Soil extracellular enzyme activities in different Horqin sandy grassland soil hydrothermal gradients

Soil extracellular enzymes affect organic matter decomposition, whereas grassland ecosystems are unstable and sensitive to climate change. Extracellular enzyme activity is important in carbon and nutrient cycling in sandy grassland soils considering global climate change. The present study investigates the effect of regional hydrothermal gradient changes on the extracellular enzyme activity (EEA) in the Horqin sandy grassland soils and the correlation between environmental factors and EEA. The enzyme activity indicators included cellulase involved in the soil carbon cycle and urease and alkaline protease involved in the nitrogen cycle. The results showed that soil urease activity increased and then decreased with increasing regional temperature (2.1～6.4 ℃). Contrastingly, with decreasing regional precipitation (451.1～370.0 mm), the urease activity decreased and then increased. An increase in regional temperature significantly increased soil alkaline protease activity (P < 0.05), whereas a decrease significantly decreased alkaline protease activity (P < 0.05). However, there was no significant difference in the effect of changes in regional temperature and precipitation on soil cellulase activity (P > 0.05). Soil urease activity was significantly and positively correlated with electrical conductivity, water content, very fine sand, and clay and silt (P < 0.05). Contrastingly, soil urease activity was negatively correlated with soil temperature and coarse and fine sand contents. Soil cellulase activity was positively correlated with water content and negatively correlated with soil temperature. Soil alkaline protease activity was positively correlated with soil water content (P < 0.05) and negatively correlated with soil temperature. Furthermore, soil water content, temperature and clay and silt influenced EEA in the Horqin sandy grassland soils, among which the direct and indirect effects of soil water content on EEA were higher than those of other environmental factors. The results of the present study provide a theoretical basis for soil ecoenzymology on the effects of changing hydrothermal conditions on the soil carbon and nitrogen biogeochemical cycling processes in sandy grassland ecosystems.