Nearly all tree species develop symbiotic relationships with either arbuscular mycorrhizal (AM) or ectomycorrhizal (EM) fungi to acquire nutrients from soils, and hence influence soil carbon (C) and nitrogen (N) cycles in terrestrial ecosystems. It is crucial to understand the differences in soil C and N cycles between AM and EM forests and the underlying mechanisms. In this review, we first compared the differences in the soil C and N cycles between AM and EM forests, and synthesized the underlying mechanisms from perspectives of the inputs, stabilization, and outputs of soil C and N in forest ecosystems. We also compared the responses of soil C and N cycles between AM and EM forests to global changes. In this field, one major research priority is comparing the structure and function (including the soil C and N cycles) between AM and EM forest ecosystems to provide theoretical basis and solid data for improving forest productivity and ecosystem services. The second research focus is deepening the understanding of the effects of interactions between aboveground litter and belowground mycorrhiza and free-living microbes on soil C and N cycles to reveal the potential underlying mechanisms in forests with different mycorrhizal symbioses. Third, the research methodology and new techniques need refining and applying to explicitly focus on scaling up the fine-scale measurements to better expound and predict the C and N cycles in forest ecosystems. Finally, more studies on the stability of soil organic matter among different mycorrhizal forests are needed to precisely assess responses of the structure and function of forest ecosystems to global changes.

Aims Understanding the effects of soil microorganism at different elevations on plant C:N:P stoichiometry can help us to understand the plant-soil interactions in the context of climate change. Our aim was to quantify the independent and interactive effects of soil microbial communities and temperatures on the C, N, and P in the leaves of Dodonaea viscosa—a global widespread species. Methods Rhizosphere soils of D. viscosa were collected from two elevation zones in Yuanmou County, Yunnan Province. A 2 × 3 factorial experiment with six replications was conducted using climate chambers. The leaf C, N and P contents and the soil properties were measured after three months of the treatments. Important findings Compared with the autoclaved treatment, inoculated rhizosphere soils from both high and low elevations had higher nutrient absorption, especially P uptake. Temperature produced no significant effect on leaf C:N:P stoichiometry, but the interactive effect of temperature and microbial treatment appeared significant. For inoculated rhizosphere soils from high elevation, temperature had no significant effect on leaf C:N:P stoichiometry. For inoculated rhizosphere soils from low elevation, leaf N and P contents under low temperature were significantly lower than those with warmer soils. The promoting effect of soil microorganisms on nutrient uptake may be due to the direct effect of beneficial microorganisms (e.g., mycorrhizal fungi), but not through the alteration of nutrient cycling process. Because D. viscosa in the inoculated rhizosphere soils absorbed more N and P from the soil than those in autoclaved soil, the available N and P in inoculated rhizosphere soils were lower than those in autoclaved soils. As predicted future temperature will be lower in the studied region, the growth of D. viscosa may be negatively affected through plant-microbe feedbacks.

Aims Ligularia virgaurea is an indicator species of alpine meadow degradation. Recently, the vast spreading of L. virgaurea has brought the serious economic loss of grassland ecosystem, but it remains unclear whether soil microbes involve in the spreading of L. virgaurea.

Methods We chose four patches with different density of L. virgaurea to measure the influence of spreading of L. virgaurea on the functional diversity of soil microbial community in the Qinghai-Xizang Plateau.

Important findings The spreading of L. virgaurea increased soil microbial activity, but reduced soil available nitrogen concentration. The Shannon index, utilization number of carbon resource and evenness index of soil microbial community displayed no significant differences among patches, but the utilization structure of carbon resource in high density patch was significantly different from control patch. Our findings indicate that the limitation of soil nitrogen caused by the changing functional diversity of soil microbial community in the distributed sites is one of the mechanisms for the vast spreading of L. virgaurea in alpine meadow ecosystem.

Aims Soil microbe plays key role in mediating terrestrial carbon cycles. It has been suggested that climate warming may affect the microbial community, which may accelerate carbon release and induce a positive feedback to soil climate warming. However, there is still controversy on how microbial community responds to experimental warming, especially in cold and drought environment.

Methods We conducted an open top chambers (OTCs) experiment to explore the effects of warming on soil microbial community in an alpine steppe on Qinghai-Xizang Plateau. During the maximum of the growing seasons (August) of 2015 and 2016, we monitored the biomass and structure of soil microbial community in warming and control plots using phospholipid fatty acids (PLFA) as biomarkers.

Important findings Short-term warming treatment significantly increased the soil temperature by 1.6 and 1.6 oC and decreased soil moisture by 3.4% and 2.4% (volume fraction) respectively, but did not alter either soil properties or normalized difference vegetation index (NDVI) during the growing season (from May to October) in 2015 and 2016. During the maximum of growing seasons (August) of 2015 and 2016, the magnitude of microbial biomass carbon (MBC) were 749.0 and 844.3 mg·kg^-1, microbial biomass nitrogen (MBN) were 43.1 and 102.1 mg·kg^-1, and the microbial biomass C:N ranged between 17.9 and 8.4. Moreover, all three showed no significant differences between warming and control treatments. The abundance of bacteria was the most in microbial community, while arbuscular mycorrhizal fungi was the least, and warming treatment did not alter the abundance of different microbial group and the microbial community structure. Nonetheless, our result revealed that warming-induced changes in MBC had significant positive correlation with changes in soil temperature and soil moisture. These patterns indicate that, microbial community in this alpine steppe may not respond substantially to future climate warming due to the limitation of soil drought. Therefore, estimation of microbial community response to climate change calls for consideration on the combined effect of warming and drought.

Aims Clonal integration contributes greatly to the adaption of clonal plants to heterogeneous habitats. However, effects of transportation direction of photosynthate on microbial processes need to be further investigated in the rhizosphere. The purpose of this study is to determine the effects of directional differences in photosynthate transport on microbial processes in the rhizosphere of clonal plant Phyllostachys bissetii.
Methods By removing the aboveground parts of the ramets, acropetal treatment and basipetal treatment were applied in this study to control the transportation direction of photosynthate. In acropetal treatment, aboveground parts of distal ramets were cut off (with 20 cm above ground kept), and proximal ramets were left intact. While in basipetal treatment, aboveground parts of proximal ramets were cut off (with 20 cm above ground kept), and distal ramets were left intact. Rhizomes between the two ramets were either connected or severed. Carbon (C) and nitrogen (N) availabilities, and enzyme activities in the rhizosphere soils were measured.
Important findings In acropetal treatment, total organic carbon (TOC), dissolved organic carbon (DOC), dissolved organic nitrogen (DON) and soil inorganic nitrogen (NH₄ ⁺-N and NO₃ ^--N) content in the rhizosphere soil of distal ramets with connected rhizomes were significantly higher than those with severed rhizome. The activities of urease, polyphenol oxidase (POXase), N-acetyl-β-D-Glucosaminidase (NAGase) were significantly enhanced. Further, clonal integration had a significant effect on C and N availability, and microbial processes in the rhizosphere soil of neighbouring ramets. In basipetal treatment, clonal integration did not show a significant effect on C availability in the rhizosphere soil of proximal ramets, but microbial processes along with soil enzyme activities were altered accordingly. Effects of transportation direction of photosynthate on microbial processes in the rhizosphere of P. bissetii provides insights into the adaptation mechanisms of clonal plant populations.

Aims In order to discuss the underlying mechanism of desertification effect on the ecological stoichiometry of soil, microbes and extracellular enzymes, we studied the changes of soil, soil microbial and extracellular enzyme C:N:P stoichiometry during the desertification process in the desert grassland in Yanchi County, China.
Methods The “space-for-time” method was used.
Important findings The results demonstrated that: (1) Soil C, N, P contents and soil C:P, N:P significantly decreased, but soil C:N gradually increased with increasing desertification. (2) Soil microbial biomass C (MBC):soil microbial biomass P (MBP), soil microbial biomass N (MBN):MBP and soil β-1,4-glucosidase (BG):β-1,4-N- acetylglucosaminidase (NAG) gradually decreased, soil BG:alkaline phosphatase (AP) and NAG:AP basically showed an increasing trend with increasing desertification. (3) Desertification increased the soil microbial carbon use efficiency (CUE_C:N and CUE_C:P) gradually, while soil microbial nitrogen use efficiency (NUE_N:C) and soil microbial phosphorus use efficiency (PUE_P:C) basically decreased. (4) Soil, soil microbial and soil extracellular enzyme C:N stoichiometry (C:N, MBC:MBN, BG:NAG) were significantly negatively correlated with the soil, soil microbial and extracellular enzyme N:P stoichiometry (N:P, MBN:MBP, NAG:AP), the soil and extracellular enzymes C:N (C:N, BG:NAG) were significantly positively correlated with the soil and extracellular enzymes C:P (C:P, BG:AP). Soil N:P was significantly positively correlated with the soil MBN:MBP, but was significantly negatively correlated with the soil NAG:AP. The analysis demonstrated that soil microbial biomass and extracellular enzyme activity changed with soil nutrient during the desertification process in the desert grassland. The covariation relationship between soil nutrient and C:N:P stoichiometry of microbial-extracellular enzyme provides a theoretical basis for understanding the underlying mechanism of C, N, P cycling in the soil-microbial system in desert grasslands.

