Data from: Herbivory and eutrophication mediate grassland plant nutrient responses across a global climatic gradient

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.

植物化学计量学（Plant stoichiometry）指植物体内各元素的相对浓度，是调控生态系统功能的关键因子，同时其格局也正受到人类活动的显著改变。本研究旨在解析全球尺度下植物化学计量学的驱动因子，并对比气候因素与人为活动影响的相对贡献。为达成该研究目标，我们在六大洲的18个野外样地开展控制实验，测定了植物元素（碳C、氮N、磷P和钾K）对富营养化（eutrophication）及脊椎动物食草动物排除（vertebrate herbivore exclusion）处理的响应。跨样地尺度的分析结果显示，气候与大气氮沉降是调控样方水平植物组织养分含量的强预测因子，其作用由植物生物量与植物化学组成介导。在单个样地内部，施肥处理显著提升了植物总养分库，但实验结果受土壤肥力以及草本生物量相对于其他植物功能群的占比所调控。当样地施加施肥处理时，排除食草动物会使植物总养分库出现显著分化：在低降雨的水分受限生境中，未遭受啃食的样地响应幅度最大；而食草动物的啃食行为会显著削弱植物群落对施肥处理的养分响应。本研究明确了三项核心结论：（1）气候通过调控植物生物量进而决定植物养分浓度的重要作用；（2）富营养化可通过土壤与大气双重途径影响草地生态系统的养分库；（3）土壤、食草动物与富营养化之间的交互作用，在小尺度上主导了植物养分响应，尤其是在水分受限生境中。