Study On The Shading Effect Of Vitex Negundo On The Seedlings Of Quercus Variabilis

In the spring and autumn when the soil is fully supplied with water and mildly drought,the leaf temperature of the seedlings of Quercus variabilis is within the corresponding high temperature index.In the summer with persistent high temperature,when the soil is moderately dry,the leaf temperature of the seedlings of the Quercus variabilis is lower than that of the high temperature index,but the leaf temperature of the CK is close to the moderate drought leaf temperature index.Under severe drought conditions,the ultra-high temperature index appeared in the lower leaf temperature of the CK.The highest temperature exceeded the temperature of6.97 °C,the duration was about 7 h,and the hourly accumulated temperature was 2558.7 °C.Based on the investigation of seedling afforestation,the design of natural environment and control of water environment,combined with the spatial and spatial indicators of temperature and moisture of Quercus variabilis,the effects of transpiration rate and solar radiation on leaf temperature and the changes of photosynthetic effects of leaves were determined to determine the vitex of Vitex The climate spatial regulation characteristics of the seedlings of the Quercus variabilis.The research results are as follows:In the natural environment and artificial climate chamber,the transpiration rate of Quercus variabilis seedlings was affected by the combination of light,temperature and humidity factors.Under the test conditions,32 °C is the optimum transpiration temperature of the seedling leaves.The transpiration was calculated by the dry reference surface energy method and the "three-temperature model" method,and it was found that there was a seasonal difference in the effect on leaf temperature.That is,the spring transpiration rate is the largest,the summer is small,the transpiration rate is further reduced in July and August with more precipitation,and the contribution of transpiration to leaf temperature is less than 3 °C.Under different soil moisture conditions,the leaf temperature of Quercus variabilis seedlings in the CK-free shrubs was higher than that under Vitex,while the leaf temperature in the south side of Vitex was higher than that in the north of Vitex.The trend of leaf temperature and temperature was consistent with the temperature."U" type.The specific performance is as follows:with the increase of soil drought degree,the leaf temperature of Quercus variabilis seedlings increases continuously.The seasonal variation of leaf temperature is as follows: from spring to autumn,the temperature of the inner and outer leaves of the shrubs increases and then decreases.Under drought conditions,the difference between radiation and leaf temperature increased,and the effect of shading and cooling of Vitex negundo was significant.Under severe drought conditions,the difference in radiation decreases and the difference in leaf temperature increases.The chlorophyll fluorescence parameters can reflect that the photosynthesis status of the leaves of Quercus variabilis seedlings is better than that of CK,especially in the summer of high temperature and strong light.When the seedlings suffer from severe drought stress,they are very likely to die.Therefore,the wattle shrubs are required to provide a shady environment.However,the effect of shading on seedlings,the selection of the best shading position should refer to the change of energy balance in LAI and DIFN of different seasons.