Livestock grazing strongly affects biodiversity and ecosystem functioning in grasslands. However, it remains unclear how different grazing impact multiple biodiversity, ecosystem multifunctionality (EMF), and their relationship with the interactions of grazing duration, livestock type and climatic factors. Here, we conducted a global synthesis from 104 published studies. Our results showed that light and moderate grazing improved multi-diversity, but heavy grazing significantly decreased multi-diversity and EMF. The grazing-induced decrease of EMF intensified with grazing duration, and the reduction of multi-diversity and EMF under intensive grazing was stronger in more arid climates. The response of EMF increased linearly with that of multi-diversity under all grazing intensities. Moreover, grazing intensity reduced EMF largely via decreasing multi-diversity, whereas a shift of livestock type from small to large size promoted EMF by increasing multi-diversity. This study provides first empirical evidence and new insights into the relationship between multi-diversity and EMF under grazing in global grasslands.
Soil carbon plays an important role in mediating global climate change and securing food production. Despite rapid declines in plant diversity worldwide, uncertainties remain concerning the relationships between tree diversity and soil carbon stock in natural forests, as well as the climatic factors that drive their directions and magnitudes. Using Canada's National Forest Inventory data, we tested the relationships between soil carbon stocks to tree functional diversity and identity, and how these relationships varied with stand age and climate gradients in the organic horizon, mineral horizon and entire soil profile. We found that the effects of functional diversity on soil carbon stocks were highly climate-dependent, shifting from negative in warm or moist climates to positive or null in cold and dry climates. In addition, tree species with acquisitive traits, such as high specific leaf area, leaf nitrogen content and phosphorus content, increased mineral soil carbon stocks in warmer sites, but decreased those in colder sites. Our results suggest that tree diversity effects on soil carbon are strongly dependent on climate context and promoting high functional diversity is important to increase soil carbon stocks of colder and drier sites in boreal and temperate forests.
Growing evidence has revealed that ecosystem productivity depends more on the functional characteristics of species than on their number. However, just how the extent of tree diversity effects on ecosystem productivity is influenced by functional trait variability and composition has been rarely tested across and within species richness levels. Employing a meta-analysis of data from 59 global scale tree diversity experiments, we examined how functional dispersion and identity determine the outcomes of tree mixture effects on productivity, both across and at given species richness levels. We found that the positive effects of tree mixtures on productivity were strengthened by the increasing multidimensional functional dispersion and the community-weighted mean of leaf nitrogen content both across, and within, two- and four-species mixtures. Our analysis provides mechanistic insights into the potent roles of functional trait attributes in determining the magnitude (and even directionality) of the biodiversity-ecosystem functioning relationship in forest ecosystems.
Fine root traits are critical to the plant's capacity and efficiency to uptake water and nutrients. Although plant diversity is decreasing, our understanding of its effects on fine root traits remains elusive. By synthesizing 103 studies, we found that the effects of plant mixtures were highly dependent on species richness in mixtures, stand age, and soil depth. The positive mixture effects on root biomass increased with species richness, soil depth, and mean annual temperature. Plant mixture effects on root length density shifted from negative to positive, from young to older stands, topsoil to deep soils, and warm to cold climates. The mixture effects on specific root length shifted from positive to negative, from two to higher number species mixtures and topsoil to deep soils, and then negative to positive with increasing stand age. Our results demonstrate the profound plasticity of root traits in response to productivity dynamics in plant mixtures.