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Caragana stenophylla belonging to genus Caragana, is one of species which has widest distributing area and largest number in Mongolia plateau. C. stenophylla range broadly in typical steppe, steppe desert, and desert steppe, where it dominates and becomes into bush woods in west sandy ridge-land. C.stenophylla has good ecological adaptation, and good ability in windbreak and sand-fixation, keeps water and soil, and beautifies the environment, so that it can be one of sand-fixation forestation species in arid and semiarid area. In addition, the stems of C.stenophylla are rich in nourishment to provide the stock high quality forage, in that way, it is not only of high ecological value, but also of important economic effects. Here we sampled in dominant location of C. stenophylla, in Ordos desert steppe and SiZiWangQi desert steppe, studied its biological and community characteristics, and then did compare between C.stenophylla and Caragana microphylla Lam, in order to explore external morphological and internal regulating factors that effected draught-resistance of C.stenophylla, and to understand its wide-spread adaption mechanism.Results of our study are as following:1.In natural condition, C.stenophylla germinated in early May, its flower buds appeared in late May, it flowered between late May and early June, with long flowering period and big difference among individuals, and in early July, it began to seed and matured one after another. During its growing season, it was in May that SLA arrive its highest value, while July shrub height and diameter in highest point. Besides of Sexual reproduction, C.stenophylla could also do asexual reproduction, which with large number and well-developed rhizomes that could sprout many branches, which could produce adventitious roots and buds to grow up as new branches when they were buried by sand.2.Leaf water content(LWC) of C.stenophylla was significantly lower in July than in other growing months, while natural water saturation deficit (NWSD) was significantly higher than others. When comparing with C.microphylla Lam, LWC and NWSD of C.stenophylla was higher than the former in months with low soil water, just on the contrary while in months with good soil water. After 4hours, rate of water loss of C.stenophylla was lower than C.microphylla Lam, meanwhile, time when leaves weight keeps still was longer in the former than the latter.3.According to seasons and water in environments changing, osmotic adjustment of accumulation showed significantly adaptable regulation. When in July and August with low environmental water, C.stenophylla significantly accumulated osmotic regulation substances, in the form of free proline, organic acid and cytosolic calcium concentration. Besides, substances engaged in osmotic regulation were different according to different degree of drought-stress in different season.Comparing with C.microphylla Lam, free proline and other osmotic regulation substances of C.stenophylla accumulated more than C.microphylla Lam when in arid seasons.4.CAT, SOD and MDA of C.stenophylla was more sensitive with increasing in arid months, and activity of three protective enzymes were higher than C.microphylla Lam, while the content of MDA was lower than the latter. According to membership function, we did comprehensive analysis to osmotic regulation substances, protective enzymes and other physiological and biochemical parameters and found that membership value of C.stenophylla was higher than C. microphylla Lam.5.In natural sunshine weather, net photosynthetic rate, transpiration rate and stomatal conductance of C.stenophylla indicated different daily changing curve types, that were,one-peak-curve, two-peak-curve and gentle curve because of photosynthetic middy depression at noon. Seasonal dynamic regulations of net photosynthetic rate and transpiration rate of C.stenophylla were similar, with June highest, and September lowest, and there were significant difference between two months. Doing comprehensive analysis for all factors in the whole growing seasons, we concluded that the major factor effecting Pn of C.stenophylla were Tr、Ca and PAR, while major factor effecting Tr was Gs. Comparing with C.microphylla Lam, the daily mean of net photosynthetic rate, transpiration rate and stomatal conductance of C.stenophylla was higher than C.microphylla Lam in months with high temperature and low environmental water. While light compensation point(LCP)and the light saturation point(LSP), optimum temperature and atmospheric moisture of C.stenophylla were all higher than C.microphylla Lam, but quite the opposite for CO2 compensation point.6.In the communities of varying degree of bush woods, of C.stenophylla mainly distributed in the way of aggregation, while in large scale, there was random distribution for communities of lower degree of bush woods. In the formation of bush woods of C.stenophylla, it is shown positive (mutually promoted) ecological correlations for inner-community.7.Total dry biomass in the aboveground, vegetation coverage and bio-diversity in C.stenophylla communities increased with the degree of bush woods. Our study results indicated that all of four explored communities were in some degree of desertification, and communities I was in lowest degree. Most of soil nutrient contents were higher in C.stenophylla communities than grass community I when doing compare, meanwhile, there was some way of difference among these soil nutrient. From under-bush woods to inner-bush woods, Most of soil nutrient contents of C.stenophylla decreased gradually; moreover, the difference between under-bush woods and inner-bush woods became bigger with the degree of bush woods increasing.
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