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Microbes play an integral role in forest soil phosphorus (P) cycling. However, the variation of microbial P-cycling functional genes and their controlling factors in forest soils is unclearly. We used metagenomics to investigate changes in the abundance of genes involved in P-starvation response regulation, P-uptake and transport, and P-solubilization and mineralization along the five elevational gradients. Our results showed the abundance of three P cycling gene groups increasing along the elevational gradient.

Cover crops provide multiple agronomic and environmental benefits, such as enhanced soil carbon sequestration, aggregation, water infiltration, and reduced erosion and nutrient leaching compared with no cover crop. However, little is known regarding the effect of cover crop species, biomass quality and quantity, and method of residue placement on greenhouse gas (GHG) emissions. Using meta-analysis, this study examined the effect of cover crop species, quality and quantity of biomass, and residue management on response ratios (RRs) of cover crops to no cover crop on CO2 and N2O emissions following cash crops. All cover crop species increased CO2 emissions, but reduced N2O emissions compared with no cover crop, except legumes which increased N2O emissions. Cover crop biomass explained 63% of variability in increased CO2 emissions and 55% of variability in decreased N2O emissions. Both CO2 and N2O emissions decreased polynomially with increased cover crop biomass C/N ratio, with greater rate of decline for legumes than nonlegumes. Cover crop residue incorporated into the soil increased CO2 and N2O emissions compared with the residue placed at surface or removed from the soil. Cover crops emitted lower CO2 and N2O emissions than no cover crops in silty loam and sandy clay loam soils, respectively, compared to clay loam and silty clay loam soils. Both soil organic carbon and total nitrogen increased with cover crop compared to no cover crop. Although CO2 and N2O emissions varied with cover crop species, using legume and nonlegume cover crop mixture to enhance residue C/N ratio compared to legumes and placing the residue at the surface instead of incorporating into the soil can reduce GHG emissions. Because of enhanced soil C and N storage and other known benefits, improvement in soil health and environmental quality due to cover crop may outweigh CO2 emissions compared to no cover crop.

Soil microbial communities are closely associated with aboveground plant communities and soil properties. This study explored the dynamics of soil bacterial communities during the plant growing season and their interaction with soil carbon and nitrogen, physicochemical properties, plant biomass and diversity following afforestation. The study investigated afforested lands containing Robinia pseudoacacia L (RP) and Caragana korshinskii Kom (CK), as well as abandoned land (AL) and farmland (FL) in the Loess Hilly Region of northern China. After establishment on former FL for 40 years, the Richness and Shannon's index, above-ground herbaceous biomass (AGB) and below-ground biomass (BGB) in RP and CK increased by 0.5, 0.1, 1.2 and 1.7 times, respectively, compared with AL. Additionally, the soil organic carbon (SOC), total nitrogen (TN), dissolved organic carbon/nitrogen (DOC/N) and microbial biomass carbon/nitrogen (MBC/N) increased by 1.7, 1.9, 0.8 and 2.5 times, respectively, while the soil bacterial abundance and alpha diversity (Shannon index) increased by 4.7% and 2.0% compared with FL. During the growing season, the soil carbon and nitrogen content was higher in August or October than in April or June. Particularly, the AGB, DOC and MBC showed a temporal pattern of normal distribution that was 36.7%, 48.2% and 74.9% higher in August than the rest of the study period. The BGB also increased by 123.5% in October compared with June in all study areas. The soil bacterial abundance in afforested lands was also higher in October, and beta bacterial diversity (Principal coordinates analysis plots: PCoA) was greater in June and August than in April and October. The dominant bacterial taxa, Proteobacteria and Bacteroidetes, were significantly higher in afforested lands than in FL, and Proteobacteria increased from April to October, while Actinobacteria and Acidobacteria peaked in June or August. These seasonal changes in the soil bacterial community were significantly correlated with carbon and nitrogen levels of soil and plant biomass, especially with DOC and BGB. Additionally, soil variables explained 41.2% of the total variation in bacterial-dominant phyla, while plant biomass only explained 20.2% of it, which indicates that soil properties are more important controlling factors of the bacterial community than plant biomass. In conclusion, soil variables change seasonally, which drives the composition and diversity of the soil bacterial community to exhibit a temporal pattern over the growing season after return of AL to forest.

