Functional traits and responses to nutrient and mycorrhizal addition are inconsistently related to wetland plant species’ coefficients of conservatism

Floristic quality assessment (FQA) is a commonly used indicator system to evaluate the condition of wetlands. FQA metrics are based on coefficients of conservatism (C-values), numeric values assigned to plant species by expert botanists. C-values reflect a species’ fidelity to high quality natural areas and intolerance to human impacts. Although FQA metrics are widely used in wetland management, few studies have characterized the ecological traits associated with C-values. These few studies have found consistent relationships between functional traits and C-values. Moreover, some research also suggests that conservative species may benefit from arbuscular mycorrhizal fungi (AMF). We conducted a greenhouse experiment to characterize the functional and growth characteristics associated with C-values. We grew 42 species found in midwestern (USA) wetlands and measured nine functional traits of the study species, as well as their responses to AMF addition and nutrient addition treatments. We supplemented the greenhouse experiment with leaf functional trait data from 72 wetland species collected in the field. For the greenhouse experiment, we found weak negative associations between C-values and both height and total biomass, and a positive association between C-values and seed mass. However, in both the greenhouse experiment and the field-collected data, most functional traits did not significantly relate to C-values. AMF addition generally decreased biomass, whereas nutrient addition increased biomass. Response to AMF addition was not significantly related to C-values. Species with lower C-values were more responsive to nutrient treatments compared to those with higher C-values, though this relationship was due to nonnative species with C-values of 0. Our findings could reflect functional differences between dominant wetland matrix species with low C-values, especially nonnative species, and species that are smaller and more conservative. Our data indicate that C-values may not consistently or strongly correspond to functional traits and treatment responses.