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 Understanding the mode of nutrient limitation on ecosystem net primary production is an important issue of modern ecology. Nutrient availability is a key determinant of ecosystem dynamics, but the relationship between soil resource availability and ecosystem nutrient limitation is still unclear.
Methods A series of nitrogen and phosphorus nutrient addition experiments were set up in four types of alpine grasslands (alpine meadow, alpine meadow-steppe, alpine steppe and alpine desert-steppe) along the precipitation gradient on the Northern Xizang, to systematically study the effects of nitrogen and phosphorus addition on different types of alpine grasslands, and to explore the nitrogen and phosphorus limitation models of different alpine grasslands.
Important findings The results showed that: (1) The effects of nitrogen and phosphorus addition on different alpine grasslands varied. Nitrogen addition significantly increased the aboveground biomass of alpine meadows and alpine meadow grasslands, but had no effect on alpine meadows and alpine desert grasslands. The addition of phosphorus alone had no significant effect on the four alpine grasslands, while the addition of nitrogen and phosphorus had a promoting effect on the aboveground biomass of the four alpine grasslands. (2) With the decrease of precipitation, the nitrogen limitation index of the alpine grasslands gradually decreased from 1.18 to 0.52-0.64, and the nutrient limitation mode transitioned from nitrogen limitation to co-limitation by nitrogen and phosphorus; the phosphorus limitation index was negative in the alpine meadow-steppe and alpine steppe, indicating that phosphorus addition alone has side effects on these two grassland types. These results suggest that alpine meadow is mainly limited by nitrogen availability, and phosphorus addition alone has side effects; the alpine meadow-steppe is between the nitrogen limit and the joint nitrogen and phosphorus limitation, and phosphorus addition alone also has side effects; the alpine steppe is limited by both nitrogen and phosphorus availability, and the addition of phosphorus has side effects; the alpine desert-steppe is jointly limited by nitrogen and phosphorus availability. These results show that nutrient limitation mode transits from nitrogen limitation to nitrogen and phosphorus co-limitation with the decrease of precipitation. This study implies that the impacts of increasing nitrogen deposition under future climate change on different types of alpine grasslands may be different. Additionally, the differences in nitrogen and phosphorus limitation mode should also be taken into consideration when nutrient addition is used to restore different types of degraded alpine grasslands.

Aims Altitude has prominent effects on many environmental factors, such as atmospheric pressure, temperature, precipitation, soil moisture and wind velocity. The relationship between plant functional traits and altitude are critical for predicting the effects of climate change on montane plants. Our objective is to examine the effect of altitude on community-level plant functional traits in the Qinghai Lake Basin, China.
Methods Five sites were selected with 200 m increase in altitude (3 400-4 200 m) in the Qinghai Lake Basin, China. Community structure, plant functional traits, soil property and atmospheric factors were surveyed and analyzed in this study. Community-weighted mean functional traits (CWM) was calculated according to the relative abundance of species.
Important findings The results showed that: (1) Community-weighted mean plant height (H), leaf dry matter content (LDMC), leaf C:N ratio (C:N) and leaf N:P ratio (N:P) decreased significantly along altitude, while specific root surface area (SRA) fluctuated with altitude. Specific leaf area (SLA), leaf nitrogen content (LNC) and leaf phosphorus content (LPC) increased significantly along altitude, while altitude had no significant effect on leaf carbon content (LCC), root tissue density (RTD) and specific root length (SRL). (2) The variation in CWM along altitude could be explained by species turnover more rather than intraspecific variability. N:P and LPC had a positive covariation, other CWM had a negative covariation. (3) Precipitation and 0-10 cm depth soil nutrients content explained the largest proportion change of SLA. Temperature and 10-20 cm depth soil nutrients content explained the largest proportion change of other CWM along altitude. Overall, these findings suggested that the plant communities in our study adapted to altitude through species turnover, and the non-dominant species tended to occupy opposite trait spaces to the dominant species in the Qinghai Lake Basin, China. Temperature and deeper soil nutrients content had significant effects on CWM along altitude.

