Kobresia Humilis Research Articles

Shifts in Structure and Assembly Processes of Root Endophytic Community Caused by Climate Warming and Precipitation Increase in Alpine Grassland.

Climate change poses great challenges to the survival of plants. Plant endophytes play important roles in improving plant adaptability. However, our knowledge of the effects of climate change on endophytic community structures is limited. Relying on a field experimental platform simulating climate warming, precipitation increases, and their combination in an alpine grassland, the root endophytic bacterial community structures and assembly processes of three coexisting plant species (Elymus nutans, Kobresia humilis, and Melissilus ruthenicus) were measured. The results indicated that Proteobacteria was the dominant phylum, with a relative abundance ranging from 50% to 80%, followed by Actinobacteria and Bacteroidetes. Bacterial diversity decreased significantly under the combined treatment for all three plant species, with the largest reduction observed in E. nutans. The climate manipulation treatments had a minimal effect on the endophytic bacterial community structures. The relative abundance of Burkholderiaceae increased significantly under the combined treatment for the three plant species. Moreover, the endophytic community assembly processes changed from stochastic dominated under control plots to deterministic dominated under the combined plots for E. nutans, while this shift was reversed for M. ruthenicus. The root endophytic bacterial community was affected by the soil's available nitrogen and stoichiometric ratio. These results revealed that the sensitivity of endophyte community structures to climate change varies with host plant species, which has implications for plant fitness differences.

Kobresia humilis via root-released flavonoids recruit Bacillus for promoted growth

Alpine meadows, which are critical for biodiversity and ecosystem services, are increasingly degrading, necessitating effective restoration strategies. This study explored the mechanism by which Kobresia humilis, an alpine meadow-constructive species, modulates the rhizosphere microbiome via root exudates to enhance growth. Field investigations revealed that the plant height of K. humilis in a severely degraded (SD) alpine meadow was significantly higher than that in other K. humilis populations. Consequently, we analysed the differences between this plot and other K. humilis samples with different degrees of degradation to explore the reasons underlying the phenotypic differences in K. humilis. 16 S rRNA amplicon sequencing results showed that the SD plots were significantly enriched with more Bacillus, altering the composition of the rhizosphere microbial community of K. humilis. The collection and analysis of root exudates from various K. humilis locations revealed distinct differences. Procrustes analysis indicated a strong correlation between the root exudates and the rhizosphere microbiome composition of K. humilis. Model-based integration of metabolite observations, species abundance 2 (MIMOSA2), and Spearman's rank correlation coefficient analysis were used to identify the root exudates potentially related to the enrichment and recruitment of Bacillus. Bacillus from SD samples was isolated and screened, and the representative strain D334 was found to be differentially enriched compared to other samples. A series of in vitro experiments with the screened root exudates and strain D334 demonstrated that K. humilis could recruit Bacillus and promote its colonisation by releasing flavonoids, particularly baicalin. Additionally, K. humilis can release sucrose and riboflavin, which promote strain growth. Finally, soil microbiome transplantation experiments confirmed that different K. humilis phenotypes were closely related to the functions of the rhizosphere microbiome, especially in root morphological shaping. Moreover, the effects of Bacillus inoculation and the microbiome on the plant phenotypes were consistent. In summary, this study revealed a new mechanism by which K. humilis recruits rhizosphere growth-promoting bacteria and enhances soil nutrient utilisation, thereby promoting plant growth. These findings provide a theoretical basis for ecological restoration using soil microbial communities and clarify the relationship between plant metabolites and microbial community assembly.

