Effects Of Simulated Nitrogen Deposition On Soil Fauna Diversity In Abandoned Farmland, Rainy Area Of West China

With the rapid development of global industry and agriculture, a large number of nitrogen compounds have been discharged into the environment. It has become one of the major reasonsleading to global change. Most of the nitrogen form wet or dry deposition fall into the soil, which significantly affects the structure and function of the soil ecosystem. Soil faunas are important soil ecosystem consumers and decomposers, and as the underground ecosystem higher life forms which play an important role in material cycle and energy transportation of the soil ecosystem. Soil faunas are also the important biological indicator of the soil fertility, health and pollution. Therefore, the response of soil faunas to nitrogen deposition is importantto assess the impact of nitrogen deposition. This study will provide a basis data and theoretical support for soil fauna management and evaluation of the impact caused by nitrogen deposition. Subsequently, a 4 years simulated nitrogen deposition experiment (LN:45kg·hm-2·a-1、MN:90 kg·hm-2·a-1、HN:180 kg·hm-2·a-1、CK:0 kg·hm-2·a-1) was carried out in the abandoned farmland, Rainy Area of West China. The objectives were to explore the effects of nitrogen deposition on soil fauna diversity and the relationship between soil fauna and its ambient factors. The main findings were as follows:(1) In this study, a total of 42,098 individual soil fauna were collected, which belonged to 4 phyla,11 classes,23 orders,36 families. There were 55 groups in total. Acarina (35.51%), Nematoda (30.94%) and Collembola (23.74%) were the dominant groups. Coleoptera larvae (1.82%), Formicidae (1.78%) and Porcellionidae (1.31%) were the frequent groups;and the other 50 groups were the scarce groups, with the percentage of 4.91%. The nitrogen addition had positive effects on the numbers of groups and individuals; and the positive effects of nitrogen addition on the number of soil animals was MN<LN <CK<HN while that of soil animal groups was LN<CK<MN<HN.(2) Nitrogen deposition had minor effects on soil animal biomass(P= 0.105), and there’re no obvious dynamics between different nitrogen deposition treatments. Soil animal biomass had been larger affected by seasonal changes, which was November (3.72g)> September(2.34g)> July (1.79g)> January (1.09g)> March (0.32g)> May (0.18g).(3) The abundance index of soil animals affected by both nitrogen deposition and seasonal variation. Shannon Wiener index and Evenness index showed a significant response to nitrogen deposition, and the maximum generally appeared in MN. Overall, dominant groups on nitrogen deposition in the area had anupward adaptability, and the Shannon Wiener index and evenness index from CK to MN with an increasing trend, but decreased in HN.(4) Thenitrogen deposition had significantly affected on soil pH, and seasons had minor effects on the pH. The minimum and maximum of soil pH value were between 6.65 and 7.35, which maintained at a neutral level and was inconsistent with the other studies. Soil organic carbon, nitrogen and phosphorus were significantly affected by nitrogen deposition, in which phosphorus showed no regularity at all times. Both soilorganic carbon and soil nitrogen content with enhanced nitrogen deposition increased first and decreased then.(5) The habitat had significant effects on Soil macrofauna biomass. Fine root content and soil enzymeactivity were the major factor affecting soil fauna.