Effects of grazing on leaf traits and ecosystem functioning in Inner Mongolia grasslands: scaling from species to community

摘要

Understanding the mechanistic links between environmental drivers, humandisturbance, plant functional traits, and ecosystem properties is afundamental aspect of biodiversity-ecosystem functioning research. Recentstudies have focused mostly on leaf-level traits or community-level weightedtraits to predict species responses to grazing and the consequent change inecosystem functioning. However, studies of leaf-level traits orcommunity-level weighted traits seldom identify the mechanisms linkinggrazing impact on leaf traits to ecosystem functioning. Here, using amulti-organization-level approach, we examined the effects of grazing onleaf traits (i.e., leaf area, leaf dry mass and specific leaf area) andecosystem functioning across six communities of three vegetation types alonga soil moisture gradient in the Xilin River Basin of Inner Mongoliagrassland, China. Our results showed that the effects of grazing on leaftraits differed substantially when scaling up from leaf-level to species,functional group (i.e., life forms and water ecotype types), and communitylevels; and they also varied with vegetation type or site conditions. Theeffects of grazing on leaf traits diminished progressively along thehierarchy of organizational levels in the meadow, whereas the impacts werepredominantly negative and the magnitude of the effects increasedconsiderably at higher organizational levels in the typical steppe. Soilwater and nutrient availability, functional trade-offs between leaf size andnumber of leaves per individual, and differentiation in avoidance andtolerance strategies among coexisting species are likely to be responsible for theobserved responses of leaf traits to grazing at different levels oforganization and among vegetation types. Our findings also demonstrate that,at both the functional group and community levels, standing abovegroundbiomass increased with leaf area and specific leaf area. Compared with thelarge changes in leaf traits and standing aboveground biomass, the soilproperties were relatively unaffected by grazing. Our study indicates that amulti-organization-level approach provides more robust and comprehensivepredictions of the effects of grazing on leaf traits and ecosystemfunctioning.