Studies On Drought Resistance Of Xanthoceras Sorbifolia Seedlings

Xanthoceras sorbifolia bunge also called papayas and Wendengge was a plant ofxanthoceras department of Sapindaceae, a single species. X.sorbifolia bunge was widelydistributed in north China, which are with high resistance to cold, poor soil, drought. And itbecame a kind of preferred trees for mountain afforestation, returning farmland to forest,and the biodiesel. So the X.sorbifolia Bunge is endemic species of subtropical oil trees inChina. It has high integrated economic benefit for its oil, edible, medicinal and ornamentalusages. In the north of China, it is in arid and semiarid areas, water is the key factors thataffected plant growth. Water stress can interfere with the normal physiological activity ofthe trees. Production loss caused by drought stress was greater than the sum of productionloss caused by other environmental stress factors. The characteristics of plant itself was animportant factor to determine water use efficiency, so it has importantly theoretical andpractical value to measure and analyze the physiological characteristics, photosyntheticcharacteristics and drought-resistant ability.The trees tested were collected from Yan’an of Shanxi, Jingyuan of Gansu, Xunhua ofQinghai, Chifeng of Inner Mongolia, Kashi of Xinjiang. Drought stress experiment wasperformed by being prior to rhizosphere water stress with pot gradient method. As pot watercontrol test was under different drought: Ck was75%~80%; light drought stress was55%~60%; moderate drought stress is40%~45%; severe drought stress was30%~35%. Thephysiological characteristics under drought stress were investigated through determining leafsoluble sugar, peroxidase activity, MDA and so on; the photosynthetic characteristics ofplants under drought stress were investigated through the determination of the photosyntheticand fluorescent parameters with the Li-6400portable photosynthesis system (Li-COR, USA)and fluorescence spectrometer(FMS-2, UK). The main conclusion was following.(1)With the drought stress intensifying, osmotic regulation substances such as solublesugar content, proline, soluble protein, rose gradually, reach the maximum under severedrought stress. Under the severe drought stress, soluble sugar increased much more thansoluble protein and proline, which indicated that the more accumulation of soluble sugar wasthe compensation of the proline and soluble protein under the severe drought stress.(2)Under the different drought stress, the protective enzyme activity changed differently; under light drought stress, the SOD activity increased, the CAT activity decreasing; undersevere drought stress, SOD, CAT activity decreased obviously, which could not effectivelyfree oxygen radicals, so membrane lipid peroxidation was strengthened. It was consistent withthe increased MDA. It was obvious that SOD and CAT played a main role in removal of freeoxygen radicals, which reduced the membrane lipid peroxidation and maintained the structureand function of membrane system under drought stress.(3) With the drought stress intensifying, Ci also significantly reduced with Pn falling atthe same time, but the Ls rose higher differently. It showed that under the drought stress, thereduction of the photosynthetic rate was caused by the stomatal conduction. While under themild drought and severe drought stressWith Pn and Ci declining, Ls did not decline significantly compared with controls. Itshowed that under moderate and severe drought stress, the reduction of the photosyntheticrate was not caused by the stomatal limitation.(4) As the drought stress aggravated, biomass of X.sorbifoliafrom different provenancesignificantly reduced; however the root-shoot ratio increased. It meant that X.sorbifoliareduced the part of the allocation in the stem and leaves, and increased the organic material inthe root. So it was the strategy drought resistance of X.sorbifolia was enhanced at the cost ofbiomass.(5)13physiological indexes of the five provenance of X.sorbifolia under drought stresswere calculated with the subordinate function analysis, which showed that the average of theindex was higher, the strength of their drought resistance was stronger; then to evaluatedrought resistance ability of the X.sorbifolia from different provenances. The results showedthat the drought resistance ability ranged from strong to weak in order: Kashi of Xinjiang>Jingyuan of Gansu> Chifeng of Inner Mongolia> Xunhua of Qinghai> Yan’an of Shanxi.