Climate change affects plant aboveground biomass by regulating the growth periods in alpine grasslands of the Tibetan Plateau, China

Climate change significantly affects plant biomass and phenological occurrence time in alpine grasslands of Tibetan Plateau. The changes in phenological periods are closely related to the length of vegetative and reproductive growth periods, which may further affect aboveground biomass accumulation. In this study, based on fixed-point observations of plant biomass and phenology as well as the corresponding climatic data from 1997 to 2020 in the alpine grasslands of Tibetan Plateau, we used statistical methods such as ordinary linear regression and piecewise structural equation model to explore the characteristics of interannual climate change in the study area, the variation trends of plant biomass and phenological periods, and the correlations between biomass and phenological and climatic factors. The results showed that mean annual temperature and annual precipitation in the study area increased significantly from 1997 to 2020, suggesting a clear "warm-wet" trend. Aboveground biomass and relative biomass of Stipa sareptana var. krylovii (the dominant species) decreased significantly. However, absolute and relative biomass of subdominant species (Kobresia humilis) increased significantly, indicating that the dominance of K. humilis increased. The warm-wet climates enhanced aboveground biomass accumulation of K. humilis by extending the period of reproductive growth. Mean annual temperature and annual precipitation decreased aboveground biomass of S. sareptana by shortening the length of vegetative growth period. In a word, the warmer and wetter climate significantly affected aboveground biomass accumulation by regulating the changes in the phenological period, and the interspecific difference in their response resulted in a larger change in community composition. This study area may show a trend from alpine grassland to alpine meadow, and thus further works are urgently needed.

Effects of warming conditions on plant nitrogen–phosphorus stoichiometry and resorption of three plant species in alpine meadows on the Tibetan Plateau

Abstract Global climate change is expected to have a significant impact on ecosystems worldwide, especially for alpine meadows which are considered as one of the most vulnerable components. However, the effects of global warming on the plant nitrogen–phosphorus stoichiometry and resorption in alpine meadows remain unclear. Therefore, to investigate the plant nitrogen–phosphorus stoichiometry and resorption in alpine meadows on the Qinghai-Tibet Plateau, we conducted an artificial warming study using open-top chambers (OTCs) over the 3 years of warming period. We selected three dominant species, four height types of OTCs (0.4, 0.6, 0.8 and 1 m) and four warming methods (year-round warming, winter warming, summer–autumn–winter warming and spring–summer–autumn warming in the experiment) in this experiment. In our study, soil temperature significantly increased with increasing the height of OCTs under the different warming methods. Kobresia pygmaea presented an increase in nitrogen (N) limitation and Kobresia humilis presented an increase in phosphorus (P) limitation with increasing temperature, while Potentilla saundersiana was insensitive to temperature changes in terms of nitrogen and phosphorus limitations. Both nitrogen resorption efficiency:phosphorus resorption efficiency and N:P trends in response to rising temperatures were in the same direction. The differential responses of the chemical stoichiometry of the three species to warming were observed, reflecting that the responses of nitrogen and phosphorus limitations to warming are multifaceted, and the grassland ecosystems may exhibit a certain degree of self-regulatory capability. Our results show that using chemical dosage indicators of a single dominant species to represent the nitrogen and phosphorus limitations of the entire ecosystem is inaccurate, and using N:P to reflect the nutritional limitations might have been somewhat misjudged in the context of global warming.

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.

Diazotrophic abundance and community structure associated with three meadow plants on the Qinghai-Tibet Plateau.

Symbiotic diazotrophs form associations with legumes and substantially fix nitrogen into soils. However, grasslands on the Qinghai-Tibet Plateau are dominated by non-legume plants, such as Kobresia tibetica. Herein, we investigated the diazotrophic abundance, composition, and community structure in the soils and roots of three plants, non-legume K. tibetica and Kobresia humilis and the legume Oxytropis ochrocephala, using molecular methods targeting nifH gene. Diazotrophs were abundantly observed in both bulk and rhizosphere soils, as well as in roots of all three plants, but their abundance varied with plant type and soil. In both bulk and rhizosphere soils, K. tibetica showed the highest diazotroph abundance, whereas K. humilis had the lowest. In roots, O. ochrocephala and K. humilis showed the highest and the lowest diazotroph abundance, respectively. The bulk and rhizosphere soils exhibited similar diazotrophic community structure in both O. ochrocephala and K. tibetica, but were substantially distinct from the roots in both plants. Interestingly, the root diazotrophic community structures in legume O. ochrocephala and non-legume K. tibetica were similar. Diazotrophs in bulk and rhizosphere soils were more diverse than those in the roots of three plants. Rhizosphere soils of K. humilis were dominated by Actinobacteria, while rhizosphere soils and roots of K. tibetica were dominated by Verrumicrobia and Proteobacteria. The O. ochrocephala root diazotrophs were dominated by Alphaproteobacteria. These findings indicate that free-living diazotrophs abundantly and diversely occur in grassland soils dominated by non-legume plants, suggesting that these diazotrophs may play important roles in fixing nitrogen into soils on the plateau.

