Alpine Meadow Communities Research Articles

Transcriptional Changes Underlying the Degradation of Plant Community in Alpine Meadow Under Seasonal Warming Impact.

Global warming is exhibiting a seasonal trend, while different seasons have different warming variations. However, the impact of seasonal warming on plants remains unclear. This study employed Open Top Chambers (OTCs) to simulate future seasonal warming scenarios in alpine meadow. The study examined plant community dynamics following long-term seasonal warming. The transcriptional and physiological responses of two dominant species (Kobresia pygmaea and Stipa purpurea) were examined. Results suggest that seasonal warming effects are correlated with both the duration of warming and the season which warming occurs. A long annual warming duration, especially growing season warming, made plants confront various stresses. K. pygmaea adopted a stress-avoidance strategy, showing a negative response, and leading to population decline or disappearance. This kind of dieback had also been observed in other Cyperaceae species. Meanwhile, due to positive responses, S. purpurea adopted a stress-tolerance strategy and overcame the impact of warming, partially gained the dominance over Cyperaceae species. Overall vegetation coverage and plant community diversity decreased over the years. These results reveal the impact of seasonal warming to plants, explaining the reasons for changes in plant communities under seasonal warming and providing new insights for future plant conservation under seasonal warming.

Livestock grazing modes induced the rapid differentiation of community recruitment in alpine meadow

Herbivores moderate grazing is a fundamental driver of plant diversity maintenance in grassland ecosystems. However, the effects of grazing with different herbivores on plant community composition and recruitment are still little known. Here, we conducted a field moderate grazing experiment to examine the effects of different grazing modes under moderate intensity in the cold season, including sheep grazing (SG), yak grazing (YG), and mixed grazing by sheep and yak (MG), on plant community composition and recruitment. Results showed that all grazing modes significantly decreased plant cover and average height of standing plant litter. Additionally, herbivores grazing significantly increased species richness but decreased community evenness (P < 0.05), with highest richness and evenness found in YG and SG plots, respectively. The trends of increasing aboveground biomass of common and rare species groups were most pronounced in the SG plots relative to the YG and MG plots. MG promoted the increasing of the common species group. From community recruitment, moderate grazing increased the sexual recruitment and decreased the asexual recruitment, and MG significantly inhibited the recruitment of asexual seedlings. Meanwhile, all grazing modes increased the species of poor palatability. These findings imply that the cold-season grazing with moderate intensity facilitated a rapid divergence succession of alpine meadow community by regulating the relative abundance of common and rare species, as well as the asexual seedlings recruitment induced by the removal of standing plant litter. Consequently, the cold-season grazing with different herbivores under moderate intensity can be used as a management tool to modulate grassland community structure and maintain species diversity in alpine grassland ecosystem.

Grazing and selenium influence community stability by increasing asynchrony and sedge, forbs stability in alpine meadow of Qinghai-Tibet Plateau

Grazing is a major driving force of biodiversity, functions and stability of alpine meadows. In selenium-deficient alpine meadows, moderate selenium supplementation can promote plant growth and increase selenium content within the food web. However, the combined effect of grazing and selenium (Se) addition on the stability of alpine meadow communities within selenium-deficient soil is still unclear. Therefore, we conducted a three-year experiment in an alpine meadow of Qinghai-Tibetan Plateau (QTP), with two stocking rates (0 and 6 sheep months ha−1) and six levels of Se addition (0, 5, 10, 20, 40 and 80 g ha−1) to explore how grazing and Se addition affect community stability and its relationship with species richness, species asynchrony and functional group stability. Results showed that the community stability, species richness and biomass response ratio of the community increased gradually with the increase in the selenium application under grazing and enclosure treatments, reaching the maximum values at 20 g ha−1. However, when the selenium addition exceeded 20 g ha−1, the above mentioned indexes were decreased gradually, especially under grazing. Structural equation model showed that grazing and selenium addition indirectly affected the temporal stability of sedges and forbs, thus influencing the temporal stability of the community. Results of this study indicated that the alpine meadow can maintain high species diversity and community temporal stability under moderate grazing combined with selenium addition, providing a scientific basis for selenium-enriched grazing management in alpine meadows.

