| Four tress species (Gleditsia sinemis Lumjuglans regia L.,Diospyros kaki L.f and Diospyros coins L.) are the main planting trees of restoring farm to forest in low hill of Hebei province. In order to refer the theoretical basis on planting the seedlings, the drought resistance ability of the four seedlings were studied in terms of porting treatment. Photosynthesis and fluorescence of the four one-year-old seedlings were studied under normal culture in field and in pot culture as well as photosynthesis, fluorescence, water status, osmotic adjustment, turgor maintain, protective enzyme(SOD and POD) and the membrane lipid permeability were studied under artificial water controlled in pot. There are inclusions that are showed as follows:1. The photosynthesis and fluorescence of the four seedlings planed in field were different from in pot. In coMParison with planning in the field, the photosynthesis and fluorescence of the seedlings were influenced deeply to the restriction of pot, of which the seedling of J. regia is the most one.2. Some indexes of physiology of four seedlings, such as net photosynthesis(Pn), stomatal resistance(Rs), transpirement(TRN), water utility efficiency(WUE),COi/CO2 value and Tleaf-Tair value, were decreased or increased clearly by water stress, and the more water stress developed, the more change of indexes were obvious. There were some indexes showing that the photosynthesis was limited by two factors of stomata and non-stomata. But when field filled-water content(FFC) dropped at 40-30%, non-stomata factor played the dominance role in photosynthesis.3. The leaves of chlorophyll a fluorescence indexes of seedlings, such as photochemical quenching(qP), non-photochemical quenching (qN) and the ratio of Fv/Fm, were different with the two water stress ways, i.e. detached and drying in air and pot treatment. It demonstrated that the indexes response of seedlings were different in two treatment that mentioned above, especially the value of qN. The changes of the qN values of G. sinensis,J. regia and D. coins, however, all showed reverse trends with the two treatments, which might show that some difference or changes in mechanism of excess light energy dissipation had happened.4. Being the analysis of the leaf water-holding ability of the seedlings, the drought-toleration ability of G.sinensis, J.regia and D.kaki were higher than the D. colus.But the water-holding ability of D. coins had enhanced sharply with the drought stress increased smoothly, and the J. regia, which have higher drought-toleration ability, had no significant change.5. The cell osmotic adjustment and cell elasticity adjustment of seedlings leaves were influenced clearly by water stress. Based on the P-V tech analysis, the RWD?value of G.sinensis, J.regia and D.kaki under 80% FFC was higher than that of 60% FFC, but the ROWC0, 100, 0 was lower than the latter, of which G.sinensis and J.regia. were the outstanding. It seemed that the 80% FFC was over the three seedlings needed if they grew in the 80% FFC at a long period of time. In contrast with three trees mentioned above, the seedling RWD0 of D. colus under 60% FFC was higher than that of 80% FFC, which showed that it had a relative higher ability to tolerate higher SWC than others. Along with the more strength water stress, such as 30%-60% SWC, all kind of seedlings expressed the same trend, i.e. the value of RWD0 increased and ROWC? 100 and 0 decreased. To sum up the indexes, the ability of osmotic adjustment and turgor maintain, from higher to lower, was G.sinensis> J.regia >D.kaki>D. colus. As a kind of cell osmotic substances, the soluble sugar of all seedlings content were increased and that of starch decreased with water stress strengthened. On the other hand, the three trees seedlings soluble proline and soluble protein content, i.e. G.sinensis, J.regia and D.kaki, increased sharply. And the last tree D. colus was contrary with them. It demonstrated that different trees had different available osmotic substances whe...
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