Aims The alpine wetland is one of the most important sites for ecological and water conservation in Qingzang Plateau, and also an effective regulator of the local climate. Research is needed to understand the dynamics and drivers of changes in this alpine wetland landscape.
Methods This study was conducted with combination of methods in remote sensing image analysis, GIS spatial analysis and landscape attributes analysis. Changes in the alpine wetland patterns in Maqu County, which is located in the first meander of the Yellow River, was determined for six periodic samplings from 1995 to 2018.
Important findings The alpine wetland area in Maqu County continuously degraded from 1995 to 2010, and decreased by 18 680.31 hm² over the period. From 2010 to 2018, the wetland area increased. Compared with the level in 1990s, the wetland area has generally declined since the beginning of the 21st century. From 1995 to 2010, the patch number and density of the wetland increased continuously, but the average patch size decreased, with increased degree of landscape fragmentation. In contrast, from 2010 to 2015, the patch number and density of wetland decreased. From 2015 to 2018, the patch number and density of wetland increased, and the average patch size first increased and then decreased, with the landscape fragmentation first decreased and then increased. Both the Shannon diversity index and evenness index showed a downward trend from 1995 to 2010; the landscape structure tended to be simpler and the distribution of landscape types became more clustered. From 2010 to 2018, the Shannon diversity and evenness indices showed an upward trend; the landscape structure tended to be more complex, and the landscape types became more diverse and dispersed. Further analyses revealed that the main factors driving the changes in the alpine wetland landscape patterns in the first meander of the Yellow River are evaporation and precipitation, followed by human activities such as the population and the quantity of large livestock. Climate is the main factor driving the changes in the alpine wetland area in the first meander of the Yellow River. Intensive human economic activities have aggravated the wetland changes to some extent.

Aims β diversity reflects species turnover rate across environmental gradients, and this study attempts to use β diversity to reveal relevant ecological processes underlying the changes in plant community composition along a disturbance gradient induced by small burrowing herbivores.
Methods This study conducted a field survey at Gangcha County in the Qingzang Plateau to determine the effect of disturbance intensities of plateau pika (Ochotona curzoniae) on the β diversity of an alpine meadow measured by Whittaker’s index. Then a variance decomposition was used to measure the contribution of individual species to overall β diversity (SCBD) and single interference sites to overall β diversity (LCBD) according presence- absence community matrix.
Important findings The turnover rate of species in the plant community first increased and then decreased with the increase of the disturbance intensities induced by plateau pika. Species with intermediate site occupancy had a greater contribution to β diversity, in which Agropyron cristatum, Artemisia hedinii and Anemone rivular var. flore-minore were the single-species plants that contributed the most to the β diversity of the study regions. The disturbance plot T₀ with the absence of plateau pika had the greatest contribution to the β diversity of whole study region. LCBD of individual site was negetively related to species richness of that individual site, and had no significant correlation with the disturbed intensity of plateau pika. These results indicate that alpine meadows distributed in high LCBD and Agropyron cristatum, Artemisia hedinii and Anemone rivularis var. flore-minore with high SCBD should be protected to conserve plant diversity when the plateau pikas are present.

Aims Accurate assessment of plant aboveground biomass is important for optimizing grassland resource management and for understanding the balance of carbon, water and energy fluxes in grassland ecosystems. This study constructed the optimal empirical models by near-surface remote sensing normalized difference vegetation index (NDVI) data, and then estimated plant aboveground biomass in an alpine grassland on the Qingzang Plateau.
Methods Using the dataset of both the field-measured aboveground biomass and the NDVI_RS observed by plant canopy spectrometer (RapidSCAN), we constructed the empirical models for estimating aboveground biomass in different phases of the growing season across 2018 and 2019. Using the NDVI_Cam time series observed by phenology camera and the estimated models, we simulated seasonal dynamics of aboveground biomass in 2018.
Important findings (1) The seasonal dynamics of NDVI_Cam, NDVI_RS and aboveground biomass exhibited a similar unimodal pattern; however, the timing of peak NDVI (August) preceded that of peak aboveground biomass (July). (2) The best model for estimating aboveground biomass is the power function in May, July and September, and the quadratic equation in June and August. The estimation accuracy ranged from 0.29 to 0.77. (3) The estimation of aboveground biomass based on the models in different phases of growing season (R² = 0.91) showed a higher accuracy compared to that based on the model at a single time (September)(R² = 0.49). Our results suggest that the near-surface remote sensing is an effective approach for estimating alpine grassland aboveground biomass, and further investigation on the seasonal growth of plants will help accurately evaluate grassland resources.

