[Water distribution patterns in different degraded desert grasslands of Reaumuria soongorica]

Water distribution pattern and water use-efficiency in soil-plant-atmosphere system for light, medium, and heavy degraded Reaumuria soongorica grasslands were studied in Alashan region of Inner Mongolia. The total precipitation in 2001 was 124.3 mm, of which 119.4 mm occured during experimental period. Soil water content (SWC) in 10-40 cm layer was greatly affected by the evapotranspiration. The SWC in 10-20 cm layer of medium degraded grassland paddock was significantly lower (P < 0.05), and the SWC in 20-40 cm layer of light degraded paddock was lower than that of other paddocks due to different transpiration rate and root distribution depth between the main co-existing plant species of R. soongorica and Cleistogenes soongorica in the paddocks. The annual average bare land evaporation and R. soongorica population transpiration were 30.6 mm and 11.9 mm, respectively. As the grassland further degraded, the bare land evaporation and transpiration through Peganum nigellastrum population, a degradation indicating plant species, increased, while the transpiration of R. soongorica decreased. In addition, the water use-efficiency of the grassland and dominant plant species markedly decreased with the increasing grassland degradation. Compared to the light degraded paddocks, for instance, the water use-efficiency of medium and heavy degraded paddocks were reduced by 14.6% and 46.1% for total biomass production, and by 37.8% and 73.8% for R. soongorica, respectively.