Study On Water-Consumption Characteristics And Drought-Resistancemechanism Of Four Native Gramineous Grass In Loess Plateau

The growth development, strategy of water using and drought-resistance mechanism of four native gramineous grass(Stipa bungeana, Bothriochloa ischaemum, Cleistogenes songorica and Agropyron cristatum) in Loess plateau were studied by pot culture experiments simulating different soil water status in Yangling of China. The different levels of soil-water-treatments were set by artificially controlling soil moisture. This paper mainly studied the time and space changes of water metabolism and growth, photosynthesis characteristic and photosynthesis pigment, water physiological characters, protective enzymes activities, osmotic adjustment substances, WUE ,and the community biomass of four species, expecting to discover the differences of the drought-resistance ability and the strategy of water-using between them. The results provided scientific basis of vegetation restoration and community succession in Loess plateau. The main results are as follows:1. Different soil water content had obviously affected on water consumption characteristics of four species. The trends of water consumption of four species in a month and the total water consumption were adequate water(75%θf)>medium stress(55%θf)>severe stress(40%θf). The results showed that water consumption of those species decreased with the increase of soil drought stress, and water consumption of those grasses was different: Bothriochloa ischaemum>Agropyron cristatum> Cleistogenes songorica>Stipa bungeana. The highest water consumption in one day, ten-day and one month were different. The highest water consumption day of medium and severe drought stress occurred about 10 days earlier than the adequate soil water content. The time of day when the greatest water consumption occurred arrived early with the decrease of soil water contents.2. The growth of plant height and single leaf area of the four native grasses were the fastest under adequate soil water contents, and were the lowest under severe drought .Under drought condition, the growth of four grasses was all inhibited, especially for S. bungeana and C. songorica. The growth of four species had been restrained and WUE was affected strongly under drought stress. Water use efficiency of S. bungeana and C. songorica decreased with the decrease of soil water content, they had lower water consumption and low WUE characteristics. A. cristatum and B. ischaemum had the highest WUE under medium drought treatments, respectively. A. cristatum had low water consumption and high WUE characteristic, B. ischaemum had high water consumption and high WUE characteristic.3. The leaf water content of different species decreased with the increase of soil water stress. The RWC of A. cristatum and B. ischaemum were higher than that of S. bungeana and C. songorica obviously under three different soil water conditions in the different growth stage, and maintained stable range, had better water preserving capacity. Besides, the content of photosynthesis pigment of four species decreased at early stress stage under three soil water conditions, which shows that drought-stress affected the synthesis of photosynthesis pigment .But the content of photosynthesis pigment of A. cristatum and B. ischaemum were higher than that of S. bungeana and C. songorica obviously under drought treatments to keep the normal metabolism.4. The effects of protective enzymes activities and osmotic adjustment substances were different on four species under different water contents. The content of O2-·and the content of MDA increased under drought stress. With the extending of water stress, the activity of four species enzymes, such as SOD, POD, CAT, APX in the leaves of the four species were up-down fluctuating, and coordinated interactively. In the meanwhile, the content of osmoregulation substance, such as proline, soluble sugar, soluble protein, and K+, accumulated continuously under drought stress, which combined action with protective enzymes above and made the content of O2-·and the content of MDA down in the middle-later period. At the early and middle water stress stages, they may boost up the protective enzymes activities to protect the endosmosis from damaging. As the protective enzymes activities weaker at the following stage, they may adopt the strategy of improving osmotic adjustment substances content to adapt drought. The content of proline, soluble sugar and soluble protein of A. cristatum and B. ischaemum were more than those of S. bungeana and C. songorica under drought treatments. But the content of K+, Ca2+ and Na+ of C. songorica were more than the others. Main components analysis was conducted to reveal the ability of drought-resistance of four species. The result is A. cristatum >B. ischaemum>S. bungeana > C. songorica.