Spatial and Temporal Variations of Water Poten tia l of theMa in Tree Spec iesfor Vegeta tion Restora tion in the Dry-hot Va lleys of the Jin sha River

The spatial and temporal variations of water potential of 18 tree species for vegetation restoration in thedry-hot valleys of the J insha riverwere systematically analyzed on typ ical sunny day of different seasons in 2005 and2006, some main conclusionswere gotten as follows: (1) The daily water potentials within leaves of the main treespecies in the dry-hot valleys of the Jinsha river all obviously p resented a figure of single2peak in different seasons,the most peak values of dailywater potentials of the leaves appeared at 14: 00; (2) The water potentialwithin leavesof the main tree species in the valleys was deep ly affected by the change of seasons, the characteristic seasonalchange ofwater potentialwithin leaves for all the tree species studied was that the water potential inMarch was bigger than water potential inMay and water potential inMaywas smaller than water potential in October; the dry andhot inMay p romoted the diversity ofwater potential, and the relief of dry and hot stress after rainy season decreasedthe diversity; the diurnal variation of water potentialwithin leaves of the tree species inMay was relatively stable.(3) The water potential within leaves had the negative, positive and negative linear correlation with temperature, humidity and light intensity. (4)Different tree specieswere differently affected by altitude, the change of environmental factors and phenology caused by changeable altitude could affect the diurnal and seasonal variation of waterpotentials of some tree species; the lower location of slope was beneficial to keep ingwater potential at a relative highlevel; the order of leaf water potential of Azad irachta indica in three mixed stands from high to low was Azad irachtaindica & Acacia auric, Azadirach ta indica & Leucaena leucojpha la, and Azadirachta indica & Sctdeichera oleosa,which was closely related to the supp ressed condition of Azadirachta ind ica, the extremely dry and hot environmentcould decrease the affection of differentmixed stands on p lant leafwater potential; the water stress caused by the extreme drought inMay could be relieved by irrigation.