Seasonal shifts from plant diversity to consumer control of grassland productivity

Plant biodiversity and consumers are important mediators of energy and carbon fluxes in grasslands, but their effects on within‐season variation of plant biomass production are poorly understood. Here we measure variation in control of plant biomass by consumers and plant diversity throughout the growing season and their impact on plant biomass phenology. To do this, we analysed 5 years of biweekly biomass measures (NDVI) in an experiment manipulating plant species richness and three consumer groups (foliar fungi, soil fungi and arthropods). Positive plant diversity effects on biomass were greatest early in the growing season, whereas the foliar fungicide and insecticide treatments increased biomass most late in the season. Additionally, diverse plots and plots containing foliar fungi reached maximum biomass almost a month earlier than monocultures and plots treated with foliar fungicide, demonstrating the dynamic and interactive roles that biodiversity and consumers play in regulating biomass production through the growing season. Evidence of plant diversity controls on biomass have historically relied on single time point measurements within the growing season and rarely account for consumer effects on plant biomass. Consequently, we know very little about within‐season variation in these biotic controls. Here, in a grassland diversity and consumer removal experiment, we found that both plant diversity and consumer controls on plant productivity shift in magnitude across the growing season, and diversity and consumers alter the timing of peak grassland biomass. This study offers new evidence that loss of consumer and plant diversity is having previously undocumented impacts on the productivity of terrestrial ecosystems.