Seven years of chronic fertilization affects how plant functional types respond to drought, but not plant production.

Abstract

Nitrogen deposition continues to change grassland plant community composition particularly in more mesic systems; however, whether these altered plant communities will respond differently to other global change factors remains to be seen. Here, we explore how nutrient-altered tallgrass prairie responds to drought. Seven years of nutrient treatments (control, nitrogen (N), phosphorus (P), and N + P) resulted in significantly different plant communities. Within this experimental context we imposed a 3-year drought followed by 3 years of recovery from drought. The response of plant functional types depended on the nutrient treatment. During recovery years, C₄ grasses recovered in the first year in all treatments but the N + P treatment, where instead annual grasses increased. These differential responses during recovery resulted in greater shifts in community composition in the N + P treatment compared with the controls. Despite the effects on community composition, we found no interaction between nutrient treatment and drought treatment on species richness or evenness and standing biomass during drought or recovery. We found drought induced shifts in plant functional groups led to the composition of previously droughted N + P plot becoming more dominated by annual grasses during the recovery years, likely creating a lasting legacy of drought.