Studies On The Physiological And Biochemical Adaptability Of Suitable Tree Species Under Simulation Of Soil Dynamic Submergence Of The Hydro-fluctuation Belt In The Three Gorges Reservoir Area

Four different kinds of water treatment were applied to comparatively study the adaptive mechanisms of Taxodium distichum and Taxodium ascendens seedlings in photosynthetic phyiso-ecology, secondary metabolites and soil nutritional elemental change, under simulation of soil dynamic submergence of the hydro-fluctuation belt in the Three Gorges Reservoir Area. The aim was to elucidate the plants' adaptability to changing water levels for tree species selection and revegetation purposes. The water treatments were 1) normal growth water condition (i.e. CK with soil water content being 60%-63% of soil water field capacity), 2) light drought water stress condition (i.e. T1 with soil water content being 47%-50% of soil water field capacity), 3) soil water saturation condition (i.e. T2 with soil water content being saturated) and 4) soil submersion condition (i.e. T3 with soil being submerged 1 cm).1. T3 of T. distichum seedlings had the lowest content of photosynthetic pigment; T1 and T2 did not differ from CK in the content of chlorophylls and carotenoids in dry weight condition. In group Tl the seedlings of T. distichum had lower apparent light use efficiency, lower apparent CO₂ use efficiency and lower net photosynthetic rate, with the net photosynthetic rate 24.9% lower than that of group CK. However, T2 and T3 did not differ from CK in apparent light use efficiency, apparent CO₂ use efficiency and net photosynthetic rate.2. The group T3 of T. ascendens seedlings had the lowest content of photosynthetic pigment, compared with the highest content of photosynthetic pigment of T2. In contrast, the dry weight content of photosynthetic pigment of T1 was less than that of CK but more than that of T3 in T. ascendens seedlings. The average net photosynthetic rate of T3 was no significant difference in comparison to that of CK. While the average net photosynthetic rate of T1 got negative response ability the group T2 appeared significant higher response ability of net photosynthetic rate with an increase rate of 9.4% than CK.3. 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 (Pn), transpiration rate (Tr), 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. The Tr and G_s of T. ascendens seedlings in T1 did not differ from those of its CK, whereas the Tr and G_s of T. distichum seedlings in T1 were significantly lower than those of its CK.