Mulching enhances soil C and N fractions compared to no mulching, but its impact on soil microbial communities and their relations to C and N fractions with mulching are not clear. We studied the 9-yr effect of no mulching (CK), straw mulching (SM), and plastic film mulching (PM) on soil bacterial and fungal community structure and their relationships to soil C and N fractions under dryland winter wheat in the Loess Plateau of China. The SM did not affect bacterial diversity and richness, but enhanced fungal diversity and richness compared to CK in subsoil layers. The PM also increased fungal diversity and richness, but reduced bacterial diversity and richness compared to SM and CK. Compared to CK, the relative abundance of Actinobacteria was lower with SM at 0–10 cm, but the abundances of Nitrospirae, Firmicutes, WS3, and Zygomycota were greater with PM at most soil depths. Bacterial diversity correlated with soil C and N fractions, and fungal richness with potential N mineralization and microbial biomass C and N. Although plastic film mulching enhanced fungal diversity and richness compared to no mulching, straw mulching was more effective in maintaining soil microbial diversity and richness and enhancing soil C and N fractions under dryland winter wheat.

Secondary succession has great impact on plant and soil characteristics, however, the trends of microbial patterns and the influencing factors during grassland succession without human disturbance remains unclear. Therefore, we investigated the changes of bacterial community in sloped farmlands abandoned for 0, 20, 30, and 40 years (GL-0 yr, GL-20 yr, GL-30 yr, and GL-40 yr). Additionally, plant traits (coverage, diversity, richness, evenness, biomass, and biomass carbon) and soil nutrients were also determined. The results showed that soil bacterial alpha diversity was positively and significantly correlated with the succession time, and the secondary succession greatly affected soil bacterial beta diversity, in contrast, the effects on soil bacterial beta diversity at the late succession time (GL40 and GL30) were larger than that at the early succession time (GL20). For the bacterial taxa, the dominant phyla including Actinobacteria (34.8%), Proteobacteria (26.0%), Acidobacteria (15.0%), Chloroflexi (7.5%), Gemmatimonadetes (8.7%), Nitrospirae (1.6%), Bacteroidetes (2.1%), Verrucomicrobia (1.1%), and Planctomycetes (1.0%) were found. Particularly, the relative abundance of Proteobacteria was higher at the late time (RP40), while the Actinobacteria was higher at the early time (RP20). Such different responses of bacterial diversity and taxa were largely explained by plant traits and soil nutrients, especially for TOC and TN. Collectively, our results indicate that plant secondary succession shifts the bacterial community structure, largely driven by changes in soil nutrients and plant diversity and composition, and also supported the growing view that soil bacterial community are the key determinants of aboveground and belowground linkages that functionally control terrestrial ecosystems.

Soil microbes have a great influence on the feedbacks of carbon (C)-climate, and their metabolic activities are limited by resource availability. Altitudinal gradients strongly affect soil microbial communities, but the effects on microbial resource limitation and their regulation for C dynamics remain unclear. In this study, we designed an altitudinal gradient experiment that included six altitudinal sites from 1308 m to 2600 m in the Qinling Mountains, China. The enzymatic stoichiometry was determined and modeled to investigate microbial resource limitations and major microbial metabolism processes (e.g., organic C decomposition rate and microbial respiration rate) along the elevation gradient. Other environmental variables including mean annual temperature (MAT) and mean annual precipitation (MAP), the C: nitrogen (N): phosphorus (P) ratio in soil total nutrients, available nutrients, and microbial biomass were also measured. The results showed that soil microbes suffered from N limitation in our study and microbial N limitation significantly increased with increasing elevation. But the rates of both organic C decomposition and microbial respiration greatly decreased with increased elevation. These trends suggest that warming induced by elevation change might relieve N limitation for microbes and lead to increased soil C release. Redundancy analysis (RDA) showed that MAT and soil nutrient stoichiometry, particularly for the DOC: TDN ratio, explained more variations for changes in microbial N limitation and major microbial processes. Collectively, our study demonstrated that the higher microbial N limitation at high elevation may be beneficial to soil carbon accumulation by changing the C: N ratio, which provided insights into microbially mediated soil carbon release under global warming.

