Vegetation in the sand zone of the Baiinxile Livestock Farm of Xilingol Steppe Natural Reserve was investigated during 1985–1986. The paper describes the distribution and succession of vegetation in tile sand zone,

1. Vegetation in the sand zone shows mosaic patterns of open forests-brushwood-steppe in its western part and of closed forests-brushwood -steppe in its eastern part. There exists a vegetation ecological series from west to east as the elevation increases. The Principal Component Analysis of the vegetation highlights the fact that it is the gradient of stability of sand dunes and the gradient of soil water content that control the distribution patterns of the plant communities in the sand zone;

2. Succession of primary vegetation in the sand zone is described, The successional stage coincides with the process of sand-dune fixation. The stability of plant communities is highly correlated to the stability of sand dunes. As the soil water content and heat vary with the variation of topography, the succession of vegetation has the sunlight-slope sere and the shade-slope sere, the former developing towards forests and the latter towards steppe.

3. As regards the use and conservation of vegetation resources in the sand zone, 6 suggestions are put forward.

In natural condition, the diurnal and seasonal changes in the photosynthetic rates of Aneurolepidium chinense and Stipa grandis were measured by means of a simulation chamber. The chief results obtained are as follows:

1.The types of diurnal changes in the photosynthetic rates of Aneurolepidium chinense and Stipa grandis all showed double peak curves. The high peak appeared in the morning and afternoon respectively. But the peak values in the morning always were higher than those of the afternoon.

2.The trends of seasonal changes in the diurnal net photosynthesis of two the communities were similar; The diurnal net photosynthetic rate increased rapidly from the period of turning green to the beginning of July, their maxmum values were 31.68 and ll.5gCO2/m2d respectively, and after then they gradually decreased.

3.The photosynthesis abilities of the plants, the values of the peaks and their appearance times, the fall range of photosynthesis at noon and the characteristic of the seasonal changes etc. of the two communities were closely correlated with the characteristics of the plants growth and environmental conditions.

4.The instantaneous photosynthetic rate, diurnal net photosynthesis, LAI and biomass of the Aneurolepidium chinense community were higher than those of the Stipa grandis one,but under poor(drought) environmental conditions, the increase of the photosynthesis of Stipa grandis was less than under good conditions.

5.Stipa grandis community was more drought resistant than Aneurole pidium chinense commumity, but its productivity increase under good conditions was less.

In this paper, the relationships between meso-microfauna and soil ecological factors in various types of vegetation were discussed. The major results are as follows,

1. Vertical and horizontal quantity distributions of mesomicrofauna in the different habitats were not only conditioned by a certain single ecological factor,but were also the result of the combined effect of many ecological factors.

2. There were different relations between the meso-microfauna and the organic matter content of soil in different ecological conditions.

3. The vertical quantity distribution of the meso-microfauna in the sandy land of Festuca dahurica grassland depended probably upon changes of soil temperature. That is why the sandy land has a particular pattern.

4. The responses of the meso-microfauna to the man-made changes of the ecological factors were sensitive in the grassland ecosystem.

This paper is a perliminary study of the decomposition of litter of the Xilinguole grassland major plants Aneurolepidium chinense and Stipa grandis and the dynamic changes of biomass of various of decaring microorganisms, and the effect of soil biology with decomposing litter.

The study results shows:

1. The decomposing rate of litter of Aneurolepidium chinense and Stipa grandis stems and leaves is comparatively slow. The weight loss rates were respectively 15.9%, 16.9% and 21.5% on soil aboveground; In soil underground they were 21.4%, 23.5% and 26.5% in the past two years. And the decomposing rate became more and more slow with the passage of time. The decomposing rate of litter in soil underground is higher than that on the soil aboveground.

2.In the process of decomposition of litter,the biomass of the various groups of microorganims increased markedly. Compared with microbial biomass sticking to the surface of litter, progress increase ranged from 10 to 300 times.

3. The ratio of the carbon content to the nitrogen content of the rotting residues decreased with the progress of decomposition.

4. Decomposition of litter could stimulate the increase of microbiological activity in soils of different depths, and an increase of soil organic content as well.