Tsunahide Shidei

An ecological study of soils in the Highlands of western Tibet I. Soils along an iso-altitudinal transect across western Tibet

A variety of soil studies were carried out along a 920-km transect running SE to NW from near the border with northern Nepal, through the Western Tibet Highlands (soils sampled at six locations at an elevation of about 4200 m), to the Takla Makan Desert. This transect, which parallels the China-India border, covers a range of aridities. Annual precipitation decreased exponentially (from 169 mm to ca. 50 mm) north-westwards along the transect. The humidity index also decreased exponentially to the desert zone in the Western Tibet Highlands, and decreased further in the Takla Makan Desert because of the high temperature in the latter area. Vegetation changed fromCaragana thorn-bush steppe, throughArtemisia sparse steppe, to desert. Soil properties were studied in relation to the humidity index. Organic C, total N, cation exchange capacity, and very low C/N ratio values (a maximum of 12.8) of soils decreased with the decrease in humidity index. In contrast, carbonate, pH (KCl), and sulfate increased exponentially. Available P and ammonia content were inversely related to the abundance of carbonate, whereas nitrate increased where carbonate was abundant. Illite was the most abundant of the clay minerals, followed in order by kaolinite and montmorillonite.

An ecological study of soils in the Highlands of western Tibet. II: Vertical change from 3900 m to 5450 m in elevation

AbstractsTwo kinds of soil study were carried out in the south-western Tibet region of China. Changes in soil properties with elevation were examined from the snout of a glacier at 5450 m above sea level down to a village (Burang) at 3900 m. The area close to the glacier was devoid of vegetation, probably because of the coldness. With a decrease in elevation, the landscape changed from desert to sparseArtemisia steppe, and below 4750 m, to a thorn-bush steppe dominated byCaragana spp. which continued down to the village (where the annual precipitation was 169 mm). Organic C, total N and cation exchange capacity (CEC) all increased with decreasing elevation down to 4700 m due to the increase in warmth, but the parameters decreased below 4700 m, reflecting the increase in aridity. Almost no carbonate was detected in areas above 4700 m, but below this elevation it increased exponentially, also reflecting the increase of aridity. Available P tended to decrease with both the decrease in elevation and the increase in carbonate.The vertical distribution of soil parameters was investigated in the soil profiles of dry and wet plots at 4700 m. Organic C, total N, and CEC decreased with increasing soil depth. Their values were higher in the dry plot than in the wet plot. In the dry plot, carbonate increased with depth. Total P was found to be similar in both the wet and dry plots, but there was less available P in the soil of the dry plot, reflecting the abundance of calcium carbonate.