Seabloom, E. | Search bioRxiv

bioRxiv2026

Intra-annual precipitation variability mutes or magnifies the impact of wet and dry years on plant biomass.

As the atmosphere warms, both the amount and timing of precipitation are changing, but how those two trends interact to influence plant growth remains unresolved. Using 5-15 years of data from 48 globally distributed grassland sites, we quantified how the temporal distribution of precipitation within the year (evenness) interacts with annual precipitation amount and nutrient limitation to influence plant biomass. Annual precipitation anomalies had a large influence on plant biomass when intra-annual precipitation was more evenly distributed (frequent small events) and little impact when less even (infrequent large events). This relationship was consistent across aridity gradients and nutrient limitations and strongest in systems with warm wet seasons. Our work shows that the response of plant systems to changes in annual precipitation amount are largely dependent on how evenly it is temporally distributed.

ecology↗

bioRxiv2021

Multiple resource limitations explain biomass-precipitation relationships in grasslands

Interannual variability in grassland primary production is strongly driven by precipitation, nutrient availability and herbivory, but there is no general consensus on the mechanisms linking these variables. If grassland biomass is limited by the single most limiting resource at a given time, then we expect that nutrient addition will not affect biomass production at arid sites. We conducted a distributed experiment manipulating nutrients and herbivores at 44 grassland sites in 8 regions around the world, spanning a broad range in aridity. We estimated the effects of 5-11 years of nutrient addition and herbivore exclusion treatments on precipitation sensitivity of biomass (proportional change in biomass relative to proportional change in rainfall among years), and the biomass in the driest year (to measure treatment effects when water was most limiting) at each site. Grazer exclusion did not interact with nutrients to influence driest year biomass or sensitivity. Nutrient addition increased driest year biomass by 74% and sensitivity by 0.12 (proportional units), and that effect did not change across the range of aridity spanned by our sites. Grazer exclusion did not interact with nutrients to influence sensitivity or driest year biomass. At almost half of our sites, the previous year's rainfall explained as much variation in biomass as current year precipitation. Overall, our distributed fertilization experiment detected co-limitation between nutrients and water governing grasslands, with biomass sensitivity to precipitation being limited by nutrient availability irrespective of site aridity and herbivory. Our findings refute the classical ideas that grassland plant performance is limited by the single most limiting resource at a site. This suggests that nutrient eutrophication will destabilize grassland ecosystems through increased sensitivity to precipitation variation.

ecology↗