Plant community re-organization and increased productivity due to multi-year nutrient enrichment of a coastal grassland

Abstract

Nutrient enrichment alters plant community structure and function at a global scale. Coastal plant systems are expected to experience increased rates of nitrogen and phosphorus deposition by 2100, caused mostly by anthropogenic activity. Despite high density of studies investigating connections between plant community structure and ecosystem function in response to nutrient addition, inconsistencies in system response based on the ecosystem in question calls for more detailed analyses of nutrient impacts on community organization and resulting productivity response. Here, we focus on nutrient addition impacts on community structure and organization as well as productivity of different lifeforms in a coastal grassland. We established long-term nutrient enrichment plots in 2015 consisting of control (C), nitrogen (N), phosphorus (P), and nitrogen + phosphorus (NP) treatments. In 2017 we collected graminoid and forb productivity, root productivity, and community composition for each plot. We found no N x P interaction, but N enrichment was a significant main effect on productivity, highlighting N limitation in coastal systems. Importantly, nutrient enrichment treatments did not alter root productivity. However, all treatments caused significant differences in community composition. Using rank abundance curves, we determined that community composition differences were driven by increased dominance of nitrophilous graminoids, re-organization of subordinate species, and species absences in N and NP plots. Results of this study highlight how coastal grassland communities are impacted by nutrient enrichment. We show that community re-organization, increased dominance, and absence of critical species are all important mechanisms that reflect community-level impacts of nutrient enrichment in our coastal grassland site.

Competition model explains trends of long‐term fertilization in plant communities

“…Following Kempton's (1979) report that fertilization altered species composition and the shape of the RAD, many similar reports have emerged based on different systems (Avolio et al, 2019;Brown et al, 2022;Collins et al, 2008;Kirkham et al, 1996;Sand-Jensen et al, 2008). Trait-based research revealed that plant responses to fertilization were essential for the changes in community structure (Avolio et al, 2019;Brown & Zinnert, 2021;Dickson & Gross, 2013;La Pierre & Smith, 2015;Suding et al, 2005).…”

“…Avolio et al ( 2019 ) showed that species reordering in RAD explains community change observed in the long‐term fertilization experiments. Brown et al ( 2022 ) also studied species reordering in a coastal grassland community under multiyear nutrient enrichment, associated with changes in both plant traits and RADs. These studies suggest that fertilization of nutrient(s) causes responses of plants in trait expression, which drives reordering of species abundance, resulting in changes in community structure.…”

“…Why did not the improvement of nutrient conditions increase biomass in some systems? Thus, a relationship between fertilization and biomass change should be studied more deeply concerning the change in community structure (Brown et al, 2022 ).…”