Inundation depth controls leaf photosynthetic capacity by regulating leaf area and N content in an estuarine wetland

Background and Aims Estuarine wetlands are important carbon sinks, with plant photosynthesis being a vital component of this process. Changes in the inundation depth of wetlands could alter leaf photosynthesis and thus ecosystem carbon uptake capacity, ultimately determining the size of carbon sink. However, the relationship between inundation depth and photosynthetic capacity has yet to be determined, especially in estuarine wetlands with complex hydrological conditions. In addition, there is also conflicting evidence regarding the effect of inundation depth on photosynthetic capacity. Methods To better understand the mechanisms of photosynthetic capacity responding to inundation depth, we performed a field experiment with a gradient of inundation depths (0, 5, 10, 20, 30 and 40 cm) in estuarine wetland dominated by Phragmites australis in the Yellow River Delta, China. Results Our results showed that inundation depth significantly altered leaf morphological traits, elements and photosynthetic capacity. In particular, leaf photosynthetic capacity was obviously increased with increasing inundation depth. The increased leaf area enhanced light harvesting ability of leaves, and then increased Pn at different inundation depths. Besides, higher leaf N content promoted leaf photosynthetic capacity at different inundation depths. Conclusion Overall, the findings demonstrated that inundation depth significantly enhanced the photosynthetic capacity of P. australis , which was correlated with altered leaf functional traits in wetlands. Our results hold important implications for more accurately predicting the relationship between photosynthetic capacity and inundation depth in wetland ecosystems under climate change and more accurately estimating of the carbon sink capacity of wetland ecosystems in the future.