Functional and Taxonomic Diversity is Associated With Resource Use Efficiency in Epilithic Algae of Subtropical Qinhuai River, China

ABSTRACT The effects of biodiversity on ecosystem functioning comprise a central ecological theorem (BEF), because more diverse communities are expected to perform better, for example, in terms of resource use efficiency (RUE). Although biodiversity affects ecosystem functioning, it is seriously constrained by global environmental change. Epilithic algae are a crucial benthic functional group in aquatic food webs, but the effect of their biodiversity on ecosystem functioning is yet to be understood. Here, we compared the capacity of taxonomic versus functional richness and evenness to predict RUE in a dataset on epilithic algae from the Qinhuai River, Nanjing, China. We examined associations between environmental variables and taxonomic and functional diversity (response and ecological indication), and assessed whether taxonomic and functional diversity measures predicted RUE (quantified as total algal biomass standardised by total phosphorus (RUE TP ), and total nitrogen (RUE TN )). Taxonomic and functional diversity varied more across seasons than space, peaking in spring and summer in association with pronounced environmental changes. Water temperature and nutrient concentrations positively and significantly predicted taxonomic and functional diversity measures. Taxonomic and functional richness positively associated with RUE, while functional evenness negatively associated. However, taxonomic evenness was not related to RUE. Structural equation modelling showed that taxonomic and functional diversity were positively associated with RUE TP and RUE TN . However, taxonomic diversity was more strongly predictive of RUE than functional diversity. Our results suggest that RUE is closely linked to species diversity, and functional diversity provides a complementary approach for better understanding of mechanisms underlying the BEF relationship for benthic algae in large rivers. We suggest using taxonomic and functional approaches in a complementary way to gain a deeper understanding of the interplay among environmental factors, community diversity and ecosystem functioning.