Response Of Cluster Mulberry To Soil Water Stress

Cluster mulberry is a multi-value deciduous tree species, which has wide distribution and adaptability characteristics. Understanding the growth, physiological and biochemical reaction of cluster mulberry under different soil water content treatments (levels) is essential to establish various cluster mulberry plantations. Two methods, gradient water control and continuous drought stress were taken to measure the growth, Photosynthetic characteristics, moisture physiology, osmotic adjustment substances and protective enzyme activity of cluster mulberry, and to determine the reactions of growth, physiology and biochemistry with varying soil water levels. Three soil water levels were employed, and the time of treatment was 150 days. The results were as follows:1. In the condition of water stress, the plant hight and leaf area growth of cluster mulberry was restrained obviously; In comparison with Normal soil moisture, the plant hight and leaf area growth of middle drought decreased 67.13% and 63.87% respectively, the difference was significant, but the differences was not obvious with light drought; With the lengthening and deepening of drought stress, the effected of soil moisture on the accumulation of photosynthetic products in the distribution of organs significantly, and also on the above ground biomass and below ground biomass, the Root-Crown ratio increased.2. The effect on net photo synthetic rate, transpiration rate, stomatal conductance, and water use efficiency of treat leaves was increased by water stress; The diurnal course of net photosynthetic rate (Pn) displayed a two-peak pattern under different soil moisture conditions; Under the normal soil moisture and light drought conditions, the peak value were 17.55 and 15.20μmol/(m²Â·s¹) respectively, which occurred at 11:00 o'clock in the morning, but the peak value appeared at 10:00 o'clock under the middle drought condition, which was 9.60μmol/(m²Â·s¹), and the mid-day depression in net photosynthesis starts ahead by one hour and its duration is longer, both Pn and stomatal conductance (Sc) were decreased; Water use efficiency (WUE) culminated in the early morning, WUE in forenoon was higher than that in afternoon, and the decrease in daily mean of WUE was less than that of Pn; the limiting factor of photosynthesis were stomatal limitation and non-stomatal limitation, with the soil moisture content reducing, the role of non-stomatal limitation increase.3. The content of Chla and Chlb was decreased and the content of Car was increased by water stress; With the lengthening and deepening of drought stress, minimal fluorescenc (Fo) increased, maximal fluorescenc (Fm) and original light energy transforming rate (Fv/Fm) decreased, and changes in the rate increased.4. The water congtent when the phase starting to close and after phase closing were increased and the value of d, stomatal transpiration and cuticula transpiration were decreased by the water stress; The results show that stomatal transpiration is the major form of water consumption of cluster mulberry under drought stress, stomas close sensitively and quickly to decrease the transpiration rate and the loss of water.5. In the condition of water stress,ψ^sat,ψ^tlp,RWC^tlp,ROWC^tlp reduced obviously, and m_a however, increased, indicating that the cluster mulberry has capabilities of osmotic adjustmen, and the capability of water absorption and anti-dehydration increased by the water stress.6. With the increase of intensity of drought stress, the activities of SOD, POD, CAT and the solube sugar content showed an increase-and then-decreased trend; The proline and MDA content and relative conductance rate kapt a continual increasing trend, and however the solube protiein content decresed. It is showed that the protective enzyme and osmotic adjustment substances were important in the drought resistance for cluster mulberry.