Land plants are constantly growing in environments not optimal for their growth and development, drought and saline stresses are often encountered by plants. These stresses will significantly affect the transpiration, ion absorption and photosynthesis of the plants. Because the photosynthesis of land plants is always accompanied by transpirational water loss, and because the xylem sap being transported to leaves during the transpiration process is not pure water, this in turn will result in the accumulation of ions in plant leaves. This is because the when the water in the xylem sap is transpired into the air, ions will be left in leaves. For this reason, the ratio between the amount of carbon assimilation and ion accumulation in plants may vary significantly under different environmental conditions even within the same plant. This is an important part of plant metabolism in terms of ionic nutrition and salt resistance. However, the relation between the simultaneous change and accumulation of ions and photosynthetic yield is rarely addressed and little is known about the relationship between the accumulation of ions and photosynthetic assimilatant in Vitex trifolia L, a salt and drought resistant plant, the effect of environmental factors on that relationship is even more scarce. In this paper, the photosynthesis and transpiration in relation to ion accumulation in V. trifolia under varied light intensity (on cloudy / overcast and sunny days, respectively). The diurnal accumulation of photosynthetic assimilatant was calculated through the integration according to the instantaneous photosynthetic rate of leaves against time, and the ion accumulation in leaves was yielded by integrating the instantaneous ion concentration of xylem sap against time. In this way, the ion concentrations, in relation to the transpiration rate and the water potential of V. trifolia, as well as the photosynthetic rate, were analysed on cloudy / overcast and sunny days,
Perennial plants that normally experience dormancy during winter may be subjected to more cycles of freeze鄄thaw caused by warming winter. We explored the physiological mechanisms of adaptation of white clover, Trifolium repens Linn, to freeze鄄thaw stress. In late fall of 2009, uniform plots of white clover grown in a natural environment (NE) were covered with a plastic house (pH) to simulate the effect of a warmer winter or left uncovered (control). During the winter and following spring, growth capacity and physiological indices related to resistance to adverse environment were measured in leaves of white clover grown in both conditions. In the winter of 2009, the average temperature ranged from below zero (-10益) to 7益 in the NE during which leaves experienced thawing鄄freezing鄄thawing鄄freezing, and above zero (from 1 益 to 7 益) in the pH where leaves were never frozen. In late fall of 2009, all white clover was of uniform height. But in spring 2010, plants grown in the PH (26 cm) were 3 times taller than those in the NE (8 cm). This difference in height disappeared by June 2010. In winter, the relative membrane permeability, MDA(malondialdehyde) , proline, and soluble
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