Plant height bridges hierarchical community responses to nitrogen enrichment

Abstract

Abstract Nitrogen enrichment impacts ecosystems productivity by altering different hierarchical community processes, ranging from responses of individual species traits to species reordering and ultimately species turnover. Most previous studies have focussed on examining the responses of these processes separately, but little has been done to examine how hierarchical community responses are linked and contribute to the changes in productivity. To fill this knowledge gap, we conducted a 4‐year nitrogen addition field experiment to investigate the hierarchical community responses of above‐ground net primary productivity (ANPP) in an alpine meadow ecosystem. We found that the individual species response contributed more to ANPP changes under nitrogen addition, while species reordering and species turnover contributed little over the 4‐year experiment. In particular, plant height was a key trait to ultimately explain and bridge nitrogen addition effects on ANPP across different community levels. Nitrogen addition promoted plant height and growth of individual species, and reordered functional groups by increasing taller grasses and sedges and decreasing shorter forbs and legumes. Species turnover had a weak effect on ANPP changes due to low biomass of both lost and gained species. Finally, taller persistent plants promoted ANPP more with nitrogen addition. Synthesis. This study provides a new perspective on how ecosystem productivity responds to nitrogen enrichment in a hierarchical manner linked to plant height, which is helpful for elucidating complex community processes and establishing direct links between plant traits and ecosystem function.