Synthesis of nitrogen fertilization experiments in North America - plant species relative abundance

Nitrogen (N) is a limiting nutrient to plant growth in many ecosystems, and human-caused N enrichment has the potential to fundamentally alter the structure and functioning of plant communities. Nutrient limitation of primary production has been of interest to ecologists for many years, as a result there are many fertilization experiments in diverse community types. A group of Long Term Ecological Research (LTER) network researchers founded PDT-Net (Productivity, Diversity &Traits Network), to synthesize datasets from fertilization experiments in herbaceous communities across North America. Although responses to N addition were highly variable, several clear patterns emerged. We found that N addition increased productivity, reduced plant species diversity, and that plant species with particular functional traits (e.g. N-fixation ability, native and annual species) declined with fertilization, while others increased in dominance. Differences among responses of particular species common to several sites, as well as responses of species diversity in general, could be explained by differences in environmental context across sites. Finally, we found that fertilization altered community structure, by altering the distribution of species rank abundances, and by creating greater spatial heterogeneity. The dataset archived here contains relative abundances by species for ten sites (and many experiments within those sites) in control and fertilized plots. Species traits, productivity, and other environmental data are archived separately but link with this dataset.