Reduced plant species diversity and soil carbon and nitrogen contents driven by vegetation patchiness in alpine meadows

AbstractQuestionPatchiness of herbaceous species is a common feature of degraded alpine grasslands on the Qinghai–Tibet Plateau; however, the impact of this phenomenon on vegetation, soil seed bank (SSB), and soil carbon (C) and nitrogen (N) is largely unknown. We asked how different herbaceous patches affect above‐ground vegetation, the SSB and soil organic C (SOC) and total N (TN) contents in alpine meadows.LocationAn alpine meadow on the Qinghai–Tibetan Plateau, China.MethodsWe used field and greenhouse experiments to evaluate above‐ground vegetation parameters, the SSB composition, and SOC and TN contents of four commonly distributed herbaceous patches (Leymus secalinus, Kobresia humilis, Leontopodium nanum and Pedicularis kansuensis) and non‐patch vegetation (control).ResultsThere were significant differences in the species composition of above‐ground vegetation, with the plant species richness, Shannon–Wiener index, Simpson index, and Pielou evenness index reduced in the four patches compared to the control. In addition, patches had increased above‐ground biomass (AGB) and a lower below‐ground biomass to above‐ground biomass ratio (BGB:AGB); while the species diversity indices did not change considerably among the patches. The species composition of the SSB in the four patches differed from that in the control and the seed density increased markedly, but the species richness and diversity of the SSB remained unaltered. Moreover, the contents of SOC, total C, TN, microbial biomass C, and microbial biomass N in the four patches were markedly lower than in the control.ConclusionsThese findings suggest that patchiness of herbaceous species can alter the flora composition of alpine meadows and reduce plant species diversity, as well as the SOC and TN contents, which will adversely impact grassland biodiversity conservation and soil C sequestration, and then may intensify the degradation of alpine meadows on the Qinghai–Tibet Plateau.

A dataset of biomass of the alpine shrub meadow (2003–2020) and the alpine Kobresia humilis (2002–2020) observed at the CO2 flux monitoring station in Haibei, China

The Qinghai-Tibet Plateau (QTP) is a hotspot and sensitive region affected by global climate change. The alpine shrub and alpine Kobresia humilis meadow are the primary types of alpine meadow found in this area, which play an important role in the sustainable development of the QTP and even the global alpine meadow ecosystem. Biomass, as a direct index reflecting the production function of grassland ecosystem, can be used to effectively study the relationship between grassland ecosystem function and other influencing factors. The precise measurement and assessment of the biomass of the alpine shrub and alpine Kobresia humilis meadow are crucial elements for gaining a scientific understanding of the ecological functions of the alpine meadow on the QTP. The National Field Scientific Observation and Research Station of Alpine Grassland Ecosystem located in Haibei Prefecture, Qinghai Province (Haibei Station) has been conducting scientific monitoring of the biomass of alpine Potentilla fruticosa shrub and alpine Kobresia humilis meadow respectively since 2002 and 2003. Haibei Station has continuously accumulated the original data of these two ecosystems for 17 and 18 years respectively. In order to precisely evaluate the carbon sink potential of the alpine shrub and alpine Kobresia humilis meadow ecosystems in the QTP and even the global, and accurately predict the long-term response of the ecosystem to climate change, we published the biomass data of the alpine shrub (2003-2020) and alpine Kobresia humilis meadow (2002-2020) in the Haibei Flux Monitoring Station. This dataset includes aboveground biomass and underground biomass of the alpine shrub and alpine Kobresia humilis meadow. It can provide ground observation data support for scientific cognition, remote sensing inversion and model verification of the spatial and temporal dynamics of ecosystem biomass in alpine meadows, and contribute to the healthy and sustainable development of alpine meadows.

