Effects Of Drought Stress On Leaf Structure And Physiological Characteristics Of Melliodendron Xylocarpum

Meliodendron xylocarpum Handel-Mazzetti is a tree specie of Melliodendron genus belongs to Styracaceae,which is endemic to China.It is also an economic tree specie used for landscaping,oils and materials.It has high value for research and utilization.In the research,taking one-year-old seedlings of M.xylocarpum from five different provenances as materials to carry out drought stress experiments by potted weighing and water control method.Four drought gradients were set:control check?soil water content 85%-90%?,light drought?70%-75%?,moderate drought?50%-55%?and severe drought?30%-35%?,to explore the photosynthetic characteristics,physiological and biochemical responses and leaf anatomical structure changes of M.xylocarpum from five provenances under different drought stress levels.The drought tolerance of M.xylocarpum seedlings from different provenances evaluated by means of membership function,which provided a scientific basis for the adaptive introduction and domestication of M.xylocarpum and the screening of high quality provenance.The main results of this study are as follows:?1?Drought stress caused the photosynthesis of five provenances M.xylocarpum seedlings decreased.During the whole drought stress test,the net photosynthetic rate?Pn?and transpiration rate?Tr?of leaves of M.xylocarpum seedlings from different provenances continued to decrease the whole drought stress,and stomatal conductance?Gs?and intercellular CO₂ concentration?Ci?decreased first and then increased with severity of drought stress.Water use efficiency?WUE?of M.xylocarpum seedlings from different provenances changed slightly in each drought stress stage,but the water use efficiency?WUE?was significantly lower in severe drought stress than that of the control check.?2?Under drought stress,the variation of the physiological and biochemical indexes of leaves of M.xylocarpum seedlings from five provenances was different.During the whole drought stress,the response of chlorophyll content?Chl?of M.xylocarpum seedlings from five provenances was not obvious.With the increase of drought stress,the relative water content?RWC?of leaves of M.xylocarpum seedlings from five provenances decreased continuously while MDA content and relative conductivity continued to increase.The content of isotonic modulating substances?soluble sugar,soluble protein and proline?and antioxidant enzyme activities?SOD,POD?in leaves of M.xylocarpum seedlings from different provenances showed a trend of increasing first and then decreasing.It means that M.xylocarpum seedlings from five different provenances responded to drought stress by increasing antioxidant enzyme activity and enhancing osmotic adjustment.?3?Under drought stress,the anatomical structure of leaves of M.xylocarpum seedlings from five provenances changed significantly.With the increase of drought stress,the leaf thickness,palisade tissue thickness and sponge tissue thickness of of M.xylocarpum seedlings from five provenance showed a decreasing trend,while the ratio of palisade tissue thickness to sponge tissue thickness showed an increased trend.The thickness of the upper epidermis and the thickness of the lower epidermis in the leaves of different provenances changed slightly,and the change patterns were different under different drought stress levels.?4?There were differences in response to drought stress and drought tolerance of M.xylocarpum seedlings from five provenances.Based on the subordinate function values of 20indexes,such as morphology,photosynthesis,physiology and biochemistry,the drought tolerance of M.xylocarpum seedlings five provenances to drought stress were:Jiangxi Qiyun Mountain provenance?QYS?>Guangxi Jinxiu provenance?JX?>Guangdong Ruyuan provenance?RY?>Guangxi Luzhai provenance?LZ?>Sichuan Emei Mountain provenance?EMS?.