The priming effect is a pivotal mechanism for microbial regulation of soil C cycling; however, the microbial mechanisms underlying priming effects remain elusive. Here, we combined an isotopic approach with metagenomic sequencing to investigate priming effects at five forest sites along an elevational gradient. Positive priming effects were found across the Quercus aliena var. acutiserrata (low elevation), Q. wutaishanica (low-mid elevation), Betula albosinensis (mid elevation), Abies fargesii Franch (mid-high elevation), and Larix chinensis Beissn (high elevation) forest sites. A significant positive correlation was found between the abundance of microbial C decomposition genes and priming effects (p

Soil aggregation is one of the most important factors affecting soil organic carbon (SOC) stabilization, and the stability of aggregates depends in part on soil microbial diversity and composition. Interactions between the soil bacterial community and SOC content in soil aggregates after afforestation are poorly understood. In this study, we investigated difference in the diversity of soil bacterial with high-throughput 16S rRNA sequencing, as well as the SOC content in soil aggregates representing a chronosequence of 42, 27, and 17 years of Robinia pseudoacacia L. succession (RP42, RP27, and RP17), and in farmland (FL) soil for comparison (millet (Setaria italica) and soybean (Glycine max) rotation).The SOC content in RP17, RP27, and RP42 plots were significantly higher than that of FL by an average of 85.57%, 142.37%, and 76.69% in large macro-aggregates (>1 mm), small macro-aggregates (0.25–1 mm), and micro-aggregates (

Afforestation has been shown to strongly affect substrate stoichiometry and profoundly influence the microbial community. However, the degree to which microbial and activity are linked to soil carbon (C), nitrogen (N) and phosphorus (P) stoichiometry in afforested ecosystems remains unclear. In this study, soil samples were collected from Robinia pseudoacacia L. (RP42, RP27, and RP17) and farmland (FL) sites with a chronosequence of 42, 27, and 17 years. We determined the microbial biomass C (Cmic), N (Nmic), Cmic to organic C (Csoil) ratio (Cmic:Csoil), Nmic to total nitrogen (Nsoil) ratio (Nmic:Nsoil), and metabolic quotient (Rmic:Cmic) to investigate microbial. We also measured soil b-glucosidase (BG), N-acetylglucosaminidase (NAG), acid phosphatase (AP), as well as Csoil, Nsoil, and total phosphorus (Psoil). The results showed that, compared with FL, Csoil:Psoil and Nsoil:Psoil were increased during aggradation, whereas Csoil:Nsoil increased in RP27 and RP17 but decreased in RP42. Cmic:Csoil and Nmic:Nsoil were 94% and 182% higher in RP42 than FL, respectively. However, Rmic:Cmic was lower in RP42, RP27, and RP17 than FL by 64%, 36% and 25%, respectively. Moreover, we found that BG, NAG, AP, BG:NAG, and BG:AP in RP42, RP27, and RP17 were higher than in FL. Compared with global soil (0.62 and 0.13), the lower BG:AP (0.42) and BG:NAG (0.03) ratios in present study indicated that Psoil may be limited. Additionally, redundancy analysis (RDA) revealed that the Csoil: Nsoil was positively correlated with Rmic: Cmic but negatively with Cmic: Csoil and Nmic: Nsoil, while Csoil:Psoil and Nsoil:Psoil were also significantly and negatively correlated with BG:AP, BG:NAG, and NAG. Therefore, our results indicated that afforested ecosystem are highly susceptible to changes in soil microbial and enzyme stoichiometry during aggradation and may become P-limited. Such changes were modulated by soil nutrient stoichiometry.

