Study On The Ecophysiological Characteristics Of Drought-Resistance Of Three Tree Species

The pot cultured one-year-old seedlings of Robinia pseudoacacia, Acer trancatum and Platycladus orientalis were tested with water grade method to study their physiological biochemical characteristics under water stress. The growth status, water consumption patterns, photosynthesis and dynamics changes of protective enzymes activity and osmotic adjustment substances were measured to evaluate and compare the drought-resistant ability of the three seedlings, based on which evaluation indexes system was established to provide theoretical basis for selecting afforestation tree species and forest management measures in arid and semi-arid area. The results are as follows:(1) The growth of height and ground diameter was inhibited significantly under water stress; and with the aggravation of water stress, the degree of inhibitory increased.(2) The diurnal changes of net photosynthetic rate of the three tree species showed single peak type. The diurnal changes of stomatal conductance of R. pseudoacacia was single peak type and that of A. trancatum and P. orientalis were double peak type. With the enhancement of water stress intensity, the net photosynthetic rate and stomatal conductance were induced and the water use efficiency increased at different degrees. Compared with that under normal water supply, the transpiration rate decreased under medium and sever water stress but increased under light water stress. With increasing degree of water stress, Pmax and LSP of the three seedlings decreased significantly however LCP and Rd increased significantly. AQY values of R. pseudoacacia decreased significantly under medium and sever water stress, but water stress had no significant effects on those of A. trancatum and P. orientalis.(3) During the growth process, the total chlorophyll content of the three seedlings decreased continuously; and the total chlorophyll content in the leaves under medium and sever water stress was significantly lower than those under normal water supply and light water stress. The ratios of Chla and Chlb decreased at first and then increase under normal water supply and light water stress. Chla/Chlb values decreased continuously under medium and sever water stress and were significantly lower than those under normal water supply and light water stress. (4) With the aggravation of water stress, the relative water content of leaves of the three seedlings decreased, and the nature saturated deficit enlarged. Under the same water condition, the relative water content and 24h water retention capacity of isolated leaves of the three seedlings was listed in descending order as follows: P. orientalis >A. trancatum >R. pseudoacacia. The ability of turgor maintenance of R. pseudoacacia was the poorest and that of P. orientalis was the strongest. But R. pseudoacacia made its turgor maintaining ability exceed A. trancatum and P. orientalis through reducingΨ0π,Ψ100π, RWC0 and ROWC0and improving the differential value ofΨ100πandΨ0π, AWC and RWD0. With increasing intensity of water stress, the water consumption rate of the three seedlings decreased and the sap flow rate per area of three seedlings was as follows: A. trancatum > P. orientalis >R. pseudoacacia. The period of the highest water consumption of A. trancatum and R. pseudoacacia was in August, and that of P. orientalis in July.(5) With the aggravation of water stress, the content of free proline and soluble sugar content in the leaves of the three seedlings increased obviously, while the soluble protein content decreased significantly. In the whole growth process, the free proline content was significantly positively correlated with soluble sugar content, but they were weakly negatively correlated with soluble protein content.(6) MDA content of the three seedlings increased with the growth course and the aggravation of water stress. Three enzymes showed different activity at different growth stages. Whether under water stress or not, enzymes activities of R. pseudoacacia were maintained at higher level as compared with other two seedlings.(7) The adaptability and productivity of the three seedlings under water stress were contrasted and compared through subordination function of fuzzy mathematical analysis. The drought-resistant ability of three seedlings was listed in descending order as follows: A. trancatum> P. orientalis> R. pseudoacacia.