Data from nutrients and herbivores impact grassland stability across spatial scales through different pathways

Nutrients and herbivores are well-known drivers of grassland diversity and stability in local communities. However, whether they interact to impact the stability of aboveground biomass and whether these effects depend on spatial scales remain unknown. It is also unclear whether nutrients and herbivores impact stability via different facets of plant diversity including species richness, evenness, and changes in community composition through time and space. We used a replicated experiment adding nutrients and excluding herbivores for 5 years in 34 global grasslands to explore these questions. We found that both nutrient addition and herbivore exclusion alone reduced stability at the larger spatial scale (aggregated local communities; gamma stability), but through different pathways. Nutrient addition reduced gamma stability primarily by increasing changes in local community composition over time, which was mainly driven by species replacement. Herbivore exclusion reduced gamma stability primarily by decreasing asynchronous dynamics among local communities (spatial asynchrony). Their interaction weakly increased gamma stability by increasing spatial asynchrony. Our findings indicate that disentangling the processes operating at different spatial scales may improve conservation and management aiming at maintaining the ability of ecosystems to reliably provide functions and services for humanity.养分与草食动物是学界公认的当地草原群落多样性与稳定性驱动因子。然而，二者是否可通过交互作用影响地上生物量稳定性，以及其效应是否依赖空间尺度，目前仍未明确。此外，学界尚不清楚养分与草食动物是否会通过植物多样性的不同维度（包括物种丰富度、均匀度，以及群落组成随时间与空间的变化）来调控群落稳定性。本研究依托一项在全球34处草原开展的为期5年的重复野外控制实验展开，实验设置了养分添加与草食动物排除两种处理，旨在解答上述科学问题。研究结果显示，单独施加养分添加与单独排除草食动物，均会降低大空间尺度下的群落稳定性（即聚合局部群落得到的γ稳定性（gamma stability）），但二者的作用路径存在显著差异。其中，养分添加主要通过加剧群落组成随时间的变化来降低γ稳定性，而该变化主要由物种更替驱动。草食动物排除则主要通过降低局部群落间的异步动态（空间异步性（spatial asynchrony））来降低γ稳定性。二者的交互作用可通过提升空间异步性，微弱提高γ稳定性。本研究表明，厘清不同空间尺度下的生态过程，可为旨在维持生态系统稳定持续为人类提供功能与服务的保护与管理实践提供理论依据。