ECOPHYSIOLOGICAL STUDY ON DROUGHT TOLERANCE OF PLANTS LIVING IN ARID REGION

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1.Effects of long-term and short-term water stress on the ecophysiological characteristics of plants living in arid and semi-arid regions were investigated, By the measurement of chlorophyll fluorescent reaction, the drought tolerance of photochemcal system in chloroplast was compared among plants in China and Japan2. Methods and materials. (1)Short term water stress : Rate of photosynthesis and chlorophyll fluorescent of seedlings of Pinus tabulaeformis, P.sylvestris, Hippophae rhamnoides, Hedysarum fruticosum, Caragana korshinskii and Artemisia ordosica from China and Pinus densiflora, P.thumbegii and Artemisia princeps from Japan growing in a small jiffy pot were measured under the changes in soil water condition from pF0 to pF6 in about 10 days. (2)Long term water stress : Seedlings were planted in gravel culture using water solution The osmotic potential of the water solution were maintained at -0.02MPa, -0.04MPa and -0.30MPa for four years by polyethylene glycol treatments.3. Results and discussion. (1)Acute water stress : There was a remarkable difference in the changed of fluorescent reaction among plant species during the desiccation process in soil water condition. It indicated that plant species from arid region in China had a higher drought tolerance than these in Japan. Pine trees from arid region could maintain higher photosynthetic activity than Japanese pine species. (2)Chronic water stress : Both the top and root growth of all species were severely affected by long term water stress. Some species was restricted in branch elongation and other species decreased in the number of leaf flash. Although the rate of transpiration did not differ among water stress treatments, the water used efficiency showed significant difference among treatments.