Data from: Interactions among nutrients govern the global grassland biomass, precipitation relationship

Ecosystems are experiencing changing global patterns of mean annual
precipitation (MAP) and enrichment with multiple nutrients that
potentially co-limit plant biomass production. In grasslands, mean
aboveground plant biomass is closely related to MAP, but how this
relationship changes after enrichment with multiple nutrients remains
unclear. We hypothesized the global biomass-MAP relationship becomes
steeper with an increasing number of added nutrients, with increases in
steepness corresponding to the form of interaction among added nutrients
and with increased mediation by changes in plant community diversity. We
measured aboveground plant biomass production and species diversity in 71
grasslands on six continents representing the global span of grassland
MAP, diversity, management, and soils. We fertilized all sites with
nitrogen, phosphorus, and potassium with micronutrients in all
combinations to identify which nutrients limited biomass at each site. As
hypothesized, fertilizing with one, two, or three nutrients progressively
steepened the global biomass-MAP relationship. The magnitude of the
increase in steepness corresponded to whether sites were not limited by
nitrogen or phosphorus, were limited by either one, or were co-limited by
both in additive, or synergistic forms. Unexpectedly, we found little
evidence for mediation of biomass–MAP relationships by plant community
diversity because relationships of species richness, evenness and beta
diversity to MAP and to biomass were weak or opposing. Site-level
properties including baseline biomass production, soils, and management
explained little variation in biomass-MAP relationships. These findings
reveal multiple nutrient co-limitation as a defining feature of the global
grassland biomass-MAP relationship.