Invasive alien plants not only influence plant community composition, biodiversity and ecosystem structure and function, but also have severe impacts on soil nitrogen transformation processes. The effects of invasive alien plants on nitrogen (N) cycling have been one of the hot topics in invasion ecology. Litter decomposition and its nutrient release play an important role in nutrient cycling. In addition, invasive alien plants have the potential to influence soil N transformation through allelopathy. All these processes are tightly related to soil microbes. Therefore, this review mainly focuses on litter decomposition and its nutrient release, and allelopathy to understand the effects of plant invasion on soil N transformation. Changes in soil N transformation and soil microbes (esp. Ammonia oxidizing bacteria and Ammonia oxidizing archaea) due to plant invasion, as well as the feedbacks of these changes to further invasion of alien plants were discussed. Finally, the interactions between arbuscular mycorrhizal fungi and plant invasion were reviewed.

Aims Microorganisms play a crucial role in the litter decomposition process in terrestrial ecosystems. Understanding the independent and interactive relationship between fine root decomposition and bacteria community related to substrate characteristics can help to predict the consequences of changes on ecosystem function. Therefore, the aim of this study was to identify fine roots’ influences on rhizosphere microbial structure and diversity.

Methods The decomposition of root litters of four dominant tree species of Mount Taishan (Robinia pseudoacacia(RP), Quercus acutissima(QA), Pinus tabulaeformis(PT) and Pinus densiflora(PD)) was tested in a Yaoxiang Forest Farm. Using Illumina high-throughput sequencing of 16S rRNA genes, bacterial community composition was determined. Composition, diversity and relative abundance of bacteria were calculated for per fine root litter.

Important findings (1) Fine root litter decomposition differed significantly among different root types. There was no difference in decomposition rate between broad-leaved species and conifer species. In all species, fine roots of RP and QA were more strongly decomposed than that of PT and PD, and these differences were significant (RP > QA > PT > PD). (2) The number of observed species, operational taxonomic units, Ace index and phylogenetic diversity in broad-leaved species were significantly lower than that in coniferous species. Bacterial community structure differed significantly among four species for root decomposition. Initial carbon (C), lignin:nitrogen (N) and C:N in fine root had a great influence on the bacterial community structure. (3) At the phylum level, a total of 4 phyla were dominant (>5% across all species). Based on the average relative abundance, the most abundant phyla were Proteobacteria, Actinomyces, Bacteroidetes and Acidobacteria. Proteobacteria’s and Acidbacteria’s abundance were significantly different among the four species. Particularly, the Proteobacteria of broad-leaved species was significantly higher than that of coniferous species. At the class level, a wide range of classes dominated. Based on the average relative abundance, the most abundance classes were Alphaproteobacteria, Betaproteobacteria, Gammaproteobacteria, unidentified-Actinobacteria and Sphingobacteriia. Alphaproteobacteria and unidentified-Actinobacteria had significant differences among the four species. (4) Pearson correlation analysis showed that the relative abundance of dominant phylum and class was affected by the initial properties of root litter, especially the Proteobacteria and Alphaproteobacteria. In addition, there was a significant positive correlation between fine root decomposition rate and relative abundance of Proteobacteria and Alphaproteobacteria. Redundancy analysis (RDA) also demonstrated that the initial properties of fine root litter (initial N, P, C:N) had significant effects on the structures of bacterial community. These results can improve understanding the links between fine root litter decomposition and functional microbial communities.

The increase of atmospheric nitrogen (N) deposition caused by global change and industrial and agricultural production has had an important impact on the structure and function of ecosystems. There are many forms in composition of atmospheric N deposition. However, it is not clear whether there are differences in the effects of N deposition forms on structure and function of the ecosystems. Here our objective was to characterize the effects of different forms and levels of N addition on soil net N mineralization potential of steppe ecosystem in the Nei Mongol.

A N addition experiment was carried out in the meadow steppe in Nei Mongol using five different N fertilizers, including CO(NH₂)₂, NH₄HCO₃, NH₄NO₃, (NH₄)₂SO₄, and slow-release urea separately since 2014. There were six N addition levels with 0 (N0), 2 (N2), 5 (N5), 10 (N10), 20 (N20) and 50 (N50) g·m ^-2·a ^-1. Fresh soil samples from all treatments were taken and all roots were removed in July 2016. Then these soil samples were incubated for 24 h at 25 °C with 60% field water capacity. The potential of net N mineralization and nitrification rates and the potential of soil microbial respiration (MR), soil physical and chemical properties, soil microbial biomass carbon (MBC) and N (MBN) contents were measured, respectively.

The results showed that: (1) different forms and levels of N addition significantly increased soil inorganic N content and potential net N mineralization and nitrification rates. The N20 treatment had the highest soil inorganic N content and net N mineralization rate, however the highest soil net nitrification rate was found under N50 treatment; (2) different forms and levels of N addition significantly increased MBC and MBN contents and decreased the microbial metabolic quotient (qCO₂). Lower N addition (N2) enhanced MR, but medium and higher N addition (N20, N50) restrained the MR; (3) different forms and levels of N addition significantly reduced the soil pH value, but significantly increased the available phosphorus content. No effects were found in soil water content, total phosphorus, total N and soil organic carbon contents, separately. The results verified that soil available N was the limited factor affecting plant productivity in meadow steppe in Nei Mongol steppe. No matter what type of N fertilizer can increase the activity of soil microorganism and the potential net N mineralization rate of the meadow steppe in this area.

Nutrient additions such as nitrogen and phosphorus are important strategies to improve the productivity of the grassland ecosystem. However, their effect on soil nitrous oxide (N₂O) emissions remains unclear.

A field study was conducted in an alpine grassland located in the north slope of Kunlun Mountains in Southern Xinjiang. Four treatments included nitrogen addition alone (N), phosphorus addition alone (P), mixture of nitrogen and phosphorus additions (N + P) and an unfertilized control (CK). Gas samples were collected and analyzed using the static chamber chromatography methodology during the 2017 growing season. Treatment effects on the characteristics of N₂O emissions from grassland soil were thoroughly investigated. Pearson correlation analysis was used to identify and quantify the influence of environmental variables on soil N₂O emissions.

The results showed that N and (N + P) treatments induced N₂O flux peaks after three weeks of fertilizer addition, with the maximum daily N₂O flux rates of 42.3 and 15.4 g N·hm ^-2·d ^-1, respectively. The N treatment significantly increased growing season cumulative N₂O emissions by 1.8 to 3.2 times compared to P treatment, (N + P) treatment and CK, and there were no significant differences between the three treatments. Pearson correlation analysis showed that daily N₂O flux rate was correlated negatively with soil microbial biomass carbon, and positively with soil pH and dissolved organic carbon. There was no significant correlation between daily N₂O flux rate and other environmental variables. These results suggest that simultaneous addition of nitrogen and phosphorus nutrients can significantly reduce soil N₂O emission compared to N treatment for the alpine grassland in this region.

Aims The objective was to explore the stoichiometry of rhizosphere soil enzymes under major understory vegetation and their responses to plantation types and seasons.

Methods Rhizosphere soils of understory shrubs (Loropetalum chinense, Adinandra millettii and Eurya muricata) and herbs (Woodwardia japonica and Dryopteris atrata) were sampled in the early growth stage (April) and the vigorous growth stage (July) in Cunninghamia lanceolata, Pinus massoniana and Pinus elliottii plantations at Qianyanzhou Ecological Research Station, Taihe, Jiangxi. Potential activities of β-1,4-glucosidase (BG, carbon (C) acquiring enzyme), β-1,4-N-acetylglucosaminidase (NAG, nitrogen (N) acquiring enzyme) and leucine aminopeptidase (LAP, N-acquiring enzyme), acid phosphatase (AP, phosphorus (P) acquiring enzyme) and their stoichiometric ratios were measured. Soil physical and chemical properties were also analyzed.

