Global research on plant community response to nutrient enrichment has revealed significant effects of nutrient additions on productivity, species diversity/composition, and functional trait expressions. By 2100 nitrogen enrichment in the continental U.S. is expected to increase by 19%, with the Atlantic coast experiencing the largest deposition increase (28%). Here, we ask how continued (3 year) nutrient addition affects trait-based community structure and function in a nutrient limited, low-productivity coastal mesic grassland. We quantify community-level functional trait diversity and community-weighted functional trait expressions to inform mechanisms responsible for altered trait-based community structure and ecosystem function. We established fertilization plots in 2014 that consist of control (C), nitrogen (N), phosphorus (P), and nitrogen + phosphorus (NP) plots (10 g m-2 yr-1). In 2017 we collected biomass, a suite of functional trait metrics, and species abundance (used to calculate community weighted means) for each plot. We tested for differences in biomass production, trait-based community structure, community-level functional diversity, and community-weighted functional trait expressions among treatments.
Results/Conclusions
A synergistic nutrient co-limitation affected biomass, NP treated plots had higher biomass production than either N or P did individually. Nutrient enrichment (N and NP) of low-productivity coastal systems results in biomass increase 4-6 times that of global averages. Trait-based community composition was altered by N and NP treatments, while functional alpha-diversity was only affected by NP treatments. Increased functional alpha-diversity highlights limiting trait similarity as a mechanism for species co-existence in high productivity plots (NP). Multivariate trait analysis indicated trait-based community structure is influenced by plant height, δ15N, %C, and %N, while our community-weighted univariate analysis identify plant height and δ15N as traits affected most by nutrient enrichment. These results show multivariate trait combinations are a key to understanding trait-based composition in response to nutrient enrichment. However, analysis of individual traits shows that traits we expected to change given previous research (SLA and %N), remain conserved in our system. Height exhibits a unified response to nutrient enrichment. In low-productivity coastal systems, coupling of biomass increases and altered trait-based plant community composition is expected, driven by release from environmental filters with nutrient enrichment. However, all trait responses may not be unified with global patterns due to localized vulnerability to stress.