Effects of Tourism Trampling on Soil Nitrogen Mineralization in Quercus variabilis Blume Forests Varies with Altitudes in the Climate Transition Zone

Abstract

Tourism trampling is one of the critical disturbance factors affecting forest structure and function apart from forest management activities. However, how tourism trampling affects soil nitrogen (N) mineralization rate at different altitudes in scenic forest spots is still unclear. To determine whether the responses of soil net N mineralization rate to tourism trampling varies with altitudes, we incubated soils using a field buried pipe method and analyzed soil ammonium N (NH4+-N) and nitrate N (NO3−-N) content at three altitudes (810 m, 1030 m, and 1240 m) at the Baotianman forest scenic spot in Henan Province. The results showed that tourism trampling significantly increased the soil bulk density and soil pH value but substantially reduced soil organic carbon (C) and total N content at all altitudes. Tourism trampling also resulted in a significant decrease in NO3−-N in the soil before and after incubation at all altitudes. The effects of tourism trampling on soil net N mineralization varied with latitudes, showing positive effects at 1030 m altitude (+51.4%), but negative effects at 1240 m altitude (−43.5%). For the soil net N nitrification rate, however, tourism trampling resulted in an increased rate (+141.1%) only at the 810 m altitude. Across all altitudes, soil microbial biomass C is primarily responsible for the variation in the soil net N mineralization rate. This study indicates that the effect of tourism trampling on soil net N mineralization rate varies with altitudes, which is related to the intensity of tourist disturbance and the synthetic effects of vegetation and soil microbes.