Grazing affects ecosystem traits by regulating plateau pika activities at the landscape scale

The mechanism underlying the effects of livestock grazing on grassland ecosystem traits has been greatly discussed. However, as a common small burrowing mammal on the Tibetan Plateau grasslands, the plateau pika's (Ochotona curzoniae) influence on alpine grassland ecosystem traits has rarely been investigated, especially beyond the plot scale. In this study, we flew an unmanned aerial vehicle (UAV) over a grassland landscape under grazing and nongrazing treatments. Mounted visible spectral remote sensing, in combination with field surveys, was utilized to explore how livestock and pika grazing modify grassland ecosystem traits at the landscape scale on the Tibetan Plateau (TP). Using object-oriented classification and partial least squares regression, we retrieved the pika burrow distribution and grassland ecosystem traits. Then, the relationships among livestock grazing, pika burrowing and ecosystem traits were evaluated. The results indicated that livestock grazing reduces the alpine meadow community height by 0.13 cm and the species number by 0.25 while increasing the vegetation coverage by 9.69 % and the aboveground biomass (AGB) by 10.07 g/m2. A lower statue grassland community with greater coverage caused by livestock grazing promotes pika burrowing. Pika burrow density increases 100/ha per 1.70 % increase in vegetation coverage, a 1.87 g/m2 increase in AGB or a 0.08 m decrease in community height. Under livestock grazing, both community structure and nutrients are more strongly associated with pika burrow density. The structural equation model demonstrated that livestock grazing regulates pika burrow density by moderating structural value and subsequently affecting nutritional value. Pika burrowing activity explains 40 % of the total variation in nutritional value. Our findings revealed an intrinsic linkage between mammal activities and alpine grassland ecosystems, which can provide guidelines for grassland management through pika population control by adjusting grazing intensity on the TP.

Unraveling fertilization effects on the dynamics of arbuscular mycorrhizal fungal community in the Qinghai-Tibet Alpine Meadow

Unraveling fertilization effects on the dynamics of arbuscular mycorrhizal fungal community in the Qinghai-Tibet Alpine Meadow

Plant diversity increases spatial stability of aboveground productivity in alpine grasslands.

Plant diversity can significantly affect the grassland productivity and its stability. However, it remains unclear how plant diversity affects the spatial stability of natural grassland productivity, especially in alpine regions that are sensitive to climate change. We analyzed the interaction between plant (species richness and productivity, etc.) and climatic factors (precipitation, temperature, and moisture index, etc.) of alpine natural grassland on the Qinghai-Tibetan Plateau. In addition,we tested the relationship between plant diversity and spatial stability of grassland productivity. Results showed thatan increase in plant diversity significantly enhanced community productivity and its standard deviation, while reducing the coefficient of variation in productivity. The influence of plant diversity on productivity and the reciprocal of productivity variability coefficient was not affected by vegetation types. The absolute values of the regression slopes between climate factors and productivity in alpine meadow communities with higher plant diversity were smaller than those in alpine meadow communities with lower plant diversity. In other words, alpine meadow communities with higher plant diversity exhibited a weaker response to climatic factorsin terms of productivity, whereas those with lower plant diversity showed a stronger response. Our results indicate that high plant diversity buffers the impact of ambient pressure (e.g., precipitation, temperature) on alpine meadow productivity, andsignificantly enhanced the spatial stability of grassland productivity. This finding provides a theoretical basis for maintaining the stability of grassland ecosystems and scientifically managing alpine grasslands under the continuous climate change.

Rare and common species contribute disproportionately to alpine meadow community construction and functional variation.

