| As the important components of global change,increased atmospheric nitrogendeposition and precipitation change will profoundly above-and below-ground ecosystem processes,particularly in the vulnerable desert steppe which are sensitive to climate change.Under different water supply conditions,how increased nitrogen deposition will affect soil meso-and micro-fauna communities is poorly understood.The water and nitrogen manipulation experiment in the desert steppe of Inner Mongolia was established in 2015 using split-plot design,with water as the whole-plot factor and nitrogen as the sub-plot factor,including twelve treatments.Water treatment includes CK(natural rainfall),W(30%rainfall addition),R(30%rainfall reduction),and nitrogen treatment includes 0(N0),30(N30),50(N50),100(N100)kg N·hm-2·a-1.We measured species composition,community structure and diversity of soil meso-and micro-fauna,soil chemical and physical properties and plant characteristics.Our results show that:(1)In the study area,a total of 1194 individuals were captured in two years,which were classified as 3 phyla,11 orders,45 families.Soil meso-and micro-fauna communities consists of Arachnida,Collembola and Insecta.The main groups are Oribatida,Prostigmata,Mesostigmata and Collembola.Dominant groups are Trombidiidae and Raphignathidae.There are 14 common groups including Scutoverticidae,Astegistidae,Nanhermanniidae and so on.Dominant groups and common groups constitute the main body of soil meso-and micro-fauna in the Stipa breviflora desert steppe.(2)In the Stipa breviflora desert steppe,soil meso-and micro-fauna have the characteristics of"surface aggregation",mainly concentrated in the 0-10 cm soil layer.The seasonal dynamics is October>April>July.(3)The intervention of water and nitrogen changed the individual density and group numbers of soil meso-and micro-fauna in the Stipa breviflora desert steppe.The interactive effect of water and nitrogen on individuals was found(P<0.05).Individual density of soil meso-and micro-fauna increased by 86.66%in W-N30 treatment,compared to the control,which would facilitate the survival of soil meso-and micro-fauna.Proper nitrogen addition enhanced the activity of soil meso-and micro-fauna,while excessive nitrogen addition had a negative effect,and moisture determines the range of moderate amount of nitrogen.Under the water addition,N30 increased the individual density by58.99%,but N100 reduced individual density by 18.56%.Under the R and CK treatment,it is not significantly regular.(4)Oribatida,Prostigmata,Mesostigmata and Collembola are all sensitive to water.Nitrogen addition remarkably influenced Oribatida and Prostigmata(P<0.01)over time,and the interaction between water and nitrogen was found(P<0.01).Particularly,Oribatida was more sensitive to water and nitrogen changes.Water and nitrogen treatments increased the individual density of scavenging and predatory soil fauna.(5)Community diversity of soil meso-and micro-fauna differently responded to nitrogen addition and precipitation change are in the Stipa breviflora desert steppe.With the increasing nitrogen supply,species richness index,Shannon-wiener diversity index and Pielou evenness index for the soil meso-and micro-fauna tended to initially increase and then decrease in R,CK and W treatment.Overall,the diversity of soil meso-and micro-fauna is the highest in W-N30.(6)The soil meso-and micro-fauna community in the Stipa breviflora desert steppe was affected by the combination of soil and plant characteristics,and different groups respond differently to environmental factors.Oribatida,Prostigmata,Mesostigmata,Collembola,scavenging and predatory animals were significantly affected by soil moisture content(P<0.01),except for the Prostigmata and Collembola,the rest were significantly negatively related to soil temperature(P<0.001).There was a significant positive correlation between the Oribatida and the above-ground biomass(P<0.01),and a significant positive correlation between Mesostigmata,scavenging animals and above-ground biomass,litter falls biomass,and Shannon-wiener diversity index(P<0.01).Overall,the every groups were closely related to soil moisture content,temperature,plant biomass,richness index and Shannon-wiener diversity index.Nitrogen addition and water change indirectly affected soil meso-and micro-fauna community by affecting soil environment and vegetation conditions. |
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