soil BG and ALP. Organic fertilization treatments favored the growth of the bacterial genus Lysobacter and the fungal genera Acremonium and Mortierella and were significantly positively correlated with BG and ALP activities. Redundancy analysis revealed that SOC is the most important factor in shaping microbial community structure. Co-occurrence network analysis showed organic fertilization had higher network complexity, more keystone taxa, and more associations among microbial taxa compared with non-organic fertilization (CK + NK). Structural equation models revealed that microbial community structure is the direct driving factor of BG and ALP activities and their interactions, and SOC modulated the relationship between microbial community structure and BG and ALP activities. This study highlights how the application of organic fertilizer enhanced the C- and P-cycling enzyme activities, reshaped the soil microbial communities, and regulated these crucial indicators and their interactions by SOC.

The Use of Two Locally Sourced Bio-Inocula to Improve Nitrogen and Phosphorus Cycling in Soils and Increase Macro and Micronutrient Nutrient Concentration in Edamame (Glycine max. L.) and Pumpkin (Cucurbita maxima)

Soil macro- and micronutrient nutrient availability and their uptake by plants are critically reliant upon an active presence of the soil microbiome. This study investigated the effect of two locally sourced bio-inocula, local effective microorganisms (LEMs) and false-local effective microorganisms (F-LEMs), on plant available nitrogen (N) and phosphorus (P), and the uptake of calcium (Ca), magnesium (Mg), potassium (K), and zinc (Zn) content in edamame (Glycine max. L.) and pumpkin (Cucurbita maxima) grown in a randomized complete block design with four reps, summer 2017 and 2018, respectively. LEM plots showed greater plant-available N during the first week (edamame season) and fourth week (pumpkin season) after treatment applications. During the pumpkin season, post-treatment plant-available P was greater in both summers in LEM plots. Edamame bean had 19%, 3%, 5%, and 16% greater Ca, Mg, K, and Zn content in LEM plots compared to the Control, respectively. The concentration of K in pumpkin pulp at harvest was 31% higher in LEMs than in F-LEMs, while Mg concentration was 42% higher. Pumpkin pulp and seeds also had 27% and 34% greater Ca and Zn concentrations compared to the Control. Our study suggests that LEMs were effective in solubilizing macro- and micronutrients, which led to increased plant uptake.

Effect of nutrient management and soil type on stoichiometric imbalances across the Yangtze River Basin pear districts, China

AbstractNutrition management affects soil carbon (C), nitrogen (N), and phosphorus (P) cycles, as well as their stoichiometry, causing further stoichiometric imbalances. However, research on the effect of nutrient management on soil stoichiometric imbalance is restricted to a single soil type, limiting our understanding of the interactions between these parameters. Therefore, we conducted a study comprising 212 sites throughout the Yangtze River Basin pear districts, for which nutrient management and soil properties were available under different soil types. Soil stoichiometric imbalances varied widely among the districts, with an average C:P imbalance value (C:Pim) of 6.67, higher than that of C:N imbalance (C:Nim; 6.43) and N:P imbalance (N:Pim; 2.83). Meanwhile, soil and microbial biomass stoichiometry, particularly for soil C:P and soil microbial biomass carbon and phosphorus (MBC:MBP), were significantly influenced by nutrient addition. Large N and P fertilizer inputs altered soil C:N and C:P in yellow–brown earth, while soil C:P was influenced by organic nutrient management in purplish soil. Moreover, adding organic nutrients altered the MBP, which further influenced MBC:MBP and MBN:MBP in saline–alkaline soil and yellow–brown earth. Furthermore, C:Pim increased with increasing organic nutrient input in purple soil and decreased with a large chemical fertilizer input in red soil. N:Pim and C:Nim were weakly associated with nutrient management in different soil types. In addition, nutrition management, soil type, soil properties, and microbe content collectively accounted for 45%, 32%, and 38% of the C:Pim, C:Nim, and N:Pim variation, respectively. Nutrient management also exerted a positive direct impact on C:Pim, while soil type elicited a negative direct impact on C:Nim and N:Pim. Meanwhile, all three stoichiometric imbalances were indirectly influenced by soil type. Taken together, our results indicate that soil stoichiometric imbalances, especially for C:Pim, are sensitive to nutrient management and soil type, providing novel insights into these imbalances that can inform the development of potential remedial strategies.

