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51 SummaryThe distribution of nematode communities with depth in greenhouse soil of different ages from Shenyang suburb was investigated in October 2004. Thirteen families and 23 genera were observed in our study. Heterocephalobus was dominant genus in all treatments. The numbers of total nematodes and trophic groups declined with soil depth but increased with greenhouse age. Bacterivores were the most abundant trophic group in all treatments, followed by plant parasites and omnivores-predators, while fungivores were the least, only accounted for less than 4 % of the total abundance. Maturity index (MI) and plant parasite index (PPI) were effective in distinguishing differences in nematode community structure in different ages of greenhouses. The numbers of total nematodes were positively correlated with soil organic carbon, total nitrogen, nitrate, and electrolytic conductivity, but negatively with soil pH.

Abstract. Livestock exclosure has been widely used as an approach for grassland restoration. However, the effects of exclosures on grasslands are controversial and can depend on many factors, such as the grassland ecosystem types, evolutionary history and so on. In this study, we conduct field experiments to investigate the variations of the ecosystem function in response to livestock exclosure in a Kobresia humilis meadow with 6 years of grazing exclosure on the QinghaiTibetan Plateau. We focused on two ecosystem functions: plant community structure and ecosystem carbon cycling. The plant aboveground productivity, plant diversity and the composition of plant functional groups of the meadow were addressed as the indicators of the plant community structure. The 13 C isotope pulse labeling technique was applied to evaluate the alterations of ecosystem carbon cycling during a short term. The results showed that the plant community structure was changed after being fenced in for 6 years, with significantly decreased aboveground productivity, species loss and varied composition of the four plant functional groups (grasses, sedges, legumes and forbs). Using the pulse labeling technique, we found a lower cycling rate of 13 C in the plant-soil system of the fenced plots compared with the grazed sites during the first 24 h after labeling. A higher proportion of recovered 13 C in the plant-soil system migrated into the soil as root exudates immediately after labeling at both fenced and control grazed sites, with a significantly lower proportion in the fenced site, coinciding with the lower proportion of 13 C lost from soil respiration. Thirtytwo days after labeling, 37 % of the recovered 13 C remained in the soil of the fenced plots, with significant differences compared to in the grazed plots (47 %). In addition, less 13 C (5 vs. 7 %) was lost by soil respiration in the fenced plots during the chase period of 32 days. Overall, our study suggests that livestock exclosures have negative effects on the plant community structure and partitioning patterns of the photoassimilated carbon in the Kobresia meadow, and the effects on photoassimilated carbon cycling are likely to result from the variations of community structures in the ecosystem.

The effect of cattle grazing on the soil nematode and protozoan communities, and on microbial biomass, was measured in Israel's northern highlands. Three grazing areas were compared: (1) with 1Á1 cow ha À1 y À1; (2) 0Á55 cow ha À1 y À1; and (3) control-no grazing for almost 18 years.Soil samples were collected from the upper 10 cm level of each area (n ¼ 24), in autumn, before the onset of the rainy season, in order to analyse soil moisture, organic matter, total nitrogen, microbial biomass, soil respiration, soil free-living nematodes, as well as ciliate and flagellate populations.Soil microbial biomass and soil free-living nematodes showed no clear differences in impact between heavy and moderate grazing. However, ciliates and flagellates showed a significant response to different grazing pressures.