Nutrient Inputs and Hydrology Interact with Plant Functional Type in Affecting Plant Production and Nutrient Contents in a Wet Grassland

We studied the effect of nutrient additions and hydrology on the above-ground production and shoot nutrient contents of representative species of the conservative (Carex acuta) and competitive (Glyceria maxima) plant functional types in a minerotrophic wet grassland. Above-ground samples were collected in May, late June (time of maximum biomass) and August (re-growth following cutting) from plots subjected to nutrient addition treatments in years with differing hydrology, ranging from drought to prolonged flooding. Net above-ground primary production (NAPP) and shoot nutrient contents (C, N, P) were determined separately for C. acuta and G. maxima. Between-year and species differences were analyzed by repeated measures ANOVA and generalized linear mixed models (GLMM). NAPP decreased with hydrologic stress with the proportion due to C. acuta increasing with flooding, while G. maxima responded positively to nutrient additions. As expected, C% was greater, but N and P% were lower, in C. acuta shoots compared to G. maxima. Hydrology affected above-ground production and shoot nutrient contents more than nutrients, but both interacted with plant functional type, with likely impacts on ecosystem processes. Future studies must consider multiple factors to predict the effect of climate and management changes on wetlands.