Soybean (Glycine max) rhizosphere organic phosphorus recycling relies on acid phosphatase activity and specific phosphorus-mineralizing-related bacteria in phosphate deficient acidic soils

Bacteria play critical roles in regulating soil phosphorus (P) cycling. The effects of interactions between crops and soil P-availability on bacterial communities and the feedback regulation of soil P cycling by the bacterial community modifications are poorly understood. Here, six soybean (Glycine max) genotypes with differences in P efficiency were cultivated in acidic soils with long-term sufficient or deficient P-fertilizer treatments. The acid phosphatase (AcP) activities, organic-P concentrations and associated bacterial community compositions were determined in bulk and rhizosphere soils. The results showed that both soybean plant P content and the soil AcP activity were negatively correlated with soil organic-P concentration in P-deficient acidic soils. Soil P-availability affected the α-diversity of bacteria in both bulk and rhizosphere soils. However, soybean had a stronger effect on the bacterial community composition, as reflected by the similar biomarker bacteria in the rhizosphere soils in both P-treatments. The relative abundance of biomarker bacteria Proteobacteria was strongly correlated with soil organic-P concentration and AcP activity in low-P treatments. Further high-throughput sequencing of the phoC gene revealed an obvious shift in Proteobacteria groups between bulk soils and rhizosphere soils, which was emphasized by the higher relative abundances of Cupriavidus and Klebsiella, and lower relative abundance of Xanthomonas in rhizosphere soils. Among them, Cupriavidus was the dominant phoC bacterial genus, and it was negatively correlated with the soil organic-P concentration. These findings suggest that soybean growth relies on organic-P mineralization in P-deficient acidic soils, which might be partially achieved by recruiting specific phoC-harboring bacteria, such as Cupriavidus.

The Role of Phosphate-Solubilizing Microorganisms in Soil Health and Phosphorus Cycle: A Review

The role of phosphate-solubilizing microorganisms (PSM) in soil health and Phosphorus (P) cycle is a crucial aspect of agricultural productivity. Recent research has emphasized the importance of microorganisms in maintaining soil health. Phosphorus is an essential macronutrient for plant growth and development and significantly affects crop productivity. The PSM solubilize phosphate by producing metabolites such as organic acids, inorganic acids, hydrogen sulphide, exopolysaccharide, and siderophore. Studies have shown that the combination of PSM with phosphate fertilizers increase the efficiency of the fertilizers in soils. The efforts have been made to integrate exogenous soil microorganisms into P cycling models. This review highlights the critical role of microorganisms in maintaining soil health and promoting P cycle, emphasizing the importance of incorporating them into soil management practices.

Structural Equation Modeling of Phosphorus Transformations in Soils of Larix principis-rupprechtii Mayr. Plantations

Understanding the soil phosphorus (P) cycle is a prerequisite for the sustainable management of land resources. The sequential-extraction method was used to determine P fractions in 513 soils of Larix principis-rupprechtii Mayr. plantations. With these data, this study applied structural equation modeling to evaluate the interaction between various soil P fractions. Quantitative analysis was conducted on the importance of different soil P pools and P transformation pathways on soil P availability in a larch plantation. Our study showed that soluble inorganic P (Pi) was directly positively affected by labile Pi, labile organic P (Po), secondary mineral P, and primary mineral P, and was directly negatively affected by moderately labile Po. Soluble Pi was not directly affected by occluded P. The primary mineral P (β = 0.40) had the greatest total impact on soluble Pi, followed by secondary mineral P (β = 0.32) and labile P (labile Pi and Po, β = 0.31), and then occluded P (β = 0.11), with the total impact of moderately labile Po being relatively small (β = −0.06). In summary, this study reveals the important roles of soluble Pi in P transformations and in determining overall P availability in soils, as well as the extensive effects of weathering on soil P dynamics in L. principis-rupprechtii plantations.

