Water use efficiency is an important indicator of drought tolerance of plants. The response was still unclear of water use efficiency to different grazing intensity and its adaptive mechanisms in alpine meadow. Here, we analyzed water use efficiency of plant dominant species, coexisting species and functional group level plants to grazing intensity by δ13C index in alpine meadow. Furthermore, this study revealed the driven factors of water use efficiency combined available nitrogen, soil bulk density, soil organic carbon, soil water content and evapotranspiration. Grazing increased plants δ13C by 3.37%. Moderate grazing significantly increased the δ13C of Gramineae by 4.84% (P<0.05), and increased δ13C of Cyperaceae, Leguminosae, and Forb by 3.45%, 0.81%, and 1.40% respectively. Some dominant species and coexisting species have the highest δ13C value under moderate grazing. This study indicated that moderate grazing significantly improved the water use efficiency of alpine meadows. Path analysis resulted showed that the water use efficiency was negatively correlated with evapotranspiration (P<0.05), soil water content, soil organic carbon, and soil bulk density. It was positively correlated with available nitrogen. Our study provides new insights that moderate grazing help to increase water use efficiency in alpine meadows. In addition, evapotranspiration may be the main driving factor affecting the water use efficiency of alpine meadow.

We conducted a comprehensive investigation of the interrelationships among the species diversity, productivity, community structure, and soil nutrients of vegetation communities of an alpine meadow ecosystem on the eastern Qinghai–Tibet Plateau. We performed biodiversity manipulation experiments to examine the effects of removing plant functional groups (Gramineae, Cyperaceae, Legumes, and other Forbs) for 3 and 10 years at a research station in Haibei. Interannual variation in the species richness and above- and belowground biomass of the community gradually decreased over time. Species richness and productivity were positively correlated, and this correlation became increasingly significant over time. Removal of the plant functional groups resulted in fewer Gramineae species within the community. However, 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 had difficulty recovering its previous equilibrium state within a short period of 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 have indirectly caused 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.

In the Alpine Meadow ecosystems of eastern Qinghai-Tibet Plateau, the interrelations among the species diversity of different vegetation communities, productivity, community structure as well as soil nutrients were thoroughly researched through running biodiversity manipulation experiment to explore the species survey consequences of 3 and 10 years of plant functional groups (Gramineae, Cyperaceae, Legumes, and other Forbs) removal at Haibei station. The results demonstrated that the interannual variation of the remaining species richness, above-ground and below-ground biomass of the community gradually presented a tendency to decrease as the removal time increased, and there was a positive relationship between species richness and productivity, and the correlation became increasingly significant. The removal behavior reduced the number of Gramineae within the remaining community. The content of soil total nitrogen, phosphorus, organic matter and moisture content of Legumes loss treatment increased significantly. The treatment that removal Forb had the lowest negative cohesion values, revealing that it is difficulty for this community to recover to the previous equilibrium state in a short time. In our study, all affects of species removal on ecosystem may be related to variance in the structure and composition of species in community. Meanwhile, changes in the number of Gramineae indicated that Gramineae are more sensitive and less resistant to removal behavior. Furthermore, the specific performance of Legumes removal indirectly indicates that the loss of diverse plant function groups prompted distinct replies to the starvation and compensation effects. In a nutshell, species loss at the community level leads to shifts in the niche of each species, inducing a redistribution of community resources and leading to significant changes in community structure.

Alpine meadow degradation, usually involving decreased soil N and patchy landscapes, is challenging for natural restoration. However, the mechanism underlying plant species coexistence during degradation is unclear. In this study, we evaluated plant N niche complementarity in degraded alpine meadows by a 15N-labeling (15NO3-, 15NH4+ and 15N-glycine) experiment. At the community level, the degraded alpine meadow showed larger root and all plant 15N concentrations and preferred glycine over NO3- compared with the undegraded alpine meadow. At the species level, dominant species in the undegraded alpine meadow consistently preferred NO3-. For the degraded alpine meadow, generalist species, common to both meadows, showed diverse preferences, while unique species generally preferred glycine, among which the uneven distribution could reduce glycine competition. We observed that differentiation in N sources and the uneven distribution of unique species may explain the stability of degraded alpine meadows. Our results suggested that plant spatial distribution could be powerful for community stability and emphasized the importance of considering fine-scale perspectives in studies of niche theory. This study have important implication for restoration of degraded alpine meadows.

Understanding the characteristics of long-term changes in the water use efficiency (WUE) of grassland ecosystems is vital for WUE improvement on the Qinghai-Tibet Plateau. In this study, five vegetation types, namely alpine shrub, desert, grassland, meadow, and swamp, were evaluated. The changes in WUE over the past 16 years were calculated using the total primary productivity and latent heat flux data of the ecosystem from 2006 to 2021. In addition, meteorological data were used to further explore the relationship between WUE and environmental factors. The WUE of alpine desert, meadow, and swamp showed an increasing trend. In contrast, alpine shrub and grassland WUE showed a decreasing trend, with the WUE of shrub being significantly higher than that of grassland on the interannual scale. The WUE of all vegetation types showed seasonal maximum and minimum values in July and January, respectively, and the WUE of shrubs was significantly higher than that of the other vegetation types. The structural equation model showed that precipitation, temperature, and relative humidity were the main positive influences on the WUE of grasslands on the Qinghai-Tibet Plateau, whereas net radiation had a negative influence. Climate factors may substantially impact future changes in the WUE of various ecosystems. The results of this study provide a theoretical basis for further study of WUE changes in the grasslands of the Qinghai-Tibet Plateau.

