Soil Phosphorus Cycling Research Articles

The combined nitrogen and phosphorus fertilizer application reduced soil multifunctionality in Qinghai-Tibet plateau grasslands, China

The impact of nitrogen (N) and phosphorus (P) fertilizer inputs on soil nutrient cycling and ecological function processes has garnered significant attention. Soil multifunctionality primarily refers to the soil's ability to perform multiple functions simultaneously, particularly the functions related to the genes involved in carbon (C), nitrogen (N), and phosphorus (P) cycles, which are critical for ecosystem sustainability. Despite this, the effects of N and P fertilizers on the expression of genes involved in soil carbon (C), nitrogen (N), and phosphorus (P) cycles, and their consequent influence on soil multifunctionality, remain unclear. To investigate this, we conducted a long-term nine-year experiment. The experimental site was fenced to prevent grazing and included four treatments: Control (no fertilizer), N (10 g N m−2 y−1, urea), P (5 g P m−2 y−1, Ca(H2PO4)2), and NP (10 g N and 5 g P m−2 y−1, urea and Ca(H2PO4)2). We examined the effects of these treatments on soil microbial functional gene abundance and multifunctionality. Our findings revealed that N addition altered the composition of soil microbial functional genes but did not affect functional diversity. Both N and P inputs, as well as their combination, negatively impacted soil carbon fixation and the genes encoding enzymes for the degradation of starch, hemicellulose, cellulose, and chitin. N input also disrupted soil nitrogen and phosphorus cycling by inhibiting the expression of soil denitrification genes (nirS and nosZ), phytate hydrolase gene (cphy), and a phosphatase gene (phoD). Additionally, P input significantly inhibited functional genes involved in soil nitrification, denitrification, ammonification, nitrogen fixation, and ammonia oxidation processes. It also adversely affected phytate synthesis and degradation. The combined N and P inputs had a substantial negative impact on soil nitrification (hao), denitrification (narG, nirK, nirS, and norZ), ammonification (gdh), nitrogen fixation, annamox, and nitrogen reduction, and inhibited the expression of soil phosphorus cycle genes. Long-term phosphorus application was found to have a more detrimental effect on soil multifunctionality compared to nitrogen application. Furthermore, our study showed that vegetation diversity and abundance are crucial drivers of soil carbon, nitrogen, and phosphorus cycling functional genes and multifunctionality. We concluded that N and P inputs alter soil multifunctionality by influencing vegetation diversity; therefore, maintaining vegetation diversity is essential for sustaining soil multifunctionality.

Long-term rice-crayfish farming alters soil dissolved organic carbon quality and biodegradability by regulating microbial metabolism and iron oxidation

The biodegradability of dissolved organic carbon (DOC) is a crucial process in the migration and transformation of soil organic carbon (SOC), and play a vital role in the global soil carbon (C) cycle. Although the significance of DOC in SOC transportation and microbial utilization is widely acknowledged, the impact of long-term rice-crayfish (RC) farming on the content, quality, and biodegradability of DOC in paddy soils, as well as regulatory mechanisms involved, remains unclear. To address this gap, a space-for-time method was employed to investigate the effects of different RC farming durations (1-, 5-, 10-, 15-, and 20- years) on the quality and biodegradability of DOC, as well as their relationship with soil microbial metabolism and minerals in this study. The results revealed that continuous RC farming increased the soil DOC content, but reduced DOC biodegradability. Specifically, after 20 years of continuous RC farming, the DOC content increased by 52.7% compared to the initial year, whereas the DOC biodegradability decreased by 63.4%. Analysis using three-dimensional fluorescence and ultraviolet spectroscopy demonstrated that continuous RC farming resulted in a decrease in the relative abundance of humus-like fractions, humification, and aromaticity indexes in DOC, but increased the relative abundance of protein-like fractions, biological, and fluorescence index, indicating that long-term RC farming promoted the simple depolymerization of the molecular structure of DOC. Continuous RC farming increased the activity of hydrolase involved in soil nitrogen (N) and phosphorus (P) cycles and oxidase, but decreasing the hydrolase C/N and C/P acquisition ratios; moreover, it also stimulated an increase in soil iron oxides and exchangeable calcium content. Structural equation modeling suggests that soil hydrolases and iron oxides are the primary drivers of DOC quality change, with DOC biodegradability being driven solely by soil iron oxides and not regulated by DOC quality. In conclusion, long-term RC farming promotes the catalytic decomposition of DOC aromatic substances and the production of DOC protein-like components by increasing soil oxidase activity and decreasing the hydrolase C/N acquisition ratio; these processes collectively contribute to the simple depolymerization of DOC molecular structure. Additionally, long-term RC farming induced legacy effects of soil iron oxides and enhanced chemical protection role leading to reduced DOC biodegradability. These findings suggested that long-term RC farming may reduce the rapid turnover and loss of DOC, providing a negative feedback on climate warming.