Distribution of Genes and Microbial Taxa Related to Soil Phosphorus Cycling across Soil Depths in Subtropical Forests

Although many studies have focused on the roles of soil microbes in phosphorus (P) cycling, little is known about the distribution of microbial P cycling genes across soil depths. In this study, metagenomic sequencing was adopted to examine the differences in the abundance of genes and microbial taxa associated with soil P cycling between organic and mineral soil in subtropical forests. The total relative abundance of inorganic P solubilizing genes was the highest, that of P starvation response regulating genes was second, and organic P mineralizing genes was the lowest. The soil organic carbon concentration, N:P ratio, and available P concentration were higher in the organic soil than the mineral soil, resulting in abundances of organic P mineralizing genes (appA and 3-phytase), and inorganic P cycling genes (ppa), whereas those of the inorganic P cycling genes (gcd and pqqC) and the P starvation response regulating gene (phoR) were higher in mineral soil. The four bacteria phyla that related to P cycling, Proteobacteria, Actinobacteria, Bacteroidetes, and Candidatus_Eremiobacteraeota were higher in organic soil; conversely, the three bacteria phyla (Acidobacteria, Verrucomicrobia, and Chloroflexi) and archaea taxa were more abundant in mineral soil. Therefore, we concluded that the distribution of genes and microbial taxa involved in soil P cycling differed among soil depths, providing a depth-resolved scale insight into the underlying mechanisms of P cycling by soil microorganisms in subtropical forests.

Fire intensity regulates the short-term postfire response of the microbiome in Arctic tundra soil

Arctic tundra fires have been increasing in extent, frequency and intensity and are likely impacting both soil nitrogen (N) and phosphorus (P) cycling and, thus, permafrost ecosystem functioning. However, little is known on the underlying microbial mechanisms, and different fire intensities were neglected so far. To better understand immediate influences of different fire intensities on the soil microbiome involved in nutrient cycling in permafrost-affected soil, we deployed experimental fires with low and high intensity on an Arctic tundra soil on Disko Island, Greenland. Soil sampling took place three days postfire and included an unburned control. Using quantitative real-time PCR, copy numbers of 16S and ITS as well as of 17 genes coding for functional microbial groups catalyzing major steps of N and P turnover were assessed.We show that fires change the abundance of microbial groups already after three days with fire intensity as key mediating factor. Specifically, low-intensity fire significantly enhanced the abundance of chiA mineralizers and ammonia-oxidizing archaea, while other groups were not affected. On the contrary, high-intensity fire decreased the abundance of chiA mineralizers and of microbes that fix dinitrogen, indicating a dampening effect on N cycling. Only high-intensity fires enhanced ammonium concentrations (by an order of magnitude). This can be explained by burned plant material and the absence of plant uptake, together with impaired further N processing. Fire with high intensity also decreased nirK-type denitrifiers. In contrast, after fire with low intensity there was a trend for a decreased nosZ : (nirK+nirS) ratio, indicating – together with increased nitrate concentrations – an enhanced potential for nitric oxide and nitrous oxide emissions. Concerning P transformation, only gcd was affected in the short term which is important for P solubilization.Changes in gene numbers consistently showed the same contrasting pattern of elevated abundance with low fire intensity and decreased abundance with high fire intensity. Differentiating fire intensities is therefore crucial for further, longer-term studies of fire-induced changes in N and P transformations and potential nutrient-climate feedbacks of permafrost-affected soils.

Soil microorganisms respond distinctively to adaptive multi‐paddock and conventional grazing in the southeastern United States

