| Nitrogen deposition is one of the factors driving the loss of biodiversity in terrestrial ecosystems,which is key to maintaining ecosystem function and providing ecosystem services.Soil fauna plays a key role in maintaining biogeochemical cycles and ecological functions in terrestrial ecosystems.In order to analyze the effects of nitrogen deposition on meso-micro soil faunal communities in meadows,a simulated nitrogen deposition experiment was designed in 2010 in Baikal Stipa meadow steppe,Ewenke Banner,Hulunbuir City,Inner Mongolia,with eight nitrogen deposition gradients of 0,15,30,50,100,150,200 and 300kg·N·hm-2·yr-1.Meso-micro soil fauna samples were collected in 2019 and 2020 at the re-greening(May),growing(August)and wilting(late September)periods of the forage,respectively,and the changes in soil fauna community structure and diversity and the relationships with environmental factors were analyzed.The results showed that.(1)A total of 1367 meso-micro soil fauna were captured in the deadfall layer in the study area,among which the dominant taxa were Cunaxidae and Tarsonemidae of the Prostigmata,accounting for 15.73%and 11.41%of the total number of captures,respectively.A total of 2038 meso-micro soil faunas were captured in the soil layer,among which the dominant taxa were Microacaridae of the Prostigmata and Formicidae of Hymenoptera,accounting for 28.61%of the total number of captures.The main taxa of soil fauna captured in the litter and soil layer were all Prostigmata.(2)Moderate N deposition was beneficial to the development of meso-micro soil fauna communities,and the number of individuals and taxa of soil faunas in both the litter and soil layers showed a trend of increasing and then decreasing with the increase of N gradient,and the inflection point appeared in the N200 treatment,and the N200 treatment was significantly higher than the control N0 and other N application treatments(except N300treatment)(p<0.05).The meso-micro soil fauna of Baikal Stipa meadow steppe had obvious epizootic characteristics,but there was a tendency for the soil fauna to migrate to deeper soil layers with increasing N application.The good hydrothermal conditions during the vegetation growth period in the test area are more suitable for the development of meso-micro soil fauna.(3)The diversity index of meso-micro soil fauna in the litter layer increased with the increase of N ladder,but it was not significant(p>0.05),while the maximum value of richness index and the minimum value of evenness index both appeared in N200 treatment.The diversity index,richness index and evenness index of small and medium soil fauna in the soil layer all showed an increasing trend with the increase of N gradient and then decreased,and the inflection point all appeared in N200 treatment,and the diversity index and richness index of N200 treatment were significantly higher than the control N0 and other N application treatments(p<0.05).(4)The soil fauna of the dead litter layer,warty mite family,number of taxa,long-horned mite family,thick Knight's mite family and isopodial mite family,as well as the diversity index of soil fauna in the soil layer,wakame mite family,isopodial mite family The soil faunal diversity index,the mite family,the number of taxa and the evenness index in the soil layer were the most sensitive to nitrogen deposition,and could be used as indicators for evaluating the impact of nitrogen deposition on grassland ecosystems.And the distribution of major taxa in both the litter layer and the soil layer could be effectively divided into three groups of N gradient,one group for N0-N150 treatment,one group for each of N200 and N300,and the results showed that N200 had the most distributed taxa.(5)The response of the distribution of meso-micro soil faunal communities to changes in grassland environmental factors in the context of N deposition showed that litter C/N and litter N content were the dominant factors driving the variation of N deposition on soil faunal communities in the litter layer,while soil faunal community variation in the soil layer was driven by a combination of soil environmental factors and plant community composition,with the dominant one being soil environmental factors,and long-term N deposition changed soil faunal communities by affecting their Long-term nitrogen deposition changes the community structure by affecting the living environment of soil fauna.In general,nitrogen deposition changed the environmental factors of Baikal needlegrass grassland and thus affected the structural composition,abundance and diversity of meso-micro soil fauna in the litter layer and soil layer,and nitrogen deposition promoted the development of soil fauna,but there was a threshold value,and the threshold value for the effect of nitrogen deposition on soil fauna level in this study was 200 kg·N·hm-2·yr-1. |
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