Spatiotemporal variations of CO2 fluxes in aCynodon-dominated riparian zone of the Three Gorges Reservoir (TGR), China

Abstract

Aims Riparian ecosystems play an important role in overall ecosystem function, including the global carbon cycle of terrestrial ecosystems, at both landscape and global scales. Yet few studies have reported in situ measurements of CO2 in riparian areas where flooding is a unique disturbance to carbon cycling. Methods At multiple locations across riparian zones (RZ) with different water submergences in Xiangxi Bay (XXB), we studied seasonal variations of CO2 exchange between this Cynodon-dominated community and the atmosphere for 2 years by using static chambers. Important Findings We found that the seasonal changes in CO2 fluxes were apparent and dependent on the biophysical environment. In the beginning of spring, low gross primary productivity (GPP) in lightly flooded zones (LFZ) resulted in a positive net ecosystem exchange (NEE), indicating a net CO2 source. With the increase in temperature, more species and vegetation abundance appeared, and the increased GPP turned the LFZ from a net CO2 source into a sink. This transition seemed predominantly controlled by the physiological growth of vegetation. The mean NEEs, REs and the light-use efficiency (alpha) of the vegetation at HFZ and MFZ were significantly higher than those at LFZ and UFZ. Yet the coefficients of variation (CV) of NEE and RE at MFZ and HFZ were lower than those at LFZ and UFZ. Submergence promoted the emission and uptake of CO2 to the atmosphere. Elongated submergence reduced the number of species and lowered the spatial variability of the RZ, further lowering the variation of the CO2 exchange.