Land-use change can modify terrestrial ecosystem processes with potentially important effects on below-ground carbon dynamics. Soil microbes are considered the rate-limiting factor in carbon decomposition. However, the effect of land-use change on soil microbial community and the mechanism of soil carbon dynamics remain unclear. In this study, soil samples were collected during four periods (April, June, August, and October) at sites in the Loess Plateau in China with different land- use types: Robinia pseudoacacia L. (RP) and abandoned land (AL); these areas were converted 40 years ago from similar farmlands, while the millet (Setaria italica) farmlands (FL) were selected as a control in our study. Quantitative PCR and Illumina sequencing of the 16S rRNA and ITS genes were performed to analyze the abundance, diversity, and compositions of the soil microbes (bacteria and fungi). Additionally, soil organic carbon fractions (soil organic carbon: SOC, dissolved organic carbon: DOC, microbial biomass carbon: MBC) and soil respiration components (soil respiration: SR, heterotrophic respiration: HR, autotrophic respiration: AR) were evaluated. The results showed that SOC fractions and soil respiration increased after land-use change, with significant correlation being observed. In particular, DOC was more related to SR and HR than to the other fractions. Moreover, the abundance and diversity of the microbes (bacteria and fungi) were greatly affected by the land- use change; both of them were significantly and positively correlated with soil organic carbon fractions and soil respiration components. For dominant bacterial phyla, both Proteobacteria and Bacteroidetes were significantly more abundant in the afforested soil than in the FL, while the abundances of Actinobacteria and Chloroflexi ranked as FL > AL > RP. For dominant fungal phyla, Ascomycota responded positively to land- use changes, whereas Basidiomycota responded negatively. Such changes in the abundances of microbial phyla were significantly correlated with the linkage of soil organic carbon fractions and respiration components. Altogether, these results suggest that the changes in components of soil respiration may be highly susceptible to soil organic carbon fractions, especially to DOC, and this linkage is largely modulated by microbial community across land-use changes.

Cover cropping is practiced to enhance soil health and sustain succeeding crop yield; however, the effect of cover crop on soil water storage, succeeding crop yield, and water-use efficiency (WUE) may not be consistent in all regions. A meta-analysis was carried out to evaluate the effect of cover crop on precipitation storage efficiency (PSE, the percent of precipitation that is stored in the soil during the fallow period), soil water storage at succeeding crop planting (SWSP), succeeding crop yield, and WUE from data collected from 117 studies across the world. Cover crop decreased PSE by 33.4% and soil water storage for the whole profile (SWSPT) at soil depth by 13.2%, but increased water storage to a depth of 30 cm (SWSP30) by 6.0% (P

Soil bacterial community structure, enzyme activities and their relationships to soil carbon and nitrogen in response to long-term fertilization remain poorly understood. Therefore, the objective of this study was to evaluate soil carbon and nitrogen fractions, enzyme activity, and bacterial community structure at 0–15, 15–30, and 30–60 cm depths after 34-yr of continuous application of manure and inorganic fertilizers. The study had a randomized complete block design with six treatments and three replications. Treatments were inorganic nitrogen fertilizer only (N), nitrogen plus phosphrous fertilizers (NP), manure (M), nitrogen plus manure (NM), nitrogen plus phosphorus plus manure (NPM), and unfertilized control (CK) in a winter wheat (Triticum aestivum L.) monoculture system. Most soil carbon and nitrogen fractions at 0–15 and 15–30 cm were greater with M, NM, and NPM, and winter wheat yield was greater with NPM than other treatments. The NPM increased β-glucosidase, β-xylosidase, and β-N-acetylglucosidase compared to other treatments at all depths. Soil bacterial Shannon index was similar among treatments at 0–15 and 15–30 cm and lower in N and NP than other treatments at 30–60 cm. Compared to CK, inorganic and manure fertilization increased relative abundances of Gemmatimonadetes and Bacteroidetes but decreased those of Nitrospirae, Planctomycetes, and Latescibacteria. Increases in soil enzyme activities and bacterial communities after long-term application of inorganic N and P fertilizers and manure was related to increased substrate availability. Overall, a combination of chemical fertilizers and manure can enhance soil health and quality through increased soil organic matter component, enzyme activity, and bacterial abundance.

