Plant biodiversity and consumers (herbivores, pathogens, and mutualists) are important mediators of energy and carbon fluxes in grassland ecosystems. Although the role of consumers and plant diversity in controlling peak-season biomass production has been characterized, knowledge of their roles in within-season variation of energy and carbon flux remains poorly understood. Here we measure variation in consumer and plant diversity control of plant biomass production throughout the growing season and their impact on plant biomass phenology (timing of maximum biomass). To do this, we analyzed 5 years of biweekly, non-destructive biomass measures in an experiment manipulating plant species richness and three consumer groups (foliar fungi, soil fungi, arthropods, or all groups via pesticides). We found that plant biomass differences between high diversity plots and monocultures were greatest early in the growing season, whereas the foliar fungicide and insecticide treatments increased biomass most late in the season. The impact of foliar fungi and arthropods on biomass production also varied with plant diversity, with the greatest effects of foliar fungicide in high diversity plots whereas insecticide impacts were greatest in monocultures. Finally, more diverse plots and plots containing foliar fungi reached maximum biomass earlier than monocultures and plots treated with foliar fungicide. Taken together, these results highlight the significant and interactive roles that biodiversity and consumers play in dynamically regulating the production of plant biomass through the growing season, controlling the flow of energy and carbon to support the microbial and animal communities that rely on grassland productivity.

For 8 years (2009 to 2016), we used a MSR5 multispectral radiometer (Cropscan, Inc., Rochester, MN, USA) to measure reflected radiation (reflectance) in all experimental plots. Measurements were taken every two weeks from April to August in a 2m²area above the vegetation canopy in the center of each plot. Normalized Difference Vegetation Index (NDVI) was derived from the red: near-infrared reflectance ratio (Running 1990)using 830mm (near-infrared) and 660mm (red) reflectance readings. NDVI values were calculated for each plot on each day of measurement resulting in 20,135 NDVI estimates across the entire study.