It is widely accepted that rare species are the first species to become extinct after human-induced disturbances. However, the functional importance of rare species still needs to be better understood, especially in alpine meadow communities with harsher habitats, where the extinction rate of rare species may be higher. This study established a 1.85 × 105 m2 permanent research sample plot on the eastern Tibetan Plateau. We investigated data from 162 plots at 6 different sampling scales in alpine meadows to determine the contribution of rare and common species to alpine meadow communities' structural and functional variability. The results showed that (1) Asteraceae (Compositae) was the dominant family in the surveyed localities. The trends of species diversity indices were the same, and all of them increased with the increase of sampling scale, and the plant community showed apparent scale effects. (2) The community construction of rare species at small scales with high occupancy transitioned from neutral processes to ecological niche processes, while the community construction of common species at different sampling scales was all dominated by ecological niche processes. (3) The trait values of rare species at different sampling scales were different from those of common species, and their distribution in FEs (functional entities) was also different, indicating that they contributed differently to the ecological functions of the communities. Rare species with lower abundance in the surveyed communities had a higher proportion of FEs, indicating that rare species had a more significant proportion of contribution to FEs. The functional redundancy (FR) of rare species was lower than that of common species, and the functional vulnerability (FV) was higher than that of common species. Therefore, the loss of rare species is more likely to cause the loss of community ecological functions, affecting the function and resilience of alpine meadow ecosystems.

Effects of short- and long-term plant functional group loss on alpine meadow community structure and soil nutrients.

The rapid loss of global biodiversity can greatly affect the normal functioning of ecosystems. However, how biodiversity losses affect plant community structure and soil nutrients is unclear. We conducted a field experiment to examine the short- and long-term effects of removing plant functional groups (Gramineae, Cyperaceae, legumes, and forbs) on the interrelationships among the species diversity, productivity, community structure, and soil nutrients in an alpine meadow ecosystem at Menyuan County, Qinghai Province. The variations in the species richness, above- and belowground biomass of the community gradually decreased over time. Species richness and productivity were positively correlated, and this correlation tended to be increasingly significant over time. Removal of the Cyperaceae, legumes, and other forbs resulted in fewer Gramineae species in the community. Soil total nitrogen, phosphorus, organic matter, and moisture contents increased significantly in the legume removal treatment. The removal of other forbs led to the lowest negative cohesion values, suggesting that this community may have difficulty recovering its previous equilibrium state within a short time. The effects of species removal on the ecosystem were likely influenced by the species structure and composition within the community. Changes in the number of Gramineae species indicated that they were more sensitive and less resistant to plant functional group removal. Legume removal may also indirectly cause distinct community responses through starvation and compensation effects. In summary, species loss at the community level led to extensive species niche shifts, which caused community resource redistribution and significant changes in community structure.

Distribution of rhizosphere fungi of Kobresia humilis on the Qinghai-Tibet Plateau.

Kobresia humilis is a major species in the alpine meadow communities of the Qinghai-Tibet Plateau (QTP); it plays a crucial role in maintaining the ecological balance of these meadows. Nevertheless, little is known about the rhizosphere fungi associated with K. humilis on the Qinghai Tibet Plateau. In this study, we used Illumina Miseq to investigate the fungal diversity, community structure, and ecological types in the root and rhizosphere soil of K. humilis across eight areas on the QTP and analyzed the correlation between rhizosphere fungi of K. humilis and environmental factors. A total of 19,423 and 25,101 operational taxonomic units (OTUs) were obtained from the roots and rhizosphere soil of K. humilis. These were classified into seven phyla, 25 classes, 68 orders, 138 families, and 316 genera in the roots, and nine phyla, 31 classes, 76 orders, 152 families, and 407 genera in the rhizosphere soil. There were 435 and 415 core OTUs identified in root and rhizosphere soil, respectively, which were categorized into 68 and 59 genera, respectively, with 25 shared genera. Among them, the genera with a relative abundance >1% included Mortierella, Microscypha, Floccularia, Cistella, Gibberella, and Pilidium. Compared with the rhizosphere soil, the roots showed five differing fungal community characteristics, as well as differences in ecological type, and in the main influencing environmental factors. First, the diversity, abundance, and total number of OTUs in the rhizosphere soil of K. humilis were higher than for the endophytic fungi in the roots by 11.85%, 9.85%, and 22.62%, respectively. The composition and diversity of fungal communities also differed between the eight areas. Second, although saprotroph-symbiotrophs were the main ecological types in both roots and rhizosphere soil; there were 62.62% fewer pathotrophs in roots compared to the rhizosphere soil. Thirdly, at the higher altitude sites (3,900-4,410 m), the proportion of pathotroph fungi in K. humilis was found to be lower than at the lower altitude sites (3,200-3,690 m). Fourthly, metacommunity-scale network analysis showed that during the long-term evolutionary process, ZK (EICZK = 1) and HY (EICHY = 1) were critical sites for development of the fungal community structure in the roots and rhizosphere soil of K. humilis, respectively. Fifthly, canonical correspondence analysis (CCA) showed that key driving factors in relation to the fungal community were longitude (R2 = 0.5410) for the root community and pH (R2 = 0.5226) for the rhizosphere soil community. In summary, these results show that K. humilis fungal communities are significantly different in the root and rhizosphere soil and at the eight areas investigated, indicating that roots select for specific microorganisms in the soil. This is the first time that the fungal distribution of K. humilis on the QTP in relation to long-term evolutionary processes has been investigated. These findings are critical for determining the effects of environmental variables on K. humilis fungal communities and could be valuable when developing guidance for ecological restoration and sustainable utilization of the biological resources of the QTP.

