Eutrophication Decreases Ecological Resilience by Reducing Species Diversity and Altering Functional Traits of Submerged Macrophytes

Ecosystem regime shifts attract a growing concern because irreversible non-linear, abrupt changes can significantly alter the services that the ecosystem offers to human society. Regime shifts between contrasting alternative states occur when environmental conditions cross a specific threshold, with ecological resilience decreasing as the system approaches the tipping point.    

Studies have shown that high self-facilitation strength (water clarity-macrophytes positive feedback loops) can buffer external environmental changes and delay the transition by increasing the regime shift threshold of macrophyte-dominated state. In recent years, although it became clear that positive feedback is at the core mechanism of ecosystem regime shifts, the determinants of ecological resilience remain largely unknown.    

Recently, a research group led by Prof. XIE Ping from the Institute of Hydrobiology (IHB) of the Chinese Academy of Sciences quantified the ecological resilience by quantifying the positive feedback strength of water clarity-macrophytes and explored the pathways of how eutrophication affected resilience. This study was published in Global Change Biology.   

In this study, based on the field investigation of submerged macrophyte communities in 35 lakes in China, the researchers quantified morphological complexity (MC) and plasticity (MP) by average specific surface area and general linear model was used to quantify the relationships between morphological traits and stoichiometric homeostasis at both the species and community levels. They also tested whether morphological traits were linked with species dominance and stability, as well as community biomass and stability.   

The researchers found that morphological complexity (MC) and plasticity (MP) are correlated with the stoichiometric homeostasis of phosphorus (HP) and are related to ecosystem structure, functioning, and stability.   

Positive feedback strength was calculated by the ability to increase transparency per unit of biomass. A general linear model was also used to explore the effect of functional traits on positive feedback strength. Similarly, a general linear model was used to test whether the positive feedback strength depended on biomass and species diversity. Finally, the piecewise structural equation model (SEM) was constructed to further explore the cascading effect of how eutrophication affects ecosystem resilience by altering species diversity and community morphological and physiological traits.   

The positive feedback strength of lakes dominated by macrophytes is biomass- and diversity-dependent. However, eutrophication can decrease the community biomass by decreasing community MC, MP, and HP and the species diversity through low-light availability, ultimately decreasing the positive feedback strength and resilience of clear-water states.  

The results revealed the role of functional traits and species diversity in determining community structure, functioning, and ecosystem resilience under the pressure of eutrophication, which deepens the understanding of regime shifts. These results are significant for ecological restoration and lake management in light of future environmental change scenarios. 

(Editor: MA Yun)