Spatiotemporal dependency of resource use efficiency on phytoplankton diversity in Lake Taihu

Abstract The dependency of resource use efficiency (RUE) on phytoplankton diversity is key for understanding aquatic ecosystem responses to eutrophication and climate change. Here, we studied RUE of nitrogen (RUE N ), phosphorous (RUE P ), or silicate (RUE Si ) and the associated abiotic and biotic explanatory variables in 3,016 samples collected from 30 sites in Lake Taihu during 2005‐2017, covering cyanobacteria‐ and macrophyte‐dominated regions. We further examined spatiotemporal dependencies of RUE on phytoplankton taxonomic and functional diversity and their underlying drivers. The annual mean RUE si of each site exhibited an overall increasing temporal trend, while that of RUE N and RUE P displayed U‐shaped patterns over the study period. RUE was affected by nutrients and water temperature, and also was related to phytoplankton diversity in terms of Shannon diversity and functional dispersion diversity. Interestingly, RUE showed negative spatial dependencies on phytoplankton diversity. These negative spatial dependencies had decreasing temporal trends for RUE N and RUE Si , while a hump‐shaped pattern for RUE P . The dependencies were generally related to spatial environmental mean of nutrients, such as nitrate and total phosphorus. Furthermore, RUE showed negative temporal dependencies on phytoplankton diversity mainly in the cyanobacteria‐dominated region, while it was occasionally positive in the macrophyte‐dominated region. These temporal dependencies were driven primarily by temporal environmental stability of nutrients, such as dissolved total nitrogen. Collectively, the direction and strength of spatiotemporal dependencies of RUE on phytoplankton diversity were influenced by nutrient status and stability. These findings can be considered in future environmental management plans for long‐term sustainability of ecosystem functioning under global climate change.