Food web structure and energy flux can enhance multifunctionality: Evidence from a river-lake ecosystem

Biodiversity–Ecosystem Multifunctionality (BEMF) frameworks underpin function-oriented management of ecosystems. While the importance of integrating multitrophic networks into BEMF research is increasingly recognized, the specific effects of food webs on multifunctionality (MF) remain poorly elucidated, particularly in freshwater ecosystems with complex food web structure and dynamic energy flux. We investigated the effects of food web structure and energy flux on multifunctionality across four river-lake habitats (river, ecotone marsh, lake center, outflow aquaculture zone) in Dongping Lake, China. Eleven variables across six functional categories (nutrient cycling, ecosystem metabolism, primary production, secondary production, photosynthetically active radiation, and microbial abundance) were integrated to quantify MF using averaging and threshold approaches (30%, 50%, 80% effectiveness threshold). Furthermore, we elucidated the mechanistic pathways of food web structure and energy flux on multifunctionality using Bayesian linear models and Partial Least Squares Path Modeling (PLS-PM). Results revealed significant spatiotemporal variations in MF, with an overall pattern of higher values in spring than in summer, and also in the river-lake ecotone than other habitats. Concomitantly, food web structural complexity maximized in the ecotone (elevated nodes/links/robustness/principal component scores) and minimized in the river. Total energy flux was lowest in the river, peaking at the aquaculture zone (spring) and ecotone (summer). Food web structure and energy flux (total flux, herbivory-derived energy) enhanced multifunctionality, with structural complexity primarily promoting MF at low-to-medium thresholds (β = 0.43–0.47, p < 0.05) while energy flux enhanced it across all thresholds (β = 0.38–0.61, p < 0.05), particularly at high threshold (β = 0.61, p < 0.001). Our findings highlight the enhancement of food web structure and energy flux on multifunctionality, and identify the critical role of ecotones in sustaining such multifunctionality, which will advance the current BEMF frameworks and provide a robust foundation for conservation efforts in river-lake ecosystems.