Important findings The results found that (1) rhizosphere soil extracellular enzyme activities associated with C and N acquisition and BG:AP (enzyme C:P) were significantly different among understory species, but P acquisition were not. Both forest stand types and sampling seasons influenced BG:(NAG+LAP) (enzyme C:N). Interactions of understory species, forest stand types and seasons observably affected enzyme C:P. Principal component analysis showed that rhizosphere soil enzyme activities and ecoenzymatic stoichiometry differed significantly among different understory species (Loropetalum chinense was obviously different from Eurya muricata, and both of them were evidently different from other understory species), forest stand types (Cunninghamia lanceolata was different from Pinus massoniana and Pinus elliottii plantations) and sampling seasons. Soil NO₃ ^--N, NH₄ ⁺-N, DOC content and C:N were the main edaphic abiotic factors influencing the rhizosphere soil enzyme activities and ecoenzymatic stoichiometry. (2) Standardized major axis analysis showed that there were significantly linear relationship among lg(BG), lg(NAG+LAP) and lg(AP) of rhizosphere soils of understory species. lgBG:lg(NAG+LAP):lgAP(enzyme C:N:P) was approximately 1:1:1.3. Rhizosphere soil enzyme C:P and (NAG+LAP):AP (enzyme N:P) of understory species were 0.14 and 0.15, respectively. The regression slopes of lg(BG), lg(NAG+LAP) and lg(AP) deviated significantly from 1 because AP activities were much higher than BG activities and NAG+LAP activities. This study found that rhizosphere soil enzyme activities and ecoenzymatic stoichiometry were affected by understory species, forest stand types and sampling seasons in which substrate availability played an important role. Compared with C- and N-acquiring enzymes, microorganisms allocated more resources to the production of P-acquiring enzymes, which implied that the growth and activity of soil microorganisms were much more limited by P in rhizosphere soil of understory vegetation in subtropical plantations.

Litters of emergent plants are important components of material cycling in wetland ecosystems. To clarify the effects of climate warming and habitat difference on the litter decomposition processes and phyllospheric microorganisms of wetland emergent plants is of great significance for revealing the key material cycling processes in wetland ecosystems.

Zizania latifolia, a dominant emergent plant in typical wetlands of Northwestern Yunnan Plateau, was chosen for this study. Using litter bag methods, we studied mass remaining and the abundance, community structure and metabolic potential of phyllospheric microorganisms of the litter from Zizania latifolia under simulated warming (1.5-2.0 ℃) and under three habitats (air, water and soil interface).

Simulated climatic warming and habitat difference significantly affected the litter decomposition rate. After one-year decomposition, the mass remaining of litter was 66.4% under the simulated warming treatment, while 77.7% under the control treatment. The decomposition constant (k) value was 1.64 times under warming compared to the control. The mass remaining of litter at the water and soil interface was 42.2% and 25.3%, and the k value at the water and soil interface was 3.63 and 5.25 times of that at the air interface respectively. These results indicate that habitat difference was the key factor controlling the decomposition of emergent plant litter in wetlands. Moreover, warming mainly changed the community composition of litter phyllospheric microorganisms, while decomposition interface mainly affected the abundance, community structure and metabolic potential of phyllospheric microorganisms. Notably, phyllospheric microorganisms of litter at soil interface had the highest metabolic potential and utilized alcohols as main carbon sources. The characteristics of phyllospheric microorganisms between different treatments were in good agreement with litter decomposition rate, which provides an important theoretical basis for revealing the microbial mechanisms driving the decomposition of wetland plant litter.

Carbohydrates are important components of soil organic matter, which can be decomposed to different types of monosaccharides. Neutral monosaccharides in the soil are also called neutral sugars, including xylose, ribose, arabinose, glucose, galactose, mannose, fucose and rhamnose. Among them, plant-derived sugars mainly include pentoses, such as xylose and arabinose, while microbial-derived sugars mainly consist of hexoses including galactose, mannose, fucose and rhamnose. Generally, the ratios of hexoses to pentoses are used to evaluate the contribution of microbial- versus plant-derived sugars. Neutral sugars are the main carbon and energy resources for soil microorganisms and play a vital role in aggregates formation. In this study, we review studies about neutral sugars in soils over the past 30 years and compare different methods for neutral sugar analysis. Furthermore, we compare the distribution patterns and turnover of soil neutral sugars across diverse land-use regimes, different soil density and particle size fractions and their influencing factors. The lowest neutral sugar content is found in arable soils compared with other four land-use types (coniferous forests, deciduous forests, shrublands and grasslands) in terms of absolute and relative contents. No significant difference is observed for the (galactose + mannose)/‍(arabinose + xylose)(GM/AX) ratios across the five land-use regimes. Nevertheless, the ratio of (rhamnose + fucose)/(arabinose + xylose)(RF/AX) indicates that microbially derived neutral sugars are more abundant in the soils of grasslands than coniferous forests or farmlands. The heavy fraction is characterized by an enrichment of microbial neutral sugars but a lower content of total neutral sugars compared to the light fraction. Concerning the distribution of neutral sugars across different soil size fractions (or aggregates), the microbial-derived neutral sugars are more abundant in the clay fraction (or microaggregates). As for the factors affecting neutral sugar content and distribution, many studies have focused on the human disturbances like agriculture and grazing, while the influence of environmental factors such as temperature, precipitation is poorly investigated.

Aims Soil microorganisms in forest ecosystems play vital roles in regulating above- and belowground ecosystem processes and functions such as soil nutrient cycling, litter decomposition, net ecosystem productivity, and ecosystem succession. We aim to investigate broad-scale seasonal patterns of soil microbial biomass carbon (C), nitrogen (N) and phosphorus (P) stoichiometry. Methods By synthesizing 164 samples of soil microbial biomass C, N and P content derived from the published literature, we investigated global seasonal patterns of soil microbial C, N, P content and their ratios across three vegetation types of global forests. Important findings Soil microbial biomass C, N and P content in temperate and subtropical forests were lower in summer and higher in winter. Soil microbial biomass C, N and P content in tropical forests were lower than those in temperate and subtropical forests in four seasons. Soil microbial biomass C and N content in tropical forests were relatively the lowest in autumn, and soil microbial biomass P content was relatively constant in all seasons. The soil microbial biomass C:N of temperate forest was significantly higher than that of other two forest types in spring, and that of tropical forest was significantly higher than that of other two forest types in autumn. Soil microbial biomass N:P and C:P in temperate forests remained relatively constant in four seasons, while those in tropical forests were higher than those in other three seasons in summer. The soil microbial biomass C content, N content, N:P and C:P of broad-leaved trees were significantly higher than those of conifers in four seasons, while the soil microbial biomass P content of conifers was significantly higher than that of broad-leaved trees in four seasons. There was no significant difference in soil microbial biomass C:N between broad-leaved and coniferous trees in both spring and winter, but the soil microbial biomass C:N of coniferous trees was significantly higher than that of broad-leaved trees in summer and autumn. For the change of soil microbial biomass, season is not but forest type is the main significant factor, suggesting that the seasonal fluctuation of soil microbial biomass changes with the inherent periodic change of trees. Asynchronous nutrient uptake by plants and soil microorganisms is a trade-off mechanism between nutrient retention and ecological function maintenance.

Aims Solidago canadensis, an invasive herbaceous species, has a strong capacity of potassium enrichment, that may relate to its influence on soil microbial community. Rhizosphere potassium-soluble bacteria can convert mineral potassium into soluble forms being able to be used by plants. It is not known how invasion of S. canadensis may affect diversity and potassium-solubilizing activity of the potassium-solubilizing bacteria. Methods We compared S. canadensis and its coexisting native plant Imperata cylindrica in the reclaimed Hangzhou Bay wetland, Zhejiang Province. We compared the potassium contents of soil and the plant tissues of S. canadensis and Imperata cylindrica which coexists with the invasive species, the effect of potassium supply level on biomass accumulation of plants, and the quantity, diversity and potassium-soluble activity of the rhizosphere potassium-solubilizing bacteria. Important findings The potassium contents in stem and leaf of S. canadensis were significantly higher (1.59 and 7.33 times respectively) than that of I. cylindrica, the contents of available potassium in the 0-10 cm soil layer where the two species grew were significantly different, but not in the 10-20 cm soil layer. Potassium application experiments showed significant biomass increase in both S. canadensis and I. cylindrica, and tissue potassium concentrations as well. Potassium-dissolving medium culture results showed that the number of potassium-‌solubilizing bacteria of S. canadensis rhizosphere was 2.51 times higher than that of I. cylindrica. The strains with potassium-dissolving rings were identified, and the amount of released potassium was determined. Among the 15 strains of potassium-solubilizing bacteria isolated from the rhizosphere soil of S. canadensis, nine efficiently dissolved potassium, and the content of K ⁺ in the treatment solution was 85.11%-192.54% higher than that in the control. Strain H2-20 had the strongest ability with the dissolved K ⁺ of 10.657 mg·L ^-1. The potassium- solubilizing effect of rhizosphere potassium-solubilizing bacteria of S. canadensis was significantly higher than that of I. cylindrica. According to 16S rDNA identification, the 15 strains of bacteria associated with S. canadensis were of 11 genera, and 6 of them had been reported to have the potassium-solubilizing ability. Our results suggest that potassium-solubilizing bacteria in the rhizosphere of S. canadensis is abundant, and may play an important role in potassium enrichment.

