Nutrient enrichment destabilizes aquatic food webs through synchronization within and across trophic levels

Nutrient enrichment destabilizes ecosystems globally, but the mechanistic pathways underlying this effect in multi‐trophic communities remain unclear. To address this knowledge gap, we applied biodiversity–stability theory to multi‐trophic communities by partitioning multi‐trophic stability into two key components, within‐trophic stability and cross‐trophic asynchrony. We used two complementary datasets, a decade‐long plankton time series from a large eastern Chinese lake (Lake Taihu) and time series from 30 geographically distinct lakes, to examine how total phosphorus (TP) concentration influences producer–consumer community stability. We found that increased TP consistently destabilized producer–consumer communities across both datasets. This destabilizing effect stemmed primarily from reduced within‐trophic stability caused by reduced population asynchrony within each trophic level. Additionally, increased TP destabilized communities by reducing cross‐trophic asynchrony, as elevated TP promoted phytoplankton biomass both directly and indirectly via diversity changes, thereby synchronizing dynamics across trophic levels by strengthening bottom‐up forcing. The latter destabilizing pathway was particularly pronounced in Lake Taihu. Water temperature emerged as an additional destabilizing driver, independently reducing within‐trophic stability by decreasing population stability across trophic levels. These findings advance our mechanistic understanding of how nutrient enrichment influences multi‐trophic stability and inform effective conservation strategies. Read the free Plain Language Summary for this article on the Journal blog.