Decades of empirical data have shown that anthropogenic nitrogen enrichment of soils tends to increase plant productivity but also reduces plant species richness in terrestrial communities. This means that some plant species grow more in response to nitrogen addition than others and suggests that the paradigm that plant productivity is primarily limited by nitrogen applies to the community level but does not extend to the species level. Because we currently lack the ability to predict which plants will persist (‘winners’) and which will be lost (‘losers’) in nitrogen enrichment scenarios, I use controlled greenhouse experiments, meta-analysis, and Bayesian modeling to explore the past evolutionary and current ecological mechanisms that lead to variation in the magnitude and direction of plant species growth responses to nitrogen enrichment.
Results/Conclusions
Plant phylogenies can be used as effective tools to predict plant species’ biomass responses to anthropogenic nitrogen enrichment from small (genus-level) to large (across terrestrial plants) phylogenetic scales. Although plant functional types (e.g. root type and life history) explain some variation in plant responses to nitrogen enrichment across terrestrial plants, specific functional traits do not predict plant responses to nitrogen enrichment within the group of Eucalyptus species that are native to Tasmania, Australia, as would be predicted by long-standing theory on the plant economic spectrum. Further, within the native Tasmanian eucalypts we show that phosphorus addition does not increase, and sometimes decreases, growth responses to nitrogen enrichment, contrary to the common perception that plants are limited by nitrogen and then phosphorus. Lastly, we found that native soil microorganisms can either enhance or reduce plant growth responses to nitrogen enrichment. Plant responses to nitrogen enrichment are complex, due to variable microbial mediation of responses, however phylogeny and interactions with soil fungi can enhance our ability to draw possible conclusions about winners and losers in natural anthropogenic nitrogen enrichment scenarios.