Altered precipitation regimes have a great impact on global climate change, with potentially important effects on below-ground carbon dynamics. Soil microbes and carbon (C)-degrading extracellular enzymes activities (EEAs) are considered as the rate-limiting step in C decomposition. However, the effect of altered precipitation on the microbial biomass, microbial EEAs, and mechanism for soil C dynamics has not been established. In current study, we synthesized the responses of microbial biomass, C-degrading EEAs, soil organic carbon (SOC), dissolved organic carbon (DOC), and soil respiration (SR) to altered precipitation from 70 published studies. The results showed that increased precipitation significantly enhanced soil microbial biomass and oxidative C-degrading EEAs (Ox-EEAs) by 16.18% and 6.58%, respectively, but had no effects on hydrolytic C-degrading EEAs (Hy-EEAs). Decreased precipitation led to a significant decline of soil microbial biomass and Ox-EEAs by 11.61% and 10.99%, respectively; however, Hy-EEAs increased by 25.79%. Furthermore, increased precipitation stimulated soil microbial biomass in shrub and grassland but had no effects in forest, while decreased precipitation repressed soil microbial biomass but increased Hy-EEAs in forest. The response ratios (RRs) of microbial biomass to altered precipitation were negatively correlated with the mean annual precipitation (MAP) and mean annual temperature (MAT); however, the RRs of Hy-EEAs were positively correlated with MAP. Particularly, in low MAP (≤600 mm), increased precipitation significantly increased soil microbial biomass by 21.40% but decreased precipitation did not affect soil microbial biomass; In contrast, in high MAP (>600 mm), decreased precipitation significantly declined soil microbial biomass by 15.37%, and significantly increased Hy-EEAs by 29.31% but increased precipitation did not affect both of them. Moreover, the RRs of microbial biomass and Ox-EEAs were significantly correlated with SOC, DOC, and SR; however, we only observed a negative relationship between RRs of Hy-EEAs and RRs of SOC, suggesting the concurrent responses of microbial biomass and C-degrading EEAs for below-ground C dynamics under simulated precipitation changes, and that a large amount of recalcitrant C in the soils would be highly susceptible to changing precipitation.

Soil microorganisms regulate carbon (C) transfer from terrestrial sources to the atmosphere, therefore playing a pivotal role in soil C dynamics. Worldwide, grazing is one of the most prevalent grassland management strategies, yet the effects of grazing on soil microbial community size and soil respiration (SR) are still active areas of debate. We conducted a meta-analysis of 71 publications to synthesize the responses of soil microbial community size and SR to grazing. Our results showed that grazing significantly decreased soil total microbial, bacterial and fungal community size by 11.74, 8.85 and 11.45%, respectively. However, this effect were differed when the studies were grouped by the grazing intensity. Briefly, light and moderate grazing intensity had no effect on soil microbial, bacterial and fungal community size, but heavy grazing intensity significantly reduced soil’s total microbial, bacterial and fungal community size by 14.79, 16.48 and 28.12%, respectively. The responses of microbial community size to grazing were positively correlated with those of SR both under moderate and heavy grazing intensity. Our findings indicate that soil microbial community size could be an important underlying mechanism involved in determining soil C dynamics under grazing. Hence better understanding of the responses of soil microbial community size would greatly contribute to our understanding of soil C dynamics. Lastly, our results underscore the importance of factoring grazing intensity into consideration to further improve the model’s projection of soil C dynamics.