Bacterial Community Structure Modulates Soil Phosphorus Turnover at Early Stages of Primary Succession

AbstractMicrobes are the drivers of soil phosphorus (P) cycling in terrestrial ecosystems; however, the role of soil microbes in mediating P cycling in P‐rich soils during primary succession remains uncertain. This study examined the impacts of bacterial community structure (diversity and composition) and its functional potential (absolute abundances of P‐cycling functional genes) on soil P cycling along a 130‐year glacial chronosequence on the eastern Tibetan Plateau. Bacterial community structure was a better predictor of soil P fractions than P‐cycling genes along the chronosequence. After glacier retreat, the solubilization of inorganic P and the mineralization of organic P were significantly enhanced by increased bacterial diversity, changed interspecific interactions, and abundant species involved in soil P mineralization, thereby increasing P availability. Although 84% of P‐cycling genes were associated with organic P mineralization, these genes were more closely associated with soil organic carbon than with organic P. Bacterial carbon demand probably determined soil P turnover, indicating the dominant role of organic matter decomposition processes in P‐rich alpine soils. Moreover, the significant decrease in the complexity of the bacterial co‐occurrence network and the taxa‐gene‐P network at the later stage indicates a declining dominance of the bacterial community in driving soil P cycling with succession. Our results reveal that bacteria with a complex community structure have a prominent potential for biogeochemical P cycling in P‐rich soils during the early stages of primary succession.

Dry season irrigation promotes nutrient cycling by reorganizing Eucalyptus rhizosphere microbiome

In southern China, seasonal droughts and low soil phosphorus content constrain the productivity of Eucalyptus trees. To understand the rhizosphere microbiome response to the dry season, metagenomic sequencing analysis was used to investigate the 6-year-old Eucalyptus rhizosphere microbiome under four different irrigation and fertilization treatments. The results showed that irrigation and fertilization during the dry season significantly altered the composition of microbiome in the rhizosphere soil of Eucalyptus plantations. The soil physicochemical properties and enzyme activity explained 30.73 % and 29.75 % of the changes in bacterial and fungal community structure in Eucalyptus rhizosphere soil, respectively. Irrigation and fertilization during the dry season significantly altered the physicochemical properties of rhizosphere soil. Compared with the seasonal drought without fertilizer treatment (CK), the dry season irrigation with fertilizer treatment (WF) significantly increased the content of total nitrogen (46.34 %), available nitrogen (37.72 %), available phosphorus (440.9 %), and organic matter (35.34 %). Soil organic matter (OM), pH, and available phosphorus (AP) were key environmental factors influencing the microbial community composition. Moreover, irrigation and fertilization promoted carbon fixation and nitrogen and phosphorus mineralization, increasing soil OM content and the availability of inorganic nitrogen and phosphorus. Meanwhile, compared to the CK, the increase of acid phosphatase (16.81 %), invertase (146.89 %)and urease (59.45 %) in rhizosphere soil under irrigation (W) treatment further proves that dry season irrigation promote the soil carbon, nitrogen and phosphorus cycles. Irrigation and fertilization treatment alleviated the constraints of low phosphorus in southern China's soil, which promoted Eucalyptus productivity. In conclusion, we suggest implementing reasonable irrigation and fertilization strategies in the production practice of Eucalyptus and utilizing microbial resources to improve soil fertility and Eucalyptus productivity.

Ecotoxicological effects of microplastic types and concentrations in combination with Cd on the bioenergy plant sweet sorghum: Growth and rhizosphere microbiome analysis

