Effects Of Drought Stress On Physioecological Characteristics Of Typical Plants In The Ecotone Between Dry Valley And Mountain Forest

The most serious effects of global climate change and human disturbances may well be those which related to increasing drought since drought stress has already been the principal constraint in plant growth.The content of soil available nutrient will be lower under global climate change. Nevertheless, water deficit is not the only limiting factor in arid and semiarid environments. Soils often suffer from nutrient deficiencies in these ecosystems, which can also be worsened by climate change. How to improve the poor soil quality and enhance the vegetation coverage is always the serious problem. The ecotone between Dry Valley and Mountain Forest can restraint dry valley to extend and it was one of the most earthquake damaged areas. However, it is very important to understand the adaptive mechanisms of native plant to future climate change. Four endemic plants (Setaria viridis, Cupressus chengiana, Salix paraqplesia and Hippophae rhamnoides) in ecotone between Minjiang dry valley and mountain forest were investigated under different soil water conditions. A one-year greenhouse experiment was conducted in order to understand the adaptation responses of four endemic plants. One-month old seedlings were subjected to a completely randome design with three water (80%,40% and 20% water field capacity (FC)).The main result as these:Drought stress significantly affected four typical species. Seedlings height, basal diameter, leaf number, leaf area, biomass production were decreased with increase of drought stress. An increase in below-ground biomass was observed indicating a higher root/shoot ratio (R/S) under drought stress conditions. H. rhamnoides showed higher total biomass than others, C. chengiana showed higher total biomass than S. viridis and S. paraqplesia, S. viridis has least total biomass. Drought stress significantly decreased specific leaf area (SLA), leaf area ratio (LAR) except C. chengiana.Photosynthetic pigment contents and gas diurnal changes were decreased with increase of drought stress, but there was no difference between 20%FC and 40%FC. Sever drought stress significantly decreased chloroplast pigment a/b (Chl a/b) of S. paraqplesia, increased Ch1 a/b of H. rhamnoides, and there was no effect on C. chengiana and S. viridis. Drought stress decreased net photosynthetic rate (Pn), stomatal conductance (gs), intercellular CO2 concentration (Ci), increased stomatal limitation value (Ls), intrinsic water use efficiency (WUEi). The decreased net photosynthetic rate (Pn) under relative well-watered water conditions might result from stomatal limitations, but the decreased Pn under severe water deficit condition might be attributed to non-stomatal limitations.Drought stress significantly increased membrane permeability, the content of Proline (Pro) and Malondialdehyde (MDA), and antioxidant enzyme activities (Peroxidase, POD; Superoxide Dismutase, SOD and Catalase, CAT). There was no difference on membrane permeability under the same condition. S. viridis showed least content of MDA, and S. paraqplesia showed highest content of MDA, and S. paraqplesia showed least content of Pro. Compared with S. viridis and H. rhamnoides, C. chengiana and S. paraqplesia showed lower POD activity. H. rhamnoides showed lowest SOD activity. Compared with C. chengiana and S. paraqplesia, S. viridis and H. rhamnoides showed CAT activity.Drought stress significantly reduced C, N and P accumulation with increase of drought stress, altered the distribution patterns of C, N and P, but increased N and P use efficiency of both plants. H. rhamnoides was mainly limited by phosphorus, and others were mainly limited by nitrogen. Compared with C. chengiana and S. paraqplesia, H. rhamnoides showed higher drought-resistibility and C. chengiana showed higher drought-resistibility than S. paraqplesia.The results from this study indicated that drought limited the growth of plants and their biomass production, altered their biomass and C, N and P distribution patterns, decreased leaf gas exchange and C, N and P accumulation, increased antioxidant enzyme activities. Compared with C. chengiana and S. paraqplesia, H. rhamnoides showed higher drought-resistibility and C. chengiana showed higher drought-resistibility than S. paraqplesia. The results suggested that the expanding arid region could seriously influence plant growth in ecotone, and provided efficient scientific data to plant selection and species arrangement in the procedure of vegetation practice in the ecotone between Minjiang dry valley and mountain forest.