Photosynthesis and Productivity of Cyperus rotundus and Setaria viridis in the Three Gorges Reservoir Area: An Empirical Study

Objective: To find adaptation strategies of a perennial herb Cyperus rotundus and an annual herb Setaria viridis, and evaluate their ability for the ecological restoration in the hydro-fluctuation belt in the Three Gorges reservoir area (TGR). Methods: An empirical study of photosynthesis and productivity of these two herbs was conducted. The study consisted of photosynthetic characteristics, chlorophyll and community productivity at altitude gradient from 150 to 180 m at 10 m interval which cover the flooding zone (altitude 150 m, 160 m and 170 m) and no flooding zone (altitude 180 m). Results: Perennial herb and annual herb have different adaption strategy for anti-seasonal water flooding, but both herbs were able to adapt flooding stress with the ability of photosynthesis recovery after flooding. The net photosynthesis rate (Pn) of both herbs have the highest values in shallow flooding zone (altitude 170 m), and there was no significant difference existed between deep flooding zone (altitude 150 m) and no flooding zone (altitude 180 m). Chlorophyll also recovered, and is significant related with Pn (p<0.05). Besides, the community productivity of both herbs recovered after flooding, with community productivity of C. rotundus in shallow flooding zone was higher than that of no flooding zone, and community productivity of S. viridis in moderate flooding zone (altitude 160 m) and deep flooding zone were higher than that of no flooding zone. Perennial herb enhance its tolerance to flooding by reducing biomass and enhancing their root growth, whereas annual herb mainly started its growth after flooding. Perennial herb also play an important role in water conservation in water fluctuating area by enhancing root growth. Conclusion: Taking together, C. rotundus and S. viridis both have good adaptation to anti-seasonal water fluctuation in the TGR, and were appropriate species for ecological restoration in the hydro-fluctuation belt.