Complex interactions occur when microplastics (MPs) and heavy metals cooccur as pollutants, and these interactions have become a popular research topic. However, there is a lack of research examining the impact of concurrent pollution from MPs and heavy metals on the soil microbial community and its roles in nitrogen and phosphorus cycling. Therefore, in this study, we investigated the effects of composite pollution from cadmium (Cd) and different types of MPs (e.g., PVC, PE, and PP) at different concentrations (0.1 % and 0.5 %) on the growth of sweet sorghum, an energy plant, and evaluated Cd accumulation in sweet sorghum and the expression of genes related to soil nitrogen and phosphorus cycling. The results indicated that the growth of sweet sorghum was negatively impacted by combined treatment with the three types of microplastics and Cd, with the composite stress trend being 0.5 % > 0.1 %. The contents of mineral nutrients such as nitrogen, phosphorus, and potassium in the soil decreased due to MP+Cd pollution. Cocontamination with MP and Cd significantly affected the microbial community composition and increased the activity of enzymes such as urease. MP+Cd pollution affected the composition and abundance of functional genes related to nitrogen and phosphorus cycling. The type and concentration of microplastics were identified as the primary factors influencing the composition and abundance of functional genes. Bacteria belonging to Acidobacteria and Actinobacteria are key to soil nitrogen cycling, while Acidobacteria plays crucial roles in soil phosphorus cycling. Metagenomic analysis was performed in this study to determine the impact of microplastic–heavy metal pollution on soil microbial communities and functions and to provide a reference for the environmental assessment of soils contaminated by both microplastics and heavy metals.

Soil phosphorus cycling microbial functional genes of monoculture and mixed plantations of native tree species in subtropical China.

Transforming coniferous plantation into broadleaved or mixed broadleaved-coniferous plantations is the tendency of forest management strategies in subtropical China. However, the effects of this conversion on soil phosphorus (P) cycling microbial functional genes are still unknown. Soil samples were collected from 0-20, 20-40, and 40-60 cm (topsoil, middle layer, and subsoil, respectively) under coniferous Pinus massoniana (PM), broadleaved Erythrophleum fordii (EF), and their mixed (PM/EF) plantation in subtropical China. Used metagenomic sequencing to examine the alterations of relative abundances and molecular ecological network structure of soil P-cycling functional genes after the conversion of plantations. The composition of P-cycling genes in the topsoil of PM stand was significantly different from that of PM/EF and EF stands (p < 0.05), and total phosphorus (TP) was the main factor causing this difference. After transforming PM plantation into EF plantation, the relative abundances of P solubilization and mineralization genes significantly increased in the topsoil and middle layer with the decrease of soil TP content. The abundances of P-starvation response regulation genes also significantly increased in the subsoil (p < 0.05), which may have been influenced by soil organic carbon (SOC). The dominant genes in all soil layers under three plantations were phoR, glpP, gcd, ppk, and ppx. Transforming PM into EF plantation apparently increased gcd abundance in the topsoil (p < 0.05), with TP and NO3 --N being the main influencing factors. After transforming PM into PM/EF plantations, the molecular ecological network structure of P-cycling genes was more complex; moreover, the key genes in the network were modified with the transformation of PM plantation. Transforming PM into EF plantation mainly improved the phosphate solubilizing potential of microorganisms at topsoil, while transforming PM into PM/EF plantation may have enhanced structural stability of microbial P-cycling genes react to environmental changes.

Mechanisms of phosphorus activation in charosphere and non-charosphere: The priming effect of biochar

Biochar is widely used in soil to increase the soil phosphorus content, but a special ecological zone called the “charosphere” zone is formed where biochar comes into contact with soil. The physical and chemical properties of charosphere soil are different from those of the original soil and the biochar itself, leading to uncertainty regarding the effect of charosphere soil on the phosphorus cycle. Hence, we designed a barrier device to separate biochar from soil and analyzed the impact of biochar diffusion on soil nutrient content and microbial activity. Then, the variation characteristics of the community structure of phoD-harboring bacteria and fungi in the carbonosphere (group B) and non-carbonosphere (group C) were explored. Finally, the key factors and potential driving mechanisms of soil phosphorus activation were explored. The results show that biochar improved soil microbial activity and stimulated the soil nutrient recycling, resulting in a 67.28 % greater percentage of the labile P fraction in group B than in group C. The alpha diversity and nutrient transfer efficiency of the phoD-harboring bacterial community in group B were greater than those in group C, while the phoD-harboring bacterial co-occurrence network of group C was more complex. Moreover, the synergy between the co-occurrence networks of the soil fungal community was stronger than that of the bacterial community. Biochar stimulates microbial activation of phosphorus by increasing the DOC content and pH in the charosphere, and the phoD-harboring bacterial community dominates soil phosphorus activation. These findings offer a new perspective on how biochar regulates soil phosphorus cycling, providing crucial information to guide the application of biochar in agroecosystems.

