Drought Resistance Evaluation On Some Physiological Processes For Different Chinese-Fir Families

Chinese-fir is one of the most important tree species in the south of China, featuring with fast growth, high yield, and fine material quality. Due to the Pacific subtropical high in summer, most of Chinese-fir plantation of southern China suffer from seasonal drought and autumn drought frequently, which have become a barrier to the Chinese-fir plantation growth as well as the development of forestry industry. The study is of significance in increase production capacity of the unit area of Chinese-fir, the Cultivation of high yield and the quality of Chinese-fir. Nitric oxide as a small molecule widely existing in plants has many physiological functions. Nitric oxide regulates plant growth and development, and it is a signal molecule in the defense response of plants under biotic and abiotic stresses. PEG-6000 was employed as osmotic agent to simulate the water stress and we study 10 Chinese-fir Families and measure 12 physiological indexes which relate to the drought resistance of plant. The drought resistance of 10 Chinese-fir families were evaluated by using the membership function method to choose the Chinese-fir with higher drought resistant. The research material was based on the drought resistant Chinese-fir family No.37 chosen in our previous experiments. The role of nitric oxide (NO) in enhancing the drought tolerance of Chinese fir was further studied. The main results are as follows:1. The leaf water content of the 10 Chinese-fir families were significantly decreased under the drought stress. The activity of SOD and POD in leaves of Chinese-fir were increased in the beginning, and then became lower. But the variation range of different families was different. As the stress time prolonging, MDA content and plasma membrane permeability show upward trend. Soluble protein content showed a trend of first increasing and then decreasing under drought stress. This drop in the different Chinese fir families was different. The efficiency of primary light energy conversion (Fv/Fm) slows down-down quickly under the stress stomatal. Conductance (Gs), Photosynthetic rate (Pn), transpiration rate (Tr) and wateruse efficiency decreased, while the intercellular CO2 concentration (Gi) increased under the drought stress.2. In order to eliminate the difference between basic characters, we use the relative value of the 12 indexes as the original data. The evaluations of drought resistance of 10 Chinese fir families were carried out by the method of membership function. In terms of the mean of the membership function. We have that the drought resistance of 10 families are:No.37> No.26> No.21> No.51> No.66> No.41>No.11> No.44>No.62>No. 17.3. The effects of different concentration of SNP treatment Chinese-fir leaves in the physiological and biochemical indices are:(1)The pretreatment of SNP increased the water retention capacity of Chinese-fir leaves under dehydration stress, and peaked at 200mg/L. (2) Comparing with the control, SOD and POD activity were significantly increased after 36 hours dehydration, with 74.39%,39.19% respectively. After pretreatment with different concentrations of SNP, the activity of SOD and POD showed the trend of increasing first and then decreasing. (3) SNP pretreatment can effectively reduce the content of MDA and the damage of plasma membrane permeability. (4) Soluble protein content of Chinese-fir leaves increased significantly under the dehydration stress, namely 50.65%. After pretreatment with SNP, soluble protein content presented the trend of first increasing then decreasing. (5) After exogenous nitric oxide pretreatment, the initial fluorescence (Fo) was showed the trend of decreasing and increasing with the SNP concentration increasing. While the maximal photochemical efficiency (Fv/Fm) and potential activation (Fv/F0) were showed the trend of increasing first and then decreasing. NO has double effect. For NO.37, the SNP with low density (100mg/L、200mg/L) can effectively alleviate the damage of water stress on Chinese-fir. However, the SNP with high concentrations, namly 300mg/L or 400mg/L, can accelerate the membrane lipid peroxidation, reduce the accumulation of antioxidant enzymes, decrease soluble protein concentration and inhibition of photosynthesis in leaves.