Grazing alters ecosystem multifunctionality via changes in taxonomic diversity and functional identity in temperate grassland, China

Abstract

Livestock grazing is the major land-use regime of grasslands, and affects ecosystem structure and functioning considerably. However, few studies have examined how grazing intensity impacts ecosystem multifunctionality (EMF) via biodiversity loss. We studied the responses of EMF to livestock grazing in a temperate grassland in Inner Mongolia, China. Four grazing intensities (i.e., no grazing (NG), light grazing (LG), moderate grazing (MG), and heavy grazing (HG)) were chosen based on the distance to the core zones, vegetation and soil indications of grazing, and suggestions from local guides. For each grazing intensity, three plots (10 m × 10 m) were placed randomly, and plants, soil, and four traits of the present species were sampled in three 1-m2 quadrats in each plot. We analyzed the responses of three biodiversity components (i.e., taxonomic diversity (TD), functional diversity (FD), and functional identity), multiple ecosystem functions (i.e., aboveground biomass, belowground biomass, soil water content, soil organic matter, soil total nitrogen, soil total phosphorus, soil available nitrogen, soil available phosphorus), and EMF (based on averaging approach and threshold-based approach) to different grazing intensities, and the relative importance of biodiversity components in regulating the effect of grazing intensity on EMF. Our results showed that the dominant species of the plant community shifted from slow-growing conservative traits to fast-growing acquisitive traits as grazing intensified, accompanied by a decline in Stipa baicalensis (the predominant native grass in NG), whereas Carex duriuscula became the dominant species in HG sites. TD, FD, EMF, as well as six of eight individual ecosystem functions, displayed a significant decrease trend along the grazing intensity gradient. According to Bayesian structural equation models (SEM), EMF was mainly driven by the indirect effects of grazing through TD reduction (direct effects: 0.45) and changes in functional identity (direct effects: − 0.67), but the direct effect of grazing was not significant. By using the threshold-based approach, we found TD, FD, and CWM have a prominent impact on the number of functions exceeding a threshold level of 63 %, 64 %, and 65 %, respectively. When the threshold increased to 90 %, the explanation of the SEM decreased to 41 %, and no significant direct and indirect effects of grazing on EMF were found. Our results highlighted the vital role of biodiversity in mediating the response of EMF to grazing and shed light on grassland biodiversity conservation and sustainability.