Macrogenomics reveal the effects of inter-cropping perilla on kiwifruit: impact on inter-root soil microbiota and gene expression of carbon, nitrogen, and phosphorus cycles in kiwifruit.

Intercropping systems can improve soil fertility and health, however, soil microbial communities and functional genes related to carbon, nitrogen and phosphorus cycling under the intercropping system of mesquite and perilla have not been studied. Therefore, in the present study, different planting densities and varieties of Perilla frutescens (L.) Britt and kiwifruit were used for intercropping, and changes in soil microbial communities and carbon, nitrogen, and phosphorus cycling genes in kiwifruit inter-roots under inter-cropping conditions were investigated by macro-genome sequencing technology. The results showed that intercropping with Perill caused a decrease in most soil nutrients, soil enzyme activities, and had a significant impact on the microbial (bacteria and fungi) diversity. Inter-cropping increased the relative abundance of the dominant bacterial phylum "Proteobacteria" and "Actinobacteria" by 47 and 57%, respectively, but decreased the relative abundance of the dominant fungal phylum "Chordata" and "Streptophyta" by 11 and 20%, respectively, in the inter-root soil of kiwifruit, and had a significant impact on the microbial (bacteria and fungi) diversity. In addition, inter-cropping could greatly increase the inter-root soil carbon sequestration (PccA, korA/B/C/D, fhs, and rbcl/s), carbon degradation (abfD), organic nitrogen mineralization (GDH2), denitrification (napA/B, nirB, norB), organic phosphorus mineralization (phop, phn), and inorganic phosphorus solubilization (gcd, ppk) gene abundance. The gene co-occurrence network indicated that soil korB, nirB, and gnd key functional genes for carbon, nitrogen, and phosphorus cycling in kiwifruit inter-root soils and their expression was up-regulated in the inter-cropping group. Structural equation (SEM) further showed that soil total nitrogen, organic matter, total carbon and acid phosphatase had significant effects on microbial diversity (p < 0.05) and soil carbon cycling gene korB and phosphorus cycling gene purH (p < 0.001), while korB and purH had positive effects on kiwifruit quality. In conclusion, intercropping perilla in kiwifruit orchards changed the structure of bacterial and fungal communities in the inter-root soil of kiwifruit, but I believe that intercropping perilla stimulates carbon degradation, leading to carbon emission and serious loss of soil nutrients, and that prolonged intercropping may adversely affect the quality of kiwifruit, and thus its limitations should be noted in future studies.

Soil chemical fumigation alters soil phosphorus cycling: effects and potential mechanisms

Soil chemical fumigation is an effective and popular method to increase agricultural productivity. However, the broad-spectrum bioactivity of fumigants causes harm to soil beneficial microorganisms involved in the soil phosphorous cycle, such as soil phosphorus solubilizing microorganisms (PSMs). We review the effects of soil chemical fumigation on soil phosphorus cycling, and the potential underlying mechanisms that ultimately lead to altered phosphorus availability for crops. These complex processes involve the highly diverse PSM community and a plethora of soil phosphorus forms. We discuss phosphatizing amendments aimed at counteracting the possible negative effects of fumigation on phosphorus availability, phosphorus use efficiency, and crop yields. We also emphasize distinguishing between the effects on soil phosphorus cycling caused by the chemical fumigants, and those caused by the fumigation process (e.g. plastic mulching). These are typically conflated in the literature; distinguishing them is critical for identifying appropriate amendments to remediate possible post-fumigation soil phosphorus deficiencies.

Different microbial functional traits drive bulk and rhizosphere soil phosphorus mobilization in an alpine meadow after nitrogen input

Enhanced nitrogen (N) input is expected to influence the soil phosphorus (P) cycling through biotic and abiotic factors. Among these factors, soil microorganisms play a vital role in regulating soil P availability. However, the divergent contribution of functional microorganisms to soil P availability in the rhizosphere and bulk soil under N addition remains unclear. We conducted an N addition experiment with four N input rates (0, 5, 10, and 15 g N m−2 year−1) in an alpine meadow over three years. Metagenomics was employed to investigate the functional microbial traits in the rhizosphere and bulk soil. We showed that N addition had positive effects on microbial functional traits related to P-cycling in the bulk and rhizosphere soil. Specifically, high N addition significantly increased the abundance of most microbial genes in the bulk soil but only enhanced the abundance of five genes in the rhizosphere soil. The soil compartment, rather than the N addition treatment, was the dominant factor explaining the changes in the diversity and network of functional microorganisms. Furthermore, the abundance of functional microbial genes had a profound effect on soil available P, particularly in bulk soil P availability driven by the ppa and ppx genes, as well as rhizosphere soil P availability driven by the ugpE gene. Our results highlight that N addition stimulates the microbial potential for soil P mobilization in alpine meadows. Distinct microbial genes play vital roles in soil P availability in bulk and rhizosphere soil respectively. This indicates the necessity for models to further our knowledge of P mobilization processes from the bulk soil to the rhizosphere soil, allowing for more precise predictions of the effects of N enrichment on soil P cycling.

