Can the response of above- and below-ground traits to overgrazing vary between annual and perennial species?

Abstract

Understanding functional traits that capture species response to grazing is crucial for uncovering mechanisms underlying the grazing-induced alterations in vegetation composition. Currently, the majority of studies ignore the effects of life form on the response of above- and below-ground traits to grazing. In this study we quantified i) whether below-ground traits exhibit similar response to overgrazing as do above-ground traits; and ii) whether the response of above- and below-ground traits to overgrazing varied with life form (annual versus perennial species). To testify the generality of these two questions, we compared common grassland species between an undisturbed and an over grazed meadow at each of four elevations ranging from 3000m to 3600m on the Qinghai Tibetan Plateau. We found both above-ground and below-ground traits exhibited similar resource conservation vs. resource acquisition trade-off for responding to overgrazing. Moreover, perennial species but not annual species determine the response of above- and below-ground traits to overgrazing. This work bridges the gap in the literature for the influence of land-use (in the absence and presence of overgrazing) and life forms (annual and perennial species) on species-specific response at both above-, and below-ground level.