Analysis On The Characteristics Of The Community Composition, Evapotranspiration And Ecological Use Of Water Of The Typical Steppe In The Middle Reaches Of Xilin River Basin

The paper studied on characteristics of composition and evapotranspiration of the typical steppe and its dynamic changes of the seasons in the middle reaches of Xilin River Basin from 2002 to 2004. And the ecological use of water of the typical steppe was preliminary researched. The results are as follows:The main way of utility of the typical steppe is grazing. The steppes deteriorated to different degrees, including the deterioration of both plants and the soil. The biomass of Leymus chinensis steppe reduced with the deterioration. The density and the diversity index of the species were highest in mid-deteriorated communities of Leymus chinensis steppe. The biomass, density and diversity index of species all decreased with the deterioration in Stipa grandis steppe. The adaptability of grazing stress of the perennial rhizome grasses was weaker than that of the perennial brunch grasses. Dominance of the perennial rhizome grasses was replaced by the perennial brunch grasses. Furthermore, amount of xerophytes rised gradually. With the deterioration, the communities developed to xerophilization. The leaf area coefficient-K increased gradually with deterioration. The investment on leaf growth of each species in deteriorated communities was higher than that in original communities. And the leaf area index reduced with the deterioration. Moreover, with the deterioration, the soil bulk density reduced in Leymus chinensis steppe and changed a little in Stipa grandis steppe.With the deterioration, the soil water content (SWC) decreased. The surface layer of 20 or 30cm was the main layer used by communities. The SWC in this layer responded to the precipitation quickly. So the SWC in the surface layer fluctuated more dramatically than that in the deep layer. The soil bulk density (SBD) and the community evapotranspiration affected storage water of the soil dramatically. With the deterioration, the average SBD ofgrowing period reduced in Leymus chinensis steppe and changed little in Stipa grandis steppe.Daily community evapotranspiration (ET) was synthetically affected by several factors. Daily ET of the better communities correlated positively with SWC and reached the peak value in the end of June. And daily ET of the heavy deteriorated communities correlated positively with average air temperature and reached the top in the end of July. Monthly ET of each community varied with average air temperature both in equal water years and in low water years. Community ET was equal to the precipitation approximately in the end of June and the beginning of July. And it was far lower than the precipitation in the end of July and the beginning of August. The soil water of the communities accumulated in this period.Sum ET of the growing period of Leymus chinensis steppe reduced with the deterioration and changed little in Stipa grandis steppe. Sum ET of each community was not beyond precipitation both in the equal water years and in the low water years. And the water of the soil consumed by community ET could be replenished completely by the precipitation in the same term. Water use efficient of the deteriorated communities was lower than the original communities. The ratio of sum ET in ecological use of water became lower in deteriorated communities. These showed that development of the communities trended to xerophilization.Ecological use of water consumption decreased with the deterioration in Leymus chinensis steppe and was equal in the two communities of Stipa grandis steppe approximately. Sum ecological use of water consumption of this area was lower than sum precipitation of the same period in the equal water years and higher in the low water years.