Snow depth has greater influence on moss biocrusts' soil multifunctionality than the number of freeze-thaw cycles

Continued global warming and changes in precipitation patterns, especially regarding snow depth and freeze-thaw cycles (FTCs), have significantly affected the hydrothermal environment in winter at mid- and high-latitudes. In this study, we assessed the effects of changes in snow depth and FTCs, on the biogeochemical cycling of biological soil crusts. We collected moss crust soil samples from a temperate desert in northwest China, and measured the changes in the amount of snow (65 % snow removal, ambient snow, and 65 % snow increase) and FTCs (FT0, FT5, and FT15) under an artificial environment simulation, to determine the nutrient content and enzyme activities related to soil carbon, nitrogen, and phosphorus cycles. In terms of how snowfall and FTCs affect soil multifunctionality (SMF) of desert moss crusts, the research findings demonstrated that snow depth, FTCs, and their interplay have a significant influence on the carbon, nitrogen, phosphorus contents, enzyme activities, and SMF of moss crusts. Compared to snow removal, an increase in snow depth corresponded to a significant increase in the soil water content, and an improvement in soil carbon and nitrogen cycling and SMF. The number of FTCs increased, which led to enhancements in soil phosphorus cycling, soil total phosphorus, and available phosphorus content, together with a reduction in inorganic nitrogen content and the activities of certain enzymes involved in carbon and nitrogen cycling. The structural equation model indicated that snow depth had the greatest effect (total effect of 0.165) on SMF in moss crusts compared to FTCs (total effect of 0.048). Therefore, it is necessary to consider snow depth when examining the effects of climate change on nutrient cycling in the biological soil crusts of temperate deserts.

Effects of combined microplastic and cadmium pollution on sorghum growth, Cd accumulation, and rhizosphere microbial functions

The interaction between microplastics (MPs) and cadmium (Cd) poses a threat to agricultural soil environments, and their effects on plant growth and rhizosphere microbial community functions are not yet clear. In this study, energy sorghum was used as a test plant to investigate the effects of two types of MPs, polystyrene (PS) and polyethylene (PE), at different particle sizes (13 μm, 550 μm) and concentrations (0.1%, 1% w/w), and Cd, as well as their interactions, on the growth of sorghum in a soil-cultivation pot experiment. The results showed that the combined effects of MP and Cd pollution on the dry weight and Cd accumulation rate in sorghum varied depending on the type, concentration, and particle size of the MPs, with an overall trend of increasing stress from combined pollution with increasing Cd content and accumulation. High-throughput sequencing analysis revealed that combined MP and Cd pollution increased bacterial diversity, and the most significant increase was observed in the abundance-based coverage estimator (ACE), Shannon, and Sobs indices in the 13 μm 1% PS+Cd treatment group. Metagenomic analysis based on the Kyoto Encyclopedia of Genes and Genomes (KEGG) metabolic pathways revealed that 19 groups of metabolic pathways, including microbial metabolism and methane metabolism, differed significantly under combined MP and Cd pollution. Hierarchical clustering results indicated that Cd treatment and combined MP and Cd treatment affected the abundances of sorghum rhizosphere soil nitrogen (N) and phosphorus (P) cycling genes and that the type of MP present was an important factor affecting N and P cycling genes. The results of this study provide a basis for exploring the toxic effects of combined MP and Cd pollution and for conducting soil environmental risk assessments.

Microbial phosphorus-cycling genes in soil under global change.