Construction of an Early Warning System Based on a Fuzzy Matter-Element Model for Diagnosing the Health of Alpine Grassland: A Case Study of Henan County, Qinghai, China

To maintain alpine grassland in a healthy and sustainable state, a sound warning system was developed to diagnose its potential degradation risk. Data related to grassland quality (six indicators), habitat (six indicators), and eco-carrying capacity (three indicators) at eight sampling plots were collected from Henan Mongol Autonomous County of West China in 2014 and 2017, representing five types of grassland and three grazing styles. Compared to the warning level in 2014, alpine grassland had a higher warning level in 2017, demonstrating the degradation of grassland ecosystems. Kobresia tibetica exhibited the lowest level of warning, while Kobresia humilis had the highest, indicating its corresponding safety and unsafety under the environmental change. Grassland quality is the most important index for grassland health, and soil total carbon and available phosphorus are the most important indices of habitat quality, which finally greatly influence the warning level of alpine grassland. Further analysis results suggested that winter grazing is beneficial for the health of grassland, and moderate grazing can accelerate the self-recovery of the alpine grassland due to the increase in organic matter. This study is crucial for understanding the health level of alpine grassland and its further change trends, and providing an important scientific basis for rational grazing.

Grazing practices affect phyllosphere and rhizosphere bacterial communities of Kobresia humilis by altering their network stability

The primary utilization strategy for meadow grasslands on the Qinghai-Tibet Plateau (QTP) is livestock grazing. This practice is considered as one of the major drivers of plant-associated bacterial community construction and changes in soil properties. The species of Kobresia humilis is considered as the most dominant one in grasslands. However, how different grazing practices affect the phyllosphere and rhizosphere bacterial communities of K. humilis is unknown. To address this issue, the effects of the grazing enclosure (GE), single-species grazing (YG and SG, representing yak only and sheep only, respectively), and different ratios of grazing (ratio of yak to sheep is 1:2, 1:4, and 1:6, represented by MG1:2, MG1:4, and MG1:6, respectively) on the dominant plant of K. humilis, it's phyllosphere and rhizosphere bacteria, and soil properties were investigated using artificially controlled grazing and grazing enclosure. Our data showed that grazing enclosure enhanced vegetation coverage, and rhizosphere bacterial richness and diversity, while reduced plant number and bacterial network stability of K. humilis. The NO3−-N, K+, and Cl− concentrations were lower under grazing compared to GE. SG reduced the concentration of NH4+-N, TN, K+, and Na+ compared to YG. Moderate grazing intensity had a lower relative abundance of the r-strategists (Bacteroidota and Gammaproteobacteria) with higher bacterial network stability. Yak and sheep grazing showed reversed impacts on the bacterial network stability between the phyllosphere and rhizosphere of K. humilis. Proteobacteria and Actinobacteriota were identified in the molecular ecological network analysis as keystone taxa in the phyllosphere and rhizosphere networks, respectively, under all treatments. This study explained why sheep grazing has more adverse effects on grazing-tolerant grass species, K. humilis, than yak grazing, and will contribute to a better understanding of the impacts of different grazing practices and grazing enclosure on alpine grassland ecosystems on the QTP.

