THE STUDY ON TRANSPIRATION RATE OF THE BLACK LOCUST UNDER DIFFERENT SOIL WATER CONTENT IN SEMI-ARID REGION LOESS PLATEAU

This paper mainly analyzed the transpiration characteristic of black locust,the major tree for forestation in the Loess Plateau.Physiological indices of black locust in differentsoil water conditions were measured by portable steady porometer(LI-1600) in the summer of 2004,in Fangshan,Shanxi Province(Forestry Experimental Station of Beijing Forestry University).The response processes of physiological absorbed radiation(I),stomatal resistance(R_s),leaf water potential(ψ) and transpiration rate(Tr) to different soil water content were studied.The results showed,the relationship between transpiration rate and physiological absorbed radiation of black locust in semi-arid regions of loess plateau was obtained as follows: η_t =aI~(b).Meanwhile,the relationship of transpiration rate(η_t) and stomatal resistance(R_s) with soil water content(W) was given as follows: η_t=a+bW+cW~2,R_s= a+bW+cW~2.The interrelationship between transpiration,irradiance and soil water condition was quite remarkable.Generally,the rate of transpiration increased with the raising of irradiance and soil water content.The correlation between transpiration rate and soil water content was close.(average logarithmic relations,R~2= 0.8825).Furthermore,the transpiration rate could rise greatly with the increase of soil water content.Based on the above analysis of the rate of transpiration in different soil water conditions,therefore,to lighten injuring on physiology as transpiration seriously,to increase the rate of survivor and to promote growing,it is necessary to adopt measure as avoiding violent irradiance of the sapling when the soil is short of water.The soil water content as 10%SWC15% is beneficial to increase the water use efficiency of plants,which could help plants to enhance water use efficiency in arid and semiarid region.