Grazing led to an increase in the root: shoot ratio and a shallow root system in an alpine meadow of the Tibetan plateau

Grazing is a main land use of natural grasslands in the world, which has both positive and negative impact on plant community structure and ecosystem functioning. However, the effects of long-term grazing management on the plant–soil system, in particular above- and belowground community characteristics, are still not well understood in alpine meadow community. In this study, we investigated the vegetation, roots, and soil properties under three management types (16 years of fencing since 2004-2020, moderate grazing and heavy grazing managements) in an alpine meadow on the Tibetan Plateau. The results showed that, compared with moderate grazing meadows, long-term fencing increased plant community cover, above- and belowground biomass, proportion of grass and litter but reduced forbs and soil bulk density, which caused the increases in soil organic carbon, total nitrogen and water content and the decreases in soil pH. However, heavy grazing led to opposite changes in proportion of grass, community biomass and soil physicochemical properties. The maximum of species richness and plant density appeared in moderate grazing meadows, supporting the intermediate disturbance hypothesis, and it can maintain above- and belowground biomass and soil physicochemical properties at medium level. Grazing increased the root: shoot ratio and caused root system shallow, which is consistent with the optimal partitioning hypothesis. Overall, our study suggested that moderate grazing is a more reasonable grazing management for sustainable development in alpine meadows of Tibetan Plateau, fencing could be an effective management strategy for vegetation restoration as well as for nutrient sequestration in degraded grasslands, but long-term fencing dose not benefit for biodiversity maintenance.

Eight-year warming might induce a shift toward forbs in an alpine meadow community of the Qinghai-Tibetan Plateau by increasing the soil temperature and nitrogen content

Plant biomass reveals the productivity and stability of a biotic community and is extremely sensitive to climate warming in permafrost regions, such as the Qinghai-Tibetan Plateau (QTP) in China. However, the response of the plant biomass of different functional groups to rising temperatures in such alpine zones remains unclear. Here, infrared radiators were used to simulate year-round warming on the QTP from 2011 to 2018. During the 8-year warming experiment, air temperature increased by 0.16 °C, while humidity tended to increase by 0.27 % at 20 cm above the ground. However, the rate of the increase in air temperature declined with an increasing number of years. Soil temperature and moisture increased by 1.28 °C and 3.61 %, respectively, on average from 0 to 100 cm below the ground, and the increment of soil moisture tended to rise with increasing depth. At the depths from 0 cm to 20 cm below the ground, soil organic carbon and total phosphorus tended to decrease by 0.79 g/kg and 0.04 g/kg, respectively, while soil total nitrogen tended to increase by 0.04 g/kg. Plant biomass had non-significant responses to warming, but the variation among different plant functional groups was greatest for forbs with the increment being 12.50, 147.97, and 160.47 g/m2 for plants aboveground, belowground, and total biomass, respectively. The ratios of plant total biomass tended to decrease by 2.29 %, increase by 0.60 %, and increase by 1.70 % for grasses, sedges, and forbs, respectively, so warming greatly decreased the proportion of grasses and increased the proportion of forbs in community. Warming weakened the positive correlation of grass biomass with soil temperature and enhanced the negative correlation of grass biomass with soil N and P content, along with weakening the positive correlation of sedge biomass with soil moisture and N content, while enhancing the negative correlation between sedge biomass and soil temperature. Meanwhile, forb biomass was greatly increased by soil temperature in the effects of warming. In conclusion, the 8-year warming produced negative effects on grasses and sedges by increasing soil temperature and N content and thus promoted the growth of forbs, which might induce a shift toward forbs in this community.

