Study On Water-Consumption Characteristics And Drought-Resistance Mechanism Of Three Medicinal Plants In Loess Plateau

The water consumption characteristics and drought-resistance mechanism were studied by pot-culture seedlings in Yangling of China. Three different levels of soil water treatments with 75% (CK), 55% (MD) and 40% (SD) field water capacity were set by artificially controlling the soil moisture. The three medicinal plant seedlings (Glycyrrhiza uralensis Fisch, Platycodon grandiflorum and Isatis indigotica Fort) were from loess plateau. The physiological indexes include water physiological characteristics, water use efficiency, osmotic adjustment substance, principal protective enzyme activity, photosynthetic pigment etc. of three medicinal plant seedlings under 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 plant species in Loess Plateau. The main results are as follows:1. Different soil water content had obviously affected on water consumption characteristics of 3 medicinal plants. The water consumption of 3 species was obviously different in days, ten or thirty day periods under the same soil water content and same environment. In the same water condition, the water consumption of the three medicinal plants showed Isatis indigotica Fort>Platycodon grandiflorum>Glycyrrhiza uralensis Fisch, and for the same plant species under different soil water content, that showed 75%(CK) >55%(MD) >40%(SD). Different soil water content had obviously affected the total water consumption of the three plant species, but water consumption rhythm of the three plant species under different soil water content was basically similar, and so was the distribution proportion of total water consumption in every ten or thirty days. It showed that the condition outside is the main reason which affect the water consumption of three different medicinal plants. The water consumption trend of three different medicinal plants in a day all have only one peak waving curve, and with the extending of water stress the peak of waving curve advanced. Possibly it is because plants under water stress, close some stomas in order to reduce evaporating of plants.2. Different soil water content had affected the growth of 3 medicinal plants seriously. The content of soil water effected the growth of plants both overground and underground. The growing rates of all three species were the highest under adequate soil water condition, and were the lowest under severe drought condition. Water stress limited growth of the plants seriously, and the difference of substance accumulation is obviously(P<0.05).Under 55%θf and 40%θf, Glycyrrhiza uralensis Fisch have the least descend of substance accumulation both overground and underground. It means that under water stress Glycyrrhiza uralensis Fisch have more drought-resistance ability. Because the effect of drought on overground and underground of 3 medicinal plants is disaccord, so root shoot ratio of 3 medicinal plants have much difference. The root shoot ratio of all three medicinal plants under 55%θf is higher than 40%θf, maybe because plants under 55%θf can adjust the distribution of organic substance rapidly, increase water absorbing capacity under water stress, adapt the drought. The water use efficiency of three medicinal plants have much difference, and the effect of different water stress on the water use efficiency of three medicinal plants also have much difference. The water use efficiency of three medicinal plants in the same soil water content showed Glycyrrhiza uralensis Fisch>Isatis indigotica Fort>Platycodon grandiflorum. It means that under water stress Glycyrrhiza uralensis Fisch can make the best of the limited water for there growth and development.3.The abilities of drought-resistance of three medicinal plants 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 medicinal plants had different drought-resistance mechanisms in response to soil water stress. Glycyrrhiza uralensis Fisch had higher protective enzyme activity and higher soluble sugar content and soluble sugar content,lower water consumption, developed root system, and higher root shoot ratio and variety activity of root vigor so it could absorb more water rapidly in order to complement water evaporating, have strong tolerance. Platycodon grandiflorum have higher RWC, water retaining capacity and stability membrane. In this ways plants reduce harm of superoxide anion, increase endurance to drought. Radix Isatidis have high water consumption , superoxide anion increased obviously, the content of chlorophyll reduced obviously, so the ability of drought-resistance is weak. Main components analysis was conducted to reveal the inherent mechanisms of drought resistance and compare the ability of drought-resistance of three medicinal plants.The result is Glycyrrhiza uralensis Fisch>Platycodon grandiflorum> Isatis indigotica Fort...