[Distribution pattern of Rhododendron aganniphum var. schizopeplum population at the timberline of Sejila Mountains, Tibet of China].

Rhododendron aganniphum var. schizopeplum grows at the elevation of 4300-4500 m in Sejila Mountains, being a dominant species of shrub layer at the timberline of southeast Tibet. Based on the sampling plot investigation and basal diameter structure analysis, this paper studied the distribution pattern of R. aganniphum var. schizopeplum population at the timberline of Sejila Mountains. With the increase of altitude, the population density of R. aganniphum var. schizopeplum increased, but the population height decreased. At the same altitudes, the population density on the shady slope was larger than that on the sunny slope, while the basal diameter was smaller. On the two slope directions, the distribution of the basal diameter classes of the population appeared as "(see text for symbol)" shape, i. e., middle-aged individuals were more, while seedlings and saplings were relatively less. The intraspecific competition of R. aganniphum var. schizopeplum population was in the form of wave, being stronger on shady slope than on sunny slope, and existing self-thinning.

[Characteristics of soil nematode community in Abies georgei var. smithii forest gaps in south-east Tibet, China].

In order to understand the characteristics of soil nematode community in the Abies georgei var. smithii forest gaps in southeast Tibet, an investigation was conducted to study the variations of soil nematode community at different depths of 0-30 cm soil layer in the gaps and non-gaps. The nematode individual density, diversity index, and trophic group index were taken to analyze the composition and structural characteristics of the soil nematode community. A total of 26801 soil nematodes belonging to 2 classes, 5 orders, and 64 genera were collected by shallow dish method. The nematode individual density was averagely 3552 ind x 100 g(-1) dry soil, and the individuals had a highly surface-gathering characteristics. In the gap soils, the dominant genera were Tylencholaimus and Filenchus, while the dominant trophic group was bacterivores. The soil organic matter was decomposed by both bacteria and fungi. The ecological index results showed that the nematodes diversity and richness were related to gap size. The characteristics of soil nematode community in the gaps were different from those in closed stand and forest open land, and this difference indicated the potential for using nematodes as the environmental indicator species.

[Community characteristics of soil nematode in Abies georgei var. smithii forest in Sejila Mountain of Tibet, Southwest China].

In order to understand the present status of nematode diversity in soil ecosystem of Abies georgei var. smithii forest, the typical forest type in subalpine zone of southeastern Tibet, an investigation was made on the nematode community in different soil layers of 0-30 cm depth from the summer, 2010 to the spring, 2011. The nematode individual density, diversity index, and trophic group index were taken to analyze the composition and structural characteristics of the soil nematode community. A total of 7915 soil nematodes belonging to 2 classes, 6 orders, 38 families, and 67 genera were collected by shallow dish method. The nematode individual density was averagely 620 nematodes x 100 g(-1) dry soil, and the nematode individuals in surface soil layer (0-5 cm) accounted for 56.9% of the total, indicating the obvious surface gathering characteristics of the nematode community. Tylencholaimus, Helicotylenchus, and Plectus were the dominant genus. Plant-parasite nematode was the dominant trophic group, while fungi-feeding nematode had the largest proportion among the non plant-parasite nematodes. Soil organic matter was mainly decomposed by fungi. The ANOVA analysis indicated that there were no significant differences in the Shannon, Pielou, Margalef, and Simpson indices of soil nematode community among different seasons. The Pielou index had no significant difference among different soil layers, while the differences of Shannon, Margalef, and Simpson indices tended to be increased with increasing soil depth. It was concluded that the A. georgei var. smithii forest ecosystem in Sejila Mountain had a high maturity, with strong resistance to environment disturbances.