Home-field advantage effects in litter decomposition is largely linked to litter quality

Climate change and associated environmental alterations affect plant communities, potentially decoupling links between plants and their associated soil microbial communities. This may in turn affect processes like litter decomposition, an important function that controls nutrient and carbon cycling as well as many other ecosystem processes. Microbial decomposers have been proposed to specialize, being able to easier decompose litter from its ‘home’ community than litter from other communities, in what is termed the home field advantage (HFA) hypothesis. We report a litter decomposition experiment including four alpine meadow communities spread along a geographical gradient that ranged from the Atlas in Morocco to the Iberian Peninsula to the Swiss Alps. We tested whether litter decomposition rate would differ depending on litter and soil origin, expecting interactions between litter and soil microbial communities to be at the core of responses. We expected to find HFA in all four alpine communities. HFA ranged from very negative to neutral to positive along our geographical gradient, in a variation that could be attributed to the interaction of microbial communities with soil and plant traits, and linked to the relative abundance of microbial groups performing specific functions. Litter decomposition depended on litter quality and on the fungal community, which seemed adapted to deal with poor-quality, recalcitrant litter, leading to HFA. Climate plays a role as well, indirectly through plant community composition. Phyllosphere communities competed with soil communities when in interaction, a fact that may have blurred results of some previous HFA experiments. In summary, there is a clear HFA in systems with low-quality litter that requires a specialised fungal community to maximize decomposition. By contrast, high-quality, easy to decompose litter would be dealt with by any decomposer community, not showing evidence of HFA.

Effects of vegetation and soil changes on microbial biomass carbon and nitrogen in the Napahai meadow under N deposition.

To explore the responses of soil microorganisms to short-term nitrogen deposition in alpine meadow, we set three treatments of low nitrogen (5 g N·m-2·a-1), medium nitrogen (10 g N·m-2·a-1), and high nitrogen (15 g N·m-2·a-1) addition to investigate the effects of nitrogen-deposition induced alterations in plant diversity and soil physicochemical properties on microbial biomass carbon (MBC) and nitrogen (MBN) in a typical alpine meadow community of Carex nubigena in Napahai. The results showed that nitrogen addition significantly increased soil MBC, MBN, and their quotients, with the increases of MBC being as high as 139.3% under medium nitrogen treatment. Both MBC and MBN showed significant decreases along the soil layer, with a reduction of 24.1% to 75.1%. Nitrogen addition significantly increased aboveground biomass and reduced Shannon and Simpson indices by 6.6%-65.4%. Nitrogen addition significantly decreased soil pH, increased the contents of organic matter, total nitrogen, ammonium nitrogen and nitrate nitrogen, with the highest reduction (7.0%-511.1%) being observed in medium nitrogen treatment. Soil pH increased while other physical and chemical indicators significantly decreased with the increases of soil layer, with a variation range of 19.5%-91.2%. Results of structural equation model showed that microbial biomass was significantly positively correlated with ammonium nitrogen, nitrate nitrogen and organic matter, but negatively correlated with pH and Shannon index. The interaction of plant and soil physicochemical properties explained 55%-77% of the variations in MBC, MBN and their quotient. Soil physicochemical properties had the highest effect value (0.56-0.95) on MBC, MBN and their quotients, followed by plant diversity and aboveground biomass. Therefore, nitrogen deposition increased soil MBC and MBN and their quotient, primarily through improving soil nutrient availability and plant aboveground biomass, whereas MBC and MBN and their quotient were suppressed by high-level nitrogen deposition due to soil acidification and plant diversity losses.

