The stability mechanisms of ecosystem functions have been a hot topic in ecology. However, in wetland ecosystems, the mechanisms by which biotic and abiotic factors interact to affect ecosystem stability in changing environments remain largely unclear. This study investigated the key factors and underlying mechanisms that regulate the spatial variability of wetland productivity by measuring community productivity, multiple components of biodiversity (i.e. species diversity, community functional composition and diversity) and environmental factors along a well-characterized gradient of wetland degradation in the lower reaches of the Yellow River. The results showed that the spatial variability of productivity in wetlands increased with intensified degradation. The spatial variability of wetland productivity was not related to species richness but was mainly affected by changes in community functional composition and diversity. Furthermore, degradation-induced changes in soil nutrients drove the spatial variability of productivity to increase with shifts in functional composition towards more conservative traits (i.e. higher leaf dry matter content and root tissue density), and to decrease with higher functional trait diversity. These findings reveal the driving mechanism of spatial variability in wetland productivity under degradation, and suggest that reduced nutrient availability, by altering plant resource strategies, can affect the spatial reliability of key ecosystem functions in wetlands.