AbstractVariable results from studies of the associations between grazing management and soil microbiological properties in grasslands suggest the need for further investigation. We assessed the response of soil microbiological properties to conventional and adaptive multi‐paddock (AMP) grazing management practices at paired farms at five locations in the southeastern United States. We measured total DNA and abundances of fungi and bacteria by quantitative polymerase chain reaction (qPCR) as proxies for soil microbial biomass, potential carbon, nitrogen, and phosphorus cycling activities using qPCR of functional genes, and carbon mineralization activities by respiratory assays. Abundances of fungi (p = 0.009) and bacteria (p = 0.001) were greater under AMP management compared to conventional management; however, there was no difference in the fungal/bacterial ratios between management practices. Gene copies encoding for nitrification, denitrification, and phosphate hydrolysis were significantly greater (p < 0.05) under AMP compared to conventional management. Basal soil respiration was elevated (p = 0.004) under AMP compared to conventional management presumptively due to the greater abundance of microbes that were actively transforming plant exudates and residues. In contrast, labile carbon limitation of respiratory activities was greater (p ≤ 0.01) under conventional compared to AMP management indicating decreased processing of soil carbon and formation of microbial biomass. Using discriminant function analysis, the 19 biological response variables successfully classified 94% of the 180 soil samples according to grazing management. In summary, AMP grazing management influenced the numbers and key activities of soil microbes in a distinctive manner that is associated with the retention of soil organic carbon and nitrogen reported in these grazed grasslands.

Long-Term Organic Fertilization Strengthens the Soil Phosphorus Cycle and Phosphorus Availability by Regulating the pqqC- and phoD-Harboring Bacterial Communities.

The pqqC and phoD genes encode pyrroloquinoline quinone synthase and alkaline phosphomonoesterase (ALP), respectively. These genes play a crucial role in regulating the solubilization of inorganic phosphorus (Pi) and the mineralization of organic phosphorus (Po), making them valuable markers for P-mobilizing bacterial. However, there is limited understanding of how the interplay between soil P-mobilizing bacterial communities and abiotic factors influences P transformation and availability in the context of long-term fertilization scenarios. We used real-time polymerase chain reaction and high-throughput sequencing to explore the characteristics of soil P-mobilizing bacterial communities and their relationships with key physicochemical properties and P fractions under long-term fertilization scenarios. In a 38-year fertilization experiment, six fertilization treatments were selected. These treatments were sorted into three groups: the non-P-amended group, including no fertilization and mineral NK fertilizer; the sole mineral-P-amended group, including mineral NP and NPK fertilizer; and the organically amended group, including sole organic fertilizer and organic fertilizer plus mineral NPK fertilizer. The organically amended group significantly increased soil labile P (Ca2-P and enzyme-P) and Olsen-P content and proportion but decreased non-labile P (Ca10-P) proportion compared with the sole mineral-P-amended group, indicating enhanced P availability in the soil. Meanwhile, the organically amended group significantly increased soil ALP activity and pqqC and phoD gene abundances, indicating that organic fertilization promotes the activity and abundance of microorganisms involved in P mobilization processes. Interestingly, the organically amended group dramatically reshaped the community structure of P-mobilizing bacteria and increased the relative abundance of Acidiphilium, Panacagrimonas, Hansschlegelia, and Beijerinckia. These changes had a greater positive impact on ALP activity, labile P, and Olsen-P content compared to the abundance of P-mobilizing genes alone, indicating their importance in driving P mobilization processes. Structural equation modeling indicated that soil organic carbon and Po modulated the relationship between P-mobilizing bacterial communities and labile P and Olsen-P, highlighting the influence of SOC and Po on the functioning of P-mobilizing bacteria and their impact on P availability. Overall, our study demonstrates that organic fertilization has the potential to reshape the structure of P-mobilizing bacterial communities, leading to increased P mobilization and availability in the soil. These findings contribute to our understanding of the mechanisms underlying P cycling in agricultural systems and provide valuable insights for enhancing microbial P mobilization through organic fertilization.