Aims As one of the major terrestrial ecosystems of the world, a small fluctuation of grassland soil carbon (C) would affect the carbon cycle of the terrestrial ecosystem and ecosystem multifunctionlity (EMF). The carbon accumulation rate (CAR) of aboveground community well reflects the capacity and efficiency of carbon sequestration in a field from the start to the peak of a growing season. The changes in plant CAR could influence the ability of above- and below-ground community. Currently, the majority of studies have primarily focused on the relationship between community diversity and EMF, while the linkages of CAR with EMF were understudied. We aimed to explore the process and underlying mechanism of how CAR affecting EMF in alpine grassland community. Our results would improve the understanding of EMF maintenance mechanism and provide theoretical support for alpine ecosystem management.
Methods We conducted a field transect survey which consists of a total of 115 sample sites of alpine grasslands on the Qingzang Plateau from July to August 2015. The ecosystem multifunctionality index (M) was calculated from 13 key ecosystem parameters including soil organic carbon content, total nitrogen content, total phosphorus content above- and belowground biomass etc. The normalized difference vegetation index (NDVI, 1982-2013) was adopted to obtain the phenology in 2015. We calculated the CAR value. To explore the underlying mechanism of how CAR affecting EMF, the annual total precipitation and temperature were extracted by the method of thin disk smooth spline interpolation based on observations of meteorological stations from 2011-2015.
Important findings Belowground biomass, soil organic carbon content, total phosphorus content and microbial biomass carbon content had high weighting for CAR (0.58, 0.80, 0.83 and 0.79) and M (1.05, 0.98, 1.02 and 0.97). There was a significantly positive correlation between CAR and M (R² = 0.45, p < 0.01). Our findings suggested that the synergism of plant community and soil elements affected CAR and further regulated EMF under the influences of precipitation and temperature.

Aims The balance between soil organic carbon (SOC) input and output processes determines SOC content. However, it is not clear which of the two processes dominantly affect SOC content during the degradation of alpine meadows in Zoigê Wetland. In this study, the changes in SOC contents of alpine meadows and their causes at different degradation stages (alpine meadow (AM), slightly degraded alpine meadow (SD), and heavily degraded alpine meadow (HD)) in the Zoigê Wetland were investigated using the method of spatial sequence instead of temporal successional sequence.
Methods First, the changes in C input to soil and their causes along the degradation gradient were analyzed by investigating main soil physicochemical properties, microbial biomass, plant biomass and community composition of plant functional groups at different degradation stages. Secondly, the changes in the C output from soil were estimated based on lab incubation experiments of soil C mineralization and the temperature sensitivity of soil respiration (Q₁₀) and monthly average air temperature of the Zoigê Wetland. Finally, the main causes and processes leading to changes in SOC content along the degradation gradient were analyzed.
Important findings The results showed that soil water content (SWC), SOC content, total nitrogen (TN) content, microbial biomass C and N content decreased with the increase of degradation. Plant community composition gradually changed from sedges and grasses dominated community to forbs dominated community. Plant biomass and SOC mineralization rate decreased during the degradation of alpine meadows. The potential accumulation of organic C reduced during the degradation (compared with AM, the potential input, output and accumulation of organic C in SD and HD decreased by 16%, 18%, 15% and 59%, 63%, 41%, respectively). The decrease in SWC changed soil physical and chemical properties, including bulk density, SOC content, TN content, total phosphorus content, and C:N, which led to the shifts in the distribution pattern of plant functional groups and in soil microorganisms, consequently reducing the inputs and outputs of SOC. The decrease in potential plant-derived C input to soil caused by decreased SWC was the main reason for the decline in SOC content along the degradation gradient of alpine meadows in Zoigê Wetland.

