Physiological responses of different energy willow clones under drought stress.

We studied on the drought tolerance of four different energy willow clones(Salix dasyclados,S.mesu,S.fragilis,S.viminalis).Using potted 1-year old seedlings of the four different clones,we conducted a soil-drought controlled experiment and measured the changes of SOD activity,POD activity,CAT activity,MDA content,protein content and relative growth of height.The results revealed the following consequences.(1)With the decrease of soil water content,the protective enzyme activities of 4 energy willow clones improved until the soil water content was below the level of 11.4%.This phenomenon showed that SOD,CAT and POD acted synergistically on assuring the plants' regular growth.While the water content fall below 11.4%,both S.dasyclados and S.mesu CAT and POD activities significantly reduced.It indicated that under this water condition the seedlings suffer from the drought stress.(2)The MDA contents of all the four clones increased along with the drought stress enhancing.The growth was remarkable when the water content fall to 11.4%.The change of S.mesu is especially notable.(3)The content of protein was increasing as the soil becoming more and more arid.But it turned to decrease as the water content was fewer than 8.1%.(4)The relative growth of height of all the energy willow clones reduced while the drought condition increased;(5)According to fuzzy synthetic evaluation of the activities of three protective enzymes,MDA content and protein content to water stress in leaves,the drought-tolerance of the four energy willow clones decreased in the following order:S.fragilisS.viminalisS.dasycladosS.mesu.