Abstract:

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.

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.

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 (α) 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.

Key words: CO₂ exchange, riparian, submergence, spatial variability, Q₁₀, TGD