Light controls alpine meadow community assembly during succession by affecting species recruitment from the seed bank.

Some research indicates that soil seed banks can promote species coexistence through storage effects. However, the seed bank mechanism that maintains plant assembly and its role in degraded grassland restoration are still not clear. We collected seed bank samples from early, mid and late secondary successional stages of an abandoned subalpine meadow on the Tibetan Plateau, and samples from each stage were exposed to full (i.e., natural), mid, and low light treatments in the field to represent light availability at the bottom/understory (soil surface) of a plant community in the early, mid and late stages of succession, respectively. Species richness, seed density, species composition, and community weighted mean values (CWMs) of seed mass of the species whose seeds germinated in soil samples were evaluated. In response to the light treatments, species richness increased significantly with increased light only for the late successional stage, seed density increased significantly with increased light only in the early and mid successional stages, and seed mass decreased significantly with increased light only in the mid and late successional stages. Species composition differed significantly among the light treatments only in the late successional stage. For the successional series, species richness and seed mass of the species that germinated increased significantly with succession only under mid and full light treatments. Seed density decreased significantly with succession in each light treatment. Species composition differed significantly between the early- and late stage and between the mid and late stage in each light treatment. Both the abiotic (light) and biotic (seed mass) factors influence seed bank recruitment to the plant community. Regeneration of small-seeded species in the seed bank was inhibited under low light in the late successional stage. The balance of stochastic and deterministic processes along a successional gradient was determined by regeneration from the seed bank depending on light intensity change. Differences in seed response to light intensity change largely determined plant community assembly. Our findings should help in the development of effective conservation and restoration strategies.

Biogeographical patterns and drivers of bacterial community in the Qinghai-Tibetan Plateau

Qinghai-Tibetan Plateau (QTP) has been ranked as one of the main hotspots of biodiversity. The biogeographic research on soil bacteria lags behind that of animals and plants, especially on the QTP. In this paper, we explored soil bacterial communities across two alpine grassland ecosystems (alpine steppe and alpine meadow) on QTP in China. Bacterial α-diversity differ significantly, which could be attributed to changes in plant cover and total phosphorus (TP) content. The dominant bacterial phyla were Actinobacteriota (28.54 %), Proteobacteria (22.74 %) and Acidobacteriota (12.96 %). Obvious distance-decay of bacterial community was observed across environmental factors and geographic distance (P < 0.001). Partial Mantel tests indicated that differences of bacterial community in whole data and alpine steppe were driven by the joint impacts of environmental factors and geographic distance, while differences of bacterial community in alpine meadow were driven by a sole impact of geographic distance. The MRM model explained 57.2 % and 49.4 % of the variability in the whole data and alpine meadow, respectively (P < 0.001), with pH being the most important variables explaining the similarity of bacterial community, followed by geographic distance, available phosphorus (AP) content and C/N. In addition, 25.6 % of the variability in alpine steppe was explained by the MRM model (P < 0.001), with geographic distance being the most important variables explaining the similarity of bacterial community. In summary, our findings suggested that α-diversity patterns, and the driving factors of the bacterial community structure were different across two ecosystem types, and environmental factors and geographic distance played different roles on the bacterial community structure in alpine steppe and alpine meadow. This study provides new understanding of soil microbial geography, and ecosystem functions driven by soil bacteria.

Warming reduced flowering synchrony and extended community flowering season in an alpine meadow on the Tibetan Plateau.

