| In the arid and semi-arid regions, deficient in water resource has already been primary limiting factor to agriculture production and development. There are enriched light energy resource and flush heat energy and high temperature accumulation in Yuanmou county of Yunnan province, and summer is torrid, winter is warm markedly. So it is known as natural greenhouse. It is a place that can be planted desiccation-tolerant plants and fruit trees, antiseason vegetable in dry and hot river valley. But the rainfall is little and the evaporation is great. The atmosphere humidity is low. The dry season and the humid season are distinguish clearly. The factors influence the growth of plants.The study in this essay took three years old Zizyphus mauritiana Lam. trees and one year old Zizyphus mauritiana Lam. seedlings as field sampling trees. Through controlling soil moisture factitiously, the indexes of growth, biomass, water content of leaves, water content of roots, fruit quality and yield, photosynthesis rate and transpiration ratewere mainly surveyed. The effects of different soil moisture on Zizyphus mauritiana Lam. trees and Zizyphus mauritiana Lam. seedlings were mainly analyzed. It can supply theoretical gist of increasing the yield of Zizyphus mauritiana Lam. and come up to the aim of water-saving irrigation in dry-hot river valley. The results showed that:(1) Effects of different soil moisture on Zizyphus mauritiana Lam. trees①Effects of different soil moisture on the growth of Zizyphus mauritiana Lam.trees: Four different soil moisture levels (the first level A: rate of soil moisture was 40%～55% of field moisture capacity; the second level B: rate of soil moisture was 55%～70% of field moisture capacity; the third level C: rate of soil moisture was 70%～85% of field moisture capacity; the fourth level D: rate of soil moisture was 85%～100% of field moisture capacity) all did not restrain the normal growth of Zizyphus mauritiana Lam.. Principal component analysis (PCA) and R-factor general analysis were applied to make sure the first two components accounted for 72.409% and 18.156%, and the response of Zizyphus mauritiana Lam. to the second level is the best, compositor value of responding to soil moisture is 421.201; the following is the third level, the value is 385.451; finally is the first level, the value is 281.62. And finally educed the most distinct factors responing to soil moisture. During the factors, the growth of overground foot diameter, length of new branches, new branches diameter, LAI, water content of leaves and leaf area can be looked upon the leading index of studying Zizyphus mauritiana Lam. in dry and hot river valley.②Effects of different soil moisture on photosynthesis rate, transpiration rate and water usage efficiency (WUE) of Zizyphus mauritiana Lam.trees: Photosynthesis rate of Zizyphus mauritiana Lam. had close relations with soil water. The relation of Pn and photosynthetic active radiation (PAR) is quadratic polynomial function. The diurnal variation of Pn under different soil moisture of Zizyphus mauritiana Lam. presented double-peaked curve with a slight decrease occurring in noon time. The seasonal variation of Pn under different soil moisture also presented double-peaked curve, the highest number appeared in June and the secondary number appeared in September. The number of Pn under the third soil moisture level was the highest, but there was little discrepancy between the third and the second soil moisture level. The diurnal variation of transpiration rate also presented double-peaked curve. The diurnal variation and the seasonal variation of WUE of Zizyphus mauritiana Lam. were highest under the second soil moisture level, the highest number of diurnal variation appeared at 8:00, the highest number of seasonal variation appeared in May.③Water requirement of Zizyphus mauritiana Lam.trees: The study showed: under the condition which was increased the natural growth of Zizyphus mauritiana Lam., the soil water content (SWC) range which promoted the growth was 18.15%~23.10% (rate of soil moisture was 55%～70% of field moisture capacity). In this level, 3.395m3 water of one Zizyphus mauritiana Lam. tree requires during the whole growth period.(2) Effects of different soil moisture on Zizyphus mauritiana Lam. seedlings①Effects of different soil moisture on the growth of Zizyphus mauritiana Lam. seedlings: Three different soil moisture levels (the first level A: rate of soil moisture was 40%～60% of field moisture capacity; the second level B: rate of soil moisture was 60%～80% of field moisture capacity; the third level C: rate of soil moisture was 80%～100% of field moisture capacity) all impelled the fa growth of Zizyphus mauritiana Lam. seedlings. During the three soil moistures, the less the soil moisture was the more the biomass was, which was 1.07,1.14 times higher than that of the second level and the third level. The hight and the based diameter of the first level were also higher than that of the second level and the third level. The hight increased by 7.6% and 11.52%, the based diameter increased 0.08 centimeter and 0.11 centimeter, respectively. The root number of the first level was 1.34,1.68 times higher than that of the second level and the third level. Moreover, number of root diameter between 2 and 5 centimeter and less than 0.5 centimeter is better than that of the first and the second level of soil moisture. The first level of soil moisture is better for improving the WUE and for growing of Zizyphus mauritiana Lam. seedlings.②Effects of different soil moisture on photosynthesis rate, transpiration rate and water usage efficiency (WUE) of Zizyphus mauritiana Lam. seedlings: The mean number of Pn of diurnal variation and the seasonal variation under the second soil moisture level was highest. Transpiration rate increased as the soil moisture increasing. Except for trifling decline of April, transpiration rate was increased along the whole season. The diurnal variation and the seasonal variation of WUE were highest under the first soil moisture level, the highest number of diurnal variation also appeared at 8:00 (the first level: 2.58μmolCO2/mmolH2O), WUE was increased in the whole growth period.③Water requirement of Zizyphus mauritiana Lam. seedlings: The study showed: under the condition which was not influence the natural growth of Zizyphus mauritiana Lam. seedlings, the soil moisture range which promoted the growth was 13.2%~19.8% (rate of soil moisture was 40%～60% of field moisture capacity). In this level, 0.0787m3 water of one Zizyphus mauritiana Lam. seedling requires during the whole growth period.
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