Study On Water Relations For Afforestation Plants In Horinger County, Inner Mongolia

China is one of the most countries which are most vulnerable to desertification in the world. Afforestation is an important way to prevent, stop and reverse desertification in semi-arid areas.As water condition is the main limiting factor of plant growth in arid and semi-arid regions, which has a significant impact on the growth and development of afforestation plants. It has the important academic significance and realisitic guidlines to study on water relations of plants in semi-arid areas, and reveal the physiological and ecological environment of plant adaptation to arid environment.In this study, we choose 4 species, including Pinus sylvestris var. mongolica, Pinus tabulaeformis, Picea asperata, and Caragana korshinskii, as the research objects for afforestation in Horinger County, Inner Mongolia. The characteristics of plant growth, physiological response, water balance in soil-plant-air continuum (SPAC), and its related influencing factors were researched. The main results were as follows:(1) The plant growth height, the new branches length, the coverage increment of P. Sylvestris var. Mongolica and C. Korshinskii were much more than those of P. Asperata and P. Tabulaeformis. The mixed configuration of P. Sylvestris var. Mongolica and C. Korshinskii were better than the pure configuration respectively.(2) The photosynthethic rate of P. Sylvestris var. Mongolica and C. Korshinskii were higher. The water use efficiency of C. Korshinskii is lower than P. Sylvestris var. Mongolica. The water use efficiency of C. Korshinskii in the mixed configuration was higher than that in the pure configuration.(3) The soil moisture and atmospheric environment factors were significant different in different years because the annual rainfall distribution is extremely uneven in semi-acid regions. Both of atmosphere and vegetation affected the temporal and spatial distribution of soil moisture. According to the variation degrees of influence, the soil layer could be divided into rapid change layer, active layer and stabilization layer. The shallower the soil depth is, the more obvious the atomosphere influences, so as to the effect on deep soil moisture by strong precipitation.(4) The changes of soil water storage, afforestation transpiration and soil water loss were analyzed based on the calculation of potential evapotranspiration. The planting density of different afforestation were calculated on the dynamic balance of soil water. Under the conditions of 400mm precipitation, the density of P. Sylvestris var. Mongolica, C. Korshinskii and P. Tabulaeformis were 571.0, 353.3 and 410.5 plants/hm~2 in the pure configuration, and the density of P. Sylvestris var. Mongolica and C. Korshinskii were 424.3 and 212.2 plants/hm~2 respectively.Based on the results above, the following conclusions can be obtained:P. Sylvestris var. Mongolica and C. Korshinskii can keep a good growth state with high photosynthetic rate, the resistance to drought. It was obvious for P. tabulaeformis and P. asperata affected by the stress of soil moisture. The mixed configuration of P. Sylvestris var. Mongolica and C. Korshinskii was better than the pure configuration, and the density of them in the mixed configuration was suggested as 291.1 and 145.6 plants/hm~2 respectively based on the climate change, especially the actual change of precipitation in Horinger county, Inner Mongolia.