Response Of Soil Nematode Communities To Two Shrub Species In Subalpine Meadows

The close relationship between underground biology and aboveground plant community and its change pattern are hot spots in ecological research.Previous studies in the（sub）alpine ecosystems of the Qinghai-Tibet Plateau have focused on the effects of dominant plants（e.g.,shrubs）in the plant communities on soil organisms,exploring the direct and indirect effects of shrubs on soil nematodes during the growing season.However,these studies never focused on the role of shrubs on soil nematodes during the non-growing season,and little consideration was given to differences in shrub effects with different functions（e.g.,nitrogen fixation and non-nitrogen fixation）.Given that the relative importance of shrubs influencing soil nematode pathways may vary on time scales（e.g.,different seasons within the year）and may be related to shrub species,the lack of research on how the influence of shrubs on soil nematodes varies with season and shrub species hinders our in-depth understanding of soil food web structure and function to shrub response patterns and underlying mechanisms.To explore the response of soil nematodes to shrubs in the alpine ecosystem of the Qinghai-Tibet Plateau in depth,and whether this response differs depending on the season and shrub species.We selected three sites on the northeastern edge of the Tibetan Plateau that are not far away（3-5 km）,Within 500-1000m of each site,there are two types of shrub meadows–Dasiphora fruticose（Non-nitrogen-fixing shrub）shrub meadows and Hippophae rhamnoides（nitrogen-fixing shrub）shrub meadows,and field sampling was carried out in spring,summer and autumn.Using taxonomy-based and trait-based community ecology analysis methods,we found that:（1）Compared with the role of shrubs,season was the strongest factor affecting the abundence,richness and community composition of soil nematodes,and the intensity of seasonal action in Hippophae rhamnoides shrub meadow was higher than that in Dasiphora fruticose shrub meadow,and in Hippophae rhamnoides shrub meadow,soil nematode abundance,richness and community composition varied more in different seasons.The shrub has a significant effect on soil nematodes mainly in Hippophae rhamnoides shrub meadows,which is mainly related to the nitrogen fixation capacity of Hippophae rhamnoides.And the effect of shrubs on soil nematodes does not differ from season to season（i.e.,there is no significant seasonal and shrub interaction）.（2）Seasons also affect the community-weighted mean of body size(CWM_{body size})of soil nematodes.At the community level,the role of season differed significantly between the two shrub meadows,while at the trophic level,the role of seasons differed little in the two shrub meadows.In addition,the effect of Hippophae rhamnoides on the CWM_{body size} of low-trophic nematodes is often significant.The above results show that the traits of the dominant taxa in soil nematode communities vary more from season to season,and the trait-based soil nematode indicators have a more obvious response to environmental changes,which can provide different information than the taxon-based indicators.（3）Although season significantly affected the ecological index of soil nematodes in the two shrub meadows,the influence of season on the ecological index in Hippophae rhamnoides shrub meadows was slightly stronger.In addition,the structure index in Hippophae rhamnoides shrub meadows was affected by seasonal and shrub interactions,indicating that the changes of soil food web structure in Hippophae rhamnoides shrub meadows were more complex than those in Dasiphora fruticose shrub meadows.Thus,differential responses of soil nematodes in the two shrub meadows eventually lead to differences in soil food web structure and function.Our study revealed that soil the responses of nematode to seasons and shrubs vary with shrub species,and soil nematode communities and ecological indices in Hippophae rhamnoides shrub meadows tend to respond more significantly to seasons and shrubs.These results suggest that although the increase of nitrogen-fixing shrubs can bring more available nitrogen to the soil,however,seasonal differences in the nitrogen-fixing capacity of shrubs may lead to instability in soil biology and food web structure,thereby affecting ecosystem functioning,emphasizing the importance of dominant species species in determining aboveground-underground connections.