Increasing drying changes the relationship between biodiversity and ecosystem multifunctionality

Increased drying of rivers under global climate change is leading to biodiversity loss. However, it is not clear whether biodiversity loss affects river functions. In this study, we investigated the changes in biofilm community diversity and functions in an artificial stream after different drying durations. A critical drying duration of around 60 days was found in the microbial composition and functions. Therefore, different drying durations can be divided into short-term drying (~0–20 days) and long-term drying (~60–130 days) to analyse the effect of biodiversity in terms of ecosystem functions. In summary, the dominant relationship of biodiversity on community stability got uncoupled after long-term drying. Community assembly became dominant in maintaining multifunctionality with increasing drying duration rather than biodiversity as traditionally perceived. This study reveals the importance of community assembly, extending theoretical knowledge of the relationship between biodiversity and ecosystem multifunctionality.