Aims Increasing atmospheric nitrogen (N) deposition accelerates soil N cycling, potentially resulting in decoupling of microbial biomass carbon (C):N:phosphorus (P), loss of plant species, and reductions of provision of ecosystem service. Studies on how the changes of elemental balance in microbes affect plant community composition, could provide a new insight for making clear the mechanism of N-induced loss of plant species. Methods We conducted a manipulative N addition experiment in a desert steppe in Ningxia, northwestern China to quantify the changes in plant biomass and species composition over two years. We analyzed the individual effects of microbial biomass C:N:P ecological stoichiometry and the joint effects with other key soil factors on plant community composition. Important findings The responses of plants to N addition appeared species-specific. The biomass of Salsola collina increased substantially; the biomass of Lespedeza potaninii decreased gradually. Other species showed slightly decreasing in biomass although statistically insignificant (p > 0.05). Along the N addition gradient, Shannon-Wiener diversity index, Simpson dominance index, and Patrick richness index of the plant community increased initially but decreased over time later. With increase in N addition level, the N content and N:P ratio of the microbial community increased, but the C:N ratio decreased. Plant community composition showed stronger correlations with microbial biomass N content, microbial biomass C:N ratio, microbial biomass N:P, soil NO₃ ^--N concentration, soil NH₄ ⁺-N concentration, and the total P content of the soils. Microbial biomass C:N:P ecological stoichiometry explained <3% of the variation in aboveground plant biomass and community diversity index. Surprisingly, the joint influences from microbial biomass C:N:P ecological stoichiometry and other soil properties explained 51% of the variation in plant biomass and 26% of the change in plant community diversity. These results indicate that the effect of microbial biomass C:N:P ecological stoichiometry on plant community was highly related to the effects of other soil properties under N addition.

Aims Long-time continuing cropping of peanut (Arachis hypogaea) would result in soil deterioration, which would seriously affect the productivity and the quality of peanut. Arbuscular mycorrhizal fungi (AMF) have been used as a fertilizer that may improve root microenvironment, increase nutrient uptake and stress resistance of the plants. This study investigated the effects of Funneliformis mosseae on peanut rhizosphere microenvironment under continuing peanut cropping.
Methods We conducted an experiment to examine soil properties, peanut productivity and quality between the treatments of: (1) peanut seedlings inoculated with F. mosseae in continuous cropping soil, and (2) peanut seedlings without the inoculation.
Important findings We observed that F. mosseae significantly enhanced the activity of sucrase, urease, alkaline phosphatase and nitrate reductase in soil, significantly increased the soil contents of total nitrogen, total phosphorus, total potassium, available phosphorus and available potassium. Meanwhile, the abundances of Aspergillus, Fusarium and Gibberella in the rhizosphere soil of continuous cropping were decreased, while the abundances of Gaiella was significantly increased comparing to the treatment without F. mosseae inoculation. In addition, F. mosseae significantly increased the peanut yield and quality, including protein, oleic acid and linoleic acid content. Our results suggested that F. mosseae improve the peanut rhizosphere environment, alleviate the obstacles of continuous cropping.

Biomarkers are biogenic organic compounds that carry the chemical structures specific to their biological sources and survive long-term preservation in environmental and geological systems. The abundance of biomarkers may indicate the relative contribution of specific biological sources to the natural organic matter while their chemical and isotopic compositions may also inform on the transformation stage of organic matter and the environmental settings. Compared with conventional bulk analysis, biomarkers offer highly specific and sensitive tools to track the sources, transformation and dynamic changes of natural organic matter components and have therefore been widely used in ecological and biogeochemical studies in the past decades. In particular, combined with ecosystem observations and control experiments, biomarkers have shown great potentials in revealing changes in microbial activity and carbon sources, soil organic matter dynamics, stabilization mechanisms and response to global changes. The recently-developed biomarker-specific isotope analysis also exhibits a great promise in revealing ecosystem carbon and nitrogen turnover and food web structures. This review summarizes several major categories of commonly used biomarkers, their analytical methods, applications in ecosystem studies and existing pitfalls, and discusses future directions of research to provide guidance for biomarker users in ecology and environmental sciences.

Recently developed in recent decades, the carbon isotope tracing technology is one of the most reliable methods, which has been widely used in the study of carbon (C) cycling in terrestrial ecosystems due to its high specificity and sensitivity. Here, the principle, analysis method and application process of C isotope tracing technology in C cycling in terrestrial ecosystem have been reviewed. Four different methods are currently being used in laboratory or field conditions, including natural abundance method, Free-Air Concentration Enrichment (FACE) technology coupling with ¹³C dilution method, pulse and continuous labeling with ¹³C enriched CO₂, and labeling with ¹³C enriched substrates. Results of field experiments and lab incubation experiments employing carbon isotope tracing technology were combined in order to quantify the transformation and distribution of photosynthetic C in plant-soil system. Furthermore, these techniques also help to understand the contribution of plant photosynthetic C to soil organic matter, the stabilization of soil organic matter and its microbial mechanism, to illustrate the dynamic changes of soil organic carbon (SOC), evaluate the contribution of new and old organic C to soil C storage, and estimate the micromechanism of SOC input, conversion and the stabilization in terrestrial ecosystems. Carbon cycle is affected by climate, vegetation, human activities and other factors, and therefore it is imperative to further develop a sensitive, accurate, multiscale and multidirectional isotope tracing system by combining carbon isotopes with mass spectrometry, spectroscopy and molecular biological technology. We have summarized the coupled application of carbon isotope tracing technology and the insitu detection involving molecular and biological approaches, and discussed the existing issues of carbon isotope tracing technology.

Forests are large and persistent carbon (C) sink mainly through the C sequestration of tree growth, which can mitigate the rising rate of CO₂ concentration in the atmosphere. According to C availability in trees, two mechanisms involved in controlling tree growth are attributed to limitations to C input and C utilities. Since many environmental factors influence the activities of C-source and C-sink of trees interdependently, it is difficult to quantify how the sensitivity of C-source or C-sink activity to environmental changes affects tree growth. Therefore, it is of significance to understand physiological mechanisms underlying potential limitations to tree growth in order to predict tree growth and forest C sink under global change scenarios. In this review, the debates on the C-source and C-sink limitations to tree growth were firstly introduced. Second, we discussed responses of tree growth to biotic and abiotic stresses, such as defoliation, drought and low temperature from the perspective of C-source/sink limitations. Finally, we proposed three priorities for future studies in this field: (1) to explore the regulating mechanisms on the allocation of non-structural carbohydrates (NSC) in trees, and to determine what conditions and what extent trees actively allocate the photosynthates to NSC storage at the expense of growth; (2) to strengthen studies on the tree C-sink, and determine the photosynthates allocated to all components of tree C-sink, especially the missing C-sinks such as the activities of roots and related microorganisms; and (3) to implement studies on interactions among C metabolism, mineral nutrition and hydraulics physiology, and fully understand the C-water-nutrient coupling and its effects on tree growth.

