Dissolved organic carbon and microplastics decrease the biodiversity effect on resource use efficiency of crustacean zooplankton

The relationship between biodiversity and ecosystem functioning has always been the focus of attention in ecology. Although many studies have indicated positive effects of species and functional diversity on ecosystem functioning, our understanding of how the relationships are altered in the face of environmental changes remains limited. In recent years, human activities such as urbanization have led to a significant influx of dissolved organic carbon (DOC) and microplastics into lake ecosystems, which altered the lake's water quality and ecosystem services. Here, by conducting a two-month mesocosm experiment, we found that increasing DOC concentration generally increased the crustacean zooplankton taxonomic species richness, functional richness, resource use efficiency (RUE) and body size. In addition, we found that species richness, functional richness and body size have a positive relationship with zooplankton RUE, indicating higher biodiversity and larger body size are essential for maintaining high ecosystem functions. More importantly, we found that increasing the pressure of DOC and microplastic reduced the biodiversity effect on trophic transfer efficiency, especially for the relationship between functional richness and zooplankton RUE. Our results suggested that biodiversity effects on ecosystem functioning could be probably reduced in the current global environment change context, indicating that we may underestimate the negative impact of diversity loss on ecosystem functions and services. Therefore, more efforts are needed to conserve biodiversity and to maintain the valuable services that the ecosystem provides.