The ongoing climate change on the Tibetan Plateau, leading to warming and precipitation anomalies, modifies phosphorus (P) cycling in alpine meadow soils. However, the interactions and cascading effects of warming and precipitation changes on the key "extracellular" and "intracellular" P cycling genes (PCGs) of bacteria are largely unknown for these P-limited ecosystems. We used metagenomics to analyze the individual and combined effects of warming and altered precipitation on soil PCGs and P transformation in a manipulation experiment. Warming and increased precipitation raised Olsen-P (bioavailable P, AP) by 13% and 20%, respectively, mainly caused by augmented hydrolysis of organic P compounds (NaOH-Po). The decreased precipitation reduced soil AP by 5.3%. The richness and abundance of the PCGs' community in soils on the cold Tibetan plateau were more sensitive to warming than altered precipitation. The abundance of PCGs and P cycling processes decreased under the influence of individual climate change factors (i.e., warming and altered precipitation alone), except for the warming combined with increased precipitation. Pyruvate metabolism, phosphotransferase system, oxidative phosphorylation, and purine metabolism (all "intracellular" PCG) were closely correlated with P pools under climate change conditions. Specifically, warming recruited bacteria with the phoD and phoX genes, which encode enzymes responsible for phosphoester hydrolysis (extracellular P cycling), strongly accelerated organic P mineralization and so, directly impacted P bioavailability in alpine soil. The interactions between warming and altered precipitation profoundly influenced the PCGs' community and facilitated microbial adaptation to these environmental changes. Warming combined with increased precipitation compensated for the detrimental impacts of the individual climate change factors on PCGs. In conclusion, warming combined with rising precipitation has boosting effect on most P-related functions, leading to the acceleration of P cycling within microbial cells and extracellularly, including mineralization and more available P release for microorganisms and plants in alpine soils.

Effects of land-use on soil C, N, and P stocks and stoichiometry in coastal wetlands dependent on soil depth and latitude

Coastal land-use is increasingly affected by Spartina alterniflora invasion, coastal reclamation, and climate change, which have been suggested to exert vital controls on soil carbon (C), nitrogen (N), and phosphorus (P) cycles, however, the effects on the geographical distributions of these element stocks and stoichiometry remain unclear. We analyzed the depth (0–100 cm) and latitudinal (19–41°N) patterns of soil C, N, and P contents, stocks, and ratios in 120 Chinese coastal wetlands differing in land-use (reclaimed wetlands, natural wetlands, invasive wetlands, and bare mudflats) and climate (tropics, subtropics, and temperate). We observed stable depth patterns of soil contents, stocks, and ratios, owing to the stable depth patterns of soil conditions in each land-use. Top soils (0–30 cm) generally had higher C, N, and P contents and N:P ratio but lower C:N and C:P ratios than deep soils (30–100 cm). We found that soil C content and P stock remained constant, soil C stock, N and P contents and N:P ratio increased significantly, but soil N stock and C:N and C:P ratios decreased significantly with decreasing latitude; however, such correlations tended to be weaker in reclaimed wetlands and invasive wetlands. Land-use changes also significantly altered the magnitude of soil element stoichiometry. The effects of S. alterniflora invasion on soil C, N, and P storages can be shifted from negative in tropics to positive in temperate regions, whereas the negative effects of coastal reclamation in tropics disappeared in temperate regions. Overall, compared with natural wetlands, S. alterniflora invasion slightly decreased, whereas coastal reclamation largely decreased soil C, N, and P contents and stocks. Compared with bare mudflats, S. alterniflora invasion significantly increased C and N contents and N:P ratio but decreased C:N ratio, whereas coastal reclamation significantly decreased P content and stock and C:N ratio but increased N:P ratio, especially in top soils. Our findings will be helpful for understanding and assessing soil C sequestration and nutrient cycling in globally disturbed coastal wetlands.

Plant invasion alters soil phosphorus cycling on tropical coral islands: Insights from Wollastonia biflora and Chromolaena odorata invasions

Plants may modify soil biogeochemical properties that facilitate their invasion of new sites which may be mediated by soil microorganisms. We compared microbially-mediated soil phosphorus (P) cycling among sites with different degrees of invasion by Wollastonia biflora and Chromolaena odorata on two coral islands. Wollastonia biflora and C. odorata outcompeted all native species and invested more P in leaves (45–136% more than the native species). We found a decrease in the proportion of HCl–P and organic P, and a corresponding increase in the proportion of labile inorganic P (Pi) of the soil total P concentrations following plant invasion. Leaf P concentrations in invasive species were positively correlated with the proportion of labile Pi, suggesting that HCl–P and organic P were the major P sources for invasive plants, and that plant invasion increased soil P-cycling rates as a result of root carboxylate release (evidenced by greater leaf manganese concentrations) and enhanced soil alkaline phosphatase activity. The latter was confirmed by an increased soil phoD gene abundance after plant invasion. Soil P availability was elevated after plant invasion which was associated with increases in the release of root carboxylates and microbial activities that are involved in mobilization of HCl–P and mineralization of organic P, respectively, especially in the wet season. This, in turn, strongly increased leaf P concentrations of invasive species to sustain rapid plant growth, and presumably depriving competitors of P. These novel insights into soil P cycling through the enrichment of a specific soil microbial community and root carboxylate release in invaded ecosystems enhance our understanding of plant invasion mechanisms on coral islands.

