Adaptive Plasticity of Phragmites australis in Aboveground and Belowground Productivity Under Salinization and Nitrogen Enrichment

Understanding plants’ productivity plasticity in response to environmental variations is crucial for evaluating their adaptive capacity and resilience in the face of rapid global changes. Phragmites australis, an important species in coastal wetlands, plays a vital role in ecosystem functions and wetland agriculture. Coastal areas are increasingly threatened by soil salinization due to rising sea levels and eutrophication driven by elevated nitrogen inputs. However, how P. australis adjusts its aboveground and belowground productivity under these environmental stresses remains poorly understood. We examined how P. australis alters its productivity in response to varying salinity and nitrogen enrichment levels through a mesocosm experiment. Our results showed that elevated salinity reduced both aboveground (by 2.7–13.7%) and belowground (by 15.3–24.7%) productivity, decreasing the belowground-to-aboveground biomass ratio of P. australis. In contrast, nitrogen enrichment promoted aboveground productivity (by 18.3–65.5%), but suppressed belowground biomass (by 11.7–29.7%), further reducing the biomass ratio. Nitrogen enrichment alleviated the negative impact of salinity on aboveground productivity, but exacerbated its effects on belowground biomass, further shifting resource allocation to aboveground growth. These findings underscore the adaptive plasticity of P. australis and suggest its potential role in supporting sustainable wetland agriculture, providing both ecological and economic benefits in the face of ongoing global environmental changes.