Afforestation is recognized as an important driving force for soil organic C (SOC) dynamics and soil element cycling. To evaluate the relationships between soil C:N:P stoichiometry and SOC fractions, soil C:N:P stoichiometry distributions at 0–200 cm soil depths were analyzed and the contents of SOC fractions were evaluated in 9 typical land-use systems on the Loess Plateau of China. The contents of light fraction organic C, particulate organic C (> 53, 53–2 000, and > 2 000 µm), labile organic C, microbial biomass C, and dissolved organic C decreased with increasing soil depth and were higher in afforested soil than in slope cropland soil. Compared with the slope cropland, different vegetation types influenced soil C:N, C:P, and N:P ratios, especially when C:P and N:P ratios were significantly higher (P < 0.05). Moreover, SOC fractions at the 0–10 and 10–40 cm depths were particularly affected by soil C:P ratio, whereas those at the 40–100 and 100–200 cm soil depths were significantly affected (P < 0.05) by soil N:P ratio. These results indicate that changes in SOC fractions are largely driven by soil C:P and N:P ratios at different soil depths after afforestation.

Cover crops have been increasingly grown for improving soil health and crop production and minimizing environmental impact compared to no cover crop. Systematic documentation of cover cropping effects on soil microbial abundance and community structure, however, is scarce. A meta-analysis including data from 81 available studies was conducted to elucidate the effect of “cover crop” versus “no cover crop” on soil microbial community abundance and structure. Microbial biomass C and N (MBC and MBN) and total phospholipid-derived fatty acids (PLFA) were taken as proxies for soil microbial abundance, and total fungi, total bacteria, gram-positive and -negative bacteria, actinomycete, and arbuscular mycorrhizal fungi (AMF) for microbial community structure. Compared to no cover crop, cover crop overall enhanced PLFA, MBC, and MBN by 24, 40, and 51%, respectively. Soil total bacteria and total fungi, and the groups in them increased by 7–31% with cove crop compared to no cover crop. Fungi were affected more by cover crop than bacteria as indicated by the greater fungi/bacteria ratio. In depth categorical meta-analyses revealed that the legume and nonlegume cover crop mixture reduced MBC, PLFA, and actinomycete compared to legume or nonlegume cover crop alone. Legume cover crop enhanced actinomycete in comparison to nonlegume or the cover crop mixture. Incorporation of cover crop residue into the soil increased PLFA, total bacteria, AMF root colonization, and spore density, but decreased gram-positive and -negative bacteria and AMF compared to residue placed at the surface or removed from the soil. Microbial parameters due to cover crop compared to no cover crop were related to soil properties and annual precipitation. Medium-textured soils showed greater response of cover crop on PLFA, total bacteria and fungi, and actinomycete than fine- or coarse-textured soils. We conclude that cover crops enhance soil microbial community biomass and affected community structure compared to no cover crop and the responses of microbial parameters to cover crop varied with soil and climatic conditions. Cover crops can enhance biological soil health by enhancing microbial community abundance compared to no cover crop.

