Through fertilizer application and the combustion of fossil fuels, humans provide more nitrogen (N) to the Earth system than provided by natural processes, leading to the perception of N as a pollutant causing coastal eutrophication, low-oxygen dead zones, and impaired freshwater resources. However, recent environmental changes also include elevated atmospheric CO2 concentrations (eCO2), amounting to more than a 30% increase since 1960, largely driven by the combustion of fossil fuels. It has been widely expected and more recently observed that plant responses to eCO2 include an increase in leaf C:N ratios and decreased N concentration in plants, which is expected to slow the nitrogen cycle and feed back to reductions in N availability. This pursuit would synthesize global measurements of plant N concentration to produce the first global investigation of spatiotemporal trends. The resulting data base and analysis will be an important future resource for remote sensing and global studies of plant traits. In phase two of the project, we would evaluate the ecological consequences of declining N availability to plants. This will include an investigation of the spatial coherence of trends in leaf N concentration and patterns of global greening from remote sensing. Secondly, because herbivores depend on plant N for protein, individual weight gain, and population maintenance, we would apply models to estimate the impact of declining N concentration on grazing ruminants and insects. Through these activities, we will provide the first ever estimation of the global effects of eCO2 on the dietary quality of plants to herbivores.