N enrichment, increased precipitation, and the effect of shrubs collectively shape the plant community in a desert ecosystem in northern China

Plant functional traits and biodiversity can reveal the response of ecosystem functions to grazing

Plant functional traits can elucidate the response of plant communities and ecosystems to biotic and abiotic disturbances. However, whether livestock consume more aboveground biomass (AGB) in communities dominated by species with 'acquisitive' traits or in communities where biodiversity is high is not well known. Here, we measured 22 functional traits of the grazing communities and control communities in a Mongolian Plateau desert steppe. The effects of grazing on AGB, CWM traits, species diversity, and functional diversity (FD) were analysed, furthermore, we estimated the grazing impact by using the log response ratio (LRR, an increasing value shows a higher grazing impact) and investigated the correlations between the LRR, plant growth, and community-weighted mean (CWM) traits and diversity indices. We found that grazing significantly increased the CWM dry matter content and carbon-to‑nitrogen ratio and decreased the CWM height, specific leaf area (SLA), and nitrogen and phosphorus contents. The AGB decreased, while species diversity and FD increased under grazing treatments. Additionally, we found that plant traits and biodiversity could predict the response of AGB to grazing, the LRR was higher in patches dominated by species with 'acquisitive' foliage and in patches with higher biodiversity; in these patches, plant growth was lower. In the study area, the response of CWM traits to grazing suggests an avoidance strategy, which may be more conducive for adapting to low resource utilization environments. Also, the relationship between the CWM traits and the LRR indicated that the effect of grazing on AGB was mainly related to the selective foraging of herbivores. In addition, patches preferred by livestock may not recover quickly, leading to slow growth and thus reduced biomass under grazing treatments after prolonged grazing.

C:N:P stoichiometry in plant, soil and microbe in Sophora moorcroftiana shrubs across three sandy dune types in the middle reaches of the Yarlung Zangbo River

The alpine sandy dune ecosystem is highly vulnerable to global climate change. Ecological stoichiometry in plants and soils plays a crucial role in biogeochemical cycles, energy flow and functioning in ecosystems. The alpine sandy dune ecosystem is highly vulnerable to global climate change. However, the stoichiometric changes and correlations of plants and soils among different types of sandy dunes have not been fully explored. Three sandy dune types (moving dune, MD; semifixed dune, SFD; and fixed dune, FD) of the Sophora moorcroftiana shrub in the middle reaches of the Yarlung Zangbo River were used as the subjects in the current study. Plant community characteristics, soil physicochemical properties, carbon (C), nitrogen (N), and phosphorus (P) contents of leaves, understorey herbs, litter, and soil microbes were evaluated to explore the C:N:P stoichiometry and its driving factors. Sandy dune type significant affected on the C:N:P stoichiometry in plants and soils. High soil N:P ratio was observed in FD and high plant C:P and N:P ratios in SFD and MD. The C:N ratio decreased with sand dune stabilization compared with other stoichiometric ratios of soil resources. Leaf C:P and N:P ratios in S. moorcroftiana were higher than those in the understorey herb biomass, because of the low P concentrations in leaves. C, N and P contents and stoichiometry of leaves, understorey herbs, litter and microbe were significantly correlated with the soil C, N and P contents and stoichiometry, with a higher correlation for soil N:P ratio. P was the mainly limiting factor for the growth of S. moorcroftiana population in the study area and its demand became increasingly critical with the increase in shrub age. The variation in the C:N:P stoichiometry in plants and soils was mainly modulated by the soil physicochemical properties, mainly for soil moisture, pH, available P and dissolved organic C. These findings provide key information on the nutrient stoichiometry patterns, element distribution and utilization strategies of C, N and P and as well as scrubland restoration and management in alpine valley sand ecosystems.