Vegetation Types Variations to the South of Ngoring Lake from 2013 to 2020, Analyzed by Hyperspectral Imaging

Studying the variation in vegetation types within the source region of the Yellow River (SRYR) is of great significance for understanding the response of vegetation to climate change and human activities on the Qinghai-Tibet Plateau (QTP) permafrost. In order to understand the characteristics of the variation in vegetation associations in the SRYR under the influence of climate and human activities, two hyperspectral remote sensing images from HJ-1A in 2013 and OHS-3C in 2020 were used to extract the vegetation types located in the area south of Ngoring Lake, covering 437.11 km2 in Maduo County, from the perspective of vegetation associations. Here, the hybrid spectral CNN (HybridSN) model, which is dependent on both spatial and spectral information, was used for vegetation association classifications. On this basis, the variations in vegetation associations from 2013 to 2020 were studied using the transition matrix, and the variation in noxious weeds across different altitude and slope gradients was analyzed. As an example, Thermopsis lanceolata’s spatial distribution pattern and diffusion mechanism were analyzed. The results showed that (1) in addition to noxious weeds, herbage such as Poa poophagorum, Stipa purpurea, Kobresia humilis, and Carex moorcroftii increased, indicating that the overall ecological environment tended to improve, which may be attributed mainly to the development of a warm and humid climate. (2) Most of the noxious weeds were located at low altitudes with an area increase in the 4250–4400 m altitude range and a decrease in the 4400–4500 m altitude range. More attention should be given to the fact that the noxious weeds area increased from 2.88 km2 to 9.02 km2 between 2013 and 2020, which was much faster than that of herbage and may threaten local livestock development. (3) The Thermopsis lanceolate association characterized by an aggregated distribution tended to spread along roads, herdsmen sites, and degraded swamps, which were mainly affected by human activities and swamp degradation.

Self‐stabilizing maintenance process in plant communities of alpine meadows under different grazing intensities

AbstractBackgroundsGrazing prohibition and reduced grazing intensity, as two important “vegetation close‐to‐nature recovery” methods, have been suggested as economical and effective technologies for enhancing forage production. However, numerous studies have found that the yield of forage could be increased by removing or reducing grazing in a short time in some steady stage of alpine Kobresia meadows, but not in others. To reveal the mechanism behind this phenomenon, we proposed a series of experiments.MethodsWe monitored the plant and soil characteristics in the key steady stages of Kobresia meadows under reduced and prohibited grazing conditions in the same geographic and climatic environments in the northeastern Qinghai‐Tibet Plateau for 6 years. We estimated the relationships between the plant community and soil nutrients and obtained the following results.ResultsAll measured variables were positively correlated with each other. The plant community structure had higher path coefficients to aboveground biomass, soil organic matter, total nitrogen, and nitrate nitrogen than to other factors. The plant community structure played an important role in response to grazing intensity. Different plant functional groups (PFGs) had different responses to grazing intensity, which led to plant community re‐establishment or re‐organization under different grazing intensities. Poaceae and Kobresia were more sensitive to grazing intensity than other PFGs, and the ratio of Kobresia biomass (including Kobresia humilis and Kobresia pygmaea) to the total biomass of Poaceae and Kobresia could be used as an indicator of regime shifts within plant communities. With Kobresia pygmaea as the dominant species, the prohibition of grazing was not an efficient approach to increase the yield in the steady stages because this treatment needed more time to recover aboveground biomass. If Poaceae is the dominant PFG, grazing should only be prohibited for 3 years in the steady stages because the aboveground biomass will decrease if grazing is prohibited for more than 3 years.ConclusionsTherefore, the different steady stages of alpine meadows require different recovery methods to increase recovery efficiency and speed.

