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Abstract Plant damage by invertebrate herbivores and pathogens influences the dynamics of grassland ecosystems, but anthropogenic changes in nitrogen and phosphorus availability can modify these relationships.Using a globally distributed experiment, we describe leaf damage on 153 plant taxa from 27 grasslands worldwide, under ambient conditions and with experimentally elevated nitrogen and phosphorus.Invertebrate damage significantly increased with nitrogen addition, especially in grasses and non‐leguminous forbs. Pathogen damage increased with nitrogen in grasses and legumes but not forbs. Effects of phosphorus were generally weaker. Damage was higher in grasslands with more precipitation, but climatic conditions did not change effects of nutrients on leaf damage. On average, invertebrate damage was relatively higher on legumes and pathogen damage was relatively higher on grasses. Community‐weighted mean damage reflected these functional group patterns, with no effects of N on community‐weighted pathogen damage (due to opposing responses of grasses and forbs) but stronger effects of N on community‐weighted invertebrate damage (due to consistent responses of grasses and forbs).Synthesis. As human‐induced inputs of nitrogen and phosphorus continue to increase, understanding their impacts on invertebrate and pathogen damage becomes increasingly important. Our results demonstrate that eutrophication frequently increases plant damage and that damage increases with precipitation across a wide array of grasslands. Invertebrate and pathogen damage in grasslands is likely to increase in the future, with potential consequences for plant, invertebrate and pathogen communities, as well as the transfer of energy and nutrients across trophic levels.
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How and why plant ionomes vary across North American grasslands and its implications for herbivore abundance
Abstract Plant elemental content can vary up to 1,000‐fold across grasslands, with implications for the herbivores the plants feed. We contrast the regulation, in grasses and forbs, of 12 elements essential to plants and animals (henceforth plant‐essential), 7 essential to animals but not plants (animal‐essential) and 6 with no known metabolic function (nonessential). Four hypotheses accounted for up to two thirds of the variation in grass and forb ionomes across 54 North American grasslands. Consistent with the supply‐side hypothesis, the plant‐essential ionome of both forbs and grasses tracked soil availability. Grass ionomes were more likely to harvest even nonessential elements like Cd and Sr. Consistent with the grazing hypothesis, cattle‐grazed grasslands also accumulated a handful of metals like Cu and Cr. Consistent with the NP‐catalysis hypothesis, increases in the macronutrients N and P in grasses were associated with higher densities of cofactors like Zn and Cu. The plant‐essential elements of forbs, in contrast, consistently varied as per the nutrient‐dilution hypothesis—there was a decrease in elemental parts per million with increasing local carbohydrate production. Combined, these data fit a working hypothesis that grasses maintain lower elemental densities and survive on nutrient‐poor patches by opportunistically harvesting soil nutrients. In contrast, nutrient‐rich forbs use episodes of high precipitation and temperature to build new carbohydrate biomass, raising leaves higher to compete for light, but diluting the nutrient content in every bite of tissue. Herbivores of forbs may thus be particularly prone to increases inpCO2via nutrient dilution.
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- Award ID(s):
- 2025849
- PAR ID:
- 10443846
- Publisher / Repository:
- Wiley Blackwell (John Wiley & Sons)
- Date Published:
- Journal Name:
- Ecology
- Volume:
- 102
- Issue:
- 10
- ISSN:
- 0012-9658
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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