Changes in Characteristics of Photosynthesis and Transpiration in Parakmeria omeiensis after Cutting Root and Branch in Different Seasons
拟单性木兰不同季节断根和剪枝后蒸腾和光合特性的变化

The Parakmeria omeiensis trees of 10 years treated by cutting root and branch in the spring, summer and autumn, 2005, were compared with those untreated in photosynthesis and transpiration to discuss the effects of physiological factors on the transplant survival rate in different seasons. In the spring, stomatal conductance sharply declined in the treatment, followed by decreasing transpiration and photosynthetic rates with the lowest rates as much as about 60% of those in the control, causing a small portion of water lost from the plants. The weakening in physiological function contributed to the transplant survival rate by metabolism balanced between underground and aboveground. In the summer, transpiration and photosynthetic rates significantlyincreased with stomatal conductance in the treatment. And the highest rates of transpiration and photosynthesis were about double those in the control, suggesting a great amount of water loss. The low transplant survival rate occurred because the lost water could not be compensated enough mainly by cutting branch. In the autumn, the treated plants were higher in stomatal conductance, transpiration and photosynthetic rates than the control. But the increments of both transpiration and photosynthetic rates were slight, relative to those in the summer, and the highest rates were 40% higher than those in the control shortly after treatment. The transplant survival rate could be improved by properly cutting branch or increasing water content in soil. It is concluded that the transplant survival rate is determined by altering physiological function relate to water metabolism, viz, plants capable of reducing water loss by rapidly manipulating their own physiological function have higher transplant survival rate, vise versa.