Different responses of alpine plants to natural climate change reduced coexistence through phenological niche overlap

Plant phenology is the bridge between climate change and ecosystem functions. Time coordination of interspecific and intraspecific phenology changes overlap or separate can be regarded as an important characteristic of species coexistence. To confirm the hypothesis that plant phenological niche promotes species coexistence, three key alpine plants, Kobresia humilis (sedge), Stipa purpurea (grass), and Astragalus laxmannii (forb) were investigated in this study in the Qinghai-Tibet Plateau. Phenological niches represented as the duration of green up-flowering, flowering-fruiting, and fruiting-withering by 2-day intervals for phenological dynamics of three key alpine plants from 1997 to 2016. We found the role of precipitation on regulating the phenological niches of alpine plants was highlighted in the context of climate warming. The response of the intraspecific phenological niche of the three species to temperature and precipitation is different, and the phenological niche of Kobresia humilis and Stipa purpurea was separate, especially in the green up-flowering. But the overlapping degree of interspecific phenological niche of the three species has continued to increase in the past 20 years, reducing possibility of species coexistence. Our findings have profound implications for understanding the adaptation strategies of key alpine plants to climate change in the dimension of phenological niche.

The contribution of common and rare species to species abundance patterns in alpine meadows: The effect of elevation gradients

Ecological niche modeling uses environmental variables associated with species distribution points to simulate species distribution and its importance in biodiversity conservation. This study aimed to quantify plant community composition and species abundance distribution (SAD) in alpine meadows at different elevations and to assess the contribution of rare and common species to SAD. We established a permanent study plot of 210 hm2 in Gannan Tibetan Autonomous Prefecture, China, surveyed 315 sample squares (0.5 m × 0.5 m), and calculated the Hill numbers. The results showed that (1) a total of 72 species were surveyed at different altitudes, with Kobresia humilis and Kobresia macrantha as the main dominant species; (2) the SADs of overall and common species fit the ecological niche model (GSM (Geometric Sequence Model)), indicating that ecological niche differentiation is the main factor influencing SAD. The fitted model for rare species SAD varied with elevation, suggesting that various ecological processes influence rare species SAD. (3) Hill numbers showed a “single peak” pattern with increasing elevation. The number of rare species was higher than that of common species. Still, the distribution frequency of common species was significantly higher than rare species. The correlation between common-rare species sequences and cumulative species distribution was high. This indicates that common species dominate the species diversity pattern of the community, are the main contributors to the SAD pattern, and should be protected first. Rare species are also important carriers of community function and include much spatial information. Rare and common species work together in different ways to influence and maintain the species diversity patterns of alpine meadow plant communities.

Cascading effects of seed-stem-individual spatial patterns along a grazing gradient.

Studying the seed trait-stem trait-individual spatial pattern system is helpful for understanding the developmental direction of plant dynamics and populations under grazing disturbance as well as the antagonistic relationship between animals and plants, but few systematic analyses of this spatial pattern system have been carried out. Kobresia humilis is the dominant species in alpine grasslands. We studied K. humilis seed traits and their relationship with K. humilis reproductive individuals, the relationship between reproductive and vegetative stems, and the weights and spatial patterns of reproductive and nonreproductive individuals under four grazing treatments: no grazing (control), light grazing, moderate grazing and heavy grazing. We explored the relationship among seed size and seed number with reproductive stems and vegetative stems along the grazing gradient and assessed the spatial pattern changes between reproductive and nonreproductive individuals. The results showed the following: (1) Seed size increased with increasing grazing intensity, and the coefficient of variation for seed size and seed number in the heavy grazing treatment was greater than 0.6. (2) The structural equation model showed that grazing treatment had a positive effect on seed number, seed size and reproductive stem number and a negative effect on reproductive stem weight. (3) Grazing treatment did not affect the resource allocation to reproductive stems and vegetative stems per unit length of reproductive K. humilis individuals. (4) Compared with the number of reproductive individuals in the no grazing treatment, the number in the heavy grazing treatment decreased significantly, and the negative correlation between reproductive individuals and nonreproductive individuals changed from a full-scale negative correlation to a small-scale negative correlation and a large-scale positive correlation. Our study showed that grazing could activate and change the resource allocation pattern of dominant species in a grassland and have significant positive effects on reproductive stem number, reproductive stem weight, seed number and seed size. Along a grazing intensity gradient, with the increase in distance between reproductive and nonreproductive individuals, the transformation of intraspecific relationships from a negative correlation to a positive correlation is an ecological strategy conducive to population survival.