The proliferation of beneficial bacteria influences the soil C, N, and P cycling in the soybean-maize intercropping system.

Soybean-maize intercropping system can improve the utilization rate of farmland and the sustainability of crop production systems. However, there is a significant gap in understanding the interaction mechanisms between soil carbon (C), nitrogen (N), and phosphorus (P) cycling functional genes, rhizosphere microorganisms, and nutrient availability. To reveal the key microorganisms associated with soil nutrient utilization and C, N, and P cycling function in the soybean-maize intercropping system, we investigated the changes in soil properties, microbial community structure, and abundance of functional genes for C, N, and P cycling under soybean-maize intercropping and monocropping at different fertility stages in a pot experiment. We found that there was no significant difference in the rhizosphere microbial community between soybean-maize intercropping and monocropping at the seeding stage. As the reproductive period progressed, differences in microbial community structure between intercropping and monocropping gradually became significant, manifesting the advantages of intercropping. During the intercropping process of soybean and maize, the relative abundance of beneficial bacteria in soil rhizosphere significantly increased, particularly Streptomycetaceae and Pseudomonadaceae. Moreover, the abundances of C, N, and P cycling functional genes, such as abfA, mnp, rbcL, pmoA (C cycling), nifH, nirS-3, nosZ-2, amoB (N cycling), phoD, and ppx (P cycling), also increased significantly. Redundancy analysis and correlation analysis showed that Streptomycetaceae and Pseudomonadaceae were significantly correlated with soil properties and C, N, and P cycling functional genes. In brief, soybean and maize intercropping can change the structure of microbial community and promote the proliferation of beneficial bacteria in the soil rhizosphere. The accumulation of these beneficial bacteria increased the abundance of C, N, and P cycling functional genes in soil and enhanced the ability of plants to fully utilize environmental nutrients and promoted growth.

Responses of Soil Phosphorus Cycling-Related Microbial Genes to Thinning Intensity in Cunninghamia lanceolata Plantations

Background: Microorganisms are important regulators of soil phosphorus cycling and phosphorus availability in Chinese fir (Cunninghamia lanceolata (Lamb.) Hook) plantations. However, the effects of thinning on soil phosphorus cycling by microbes in C. lanceolata plantations remain unclear. Methods: We performed a metagenomic sequencing analysis to investigate how thinning intensities (weak, moderate, and heavy) alter phosphorus cycling related microbial genes and their regulatory effects on soil phosphorus availability in C. lanceolata plantations. Results: Following heavy thinning, the contents of available and labile phosphorus increased by 13.8% and 36.9%, respectively, compared to moderate and weak thinning. Moreover, the relative abundance of genes associated with inorganic phosphorus solubilization increased significantly with the increase in thinning intensity, whereas genes associated with phosphorus uptake and transport significantly decreased. The metagenomic analysis results indicate that Acidobacteria (47.6%–53.5%), Proteobacteria (17.9%–19.1%), and Actinobacteria (11.7%–12.8%) are the major contributors to the functional phosphorus cycling genes in the soil. The random forest analysis results suggested that gcd, plc, phoN, ugpA, and phoR were the critical genes involved in the transformation and use of phosphorus, which in turn increased soil phosphorus availability. Structural equation modeling revealed that soil pH was the primary factor influencing changes in functional genes associated with phosphorus cycling in C. lanceolata plantations. Specifically, soil pH (ranging from 4.3 to 4.9) were positively correlated with genes involved in inorganic phosphate solubilization and organic phosphate mineralization, while negatively correlated with genes related to phosphorus uptake and transport. Conclusions: Taken together, our results demonstrate that the enhanced microbe-mediated mineralization of organic phosphorus and solubilization of inorganic phosphorus are suppressed when uptake and transportation are the mechanisms responsible for the increased soil phosphorus availability under appropriate thinning intensities. Changes in the soil microbial community and phosphorus cycling genes in response to different thinning intensities may maintain soil functionality and nutrient balance in C. lanceolata plantations. These findings contribute to a better understanding of the mechanisms underlying the microbial mediation of phosphorus cycling in the soil of C. lanceolata plantations.

