Stoichiometric response of nitrogen-Wxing and non-Wxing dicots to manipulations of CO2, nitrogen, and diversity

Human activities have resulted in increased nitrogen deposition and atmospheric CO2 concentrations in the biosphere, potentially causing signiWcant changes in many ecological processes. In addition to these ongoing perturbations of the abiotic environment, human-induced losses of biodiversity are also of major concern and may interact in important ways with biogeochemical perturbations to aVect ecosystem structure and function. We have evaluated the eVects of these perturbations on plant biomass stoichiometric composition (C:N:P ratios) within the framework of the BioCON experimental setup (biodiversity, CO2, N) conducted at the Cedar Creek Natural History Area, Minnesota. Here we present data for Wve plant species: Solidago rigida, Achillea millefolium, Amorpha canescens, Lespedeza capitata, and Lupinus perennis. We found signiWcantly higher C:N and C:P ratios under elevated CO2 treatments, but species responded idiosyncratically to the treatment. Nitrogen addition decreased C:N ratios, but this response was greater in the ambient CO2 treatments than under elevated CO2. Higher plant species diversity generally lowered both C:N and C:P ratios. Importantly, increased diversity also led to a more modest increase in the C:N ratio with elevated CO2 levels. In addition, legumes exhibited lower C:N and higher C:P and N:P ratios than nonlegumes, highlighting the eVect of physiological characteristics deWning plant functional types. These data suggest that atmospheric CO2 levels, N availability, and plant species diversity interact to aVect both aboveground and belowground processes by altering plant elemental composition.