The timing of phenological events is highly sensitive to climate change, and may influence ecosystem structure and function. Although changes in flowering phenology among species under climate change have been reported widely, how species-specific shifts will affect phenological synchrony and community-level phenology patterns remains unclear. We conducted a manipulative experiment of warming and precipitation addition and reduction to explore how climate change affected flowering phenology at the species and community levels in an alpine meadow on the eastern Tibetan Plateau. We found that warming advanced the first and last flowering times differently and with no consistent shifts in flowering duration among species, resulting in the entire flowering period of species emerging earlier in the growing season. Early-flowering species were more sensitive to warming than mid- and late-flowering species, thereby reducing flowering synchrony among species and extending the community-level flowering season. However, precipitation and its interactions with warming had no significant effects on flowering phenology. Our results suggest that temperature regulates flowering phenology from the species to community levels in this alpine meadow community, yet how species shifted their flowering timing and duration in response to warming varied. This species-level divergence may reshape flowering phenology in this alpine plant community. Decreasing flowering synchrony among species and the extension of community-level flowering seasons under warming may alter future trophic interactions, with cascading consequences to community and ecosystem function.

Shrub encroachment in alpine meadows increases the potential risk of surface soil salinization by redistributing soil water

Alpine meadows are undergoing shrub encroachment due to climate change and human activities, which affects the health of alpine meadow ecosystems. Previous studies mostly focused on the impact of shrub encroachment on vegetation communities, but few studies were focused on the impact of shrub encroachment on soil pH. This study shed light on this topic by measuring soil moisture and water holding capacity under different levels of shrub encroachment (shrub coverage ranging from 8% to 90%) in alpine meadows located on the Qinghai-Tibet Plateau. Results showed that the intensification of shrub encroachment increased soil saturated water content, soil capillary moisture capacity and soil field capacity, but decreased soil moisture at the uppermost soil layer (0–10 cm). The increase of soil saturated water content and soil capillary moisture capacity increased soil pH. The intensification of shrub encroachment increased soil pH at soil depth of 0–10 cm, but decreased soil pH at soil depth of 20–30 cm. Overall, shrub encroachment could increase soil water and salt upward transport by reducing soil moisture and enhancing soil capillary moisture capacity, resulting in an increase of soil pH. These findings are conducive to better understand the impact of shrub encroachment on the redistribution of soil salinity in alpine meadows, and can provide a theoretical basis for predicting the changes of alpine meadow community facing future climatic change and human activities.

Combined livestock grazing-exclusion and global warming decreases nitrogen mineralization by changing soil microbial community in a Tibetan alpine meadow

Alpine meadows play a key role in maintaining biodiversity, soil nutrient retention, and herders’ livelihoods in mountain regions. Livestock grazing-exclusion is common in grassland management to protect and promote the sustainable use of alpine meadows. However, there are few studies evaluating the effects of traditional light grazing practices in alpine regions and grazing-exclusion impacts on soil nutrient, especially under conditions of climate warming. In this study, we conducted a five-year grazing-exclusion and warming manipulation experiment to examine the effects of grazing-exclusion on soil nitrogen fractions, microbial communities, and enzyme activities under climate warming. Treatments consisted of light-intensity grazing, grazing-exclusion, and combined grazing-exclusion and warming. Our results showed that grazing-exclusion significantly decreased potential nitrogen mineralization at a 0–5 cm depth and at altitudes of 3850 m, 4000 m, 4150 m, and 4250 m. Combined grazing-exclusion and warming also significantly decreased potential nitrogen mineralization at a 0–5 cm depth and at relatively higher altitudes of 4000 m, 4150 m, and 4250 m. Grazing-exclusion, combined grazing-exclusion and warming all shifted microbial communities from bacteria toward fungi. Grazing-exclusion significantly decreased the relative abundances of phylum Chloroflexi (bacteria) and phylum Ascomycota (fungi), while combined grazing-exclusion and warming significantly increased the relative abundances of phylum Basidiomycota (fungi). The relative abundances of phylum Ascomycota (fungi) demonstrated a positive relationship with potential nitrogen mineralization, but the relative abundances of phylum Basidiomycota (fungi) had a negative relationship with potential nitrogen mineralization. The activities of dehydrogenase and protease in grazing-exclusion and combined grazing-exclusion and warming meadows were lower than those in grazed meadows. Our results demonstrated that in the context of climate change and global warming, grazing-exclusion is unsuitable as a tool for the sustainable management of alpine meadows from soil nitrogen mineralization and fractions point of view. Of concern, climate warming could potentially amplify the adverse effects of grazing-exclusion and causes depletion of soil nutrients in the alpine meadow. This research suggests that a light-intensity grazing (0.5 yak ha−1 year−1) is beneficial to increase soil enzyme activity and N mineralization in alpine meadows. Our results provide substantial evidence and a useful baseline and guidance for the sustainable grazing management of alpine meadows as environments change due to climate warming in the future.