Long-Term Effects of Altered Precipitation Patterns on Alpine Vegetation Species Composition on the Qinghai-Tibet Plateau

Changes in global precipitation patterns have had important impacts on terrestrial ecosystems. However, the relationship between alpine vegetation species composition and precipitation patterns remained uncertain. Based on in situ observations, long-term datasets of monthly aboveground biomass (AGB) and daily precipitation were applied in an alpine grassland on the Qinghai–Tibet Plateau (QTP), in order to characterize the responses of multi-species biomass to changing rainfall patterns. In this study, vegetation species composition exhibited obvious variations during 1997–2011 in alpine grasslands on the Qinghai–Tibet Plateau. Rapid increases in weed, Kobresia humilis, and Poa crymophila Keng squeezed the living space of the dominant species, Stipa sareptana var. krylovii. Meanwhile, effective precipitation had stronger effects on vegetation biomass, which were heterogeneous in different precipitation periods. Therefore, the crucial effective precipitation, accounting the effective precipitation in crucial periods, could better explain vegetation biomass variations, which could be a new representative climatic indicator to accurately describe vegetation change in alpine grasslands. In addition, crucial periods of effective precipitation appeared to influence heterogeneity for different vegetation species, which showed the heterogeneous adaptability of species to the changes in precipitation patterns. Precipitation patterns during 1997–2011 were more conducive to the growth of Poa crymophila Keng and Kobresia humilis, thereby changing the species composition in alpine grasslands. The coupling of biological environmental adaptability and abiotic crucial effective precipitation determined the variations of vegetation species composition. The new indicator of crucial effective precipitation could provide a new perspective for studying and predicting the species dynamics of alpine grassland.

An increase in livestock density increases forage nutritional value but decreases net primary production and annual forage nutritional yield in the alpine grassland of the Qinghai-Tibetan Plateau.

Pasture biomass and quality are dependent on herbivore grazing and precipitation, but the responses of vegetation to the interactive effects of climate and grazing regimes remain unclear. We conducted an eight-year sheep grazing experiment with 4 stocking rates (0, 3.5, 5.5, and 7.5 sheep/ha) in an alpine meadow of the northeastern Tibetan Plateau. The above-ground net primary productivity (ANPP) and forage nutritional value (FNV) of four dominant species (Poa annua, Kobresia humilis, Astragalus adsurgens and Potentilla fruticosa) were measured during a wet year (360 mm rainfall) and a drought year (216 mm rainfall). The FNV was used as indicator of forage quality and was calculated from the crude protein (CP) content, in vitro true dry matter digestibility (IVTD), metabolic energy (ME) yield, and neutral detergent fiber (NDF) content of the plant. The stocking rate explained a minimum of 76% of the variations of ANPP, and the precipitation sub-additive effect for ANPP ranged from 5% to 12%. The interaction of sheep stocking rate and precipitation affected ANPP of the 4 species, except for P. fruticosa. The FNV of the pasture increased with increasing grazing pressure, but ANPP and forage nutritional yield (FNY) decreased. In calculating FNY, the increase in FNV did not compensate for the decrease in ANPP. In non-grazed plots, the CP yield declined sharply (18%-55%) in response to drought, but there was no effect on ME yield. The interaction between stocking rate and precipitation affected forage quality of the 4 plant species differently. The grassland ANPP and FNY could be maintained at a grazing intensity of 3.5 sheep/ha in wet and dry years. Our results highlight that stocking density affects pasture ANPP and FNV, and is contingent on rainfall.

