Abstract:
Plant stoichiometry, the relative concentration of elements, is a key regulator of ecosystem
functioning and is also being altered by human activities. In this paper we sought to understand
the global drivers of plant stoichiometry and compare the relative contribution of climatic vs. anthropogenic
effects. We addressed this goal by measuring plant elemental (C, N, P and K) responses to
eutrophication and vertebrate herbivore exclusion at eighteen sites on six continents. Across sites, climate
and atmospheric N deposition emerged as strong predictors of plot-level tissue nutrients, mediated
by biomass and plant chemistry. Within sites, fertilization increased total plant nutrient pools,
but results were contingent on soil fertility and the proportion of grass biomass relative to other functional
types. Total plant nutrient pools diverged strongly in response to herbivore exclusion when fertilized;
responses were largest in ungrazed plots at low rainfall, whereas herbivore grazing dampened
the plant community nutrient responses to fertilization. Our study highlights (1) the importance of climate
in determining plant nutrient concentrations mediated through effects on plant biomass, (2) that
eutrophication affects grassland nutrient pools via both soil and atmospheric pathways and (3) that
interactions among soils, herbivores and eutrophication drive plant nutrient responses at small scales,
especially at water-limited sites.
