Biodiversity promotes ecosystem productivity and stability, a positive impact that often strengthens over time. But ongoing global changes such as rising atmospheric carbon dioxide (CO2) levels and anthropogenic nitrogen (N) deposition may modulate the impact of biodiversity on ecosystem productivity and stability over multiple decades. Using a multidecadal grassland biodiversity-global change experiment we show that diversity increasingly enhanced productivity over time irrespective of global change treatments. In contrast, the positive influence of diversity on ecosystem stability strengthened over time under ambient conditions but weakened to varying degrees under global change treatments, largely driven by a greater reduction in species asynchrony under global changes. Thus, over multiple decades, CO2 and nitrogen enrichment can gradually erode the positive effects of biodiversity on ecosystem stability. As elevated CO2, N eutrophication, and biodiversity loss increasingly co-occur in grasslands globally, our results raise concerns about their potential joint detrimental effects on long-term grassland stability.

Substantial evidence suggests plants and herbivores are limited by multiple resources but their role in driving plant-herbivore interactions is still poorly understood. Here we model multiple resource limitation of plants and herbivores and derive analytical solutions for steady-state plant biomass, herbivore biomass and herbivore impact. The model predicts “apparent” limitation of herbivore biomass by resources that otherwise do not limit herbivore growth. Consequently, higher supply of plant-growth limiting resources allows herbivores to persist at lower supplies of herbivore growth-limiting resources. Likewise, increased supply of these non-limiting resources to herbivores can dramatically increase herbivore impacts on plants. Additionally, the outcomes of herbivore exclusion experiments should differ along different resource gradients, depending on herbivore response to plant resource concentrations. Analysis of existing and new data from marine, freshwater and terrestrial systems supports several of these predictions. Our analysis expands ecologists’ understanding of plant-herbivore dynamics to accommodate multiple limiting resources.