Effects Of Simulated N Deposition On Soil Fauna Community Of Evergreen Broad-Leaved Forest In Rainy Area Of West China

The increasingly severe nitrogen deposition has had a significant impact on forest ecosystems,Among them,forest soil is most significantly affected by it.As important participants in the material cycle and energy flow of soil ecosystems,soil fauna play a crucial role in the formation of soil organic matter,decomposition of fauna and plant residues,and changes in soil physicochemical properties.They are considered important indicators of soil ecosystem health.At present,there is limited research on the ecological effects of soil fauna in areas with high nitrogen deposition.Area of West China region is one of the areas with severe nitrogen deposition,and changes in nitrogen deposition can affect soil biological communities.The background nitrogen deposition of the sample plot is about 95 kg hm^-2year^-1,and the nitrogen addition gradient set in the experiment mainly refers to the nitrogen addition gradient of the Harvard Forest in the United States.Based on the 7-year artificial simulation of nitrogen deposition in the evergreen broad-leaved forest of the region,this study conducted sampling analysis on three soil layers（litter layer,0-10cm,10-20cm）under three nitrogen deposition levels of CK(+0 kg hm^-2year^-1),LN(+50 kg hm^-2year^-1),and HN(+150kg hm^-2year^-1)in July and October 2021,as well as January and April 2022.The structure,distribution,and diversity characteristics of soil fauna communities under different nitrogen deposition levels were studied,The results can provide data support for the management and management of subtropical evergreen broad-leaved forests.The research results indicate that:（1）During the experiment,a total of 10704 soil animals were captured,belonging to 3phyla,12 classes,35 orders,and 128 families.The overall dominant group of soil fauna is Isotomidae,accounting for 30.84%of the total catch.The common group is mainly meso and micro soil fauna;2314 large soil fauna belong to 9 classes,26 orders,88 families,and the dominant group is Termitidae,accounting for 24.16%of the total density of soil macrofauna;8390 meso and micro soil fauna in 5 classes,9 orders,40 families,and the dominant group is Isotomidae,accounting for 30.84%of the total density of meso and micro soil fauna;（2）Compared with CK in horizontal distribution,nitrogen deposition significantly reduced the density of soil fauna,with the average density of soil fauna treated with HN being higher than that of LN;Nitrogen deposition had no significant effect on the number of soil fauna groups,with LN treatment having a higher number of soil fauna groups than HN treatment.The average density and group number of soil fauna are higher in July and October.Compared with CK,the average density and group number of soil macrofauna and meso and micro soil fauna were not significant.Compared with CK in horizontal distribution,the average density and group number of soil macrofauna increased in both LN and HN treatments,with HN having higher average density and group number than LN.There are significant differences between different seasons,with the highest in July.Compared with CK,nitrogen deposition reduced the average density of meso and micro soil fauna,with HN having a higher average density than LN;Under nitrogen treatment,the number of meso and micro soil fauna groups LN increased and HN decreased.There are significant differences between different seasons,with the highest in July and October.（3）Compared with CK in vertical distribution,the average density of soil fauna in the litter layer and 0-10cm layer is higher than that in the LN and HN plots;The number of soil fauna groups is mainly distributed in the litter layer and 0-10cm layer,while the number of soil fauna groups decreases in the 10-20cm layer;The average density and group number of soil macrofauna in vertical distribution are mostly concentrated in the 0-10cm layer,while the average density and group number of meso and micro soil fauna are mostly concentrated in the litter layer;（4）The diversity index of soil fauna is influenced by seasons,nitrogen deposition concentrations,and their interactions.Soil macrofauna are mostly influenced by seasonal changes,while meso and micro soil fauna are mostly influenced by seasonal changes and nitrogen deposition concentration.There was no significant difference in soil fauna community diversity index between different nitrogen deposition treatments.There was no significant difference in diversity between soil macrofauna and meso and micro soil fauna under different nitrogen treatments,and there were significant differences between different seasons under the same nitrogen treatment;（5）Different nitrogen deposition treatments have an impact on the proportion of soil fauna feeding habits.The proportion of functional groups of soil fauna under nitrogen deposition was ranked as follows:Fu>De>Ca>Om>He;Among them,the functional groups of soil macrofauna are ranked as follows:He>De>Ca>Om>Fu;Ranking of functional groups of meso and micro soil fauna:Fu>De>Ca>Om>He;（6）Compared with CK,nitrogen deposition promoted the individual number of macro soil fauna communities and inhibited the individual number of meso and micro soil fauna communities.After nitrogen application,the individual number of macro soil fauna in 60%of LN and 76%of HN groups increased by more than 2%compared to CK;Among meso and micro soil fauna,92%of the LN and 78%of the HN groups had an individual number reduction of more than 2%compared to CK;（7）The results of RDA analysis between soil fauna and environmental factors showed that soil water content had a significant impact on macro soil fauna such as Blattidae and Oniscidae,while total nitrogen had a significant impact on Scarabaeidae,Curculionidae larvae,Termitidae and Kalotermitidae.Soil water content has a significant impact on meso and micro soil fauna such as Malaconothridae,Parholaspididae,Sminthuridae and Phthiracaridae,while p H has a significant impact on Onychiuridae and Liacaridae.Soil fauna are affected by various environmental factors,and each factor has different effects on each soil fauna group.In summary,simulated nitrogen deposition has a significant impact on the composition of soil fauna community structure in the evergreen broad-leaved forest in the Rainy Area of West China.Compared with CK,simulated nitrogen deposition under LN and HN treatments can reduce the overall density of soil fauna communities;Increase the density of macro soil fauna communities and reduce the density of meso and micro soil fauna communities..