Aims Soil enzymes play an important role in the process of soil nutrient transformation. The main purpose of this study is to explore the chemical composition of soil organic matter and its effect on soil protease and urease activity in alpine grasslands in Northern Xizang, China.
Methods The pyrolysis Gas Chromatograph/Mass Spectrometer (Py-GC/MS) was used to obtain the chemical compositions of soil organic matter, and to analyze the relationships between soil chemical compositions and soil enzyme activity in five alpine grasslands, including alpine meadow, alpine steppe, alpine meadow steppe, alpine desert steppe and alpine desert ecosystems.
Important findings The results showed that the enzyme activities among five alpine grassland soils (0-15 cm) were different. Soil urease activity was significantly higher than soil protease activity in the alpine desert steppe, while the difference between the urease and protease activities was not significant in other types of alpine grasslands. Soil protease activity was significantly different among five alpine grassland types, but soil urease activity was not. The correlation analysis showed that soil protease activity was closely related to the relative abundance of alkanes, alkenes and aromatics in soil organic matter and the ratio of furfural to pyrrole. However, the correlation relationships between urease activity and soil organic matter chemical compositions were not significant. The results indicated that alpine grassland type and soil organic matter chemistry were the key factors affecting soil protease activity, but their effects on soil urease activity was non-significant, which calls for further study on the influencing factors on soil urease activity.

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 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 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 Nitrogen is the most limiting factor to artificial pastures. It is distributed unevenly in time and space, and has different forms, which are correlated with cultivation approaches and above-ground net primary productivity (ANPP). This study investigated the dynamics of soil nitrogen and productivity in artificial pastures of Bromus inermis, Elymus sibiricus, E. nutans, Festuca ryloviana, F. sinensis, Poa pratensis var. anceps ‘Qinghai’, P. crymophila and Puccinellia tenuiflora in pure species cultivations in the Tongde farm of Qinghai Province. The dynamics of soil soluble nitrogen pools in each artificial pasture type and their relationships with ANPP were examined.
Methods The pastures were planted in 2013 without fertilizer application, and mowed to the level with 5 cm stubble in mid-September every year. The soil ammonium nitrogen (NH₄⁺-N), nitrate nitrogen (NO₃^--N), soluble organic nitrogen (SON) and soluble total nitrogen (STN) content were measured during growing seasons. ANPP was determined in September each year.
Important findings (1) The average ANPP across the eight pasture types ranged between 329.67-794.67 g·m ^-2, with the ANPP of 794.67 g·m ^-2 for the E. nutans significantly higher than other pasture types. (2) From the second to fourth year following planting, the content of soil NO₃ ^--N, SON and STN significantly decreased, but that of the NH₄⁺-N significantly increased. (3) SON accounted for the highest proportion of STN, varying between 45.11%-88.76% in the 0-10 cm soil layer and 47.75%-88.18% in the 10-20 cm soil layer, followed by NO₃^--N in ranges of 5.81%-34.85% (0-10 cm) and 6.08%-40.42% (10-20 cm), respectively; NH₄⁺-N had the least proportion at 3.41%-22.18% (0-10 cm) and 3.09%-19.56% (10-20 cm), respectively. (4) The non-metric multidimensional scale analysis (NMDS) shows that the temporal effect on soil soluble nitrogen content by different pasture types diverged for the 0-10 cm soil layer, but converged for the 10-20 cm soil layer, and that the effect of pasture types on soil soluble nitrogen content was related to soil depth. (5) Soil SON and STN contents were positively correlated with ANPP, and negatively with inorganic nitrogen (IN) content. In summary, nitrogen fertilizer application is one of the key factors for maintaining the productivity of artificial pasture from three to four years. The above results provide a scientific basis for a more in-depth understanding of the dynamics of soil soluble nitrogen and the maintenance of productivity and stability of artificial pastures on the Qingzang Plateau.