The distribution patterns of the microbial community and enzyme activity in soil systems along an elevation gradient have attracted considerable attention; however, the differences in microbial diversity and enzyme activity between the rhizosphere and bulk soil and their drivers are still unclear. Here, we used an elevation gradient that covered six elevation levels and ranged from 1308 to 2600 m above sea level. Illumina MiSeq sequencing of the 16S rRNA gene and ITS-1 gene was used to analyze the community of bacteria, total fungi, ectomycorrhizal (EcM) fungi, and saprotrophic fungi in both rhizosphere and bulk soil; in addition, the soil enzyme activity (β-glucosidase, N-acetyl-glucosaminidase, leucine aminopeptidase, and acid phosphatase) was investigated. The results revealed that the elevation significantly affected the diversity of the bacterial, total fungal, EcM, and saprotrophic fungal community, as well as the enzyme activity dynamics. The difference in the microbial diversity and enzyme activity between rhizosphere and bulk soil diminished as the elevation increased, except for the saprotrophic fungal diversity. Similarly, the dominant phyla from the compositions of bacteria, fungi, EcM fungi, and saprotrophic fungi, such as Proteobacteria, Acidobacteria, Actinobacteria, Basidiomycota, and Ascomycota, also changed with elevation and rhizosphere. In addition, the elevation-dependent differences in the microbial community and enzyme activity between the rhizosphere and bulk soil were affected mainly by climatic factors (mean annual temperature and precipitation) and soil properties, such as the bulk density, ammonium nitrogen, and total phosphorus. The effects of the climatic factors were greater than those of the soil properties along the elevation gradient. These results suggest that changes in climatic factors, such as temperature, with elevation may affect the microbial interaction between roots and the soil. The result highlight the importance of the ecological roles of the microbial community in climate change.

Temporal variation in soil enzyme activities has important significance for soil quality after afforestation. This study investigated the temporal variation in soil enzyme activities and their response to changes in soil properties following afforestation. Soil samples were collected during different periods of vegetation growth at sites in the Loess Plateau with different land use types: 40 year-old Robinia pseudoacacia L. (RP40a), Caragana Korshinskii Kom (CK40a), and abandoned land (AL40a), as well as millet ( Setaria italica ) farmland (FL). Activities of four enzymes (catalase, saccharase, urease and alkaline phosphatase) that are involved in C, N, P cycling and soil water content (SWC), dissolved organic carbon (DOC), dissolved organic nitrogen (DON), and available phosphorus (AP) were measured. The results revealed that temporal variation and land-use have significant effects on the patterns of SWC, DOC, and DON, although not on that of AP. In addition, the activities of soil enzymes were highest in June, indicating that there are differences in the temporal variation of soil enzyme activities within a given land-use type, especially for alkaline phosphatase. The consistent ranking of soil enzyme activities was also significantly increased by afforestation. Furthermore, nonmetric multidimensional scaling analysis showed that the influence degree of afforestation on activities of the four enzymes was higher than that of temporal variation. Significant correlations between soil enzyme activities and soil properties indicated that soil enzyme activities are closely related to soil nutrients dynamics, particularly with respect to DON. The present study accordingly demonstrates that soil enzyme activities respond to farmland-to-forest conversion and hence have the potential to affect soil qualities in the Loess Plateau.

Ecological stoichiometry (C:N:P ratios) in soil plays an important role in ecosystem dynamics and functioning; however, its relationship with below-ground microbial diversity following afforestation remains poorly understood. To illustrate the linkage of C, N, and P in soil and microbial biomass, and the effect on the soil bacterial community, soil samples were collected from farmland and from three afforested land, namely Robinia pseudoacacia L., Caragana korshinskii Kom, and abandoned land, which have been arable for the past 40 years. Quantitative PCR and Illumina sequencing of the 16S rRNA genes were used to analyze soil bacterial abundance, diversity, and composition. Additionally, soil properties and C, N, and P levels in soil and microbial biomass were estimated. The results revealed that C, N, and P levels in soil and microbial biomass increased following afforestation, with a significant correlation observed, especially for the N:P ratio. Additionally, a rise in 〈alpha〉- and 〈beta〉-diversity of soil bacteria was observed in response to afforestation, and was linked to soil C:P and N:P ratios. Soil bacterial phyla with high relative abundance (relative abundance > 1%) across all samples showed inconsistent directional trends in the composition response after afforestation. An increased abundance of Proteobacteria, Acidobacteria, and Nitrospirae were observed, while the abundance of Chloroflexi was opposite (P