Impact of ambient temperature, precipitation and seven years of experimental warming and nutrient addition on fruit production in an alpine heath and meadow community

Alpine and polar regions are predicted to be among the most vulnerable to changes in temperature, precipitation, and nutrient availability. We carried out a seven-year factorial experiment with warming and nutrient addition in two alpine vegetation communities. We analyzed the relationship between fruit production and monthly mean, maximum, and min temperatures during the fall of the pre-fruiting year, the fruiting summer, and the whole fruit production period, and measured the effects of precipitation and growing and thawing degree days (GDD & TDD) on fruit production. Nutrient addition (heath: 27.88 ± 3.19 fold change at the end of the experiment; meadow: 18.02 ± 4.07) and combined nutrient addition and warming (heath: 20.63 ± 29.34 fold change at the end of the experiment; meadow: 18.21 ± 16.28) increased total fruit production and fruit production of graminoids. Fruit production of evergreen and deciduous shrubs fluctuated among the treatments and years in both the heath and meadow. Pre-maximum temperatures had a negative effect on fruit production in both communities, while current year maximum temperatures had a positive impact on fruit production in the meadow. Pre-minimum, pre-mean, current mean, total minimum, and total mean temperatures were all positively correlated with fruit production in the meadow. The current year and total precipitation had a negative effect on the fruit production of deciduous shrubs in the heath. GDD had a positive effect on fruit production in both communities, while TDD only impacted fruit production in the meadow. Increased nutrient availability increased fruit production over time in the high alpine plant communities, while experimental warming had either no effect or a negative effect. Deciduous shrubs were the most sensitive to climate parameters in both communities, and the meadow was more sensitive than the heath. The difference in importance of TDD for fruit production may be due to differences in snow cover in the two communities.

Response of species abundance distribution pattern of alpine meadow community to sampling scales

To analyse the variation of species abundance distribution (SAD) patterns with scale, and consider its formation mechanism and ecological process in alpine meadow in the eastern Qinghai–Tibet Plateau of China, study areas were established, nine permanent plots were randomly selected, and 72 quadrats were investigated. Four diversity indices were selected, including species richness, the Margalef, Shannon–Wiener and Simpson indices and relative importance values to quantify community assembly and biodiversity. Species accumulation curves were used to describe the SADs of the alpine meadow, and three model types used to fit the SADs. The results showed the following: (1) the Cyperaceae families were the respective dominance family in alpine meadow in the eastern Qinghai–Tibet Plateau of China; (2) at sampling scales from 0.25 to 2 m2, the total species richness and diversity indices increased; (3) total SADs were scale-dependent; the statistical model could not fit the SADs; the neutral theory model could explain SADs patterns at smaller spatial scales (0.25–1 m2), and the niche process gradually replaced the neutral process in importance and became the main mechanism for determining SADs with the increase of sampling scales (1.25–2 m2); (4) for common species, the niche model (geometric series model) could fit the SAD of common species at different sampling scales, which indicates that the niche process is the main mechanism to determine the SAD of common species; and (5) for rare species, with the change of sampling scale, the fitting model of rare species is different, which indicates that the SAD of rare species is affected by a variety of uncertain factors. In general, niche differentiation processes had a major effect on the biodiversity patterns of alpine meadow in Qinghai–Tibet Plateau.