Shifts in plant and soil C, N, and P concentrations and C:N:P stoichiometry associated with environmental factors in alpine marshy wetlands in West China

Ecological stoichiometry, a novel method for predicting nutrient cycling rates in different habitats, represents the demands of an organism for natural resources and links different levels of biogeochemical cycling. In this study, plant and soil carbon (C), nitrogen (N), and phosphorus (P) concentrations, their stoichiometric characteristics (C:N, C:P, and N:P ratios), and other physicochemical properties of soil were characterized using 243 soil and 81 plant samples collected from three habitats—hummocks, depressions, and meadows—in the marshy wetlands of West China. The results showed that leaf N and P concentrations, soil C, N, and P storage and concentrations, and C:N, C:P, and N:P ratios differed significantly among the three habitats (p < 0.05). Kobresia humilis leaves had the highest N and P content, followed by the leaves of Kobresia tibetica, while Carex mullis leaves had the lowest N and P content. The surface soil of depressions exhibited the highest C, N, C:P, and N:P ratios, hummocks exhibited the highest C:N ratio, whereas meadows exhibited the lowest C and N contents and C:N, and C:P ratios. A structural equation model (SEM) verified that leaf C, N, and P contents and C:P and N:P ratios were positively correlated with soil moisture (SM) and soil organic C contents, whereas the leaf C:N ratio was significantly and negatively correlated with SM content and bulk density. Our findings highlight the ability of alpine marshy wetlands to maintain and even increase the current C, N, and P storage capacities of the ecosystem under increased flooding in the study area.

UV-B Radiation Effects on the Alpine Plant Kobresia humilis in a Qinghai-Tibet Alpine Meadow.

Enhanced UV-B radiation resulting from stratospheric ozone depletion has been documented both globally and on the Qinghai-Tibet Plateau in China. The response of Kobresia humilis, an important alpine meadow plant species, to enhanced UV-B radiation was experimentally investigated at the Haibei Alpine Meadow Ecosystem Research Station (37°29'-37°45' N, 101°12'-101°23' E; alt. 3200 m). K. humilis was exposed to UV-B radiation including ambient UV-B and enhanced UV-B (simulating a 14% reduction in the ozone layer) in a randomized design with three replications of each treatment. Enhanced UV-B radiation resulted in a significant increase of both leaf area and fresh weight chlorophyll and carotenoid but had no effect on UV-B absorbing pigments. Similarly, enhanced UV-B radiation did not significantly change the photosynthetic O2 elevation rate while leaf thickness, width, and length significantly increased (p &lt; 0.01). The enhanced UV-B radiation was associated with 2-3 days earlier flowering and a larger number of flowers per spikelet. The enhanced UV-B generally resulted in larger leaves and more flowers but earlier phenology. In summary, these findings suggest that alpine species of K. humilis have adapted to the strong solar UV-B radiation intensity presented on the Qinghai-Tibet Plateau, but the interspecies differences and their influence on trophic level should be more concerning.

Air or soil temperature matters the responses of alpine plants in biomass accumulation to climate warming

Climate change has substantially affected plant phenology and growth on the Qinghai-Tibetan Plateau (QTP), while it remains unclear how plant phenology and growth impact the plant biomass under climate change. We used long-term data (from 1997 to 2017) for four plants, Stipa purpurea, Artemisia scoparia, Kobresia humilis and Astragalus laxmannii in the alpine meadow to examine the relationships among multiple climate factors, vegetative growth, reproductive growth, intrinsic growth rate and biomass. The order of returning to green determines the growth strategies of different plants, the earliest plants to green (p < 0.05) (e.g., Stipa purpurea and Artemisia scoparia) would choose the strategy of vegetative growth (p < 0.05); the earlier plants (p < 0.05) (e.g., Kobresia humilis) would be regulated by both vegetative growth and reproductive growth (p < 0.05); while the latest plant to green (p < 0.05) such as Astragalus laxmannii, would choose intrinsic growth rate rather than growing season (P < 0.05). Temperature was the most important drivers for key phenological phases and growth patterns of four species, different factors play a role in different stages of the growth period, i.e., in the early and late stage is the soil temperature, while in the middle stage is the average temperature or the maximum temperature, and all the optimum thresholds were >30 day. These findings provide the in-situ evidences of long-term changes in phenology and its associated growth on the biomass of alpine plants on the QTP in the era of climate change.