The large hydro-fluctuation belt is a special riparian wetland ecosystem following the anti-seasonal water level regulation of the Three Gorges Dam. Large hydroelectric project can directly affect vegetation types, soil properties and hydrology, ultimately modify soil carbon (C) and nitrogen (N) dynamics. But there is little known about how flooding influences the plant functional group and natural δ¹³C and δ¹⁵N abundance of plant and soil in water level fluctuation zone. 

Supervised by Prof. CHENG Xiaoli, ZHANG Dandan, a postdoctor of Key Laboratory of Aquatic Botany and Watershed Ecology at Wuhan Botanical Garden, investigated natural ¹³C and ¹⁵N abundance of C₃ and C₄ plants and soil in different fractions from six sites with two elevations (flooding zone, 145–175 m, area with revegetation due to flooding, N = 6; and unflooding zone, >175 m with original plant as a control, N = 3) in riparian zones of the Three Gorges Reservoir, China.   

Flooding significantly changed the vegetation community structure as well as vegetation functional groups (C₃ and C₄ vegetation). Anti-seasonal flooding induced significant decline in the C₄ plant in flooding zone compared with unflooding zone in the upstream, but significantly increased the C₄ plant in the downstream. Totally, the C₄ plant generally increased in the flooding zone of the whole region. The proportion of C₃-derived C in soil organic carbon pool was lower for the flooding zone compared to the unflooding zone in almost sites, while the proportion of C₃-derived C in labile C was decreased in the flooding zone compared to the unflooding zone in the downstream. But the flooding did not significantly change the proportion of C₃-derived C in recalcitrant carbon pool.    

Additionally, the δ¹⁵N values of soil were more enriched in unflooding zone compared to flooding zone in all sites, and were significantly positively correlated with soil C and N pool content, as well as dependent on soil pH.    

These results revealed different patterns and controls of soil C and N dynamics in response to flooding along riparian zones at regional scale.   

This research was financially supported by the “Strategic Priority Research Program B of the Chinese Academy of Sciences” and the National Natural Science Foundation of China . Results have been published in Science of The Total Environment entitled “Shift in functional plant groups under flooding impacted ecosystem C and N dynamics across riparian zones in the Three Gorges of China”.    

ZHANG Dandan from Wuhan Botanical Garden is the first author and CHENG Xiaoli (now  in Yunnan University) is the corresponding author. 

Effects of flooding on vegetation-soil isotope characteristics in the water level fluctuation zone of Three Gorges Reservoir, China(Image by ZHANG Dandan)