Study On Water-Consumption Characteristics And Drought-Resistance Mechanism Of Three Native Tree Species In Loess Plateau

The growth development, water consumption characteristics and drought-resistance mechanism of three native tree species (Syringa oblata Lindl.,Periploca sepium Bunge. and Forsythia suspense (Thunb.) Vahl.) were studied by pot-culture seedlings in Yangling of China . Three different levels of soil-water-treatments were set by artificially controlling soil moisture. The physiological indexes include the time and space changes of water metabolism, osmotic adjustment substance, principal protective enzyme activity, and photosynthesis pigment of three tree species of different soil-water stress. We made a comprehensive evaluation of three species, expecting to discover the differences of the drought-resistance ability among them. The results provided scientific basis of choosing tree species in Loess Plateau. The main results are as follows:1. Different soil water content had obviously affected on water consumption characteristics of 3 native tree species. The water consumption of 3 species was obviously different in days, ten-day periods and monthly under the same soil water content and same environment. Water consumption of Forsythia suspense was the highest and that of Syringa oblate was the lowest. The highest water consumption of three species concentrated on 6, 7, 8 three months. Soil water content decided on water consumption. The water consumption of the same tree species were different under different soil water content, and the trend was 70%θf>55%θf>40%θf。Syringa oblate was low water consumption specie, while Forsythia suspense and Periploca sepium were high water consumption species.2. Different soil water content had affected 3 tree species growing. Adequate soil water conditon, seedling survival rate, and growing rate under drought condition were compared. The survival rate of Forsythia suspense and Syringa oblate seedlings were over 90% under adequate soil water content, and decreased markedly with the decrease of soil water content. On the contrary, Periploca sepium had a stable survival rate, which hints a large-ranging water adaptation range of Periploca sepium. The growing rates of all three species were the highest under adequate soil water condition, and were the lowest under severe drought condition, which was more marked in Forsythia suspense. Under the same water condition, Forsythia suspense grew fastest while Syringa oblate did slowest. 3. WUE of 3 tree species had been affected by different soil water content. The result about WUE of three species under the same soil water content was Syringa oblate>Forsythia suspense>Periploca sepium. Under different soil water content, WUE of each species had its own way of changes. The WUE of Syringa oblate was the highest under adequate soil water content, and was the lowest under medium drought condition. However, the WUE of Forsythia suspense was the highest under medium drought condition while that under severe drought was the lowest. As to Periploca sepium, there was no obvious difference of WUE between adequate soil water content and medium drought condition, and WUE under severe drought condition was the lowest. Therefore, when using Periploca sepium or Forsythia suspense for afforestation, we can control soil water content at suitable level so as to reduce their water consumption and get the higher WUE. Due to the lowest water consumption and the highest WUE under the adequate soil water content, Syringa oblate could be extensively planted wherever the soil water content is adequate, so that it can grow quickly and play an important role in soil and water conservation.4. The abilities of drought-resistance of three native tree species are different. Soil water stress had obviously affected on the water physiological characters and other biological characters. Comparing all indexes of three species, we found that different tree species had different drought-resistance mechanisms in response to soil water stress. Syringa oblate had higher protective enzyme activity and lower water consumption. Especially, the roots of Syringa oblate were very strong and had the outstanding ability of absorbing water from soil. As to Periploca sepium, on one hand, it had higher relative water content and better water preserving capacity; On the other hand, it could accumulate a lot of osmotic substances to reduce water potential and lessen the damage by the destructive oxidation. Under drought condition, the SOD, POD activities of Forsythia suspense were very high. At the same time, Forsythia suspense can accumulate many osmotic regulation substances to fight with the drought condition. Main components analysis was conducted to reveal the inherent mechanisms of drought resistance and compare the ability of drought-resistance of three native species. The result is Periploca sepium>Forsythia suspense>Syringa oblate.