Microbiome is the combination of all microorganisms and their genetic information in a specific environment or ecosystem, which contains abundant microbial resources. A comprehensive and systematic analysis of the structure and function of microbiome will provide new ideas in solving the core issues in the fields of energy, ecological environment, industrial and agricultural production and human health. However, the study of microbiome largely depends on the development of relevant technologies and methods. Before to the advent of high-throughput sequencing technology, microbial research was mainly based on techniques such as isolation, pure-culture and fingerprint. However, due to the technical restrictions, scientists could only get limited knowledge of microorganisms. Since the beginning of 21st century, the revolutionary advances in the technology of high-throughput sequencing and mass spectrometry have greatly improved our understanding on the structure and ecological functions of environmental microbiome. However, the application of microbiomics technology in microbial research still faces many challenges. In addition, the descriptive studies focusing on the structure and diversity of microbiome have already matured, and the study of microbiomics is facing a critical transition period from quantity to quality and from structure to function. Hence, this paper will firstly introduce the basic concepts of microbiomics and a brief development history. Secondly, this paper introduces the related technologies and methods of microbiomics with their development process, and further expounds the applications and main problems of microbiomics technologies and methods in ecological study. Finally, this paper expounds the frontier direction of the development of microbiomics technology and methods from the technical, theoretical and application levels, and proposes the priority development areas of microbiome research in the future.

Aims The agro-pastoral ecotone is considered as fragile ecosystems which are strongly affected by agriculture and animal husbandry. The saline-alkali grassland is a unique grassland type in the agro-pastoral ecotone. A large amount of fertilizers are used to increase productivity in this area, which also promotes the emission of reactive nitrogen (N) gases and leads to the changes in soil carbon and N cycles. Mowing is a primary management practice in the agro-pastoral grassland in northern China. In order to explore the impact of N addition and mowing on carbon dynamic in this saline-alkali grassland located in the agro-pastoral ecotone, we determined the response of soil respiration to N addition and mowing.
Methods This study area is located in Youyu County, an agro-pastoral grassland ecosystem in northern China. The field experiment was set up in May, 2017. The treatments included: control (without mowing and mowing), addition of urea, addition of slow release urea, addition of urea + mowing, addition of slow release urea + mowing. Each treatment included 6 replicates. Therefore, there were totally 36 plots in this experiment. Soil respiration rate, soil temperature, soil moisture content, microbial biomass, inorganic N content, above-ground and below-ground biomass were measured under different treatments, and the cumulative carbon emissions and CO₂ fluxes were calculated.
Important findings Our results showed that: (1) Short-term (2017-2018) N addition significantly increased soil respiration rates and soil cumulative carbon emissions. Meanwhile, soil respiration rates and cumulative carbon emissions were significantly higher under urea treatment than those under slow release urea addition. (2) Mowing significantly reduced soil respiration rates and cumulative carbon emissions. (3) The interaction of short-term N addition and mowing had no significant effect on soil respiration rate. Therefore, short-term N addition can promote soil carbon release from the saline-alkali grassland in the agro-pastoral ecotone of northern China. Mowing can reduce soil respiration and decrease cumulative of carbon emissions. This may be because that mowing reduced the input of litter and further reduced soil substrate for microbes, which led to a decrease in soil microbial activity. However, long-term effect of N addition and mowing on soil carbon dynamics in saline-alkaline grasslands in the agro-pastoral ecotone still needs to be further explored.

Aims Altitude-induced changes in temperature, moisture, vegetation types and other conditions would significantly affect soil carbon (C_soil), nitrogen (N_soil), phosphorus (P_soil) concentrations and their stoichiometry. How soil microorganisms adapt to the variability of soil resource stoichiometry by regulating their biomass and extracellular enzymatic stoichiometry remains uncertain. The objective of this study was to quantify the altitudinal trends of soil-microbe-exoenzyme C:N:P stoichiometry and to explore the correlations among soil-microbe- exoenzyme stoichiometry.Methods In the present study, we investigated the C_soil, N_soil, P_soil concentrations, microbial biomass C (C_mic), N (N_mic), P (P_mic) concentrations, and the activities of C (β-1,4-glucosidase, BG), N (N-acetyl-β-glucosaminidase, NAG), and P (acid phosphatase) acquiring extracellular enzymes for microorganisms in four ecosystems along an altitudinal gradient on Mt. Datudingzi, Northeast China. These four ecosystems are a mixed broadleaf-coniferous forest at 800 m, a coniferous forest at 1 100 m, a Betula ermanii forest at 1 600 m and a grassland at 1 700 m.Important findings The results showed that: (1) altitude had no significant effect on C_soil and C_mic concentrations but had significant effects on soil and microbial biomass N and P concentrations. (2) The activities of BG and NAG decreased significantly with increasing altitude, likely due to the high elevation induced low temperature that inhibits microbial activities. (3) Altitude had significant effects on soil C:N, microbe C:N:P, and exoenzyme C:N:P; exoenzyme C:N:P decreased with the increasing stoichiometric imbalances between microorganisms and soils (ratios of soil C:N:P to microbe C:N:P, respectively). Overall, these results suggested that microorganisms can adapt to the variability of soil C:N:P by regulating their biomass C:N:P and exoenzyme C:N:P, and supported the microbial resource allocation theory.

Due to huge consumption of fossil fuels and chemical fertilizers, substantial amount of anthropogenic reactive nitrogen (N) has been released into the environment. Therefore, N deposition has gradually increased worldwide and become one of the most important issues of global change. China has been a N deposition hotspot, and N deposition is projected to last long duration, which poses serious threats to ecosystem stability and functionality. In this synthesis paper, we summarized the impacts of N deposition on aboveground vegetation, soil microorganisms and biogeochemical cycling of major elements (carbon, N and phosphorus) in terrestrial ecosystems by outlining the progresses in the research field during the past 40 years. Results indicate that the accumulation of reactive N compounds induced by N deposition alters the soil environment, ecological stoichiometric balance and species co-occurrence patterns, thereby changing biodiversity and ecosystem functions. The rates, forms and duration of N deposition and the homeostasis of biosystem together with abiotic environments determine the direction and extent of the ecosystem response to N deposition. Through analysing local and foreign studies in this research area, we explore the weaknesses of relevant research that are being conducted in China. To advance the basic research on and risk management of N deposition, we propose the establishment of a N deposition monitoring and research network across the country with consideration of different ecosystems to promote regional and global risk assessments. Future research should highlight the combined multiple factors with N deposition and conduct direct and in-depth mechanism studies.

Aims Soil microbial community composition and structure were regulated by temperature and plant species. Picea asperata and Abies faxoniana were planted in the monoculture and mixture plantations of the subalpine region in southwestern China. However, the effects of these two species and their interactions on soil microbial community under future climate warming remain unclear.
Methods An experiment was conducted to examine the effects of warming and plant species on soil microbial community composition with two levels of temperature (unwarming and warming with infrared heater) and four planting patterns (single A. faxoniana, single P. asperata, mixture of A. faxoniana and P. asperata, and unplanted bare land). Root zone soil of different planting treatments were sampled to estimating the microbial biomass and microbial community composition by the phospholipid fatty acids (PLFAs) content analysis.
Important findings The results indicated that: (1) Both P. asperata and A. faxoniana mono-planting significantly increased the biomass (PLFAs content) of main soil microbial groups and the whole community, regardless of warming, but the PLFAs content was only increased by mixed planting in unwarming plots. On the other hand, warming enhanced fungi (F) in unplanted plots and gram-negative bacteria (GN) in the P. asperata plots, respectively. However, warming significantly decreased soil microbial biomass in A. faxoniana and the mixed planting plots. (2) Principal component analysis (PCA) showed that effects of planting P. asperata and A. faxoniana on soil microbial community composition were greater under unwarming than under warming conditions. All the planting treatments significantly decreased the ratio of gram-positive/gram-negative bacteria (GP/GN) and increased the ratio of fungi/bacteria (F/B) in unwarming plots. However, significant effects on GP/GN and F/B ratios were only observed in A. faxoniana plots under warming condition. (3) PLFAs content was positively correlated with soil organic carbon, and F/B ratio was significantly correlated with soil pH and inorganic N. These results showed that the effects of warming on soil microbial biomass and composition varied among the tree species, and the effects of P. asperata and A. faxoniana were weakened under warming condition than under unwarming condition. Our results provide a vital theoretical basis for further study on the responses of soil microbial communities to vegetation and global climate change in southwestern China.

