| The photosynthetic, physiological and ecological mechanisms of Pterocarya stenoptera, Pinus elliottii and Salix rosthornii under dynamic submergence and drought stresses were studied in this research. To elucidate these mechanisms, three different kinds of water treatments simulating the soil moisture changes of the hydro-fluctuation belt in the Three Gorges Reservoir were applied to one-year-old P. elliottii and P. stenoptera seedlings, including control CK, continuous flooding CF, and flooding and drought alternation stress PF. Comparisons were made on the basis of the seedlings’ photosynthetic and ecophysiological changes between the two species, respectively. Furthermore, according to the actual water change in the hydro-fluctuation belt, effects of four different water treatments on physiological and ecological characteristics of two-year-old P. stenoptera and Salix rosthornii saplings were studied as well, including the water treatment of control (CK), soil submergence (T1), half submergence (T2) and full submergence (T3).Photosynthesis, biomass, growth and other related ecophysiological characteristics of P. stenoptera, P. elliottii and S. rosthornii were examined in this research. Research results showed that water treatment could significantly influence photosynthesis, biomass and growth of P. stenoptera and P. elliottii seedlings. Net photosynthetic rate (Pn) and stomatal conductance (Gs) in CF and PF of P. stenoptera and P. elliottii seedlings were significantly lower than that in CK respectively, while a significant higher intercellular carbon dioxide concentration (Ci) in the two groups compared to CK was detected respectively. At the same time, net photosynthetic rate (Pn) and stomatal conductance (Gs) in CF and PF of both P. stenoptera and P. elliottii seedlings declined initially and followed by recovery or maintainence tendency later. Along with extension of the treatment, there was a continuous increase in root biomass, stem biomass, leaf biomass, and total biomass, and also plant height and base diameter in CF and PF of P. elliottii seedlings respectively, which was the same as that of P. stenoptera seedlings. However, in terms of the overall average value throughout the experimental period, root biomass, leaf biomass, and total biomass, and plant height in both CF and PF of P. stenoptera showed a significant decline compared with CK, while stem biomass in CF of P. stenoptera had no significant difference. Base diameter in CF of P. stenoptera was even higher than that in the control group. No significant difference was found in root biomass, stem biomass, total biomass, plant height and base diameter between CF and PF of P. elliottii seedlings, while a significant decline occurred to these indicators of P. elliottii seedlings in both CF and PF, compared with CK respectively. Under each treatment, net photosynthetic rate of P. stenoptera and P. elliottii seedlings was not significantly different, but intercellular carbon dioxide concentration of P. stenoptera was significantly lower than that of P. elliottii. In addition, in CK and PF group, stomatal conductance of P. stenoptera was significantly higher than that of P. elliottii, respectively, but no significant difference was found in CF group between P. stenoptera and P. elliottii.On the other hand, different water treatments had significant impact on the activity of superoxide dismutase (SOD), peroxidase (POD) and catalase (CAT), content of malondialdehyde (MDA), soluble protein and free proline, and biomass of the two-year-old P. stenoptera and S. rosthornii saplings. As for P. stenoptera, the activity of SOD declined initially and then increased under waterlogging stresses (T1, T2and T3). The activity of POD in T1and T2group did not significantly decreased, while the activity of POD in T3group was significantly lower than that in CK. The activity of CAT in T1, T2and T3was significantly lower when compared with CK. At the same time, the content of MDA in T1, T2and T3group was higher than that in CK respectively, while the content of soluble protein in different water stresses was significantly lower than that in CK respectively. However, under drought stress, the activity of SOD and POD in T1, T2and T3increased, while the CAT activity decreased. In addition, the content of free proline and soluble protein in T1, T2and T3increased compared with CK. In terms of S. rosthornii saplings, under waterlogging stresses, SOD and CAT activities in T1, T2and T3group increased, while the activity of POD declined initially but then increased. Similarly, the content of MDA and free proline increased in T1, T2and T3group, respectively, while the content of soluble protein decreased. However, under drought stress, the activity of SOD, POD and CAT increased, and the content of MDA, free proline and soluble protein was also higher than that in CK group. In each treatment group, activity of POD and content of MDA in P. stenoptera were lower than that of S. rosthornii respectively, but soluble protein content was higher than that of P. stenoptera.The research results verified the trait of flooding tolerance of P. stenoptera, P. elliottii and S. rosthornii seedling. These three species could be considered as candidates for riparian revegetation in the hydro-fluctuation belt of the Three Gorges Reservoir. However, given the water level changes in the hydro-fluctuation belt of the Three Gorges Reservoir, intensive water management for their growth is of particular significance, especially under drought conditions. |
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