Changes in soil microbe-mediated carbon, nitrogen and phosphorus cycling during spontaneous succession in abandoned Pb[sbnd]Zn mining areas

The mechanism through which soil microorganisms mediate carbon and nutrient cycling during mine wasteland restoration remained unknown. Using soil metagenome sequencing, we investigated the dynamic changes in soil microbial potential metabolic functions during the transition from biological soil crusts (BSC) to mixed broad-conifer forest (MBF) in a typical PbZn mine. The results showed soil microorganisms favored carbon sequestration through anaerobic and microaerobic pathways, predominantly using efficient, low-energy pathways during succession. Genes governing carbon degradation and aerobic respiration increased by 19.56 % and 24.79 %, respectively, reflecting change toward more efficient and intensive soil carbon utilization in late succession. Nitrogen-cycling genes mediated by soil microorganisms met their maximum influence during early succession (sparse grassland, SGL), leading to a respective increase of 75.29 % and 76.81 % in the net potential nitrification rate and total nitrogen content. Mantel and correlation analyses indicated that TOC, TN, Zn and Cd contents were the main factors affecting the soil carbon and phosphorus cycles. Soil AP content emerged as the primary influencer of genes associated with the nitrogen cycle. These results shed light on the dynamic shifts in microbial metabolic activities during succession, providing a genetic insight into biogeochemical cycling mechanisms and underscoring crucial factors influencing soil biogeochemical processes in mining regions.

Coupling and decoupling of soil carbon and nutrients cycles at different salinity levels in a mangrove wetland: Insights from CUE and enzymatic stoichiometry

Soil carbon (C), nitrogen (N), and phosphorus (P) cycling, in conjunction with microbial metabolism, varies significantly with salinity in coastal areas. However, microbial metabolism limitation on salinity levels has received limited attention. Based on soil microbial carbon use efficiency and enzymatic stoichiometry, microbial nutrient limitation characteristics of soil microbial communities in different salinity levels (4.45 mS·cm−1 - 17.25 mS·cm−1) in a subtropical mangrove wetland were investigated. Compared to low-salinity levels, the activity of soil C-acquiring enzyme activities, enzymatic C:N ratios and enzymatic C:P ratios decreased with medium salinity levels and high salinity levels. Soil microbial metabolism was primarily constrained by C and N at different salinity levels. Boosted regression tree analysis revealed that abiotic factors had the greatest influence on C and N limitation of microbial metabolism at different salinity levels. This study underscores the significance of salinity in microbial metabolic processes and enhances our understanding of how future salinity changes induced by rising sea levels will affect soil carbon and nutrient cycling in coastal wetlands.

Effects of stand ages on soil enzyme activities in Chinese fir plantations and natural secondary forests.

Forest type and stand age are important biological factors affecting soil enzyme activities. However, the changes in soil enzyme activities across stand ages and underlying mechanisms under the two forest restoration strate-gies of plantations and natural secondary forests remain elusive. In this study, we investigated the variations of four soil enzyme activities including cello-biohydrolase (CBH), β-1,4-glucosidase (βG), acid phosphatase (AP) and β-1,4-N-acetylglucosaminidase (NAG), which were closely associated with soil carbon, nitrogen, and phosphorus cycling, across Cunninghamia lanceolata plantations and natural secondary forests (5, 8, 21, 27 and 40 years old). The results showed that soil enzyme activities showed different patterns across different forest types. The acti-vities of AP, βG and CBH in the C. lanceolata plantations were significantly higher than those in the natural secon-dary forests, and there was no significant difference in the NAG activity. In the plantations, AP activity showed a decreasing tendency with the increasing stand ages, with the AP activity in the 5-year-old plantations significantly higher than other stand ages by more than 62.3%. The activities of NAG and CBH decreased first and then increased, and βG enzyme activity fluctuated with the increasing stand age. In the natural secondary forests, NAG enzyme activity fluctuated with the increasing stand age, with that in the 8-year-old and 27-year-old stand ages being significantly higher than the other stand ages by more than 14.9%. βG and CBH enzyme activities increased first and then decreased, and no significant difference was observed in the AP activity. Results of the stepwise regression analyses showed that soil predictors explained more than 34% of the variation in the best-fitting models predicting soil enzyme activities in the C. lanceolata plantations and natural secondary forests. In conclusion, there would be a risk of soil fertility degradation C. lanceolata plantations with the increasing stand age, while natural secondary forests were more conducive to maintaining soil fertility.