Abstract: In order to understand the effects of vegetation succession on soil nematode community, we investigated soil properties, microorganism amount and nematode communities in dry season (April) and rainy season (August) at different stages of secondary succession in evergreen broadleaved forests of Ailao Mountain. Our results showed that the total abundance and genus number of nematodes and the densities of herbivores, fungivores and predatoromnivores increased, while the density of bacterivores decreased along vegetation succession. The mature index (MI) and trophic diversity (TD) of nematode communities were higher in mature stage forests as compared to early stage forests, but there was an opposite trend for Wasilewska index (WI). Canonical redundancy analysis showed that soil nematode communities were affected by soil moisture, pH and inorganic N contents at different stages of secondary succession. Magnitude of seasonal effects (R²) on nematode community structure was in order of evergreen broad-leaved forest (14%), Populus bonatii forest (15%), Alnus nepalensis forest (22%), and tea plantation (33%). With vegetation succession, soil nematode food web complexity increased, and its dependence on resources of plant roots and fungi was enhanced. Meanwhile, the seasonal stability of trophic structure, community structure and functional index of nematode communities increased along the chronosequence of succession.

Key words: stream fish, critical swimming speed, principal component analysis, burst swimming speed., fin