The alpine grassland shrubbization of the northern Qinghai-Tibet Plateau on the background of global change and overgrazing, is a prominent and serious problem. However, the water competition ability of shrubs and alpine grasslands is rarely reported. Here, we tracked the δ 18O and δ 2H of soil water, plant water, precipitation, and groundwater, analysed sources of water use in shrub and grassland by Mix SIAR model. Our results showed that both δ 18O and δ 2H in soil, precipitation, and plant varied significantly over time, groundwater remained relatively stable in P. fruticosa shrub and alpine grassland sites during observation. Considering groundwater, precipitation, soil water, and plant water, a progressive enrichment in δ 18O or δ 2H existed from groundwater and precipitation to soil water to plant water for each month. Alpine grassland was more susceptible to drought stress, had a stronger partitioning effect in dynamic transport than shrub. The P. fruticosa shrub displayed more flexible water utilisations, and was more competitive for water than grasslands. Furthermore, the plants in alpine shrub and grassland reached water use balance in August. Shrubs degraded from alpine grassland changed water use pattern of grassland, thereby changing soil water storage. These results contribute to in-depth understanding the alpine grassland shrubbization from water use patterns of grassland and shrub plants on the northern Qinghai-Tibet Plateau.

Studying the interrelation of soil water and plant water is essential for an in-depth understanding of eco-hydrological processes. However, water use relationships and comparative studies between shrubs and alpine grassland of the northern Qinghai-Tibet Plateau remain poorly understood. In this study, we compared δ18O and δ2H values of water from soil, plant, precipitation, and groundwater between P. fruticosa shrub and alpine grassland locations at two neighboring sites in order to better understand the interface between plant and surrounding soils of shrubs and grasslands in the northern Qinghai-Tibet Plateau. Our results showed that δ18O and δ2H of soil water, precipitation, and plant water varied significantly over time and water sources in P. fruticosa shrub and alpine grassland sites. Both soil evaporation and plant transpiration at the P. fruticosa shrub site were relatively lower than they were at the alpine grassland site. Alpine grassland plant water had a stronger dynamic fractionation effect in the process of transportation and was more sensitive to environmental conditions. However, plants at the P. fruticosa shrub site displayed more flexible water use patterns, shifted their water sources between shallow soil water and deep soil water. Shrubs from alpine grassland leaded to changes in grassland water use, thereby changing soil water storage. The results of this study will provide theoretical basis for improving the availability and sustainability of soil water, provide guidance for meadow management from ecohydrological processes on the northern Qinghai-Tibet Plateau.

Alpine meadow plants, which are adapted to humid and cold environments, are more sensitive to environmental factors such as drought and high temperatures. However, excluding species competition, the physiological responses of individual alpine meadow species to drought and heat stress remain unclear. In this study, four representative species of typical functional groups in an alpine meadow of the Qinghai-Tibet Plateau were selected as experimental materials. Heat (H1, H2), drought (D1, D2), and combined heat and drought stress (D1H1, D2H2) treatments were implemented to reveal the physiological characteristics’ response to a constant drought and heat environment. Our results showed that the leaf water content (LWC) of Kobresia humilis and Poa annua increased significantly under heat stress and the compound heat and drought stress (P<0.05). Additionally, the aboveground biomass (AGB) of Oxytropis ochrocephala and Saussurea pulchra decreased significantly under compound stress (P<0.05). The response patterns of the net photosynthetic rate (Pn) and transpiration rate (Tr) of K. humilis and P. annua under various stress treatments were similar; as were those of O. ochrocephala and S. pulchra. The stomatal conductance (Gs) variation in K. humilis, P. annua, O. ochrocephala, and S. pulchra were the same under three kinds of stress treatments. The photosynthetic characteristics were more sensitive to the effects of composite than of single factors. The drought × heat × species treatment had a significant influence on various indexes except on height and the belowground biomass (P<0.01). Within a certain range, daytime temperature (DT) promoted the height and increased the LWC of the plants, while it inhibited their AGB and intercellular CO2 concentration. The Pn, Tr, and Gs were more sensitive to soil moisture than to DT. Our results help improve understanding of the physiological response regularity of representative alpine meadow plant species to continuous drought and high temperature conditions.

The sharp rise in anthropogenic activities and climate change have caused the extensive degradation of grasslands worldwide, jeopardising ecosystem function and threatening human well-being. Toxic weeds have been constantly spreading in recent decades; indeed, their occurrence is considered to provide an early sign of land degeneration. Policy makers and scientific researchers often focus on the negative effects of toxic weeds, such as how they inhibit forage growth, kill livestock and cause economic losses. However, toxic weeds can have several potentially positive ecological impacts on grasslands, such as promoting soil and water conservation, improving nutrient cycling and biodiversity conservation, and protecting pastures from excessive damage by livestock. We reviewed the literature to detail the adaptive mechanisms underlying toxic weeds and to provide new insight into their roles in degraded grassland ecosystems. The findings highlight that the establishment of toxic weeds may provide a self-protective strategy of degenerated pastures that does not require special interventions. Consequently, policy makers, managers and other personnel responsible for managing grasslands need to take appropriate actions to assess the long-term trade-offs between the development of animal husbandry and the maintenance of ecological services provided by grasslands.