Vertical distribution and driving mechanisms of soil microarthropods in a Stipa baicalensis meadow steppe under long-term nitrogen addition

Soil microarthropods are sensitive to environmental changes and can respond quickly to external fluctuations in the environment. To investigate the response of soil microarthropod communities to long-term nitrogen addition in a Stipa baicalensis meadow steppe, six nitrogen addition treatments (0 (Control group), 30, 50, 100, 150 and 200 kg ha(-1) yr(-1)) were designed in 2010 in Ewenke Banner, Hulunbeier City, Inner Mongolia. The soil microarthropod community structure and diversity in response to long-term nitrogen additions in the litter and soil layers and the relationship with environmental factors were then analysed. The results showed the following: (1) The number of individuals and taxa of soil microarthropods significantly increased under long-term nitrogen addition; particularly, in the N200 treatment. The vertically distribution pattern showed that the litter layer (532 specimens, 47 families) > 0-10 cm soil layer (383 specimens, 35 families) > 10-20 cm soil layer (98 specimens, 19 families). The common dominant taxa in the litter layer (Poduromorpha) and 0-10 cm soil layer (Poduromorpha and Psocoptera) was Poduromorpha, and that in the 0-10 cm and 10-20 cm soil layers (Psocoptera and Prostigmata) was Psocoptera, both of which showed universal adaptability to microhabitat changes under nitrogen addition. (2) The addition of nitrogen resulted in the division of community structure of soil microarthropods in the litter layer and the 0-10 cm soil layer into 3 groups. The N0-N100 treatments formed one group, while the N150 and N200 treatments formed another two group, and the community distribution of soil microarthropods among the 3 groups was significantly different. (3) The Shannon-Wiener and Jaccard indices of soil microarthropods exhibited significantly greater values in the N150 and N200 treatment, the composition of the soil microarthropod community is evolving towards the co-development of multiple taxa. (4) With long-term nitrogen addition conditions, the community composition and diversity characteristics of soil microarthropods were regulated by litter nitrogen and phosphorus and aboveground biomass in the litter layer, soil pH, nitrate nitrogen and belowground biomass in the 0-10 cm soil layer, and soil nitrate nitrogen and soil moisture content in the 10-20 cm soil layer. In conclusion, soil microarthropod community structure was significantly different among different microhabitats under long-term nitrogen addition, and the change in environmental factors in microhabitats was the main factor driving the development of the soil microarthropod community.