Despite the evident importance of arbuscular mycorrhizal fungi (AM fungal) associated with the root and rhizosphere system of elevation gradients, limit is known about the difference in AM fungal diversity between root and rhizosphere and their influencing factors along elevation gradients. AM fungal Here, we designed an elevation gradient experiment, which covered six elevations and three vegetation types, and collected plant and soil samples. We used Illumina gene sequencing to analyze AM fungal diversity in roots and rhizosphere soils; other potential factors, such as plant diversity, leaf C, N, and P, litter, soil and microbial biomass, extracellular enzymes activity, and the bacterial and ITS broad-fungal diversity, were also determined. We found that AM fungal diversity differences between root and rhizosphere soil diminished as elevation increased, despite that AM fungal diversity had a well-known pattern with elevation (unimodal patterns). Compared with plant characteristics, soil properties (soil C, N, P, C:N, C:P, N:P) were stronger effect on AM fungal diversity between root and rhizosphere. Particularly, soil extracellular enzymes activity and bacterial and ITS broad-fungal diversity explained more variation in AM fungal diversity dynamics along the elevation gradients. Our findings indicate that the diminishment of AM fungal diversity in root and rhizosphere soil are a response to elevation gradients through changes of soil extracellular enzymes activity and the bacterial and fungi communities, which provided evidence that AM fungal community dynamics link to climate change.

The afforestation of abandoned land could offer opportunities to sequester soil organic carbon (SOC), promote nutriment elements cycling, improve plant diversity in the plantation understory and provide ecosystem services. The objectives of this study were to identify plant diversity in the plantation understory, quantify the changes in SOC and total nitrogen (TN) storage in deep soil, assess the SOC, TN, and total phosphorus (TP) stoichiometries, and investigate their relationships in the Loess Plateau Region (LPR) undergoing long-term afforestation. Soil samples were collected at a soil depth of 0–200 cm under 30-yr old Robinia pseudoacacia L. and adjacent abandoned sites, and SOC, TN and TP were determined in different soil depth. Additionally, plant composition and diversity in the plantation understory were evaluated. The results showed that land subjected to long-term afforestation had greater plant coverage, plant density, richness index ( R ) and Shannon–Wiener diversity ( H ) compared to abandoned land communities ( P P P P R CN , R CP , and R NP ratios.

Forest development gradually changes the above-ground plant community, but the potential effects on the below-ground microbial community remain unclear, particularly at the various succession stages. Here, we investigated six vegetation types that covered two succession stages (early and late stages) during forest development. The early stage showed changes from two pioneer communities (Betula platyphylla and Populus davidiana) to two mixed communities (Populus davidiana with Pinus tabuliformis), while the late stage showed changes from the two mixed communities to two climax communities (Quercus wutaishanica and Pinus tabuliformis). Illumina sequencing of the 16S rRNA gene and ITS gene were carried out to analyze soil microbial (bacterial and fungal) diversity and composition. Soil properties (i.e., moisture, bulk density, texture, ammonium nitrogen, nitrate nitrogen, organic carbon, total nitrogen, and total phosphorus) were also determined. The results showed that forest development had positive effects on microbial diversity. Particularly, bacterial diversity successions proceed faster than that of fungi at the early stage. Proteobacteria and Bacteroidetes significantly increased, but Actinobacteria and Acidobacteria significantly decreased during forest development. In contrast, the effect sizes of Proteobacteria, Actinobacteria, and Acidobacteria at the early stage were larger than those at the late stage. The dominant fungi phyla (i.e., Ascomycota, Basidiomycota, and Zygomycota) across all soil samples responded insignificantly to forest development. Such differential responses of the microbial diversity and dominant phyla were significantly correlated with soil texture, soil organic carbon, and total nitrogen. In contrast, the effect size of soil properties on bacterial phyla was larger than that on fungal phyla. Collectively, these results emphasize that the responses of the microbial community to forest development depend on the succession stage, and also suggest that bacteria and fungi may not follow the same successional trajectories due to the differed responses of bacteria and fungi to changing soil texture and carbon/nitrogen contents during forest development.