Increased grazing intensities induce differentiation of the relationships between functional traits and aboveground plant biomass in shrub- and grass-dominated community in desert steppe

Grazing disturbance plays a crucial role in regulating plant community structure and ecosystem function in drylands. However, few studies show that how grazing disturbance affects the relationships between functional traits and aboveground plant biomass (AGB). Here, we presented a comparative result from grazing experiment with three levels of grazing intensities (no grazing, moderate and heavy grazing) between shrub- and grass-dominated community in desert steppe, Inner Mongolia. We measured vegetation characteristics and plant traits (plant height, LT: leaf thickness, SLA: specific leaf area, LDMC: leaf dry matter content, LCC: leaf carbon content and LNC: leaf nitrogen content) in the two communities across 2 years (2017–2018). We used the linear regression analysis and the structural equation modeling (SEM) to examine how grazing affect the associations of AGB with plant traits. We found that grazing decreased vegetation cover, AGB and litter mass in two communities, and caused the differences in AGB among two communities. Heavy grazing eliminated the associations of AGB with SLA and LCC in shrub community, while led to their positive or negative associations in grass community. The SEM showed that grazing indirectly decreased AGB through its effect on LT in shrub community, and its effect on plant height in grass community. These results suggest that changes in leaf traits induced by heavy grazing can explain AGB in grass- rather than shrub-community, thereby possibly contributing to AGB differences between two communities. Indirect effects of increased grazing intensities on AGB in shrub or grass community are dependent on specific functional traits.