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.

Automated summary

Plant functional traits provide insights into the response of plant communities and ecosystems to disturbances. This study examined the impact of grazing on aboveground biomass (AGB), community-weighted mean (CWM) traits, species diversity, and functional diversity (FD) in a Mongolian Plateau desert steppe. Results showed that grazing increased CWM dry matter content and carbon-to-nitrogen ratio while decreasing CWM height, specific leaf area (SLA), and nitrogen and phosphorus contents. AGB decreased, but species diversity and FD increased under grazing treatments. Additionally, plant traits and biodiversity predicted the response of AGB to grazing, with patches dominated by species with 'acquisitive' foliage and higher biodiversity showing higher grazing impact. The study highlights the importance of considering plant traits and biodiversity in understanding the effects of grazing on ecosystem dynamics.