Aims As a key factor of nutrient cycling in ecosystems, soil enzyme activity is an important indicator of soil quality and ecosystem function. However, there have been very few studies on the differences of soil enzyme activities among different types of alpine grassland ecosystems. Thus, the aims of this study were to compare the differences of soil enzyme activities among five different types of alpine grassland and to reveal their influencing environmental factors on the Qingzang Plateau.
Methods Totally, 21 samples of five alpine grassland types, including alpine meadow, alpine steppe, alpine meadow steppe, alpine desert steppe and alpine desert on northern Qingzang Plateau, were selected for field in-situ investigation and sampling. The activities of 14 enzymes involved in the cycling of carbon (C), nitrogen (N) and phosphorus (P) were determined, and the relationships between enzymatic activities and environmental factors in alpine grassland were established.
Important findings The activities of C-acquisition (invertase, cellulase, β-1,4-glucosidse, polyphenol oxidase and peroxidase), P-acquisition (alkaline phosphatase) enzymes and two N-acquisition (arylamidase and nitrite reductase) were significantly different among different alpine grassland types. Moreover, correlations were found among C-acquisition, N-acquisition and P-acquisition enzymes. A significant positive correlation was found between invertase and alkaline phosphatase, and between cellulase and N-acetyl-α-D-glucosaminidase. A significant negative correlation was found between polyphenol oxidase and nitrite reductase, N-acetyl-β-D- glucosaminidase. Soil organic matter (SOM) content, gram-negative bacteria content, ratio of nitrogen to phosphorus, gram-positive bacteria content, bacteria content, actinomycetes content, total nitrogen content and fungi content were the key factors influencing soil enzyme activity among the 19 environmental indicators, and SOM content had the greatest impact (explained 11.9%). The results demonstrated that the activities of C-acquisition, P-acquisition and two N-acquisition (arylamidase and nitrite reductase) enzymes were significantly different among different types of alpine grassland, and soil enzyme activities were mainly controlled by SOM content, microbes and N elements in alpine grassland ecosystems.

Aims In recent years, under the background of climate change and human activities, the trend of biodiversity loss is increasing. Such accelerated loss in biodiversity could bring serious consequences to ecosystem functions. At present, the research on ecosystem function ignores the important driving role of carbon and nitrogen cycling in soil and microorganism on the above ground ecosystem functions. Any changes of soil carbon, nitrogen and microorganism may affect the ability of belowground community, which can have substantial effects on the aboveground ecosystem functions. Our aim was to explore the driving factors and key mechanism of abovegroud ecosystem functions (AEF) in alpine grassland.
Methods From July to August 2015, we conducted a transect survey in alpine grasslands to measure plant community and soil properties across Qingzang Plateau. There were in total 115 sample sites. The aboveground ecosystem function was calculated based on the aboveground biomass, leaf carbon, leaf nitrogen and leaf phosphorus. The effects of key elements such as soil organic carbon, total nitrogen and biomass on the aboveground ecosystem function were analyzed. Combined with mean annual precipitation and air temperature, we explored important drivers of AEF and related mechanisms.
Important findings Precipitation has a greater impact on aboveground ecosystem functions, while air temperature has a minor impact. Mean annual precipitation, soil microbial nitrogen content and aridity index had relative higher importance to aboveground ecosystem functions. Specificially, mean annual precipitation, soil microbial nitrogen content and aridity index accounted for the variations of 21.1%, 10.9% and 10.1%, respectively. The findings indicated that soil properties might play more important roles than plant community and productivity to aboveground ecosystem functions. Considering the cascading impacts of climate factors on soil nutrients cycling and microorganisms, soil microbial biomass nitrogen content plays an important role in regulating AEF of alpine grassland, Qingzang Plateau.

Aims The aim of the present study was to investigate the responses of understory vegetation to soil nutrients and bacterial communities.
Methods This study investigated the understory vegetation biomasses and species composition as well as soil physical and chemical properties in 17-year-old Chinese fir plantations with three densities (high-density (KH), medium-density (KM), and low-density (KL)) in Kaihua, Zhejiang. The changes of bacterial community structures were analyzed via 16S rDNA high-throughput sequencing techniques.
Important findings The result showed that the total above-ground biomass of the understory vegetation ranged from 0.10 to 2.10 t·hm^-2 and the dominant plant species varied in three Chinese fir plantations. The soil pH and available phosphorus content were significantly different between high-density and low-density forest stands. Correlation analysis showed that soil pH was positively correlated with the biomass of herbs, shrubs and the total of understory vegetation, while the content of soil organic matter was just positively related with the last two factors, and the available potassium content was only affected by the biomass of shrub. Based on the analysis of the soil microbial community, the Acidobacteria, Proteobacteria, Actinobacteria, and Chloroflexi were the dominant phyla in the three Chinese fir plantations. Redundancy analysis showed that soil pH, available nitrogen, available phosphorus and available potassium contents played a crucial role in regulating the soil bacterial community structures. Gp2, Gp1, Gp3 and Gp6 were the dominant subgroups of Acidobacteria, accounting for 51.32%- 57.38% of the Acidobacteria. With the decline of the Chinese fir density, the biomass of understory vegetation and the proportion of Gp1 increased, while the proportion of Gp2 and Gp6 decreased and the relative abundance of Gp6 was negatively correlated with soil pH. Obviously, the moderate reduction in stand density of pure Chinese fir forests was beneficial in the growth of understory vegetation and in maintaining a reasonable bacterial community structure, which helps to maintain the soil fertility of the Chinese fir forests and to achieve sustainable management in the long run.

Aims Degraded peatlands recovery is an important environmental issue of current concern. Exploring the response of Zoigê degraded peatlands prokaryotic microbial community structure to water level recovery could provide foundation for the ecological restoration.
Methods For exploring the response of prokaryotic microbial community structure to water level recovery in the short-term, we selected Zoigê degraded peatland and designed two water level recovery (10 and 30 cm) with a control group (-10 cm) in situ test from year 2014 to 2015. We collected 0-15 cm soil samples and determined soil organic carbon (SOC), total nitrogen (TN), total phosphorus (TP) content and soil pH, we also analyzed microbial community structure by using 16S rRNA high throughput sequencing technique.
Important findings The results showed that water level recovery could improve the content of SOC, TN, TP and its stoichiometric ratio to a certain extent, however, there was no significant difference with the control group. The dominant microorganisms at the phylum level were Acidobacteria, Proteobacteria and Verrucomicrobia. Short-term water level recovery (10 and 30 cm) had no significant effect on the alpha diversity of prokaryotic microbial, but significantly reduced the relative abundance of Verrucomicrobia and Spartobacteria, while having an increase in methanogenic bacteria. Soil pH and water level were negatively correlated with the abundance of Verrucomicrobia and Spartobacteria. Prokaryotic microbial community structure is sensitive to soil C:P, N:P and SOC content. In a word, short-term water recovery hasn’t changed prokaryotic microbial alpha diversity, but increased the methanogenic bacteria, which will probably stimulate methane production pathways. Soil C:P, N:P and SOC content control the structure variation of prokaryotic microbial community in degraded peatlands during short-term water level restoration process. Our findings enrich the understanding of the structure of prokaryotic microbial community in response to short-term water level.

Aims Human disturbance is one of the main obstacles to the forward succession of karst grassland, exploring the response of grassland to disturbance in terms of soil microorganism can provide the basis for the restoration and rational utilization of karst land. Our objective was to study the effects of different human disturbances on soil microorganisms and the underlying mechanisms in a karst grassland ecosystem of northwestern Guangxi, China.
Methods Three patterns of disturbances (burning, mowing, and mowing plus root removal) and one control treatment (enclosure) were conducted at the long-term monitoring plots in the Huanjiang Observation and Research Station for Karst Ecosystems, Chinese Academy of Sciences. We analyzed the changes of soil microbial diversity and community structure by high-throughput sequencing, and determined their relationships with environmental factors (slope position, soil physicochemical properties).
Important findings 1) For α diversity, at both middle and lower slope positions, the burning treatment significantly reduced the fungal Chao1 index, while the mowing treatment significantly reduced the bacterial Shannon index and Pedigree diversity index. However, the mowing plus root removal treatment significantly reduced the fungal Chao1 index and the bacterial Shannon index, respectively, at middle and lower slope positions. 2) For microbial community structure, burning, mowing and mowing plus root removal treatments significantly reduced the relative abundance of Acidobacteria at both middle and lower slope positions, while the fire treatment significantly reduced the relative abundance of Ascomycota from 74.49% to 34.72% at the lower slope position. 3) Redundancy analysis showed that soil microbial biomass carbon explained 29.8% and 26.8% of the changes of bacterial and fungal α diversity, respectively, and 31.7% of the changes of bacterial community structure. Root biomass explained 13.9% and 10.3% of the changes of bacterial α diversity and fungal community structure, respectively. In conclusion, the three studied human disturbances have significantly negative influence on soil microbial α diversity as well as having a significant change in and changed community structure, and the degree of influence varied among the pattern of disturbances and the type of microorganisms. Moreover, the effects were also regulated by slope position. Long-term human disturbances mainly affected the diversity and structure of soil microbial communities by changing soil microbial biomass carbon and root biomass. The decreases of α diversity and Ascomycota will not be conducive to the maintenance of soil ecosystem stability, and the decrease of Acidobacteria will not facilitate to soil organic matter degradation and iron cycling. Therefore, the long-term human disturbances such as burning and mowing will induce the functional degradation of grassland ecosystem.

