Study On Physiological Response Of Calotropis Gientea In Water Stress And Altitude Gradient

At present,one third of the earth's land is in arid or semi-arid state,and other areas have different degrees of seasonal drought.The extreme environment caused by drought has seriously affected the growth and reproduction of plants,resulting in a significant reduction in crop yields.The dry-hot valley is one of the typical areas restricted by water.The water deficit makes the dry-hot valley ecological environment extremely difficult to recover.Therefore,studying the physiological responses of native species in the dry-hot valley to drought stress and different altitudes is of great significance for restoring dry-hot valley ecology and developing local agriculture and forestry economy.Calotropis gigentea is one of the native trees in the dry-hot valley.It has strong drought-resistance ability and can grow well in arid areas with certain economic value.It can be used as a pioneer species for ecological restoration in extremely difficult areas in the dry-hot valley region.In order to clarify the basic ecological and biological characteristics of C.gigentea,the use of C.gigentea for the ecological restoration of dry-hot valleys provides basic theory and experimental data support.In this study,the C.gigentea in Honghe County of Yunnan Province was used as the research object,and the water gradient test group with the relative water content of 60%?70%,40%?50%and 20%?30%was set and the control group was 70%?80%,In the control group,photosynthesis,transpiration rate,oxidase activity,plant height,leaf area and other traits were studied to explore the physiological response of C.gigemtea to water deficit growth.Three altitude gradient test groups of 400m,700m and 1000m were set to explore the C.gigentea flower,Phenology,growth rate,stomata,fruit,leaf area and leaf thickness traits for altitude differences.The main findings are as follows:1.As the relative water content of the substrate decreased,the height of the C.gigemtea Tends to be dwarfed,the metabolism of leaves was accelerated,Expressed as the plant height,ground diameter,relative content of chlorophyll and decreased and leaf regeneration rate increased under drought stress;the Stomatal density of the leaves of C.gigentea increased and the length decreased,and the leaf vein density increased.2.As the relative water content of the substrate decreased,the net photosynthetic rate of the leaves of C.gigentea decreased with the increase of drought stress,the transpiration rate increased,and the intercellular carbon dioxide concentration increased.Among them,compared with the control group,the net photosynthetic rate under Low and moderate drought conditions decreased slowly,and severe drought decreased rapidly.3.With the increase of altitude,the height of the C.gigentea Tends to be dwarfed,the number of leaves per plant is not significantly,the leaf area becomes smaller,and the thickness increases.4.With increasing altitude,the budding time,the initial flowering time,the full flowering time,the last flowering time,and the ovary expansion period are delayed,and the fruit ripening period is shortened.The number of flowering per plant,fruit setting and length of seed fiber of C.gigentea were not significantly changed and the weight and length of the fruit decreased with increasing altitude.5.As the altitude increases,the relative water content of the leaves decreases during the rainy season and increases during the dry season;In the rainy season,SOD activity,soluble sugar concentration,MDA content and Pro content increased with increasing altitude.In the dry season,SOD activity,soluble sugar concentration,MDA content and Pro content decreased with increasing altitude.In summary,under drought stress conditions,C.gigentea reduced the water loss by dwarfing the leaf,accelerating the metabolism of leaves,and the stoma became smaller and denser.The water transport efficiency was enhanced by the increase of leaf vein density.Photosynthesis can be run effectively under low and moderate drought stress,and the drought tolerance is strong.With the increase of altitude,C.gigentea are adapted to the environment by changing dwarfing and reducing leaf thickness.In particular,as the altitude increases,the SOD activity,soluble sugar concentration,MDA content and Pro content of the leaves of C.gigentea show that,the values are decreased in the dry season indicates the positive response of the horned melon to the low temperature during the rainy season.and the values are increased indicates Positive response to water stress during the dry season.