The Response Of Photosynthetic Physiological Characteristics Of Potentilla Fruticosatosoil Moisturein The Alpine Region, Qinghaiprovince

To explore the photosynthetic physiological characteristics of potentilla fruticosa and its quantitative relations with soil moistures is the theoretical basic and auspice in the cultivation of plants in arid environment of cold region in Qinghai Province, and provides a scientific basis for field irrigation management. Potentilla fruticosa seedlings were studied as the research object under a pot experiment and leaf water potential and photosynthetic parameters were tested under different soil moisture conditions. Leaf water potential, photosynthetic parameters and photosynthesis diurnal variation process were investigated. Quantitative relations between net photosynthetic rate, transpiration rate, water use efficiency and soil water content were explored to confirm the suitable soil moisture thresholds of photosynthesis and water use efficiency of Potentilla fruticosa. The main results are as follows:(1) With the lowering of soil moisture to 12.88%, Potentilla fruticosa seedlings appeared wilting phenomenon; when the soil moisture get to 9.47% about half of the leaves dried-up; soil moisture of 5.97% made plant to death; at this point, the seedlings would restore physiological activity if the soil moisture content went up to 24% in 6-12 days. The wilting moisture content of Potentilla fruticosa is about 4.02%.(2) The morning leaf water potential, net photosynthetic rate, and transpiration rate of Potentilla fruticosa had obvious threshold response to the changes of soil moisture. When the moisture content get down to about 19.48%, morning leaf water potential declined; when soil water content was lower than 14.37% the stomatal conductance begun to decrease, at the same time, the net photosynthetic rate and transpiration rate begun to reduced substantially, and the water use efficiency increased. Non-stoma restrict would happen under severe soil water stress.(3) The transpiration rate and stomatal conductance began to pick up 1 day after re-watering, and the net photosynthetic rate experienced an obvious rise 3 days after re-watering. Transpiration was more sensitive to changes of water than photosynthesis, and stomatal conductance impacted transpiration rate greater. The water use efficiency remained at a low level after re-watering for 3 days; after re-watering for 6 days the water use efficiency rebounded more than that of the control group 15.97%; this compensation in response to drought stress process improves the adaptability of Potentilla fruticosa seedlings to drought.(4)Leaf water potential of Potentilla fruticosa had a "V" type change, and its net photosynthetic rate, transpiration rate and stomatal conductance of the diurnal variation reached a maximum at 11:00 in the morning and 15:00 in the afternoon. The increase of water stress disordered the diurnal variation, and decreased daily variation amplitude. After re-watering, leaf water potential and photosynthetic physiology parameter restored its diurnal variation before drought stress gradually.(5) The relationship between the net photosynthetic rate, transpiration rate, leaf water use efficiency of soil and soil moisture was as follow:when net photosynthetic rate reached the maximum, soil moisture content was 20.83%; the water compensation point was 4.38%; the soil moisture content was above 12.71% for maintaining 70% of the highest net photosynthetic; the soil moisture content for maintaining 70% of the highest transpiration rate should be above 13.09%; when water use efficiency rose to the maximum, the soil moisture content was 13.82%; the soil moisture content for maintaining 70% of the highest water use efficiency should be between 7.20%-21.9%; the water content of 8.33% was the point for water use efficiency varing from fast to slow.(6) Under the condition of sandy loam, soil water content varing from 8.33% to 12.71% could not only satisfy the basic need for the growth of Potentilla fruticosa, but also improve the efficiency of water use to the largest extent. Research suggests that during the growing season of Potentilla fruticosa in Qinghai Province without any rain, the irrigation should be conducted at least once every two weeks for good growth. Potentilla fruticosa was able to recover from 2-3 weeks’ drought after irrigation, but will die of the drought stress which lasts over one month. Considering the local water environment, Potentilla fruticosa is suitable for small area dotted landscape planting instead of growing in large area.