Abstract:

Four different kinds of water treatment were applied to compare the photosynthetic characteristics of Taxodium distichum and T. ascendens seedlings under simulation of soil water change of the hydro-fluctuation belt in the Three Gorges Reservoir Area. The aim was to shed light on the plants' physio-ecological adaptation to changing water levels for tree species selection and revegetation purposes. The water treatments were normal growth water condition (I.e. CK with soil water content being 60%～63% of soil water field capacity), light drought water stress condition (I.e. T₁ with soil water content being 47%～50% of soil water field capacity), soil water saturation condition (I.e. T₂ with soil water content being saturated) and soil submersion condition (I.e. T₃ with soil being submerged 1 cm). The results showed that the photosynthetic pigment content of T. distichum was significantly lower than that of T. ascendens both in T₂ and T₃. In CK, the seedlings of T. distichum did not differ from the seedlings of T. ascendens in net photosynthetic rate (P_n), transpiration rate (T_r), stomatal conductance (G_s), water use efficiency (WUE), apparent light use efficiency (LUE_app) or apparent CO₂ use efficiency (CUE_app). However, the seedlings of T. distichum had significantly lower P_n, lower LUE_app and lower CUE_app in T₂ as well as significantly higher G_s in T₃ than those of the T. ascendens seedlings in the same treatment. In T₁, the seedlings of both T. distichum and T. ascendens had significantly lower P_n, lower LUE_app and lower CUE_app than those of their respective other three treatments. The Tr and G_s of T. ascendens seedlings in T₁ did not differ from those of its CK, whereas the T_r and G_s of T. distichum seedlings in T₁ were significantly lower than those of its CK. The results verified that both T. distichum and T. ascendens took on features of water-tolerant and hydrophilic plants, which can be considered as two species to be chosen for the building of protection forest system of the hydro-fluctuation belt in the Three Gorges Reservoir Area. When compared with T. distichum seedlings, the T. ascendens seedlings have better capacity to tolerate water and drought stress, and can grow very well under soil water saturation.

Key words: Three Gorges Reservoir Area, hydro-fluctuation belt, soil water change, Taxodium distichum seedlings, Taxodium ascendens seedlings, photosynthesis