Aims Soil microorganisms are an important component of terrestrial ecosystems and play a critical role in regulating multiple ecological processes such as nutrient acquisition, carbon cycle, and soil formation, especially in the tropical forests where soils are highly weathered with poor nutrients. The objective of this study was to examine the response of soil microbial community under long-term simulated acid rain (SAR) and investigate the most important factors influencing microbial community structure.
Methods Based on a long-term (10-year) field SAR experiment, we investigate the response of soil microbial community structure to soil acidification in the south subtropical monsoon evergreen broad-leaved forest of Dinghushan National Nature Reserve. Four levels of SAR treatments were set by adding the following amount of H⁺: 0 (CK), 9.6, 32 and 96 mol·hm^-2·a^-1.
Important findings 1) The SAR treatment significantly reduced the pH value of soil (i.e., increased soil acidification). 2) Soil acidification did not significantly influence microbial carbon (C) content, but changed microbial nitrogen (N) and phosphorus (P) contents, leading to significant increases in microbial C:P and N:P in topsoil (0-10 cm). This result indicated that soil acidification might aggravate microbial P limitation. 3) Soil acidification also altered the microbial community structure and significantly increased the fungal/bacterial ratio in the subsoil (10-20 cm). Further analysis showed that soil pH and available P content were the most important factors affecting the soil microbial communities under the SAR treatment.

Aims How soil microbial diversity assembly, maintain and change is a key topic of ecology. A large number of studies show that soil microbial biodiversity is controlled not only by soil environment but also by plant species. However, due to strong covariation between the two factors in the field, it remains a challenge to isolate and clarify the role of plant diversity in regulating soil microbial biodiversity. Hence, here, we aim to clarify how plant diversity affects soil microbial diversity in environment-consistent artificial communities.
Methods In this study, we examined differences in species diversity of soil bacteria and fungi among plots subjected single- and mixed-sowing of three grass species with fertilization treatments after 13 years’ experiment on the eastern Qingzang (Tibetan) Plateau. We also analyzed the relationships between soil microbial diversity and edaphic factors as well as plant community attributes.
Important findings (1) The species richness and diversity of soil bacteria, not including soil fungi, significantly and consistently decreased in mixed-sowing plots relative to single-sowing plots, with higher relative abundances in proteobacteria and actinobacteria but lower in acidobacteria, bacteroidetes and planctomycetes in the mixed- sowing plots. (2) Soil pH and total nitrogen content significantly decreased while soil total phosphorus content increased in mixed-sowing plots relative to single-sowing plots. Fertilization significantly increased soil available phosphorus while decreased soil pH and soil humidity. However, variations in these edaphic factors contributed little in variation of soil microbial diversity. (3) Fertilization significantly increased plant aboveground biomass while decreasing richness of present plant species, which was also negatively associated with soil bacterial diversity. In short, this long-term field experiment clearly showed that mixed-sowing of common grass species did not promote diversity of soil microbes. This study provides new insight into management of grasses mixed-sowing artificial grasslands.

Aims Soil enzymes, which are mainly produced by plant roots and soil microbes, involve in the organic matter degradation and element cycling and other key processes in plant-soil systems. Study on the relationships between soil enzyme activity and plant community composition and microbial activity under changing precipitation pattern and increasing nitrogen (N) deposition can provide a new insight for evaluating the influencing mechanism of global change on the biogeochemical cycling in plant-soil systems.
Methods Based on a field experiment involving five precipitation treatments (50% reduction, 30% reduction, natural precipitation, 30% increase, and 50% increase) and two N addition treatments (0 and 5 g·m^-2·a^-1) conducted in a desert steppe of Ningxia since 2017, the changes of soil enzyme activities (sucrase, urease, and phosphatase) were studied and their relationships with plant community composition and microbial ecological stoichiometry were analyzed in 2018 and 2019.
Important findings Compared with decreasing precipitation, increasing precipitation had greater impacts on the three enzyme activities, but its effects were interacted with N addition and sampling year. Increasing precipitation had no significant impacts on the three enzyme activities in 2018, but enhanced them in 2019. By contrast, N addition had less influences on the three enzyme activities, especially in 2019. The biomass of Astragalus melilotoides was negatively correlated with urease and phosphatase activities, while the biomass of Cleistogenes squarrosa had positive correlation with the three enzyme activities. Except the Patrick richness index, plant community diversity indices were generally negatively correlated with the three enzyme activities. Soil enzyme activities were more greatly affected by soil pH, soil total phosphorus (P), and microbial biomass carbon (C):N:P. Therefore, short-term precipitation change and N addition have little effects on the soil enzymes in the studied desert steppe (especially under reducing precipitation); increasing precipitation and N addition could pose direct influences on soil enzyme activities by increasing plant biomass, changing plant diversity, regulating microbial biomass ecological stoichiometry, and enhancing soil P availability. Given the diversity and functional complexity of soil enzymes, it is necessary to deeply analyze the influencing mechanism of global change on enzyme activities by measuring the long-term responses of various enzyme activities.

Aims Nitrogen (N) availability is an important limiting factor for grassland ecosystem productivity, and soil microorganisms are the main driving factor on soil N transformation. With the increase of atmospheric N deposition, the response of soil microbial characteristics to different nitrogen input levels is still unclear especially in saline-alkaline grassland.

Methods The experiment was conducted in Youyu Loess Plateau Grassland Ecosystem Research Station, Shanxi Province. Eight different nitrogen addition levels were set, which were 0, 1, 2, 4, 8, 16, 24 and 32 g·m^-2·a^-1, respectively. The Ammonia-oxidizing microorganisms (i.e. ammonia-oxidizing bacteria (AOB) and ammonia- oxidizing archaea (AOA)) abundance, soil bacterial and fungal abundance, as well as soil microbial biomass carbon (MBC) and nitrogen (MBN) content were measured in the growing season (May to September) in 2020 to explore the effects of different levels of N addition on soil microbial characteristics.

Important findings Our results showed that: (1) Sampling month had a significant effect on soil AOB, bacteria, fungal abundance and MBC, MBN content due to the variation in soil temperature and soil water content in the growing season. (2) N addition had a significant effect on soil AOB abundance, while had no effects on soil MBC, MBN content, and bacterial and fungal composition. (3) Higher N addition (24 and 32 g·m^-2·a^-1) significantly increased the abundance of ammonia-oxidizing bacteria (AOB) on the early growth stage (May to August), while having no effect on late growth period (September). (4) Soil microorganisms were mainly regulated by soil cations concentrations and soil pH values, which explained the variation of soil microorganisms by 21.8% and 17.2%, respectively. We found that soil microorganisms were not sensitive to N addition in saline-alkaline grassland, while AOB showed a significant increase under higher N addition, indicating that higher N addition might promote soil N transformation.

Aims Variations in temperature and snow accumulations in winter will change the structure and function of the soil-microbial system. As a key biological factor in the terrestrial ecosystem, microorganisms play an important role in regulating soil nutrient cycles. However, they are very sensitive to environmental disturbances, especially to winter climate changes. It is in great need to study the response of soil nutrients and microbial properties of typical semi-arid grasslands to climate change in winter, in order to predict the ecological process and functional changes of grassland ecosystem in the long term.
Methods In the present study, the semi-arid grassland in the Yunwushan National Nature Reserve in Ningxia Province was taken as the research object. The four treatments including warming (W), snow reduction (S), interaction of warming and snow reduction (WS), and control (CK) were set to explore the responses of soil nutrients, enzyme activities and soil bacterial communities in the 0-5 cm soil layer of the typical grassland of the Loess Plateau to variations in winter temperature and snow cover.
Important findings Our results indicated that: (1) Warming, snow reduction and their interaction in winter increased the 0-5 cm soil temperature, lowered the relative humidity of the soil, but significantly increased the number of soil freeze-thaw cycles. (2) Compared with the control, other different treatments generally reduced the microbial biomass and bacterial diversity, which led to reduced activity of soil β-1,4-glucosidase (BG), β-1,4-N-acetylglucosaminidase (NAG) and alkaline phosphatase (AKP). The content of soil organic carbon, total nitrogen, available phosphorus, and nitrate nitrogen in the soil increased, while the content of nitrate nitrogen decreased. (3) The soil bacterial species in the study area were mainly Acidobacteria, Proteobacteria, Actinobacteria and Gemmatimonadetes. The dominant bacteria at the class level included Acidobacteria, γ-Proteobacteria, Thermophiles and σ-Proteobacteria. Redundancy analysis (RDA) results showed that available phosphorus (AP) content had the most significant impact on the bacterial community composition, with an explanation rate of 21.3% for the community variation. In conclusion, winter climate change can significantly affect soil temperature and humidity, especially the freezing and thawing cycles, which might further influence soil nutrients cycles, enzyme activities, and soil bacterial diversity. These results are of great significance for enriching and expanding the understanding of the process and mechanism of climate change on grassland ecosystem, as well as predicting the mid and long-term dynamic changes of typical grassland ecosystems.

