Response Of Wet Soil Fauna To Soil Moisture Of Betula Ermanii Forest Line Ecotone In Changbai Mountain

Treeline is the upper limit of the mountain,which is a sensitive area of ecological environment change and an important ecological ecotone in the world.The upper limit of Betula ermanii in the Changbai Mountain is dominated by birch seedlings newly encroachment.As the upper boundary of the treeline,it has a more positive response to the change of environmental factors.As an important environmental factor,water has a significant impact on forest line composition and upward migration.Soil water availability affects the habitat suitability of soil faunas through direct or indirect effects on plants and soil.In order to investigate the response of the upper limit wet soil fauna community structure to soil moisture in the upper limit of Betula ermanii,soil nematodes were investigated in the upper treeline of the Changbai Mountain.Statistical analysis methods such as regression analysis,Person analysis,ABT analysis and piecewise structural equation model(SEM)were comprehensively used to study the nematode community structure,composition,diversity and functional groups under different water conditions in the upper limit of Betula ermanii.The main conclusions are as follows:(1)The interactions between water distance gradient and altitude had significant effects on soil function,nematode abundance,nematode biomass and nematode energy channels(p < 0.05).Soil total carbon in the tundra was significantly higher than that in Betula ermanii treeline and Betula ermanii forest(p < 0.05).However,no significant difference was found between tundra and Betula ermanii treeline(p > 0.05).The water distance gradient had a significant difference in soil total nitrogen and available phosphorus,which showed a decreasing trend with the increase in distance;(2)Through energy channel analysis,we found that the bacterial channel,plant channel and predation channel in nematode community in tundra were significantly higher than that in Betula ermanii treeline and Betula ermanii forest in 0 m and 10 m treatment,while the bacterial channel and plant channel in tundra were significantly lower than that in Betula ermanii treeline and Betula ermanii forest in 20 m and 30 m treatment.(3)The biomass and energy channels of different trophic groups of nematodes were significantly correlated with soil physical and chemical properties,indicating that soil physical and chemical properties were affected by elevation gradient or water gradient,which could directly affect soil nematode community structure;(4)The responses of nematode communities with different altitude gradients to dry and wet stress were estimated in laboratory incubation experiments.It was found that although water increase/decrease had no significant effect on the overall abundance of nematode,however,it could change the energy structure of nematode communities by changing their compositions.In addition,the sensitivity of different altitudegradients showed different trends,which at the higher the altitude,the weaker the buffering ability of the region to water stress.In conclusion,water distance gradient changes nematode community structure and internal energy flow pathway by affecting soil water content,and thus,indirectly affects the change of system versatility.Altitude gradient directly changes nematode community structure and internal energy flow pathway,and indirectly affects the system versatility.