The core microbiota as a predictor of soil functional traits promotes soil nutrient cycling and wheat production in dryland farming

Abstract Host plants and the microbiota living in the rhizosphere are interdependent, mutually reinforced and mutually beneficial but the assembly, functions and microbial interactions of the host‐associated microbiota are still unclear. Herein, winter wheat was selected as a test plant to explore the assembly process of total bacteria from bulk soil (BS) and rhizosphere soil (RS), and phoD‐harbouring bacteria in RS at a long‐term (14 years) trial site. We also identified core microbes that are potentially relevant to soil carbon (C), nitrogen (N) and phosphorus (P) cycling genes and soil biogeochemical properties, and investigated the relationships between soil variables, functional genes and wheat productivity. The results showed that the microhabitat of the plant, rather than P fertilizer input, was the main factor affecting the microbial diversity, composition and co‐occurrence networks. The BS bacterial community was driven by deterministic processes but the RS and phoD bacterial communities were dominated by stochastic processes. The influence of deterministic processes decreased with increasing soil nutrient content. A core microbial community consisted of 10 OTUs in different microhabitats and was significantly related to soil functional genes and properties. In the rhizosphere soil, significant correlations were found between soil variables, soil functional bacteria and genes, and crop productivity. Synthesis and applications. This study provides empirical evidence that the assembly process of the microbial community is governed by environmental factors in various soil environments and provides new perspectives on the sustainable improvement of crop productivity. Read the free Plain Language Summary for this article on the Journal blog.

Metagenomics insights into the functional profiles of soil carbon, nitrogen, and phosphorus cycles in a walnut orchard under various regimes of long-term fertilisation

Soil microbial functional potential is important for productivity and sustainable agricultural development; however, the potential response of soil nutrient cycling to different fertilisation regimes remains unclear, especially in perennial tree soils. Here, metagenomic sequencing was applied to investigate the soil microbial functional profiles of carbon (C), nitrogen (N), and phosphorus (P) cycling after seven years of chemical, organic, and biofertiliser fertilisation in walnut (Juglans regia L.) orchard. Microbial communities balanced their elemental requirements through selective degradation. The highest relative abundance of genes for labile C-degradation (amyA, malZ, and xylH) was found under chemical fertilisation (F), whereas the metabolic potential for soil N and P cycling was less affected by F. Compared with CK and F, the addition of organic and/or biofertiliser significantly reduced the relative abundances of labile and recalcitrant C-degradation genes (e.g., chi, and xylH) but promoted the processes of N degradation (GDH1, GDH2, ureA, glnA, and arcC), DNRA (nrfA, napB, and napC), organic P mineralisation (phy), P solubilisation (gcd), and P uptake and transport (phnD) in walnut soils. At the phylum level, most C, N, and P cycle-related microbes were similar, and applying biofertiliser remarkably improved the relative abundances of Proteobacteria and Firmicutes involved in C, N, and P cycling processes. Furthermore, soil TN and AP were key limiting macronutrients for regulating the pathways of soil C, N, and P cycles and microbial taxa. C, N, and P cycle-related genes were tightly coupled through synergetic or antagonistic interactions, especially metabolic pathways encoded by glnA, mmsA, phy, and appA. Overall, our results provide a biological perspective on the microbial genetic potential of soil C, N, and P cycles in perennial crops and explore their interactions under different long-term fertilisation regimes in a walnut orchard.

Positive effects of biochar application and Rhizophagus irregularis inoculation on mycorrhizal colonization, rice seedlings and phosphorus cycling in paddy soils

Phosphorus (P) is an essential element for plant growth but is often limiting in ecosystems; therefore, improving the P fertilizer use efficiency is important. Biochar and arbuscular mycorrhizal fungi (AMF) may enhance P cycling in paddy soils that contain high total P but low available phosphorus (AP). In this study, the effects of biochar and Rhizophagus irregularis inoculation on the organic and inorganic P contents and phosphatase activity of paddy soil, rice seedling growth, and AMF colonization ability were investigated. Compared with the control, biochar enhanced the percentage spore germination at day 7, hyphal length, most probable number, and mycorrhizal colonization rate of R. irregularis by, on average, 32%, 662%, 70%, and 28%, respectively. Biochar and R. irregularis altered soil P cycling and transformed soil P availability. Biochar and R. irregularis, either individually or in combination, increased the soil AP content by 2%–48%. Rice seedlings treated with biochar and R. irregularis produced greater biomass, and showed improved root morphology and higher nutrient uptake compared with those of the control. The results suggest that combined application of biochar and R. irregularis is beneficial for rice cultivation in paddy soils with high total P but low AP content.