Aims Microbial biomass and their stoichiometric characteristics not only are important parameters of soil nutrient cycling, but also can contribute to prediction of climate changes, improvement of model accuracy, and understanding of terrestrial nutrient cycling. Our objective was to investigate microbial biomass carbon (MBC), microbial biomass nitrogen (MBN), and microbial biomass phosphorus (MBP) concentrations and their stoichiometric characteristics in alpine wetlands in the Three Rivers Sources Region.

Methods Using data from 50 sites, we explored MBC, MBN, MBP, their stoichiometry and their relationships with the controlling factors of alpine wetlands in the Three Rivers Source Region.

Important findings Our results showed that 1) MBC, MBN, MBP concentrations were 105.11, 3.79, 0.78 mmol·kg^-1, respectively, and MBC:MBN, MBC:MBP, MBN:MBP, MBC:MBN:MBP were 50.56, 184.89, 5.42, 275:5:1, respectively. 2) Soil physical and chemical properties could significantly affect MBC, MBN and MBP concentration. Soil moisture had significantly negative effects on both MBC:MBN and MBC:MBP, while soil density had positive effects on both MBC:MBN and MBC:MBP. Soil total nitrogen content had negative relationship with MBC:MBP, while having weak effects on MBC:MBN. Soil physical and chemical properties also had weak effects on MBN:MBP. 3) Generally, soil microbial community composition had significant effects on MBC, MBN and MBP concentration. Soil microbial community composition had similar effects on MBC:MBN and MBC:MBP. Total phospholipid fatty acid (PLFA) content, gram-positive bacteria, gram-negative bacteria, bacteria, actinomycete, arbuscular mycorrhizal fungi concentration, and other PLFA content had negative effects on MBC:MBN and MBC:MBP, while fungi:bacteria had positive effects on both MBC:MBN and MBC:MBP, but fungi had weak relationships with both MBC:MBN and MBC:MBP. Except for arbuscular mycorrhizal fungi, MBN:MBP had weak relationships with soil microbial community composition. Soil physical and chemical properties, and soil microbial community composition had significant effects on soil microbial biomass and their stoichiometric characteristics in Three Rivers Sources Regions in the alpine wetlands, which are greatly helpful for deeply understanding of terrestrial high altitude nutrient cycling.

Interactions between plants and coexisting microorganisms have significant impacts on plant growth, development, and health. Human domestication has resulted in significant differences between modern crops and their wild ancestors in physiological and genetic characteristics and growth environment, which will inevitably affect the interaction between crops and their microbiomes. Understanding the impact of domestication on the diversity and community structure of microbiome and the mechanisms involved is an important theoretical basis for application of microbiome during crop improvement and breeding. In this review, we summarize the research progress of the effects of domestication on the community composition and diversity of root and shoot microbiome (bacteria and fungi) in crops. We also analyze the involved action pathways in shaping crop microbiomes by domestication, considering the domestication effect on crop morphology, root configuration, exudates and other physiological characteristics, and the change in growth environment. The research directions that need to be focused on in this field were proposed.

Aims The formation of the geographical range boundary of species has always been an important topic in evolutionary biology. Although plant-microbe interactions have been extensively studied, we have a poor understanding of how plant's geographic range limits affect soil microorganisms. Cephalostachyum pingbianense is a rare bamboo species documented that produces bamboo shoots all year round in the wild, and is endemic to southeast Yunnan Province, China. The species is of great significance to study narrow endemic species in Bambusoideae. Here, we aim to reveal the relationship between the range limits of C. pingbianenseand soil fungal community.

Methods We assayed soil physical and chemical properties at the center, edge and beyond the range of C. pingbianense, and changes of fungal community were analyzed by means of Internal Transcribed Spacer (ITS) sequence based Illumina MiSeq high-throughput sequencing techniques.

Important findings (1) Soil pH and available phosphorus content at the range edges was significantly lower than other sites. (2) At the range center, species diversity of soil fungi was the highest, and relative abundance of Mortierella was significantly higher than other sites. At the range edges, species diversity of soil fungi was the lowest, and relative abundance of Basidiomycota was greater than 65.0%. (3) Soil pH played a crucial role in driving the variation of fungal community, which was negatively correlated with the relative abundance of ectomycorrhizal fungi, and positively correlated with the relative abundance of saprophytic fungi. Soil acidification and phosphorus deficiency may be important soil properties controlling the distribution range of C. pingbianense. Mortierella may be important mutualists of C. pingbianense, which can desorb phosphorus from soil minerals and reduce acidification of soil.

Aims The aim of this study was to explore the effects of native tree species on soil microbial biomass carbon (MBC) and nitrogen (MBN) content in subtropical Sichuan.

Methods In the present study, Cinnamomum japonicum, C. longepaniculatum, C. austrosiense, Alnus cremastogyne, C. camphora, Toona ciliata and T. sinensis in a common garden were selected as the research objects; whereas the abandoned land as the control. The effects of tree species on soil MBC content and MBN at different depths (0-10, 10-20, and 20-30 cm) were analyzed using the method of common garden.

Important findings (1) Tree species significantly affected the content of soil MBC and MBN, as well as their ratio. Compared with the abandoned land, tree species exhibited positive or neutral effects and the effects of tree species were particularly obvious in C. japonicum.For example, the contents of MBC and MBN in 0-10 cm soil layer were 108.2% and 139.6% higher than those in the abandoned land, respectively. (2) The content of soil MBC and MBN in the both tree and abandoned land generally decreased with an increase with soil depth; however, the characteristics of MBC:MBN varied with tree species. (3) The content of soil MBC and MBN varied with tree species and soil layer. The variations caused by tree species were stronger than that caused by soil layer. Compared with other species, C. japonicum was more conducive to the growth and reproduction of soil microorganisms.

Aims Phosphorus is one of the major limiting nutrients for plant growth in subtropical areas, whereas increasing nitrogen deposition may be a limiting factor in determining the availability of soil phosphorus. Here, focusing on soil microorganisms and plant fine roots, we explored the transformation of soil phosphorus to unravel the maintenance of soil phosphorus supply and plant productivity with low availability under nitrogen deposition.

Methods At the Fuzhou Changʼan Mountain in Fujian Province, China, control (0 kg·hm^-2·a^-1), low nitrogen (40 kg·hm^-2·a^-1), and high nitrogen (80 kg·hm^-2·a^-1) treatments were set up to simulate nitrogen addition. Soil and root samples of Cunninghamia lanceolata seedlings were then collected to comprehensively analyze soil phosphorus and nutrient contents as well as microbiological-plant root characteristics.

Important findings The results showed that the contents of soil labile organic phosphorus, moderately labile inorganic phosphorus and occluded phosphorus were significantly increased, whereas those of primary mineral phosphorus and moderately labile organic phosphorus decreased under the low nitrogen treatment as compared to the control treatment. However, there were no significant changes under the high nitrogen treatment. Redundancy analysis indicated that soil acid phosphatase activity, relative abundance of mycorrhizal fungi, soil microbial biomass phosphorus content, and root biomass were important soil microbiological-plant root characteristics factors that could explain the changes in soil phosphorus components. Variance partitioning analysis revealed that the soil microbiological-plant root characteristics synergy explained 57% of the alternations in soil phosphorus components, whereas correlation analysis showed a significant positive correlation between the relative abundance of mycorrhizal fungi and root biomass. Overall, these results suggest that mycorrhizal colonization is promoted under a low level of nitrogen input and the synergistic action of mycorrhizal fungi and C. lanceolata fine roots promotes the conversion of moderately labile organic and primary mineral phosphorus to labile phosphorus, thus maintaining the growth of C. lanceolata seedlings.