| Form. Helianthemum soongoricum is one of the main formation in the desert of west Edors,which is distributing on lithoid and shingly foothill around Zhuozi mountain and Gangdegermountain. Helianthemum soongoricum, single genus and species in china, remaining from Tertiary,is national secondary protective plant, which plays important roles not only in maintaining thefunction of desert ecological system but also in researching environmental evolvement,plantfloristic,biologic evolvement,biodiversity and global change. By investigating and measuredcommunity characteristics,transpiration property and community evapotranspritantion ofHelianthemum soongoricum, we just tried to discuss the mechanism of water use and communityformation of Helianthemum soongoricum. The main results are as follows:1. The roots of Helianthemum soongoricum were distributed in the surface soil layer 0—30cm, and most of them were concentrated in the layer 10—20cm; Helianthemum soongoricummainly distributed on the middle and crest of lithoid and shingly slope of the foothill whichcovered with a lot of blocks; Form. Helianthemum soongoricum, general coverage of which is 3%—13%, including Ass. Helianthemum soongoricum+Convolvulus tragacanthoides+Ajaniaachilleoides and Ass. Helianthemum soongoricum+Tetraena mongolica+Reaumuria trigyna, wasof simple structure and sparse vegetation and consisted of xeric and strong xeric undershrub,xericperennial grass and obvious annual herblayer just under better soil water condition; Among July,August and September, underground biomass increased gradually, and biomass of abovegroundpart and each organ reached the maximum value in August.2. The distribution pattern of Helianthemum soongoricum population was random andclumped. In Ass. Helianthemum soongoricum+Convolvulus tragacanthoides+Ajania achilleoides,the distribution pattern was random, which was resulted from homogenization of environmentresources due to the decrease of heterogeneity of soil moisture in the middle and top slop, and theoptimum sampling area was 8m×8m; In Ass. Helianthemum soongoricum+Tetraenamongolica+Reaumuria trigyna, the distribution pattern was clumped, which might have relation tothe placement of square and spatial heterogeneity of soil moisture, and the optimum sampling area was 16m×16m.3. The water potential of leaves, influenced distinctly by air temperature and relative humidity,reached the maximum value in the early morning, and minimum value at 13:00 pm, and rosegradually after 17:00 pm. Diurnal change curve of transpiration was convexity, and diurnaltranspiration was 0.13kg/m~2, which was mostly affected by air temperature and radiation; In Julyand August, diurnal net productivity was 0.55g/m~2 and water use efficiency was 4.23g/kg.4. In July and August, because of plenty of precipitation the average soil water content washigher, and that of crest,middle slope and lower slope reached the maximum value in the layer 0—10cm,10—20cm and 20—30cm respectively. In September, there was no precipitation, so theaverage soil water content was lower, and that of surface soil decreased. For soil water content theposition order is: middle slope＞lower slope≈crest. In July and August, the water surplus or deficitof Form. Helianthemum soongoricum tended to be negative balance, and the value of defict ofwater is 5.98mm. And most of precipitation was lost in the form of soil evaporation,surface runoffand leakage.
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