Variations in nitrification and denitrification potential following vegetation restoration in a Karst peak cluster and depression, southwest China

Nitrification and denitrification are critical processes in nitrogen biogeochemical cycling, and are closely linked with nitrogen availability, nitrogen loss, and safety of water body and atmosphere. Based on space-for-time method, three typical plant communities along the vegetation restoration course in northwest Guangxi were selected in the present study, i.e. grassland, shrubland, secondary forest, and active upland served as reference. The aims of this study were to examine the variations in soil nitrification potential (NP) and denitrification potential (DP) following vegetation restoration course and to explore the underlying mechanisms. The results demonstrated that there were significant differences in soil NP and DP among different restoration stages. Soil NP ranged between 18.78 and 49.08 mgN/(kg.d) and was in the order secondary forest>dryland≈shrubland≈grassland, while soil DP ranged between 4.09 and 15.43 mgN/(kg.d) and was in the order secondary forest≈dryland>grassland≈shrubland. In sum, soil NP was greater than DP at all restoration stages. Furthermore, soil NP and DP were significantly higher at the late stage than those at early stages of vegetation restoration. No significant differences were observed in soil NP and DP between grassland and shrubland. Both soil NP and DP were highly significantly correlated with soil organic carbon (SOC) and nitrate contents (P<0.01). Additionally, soil NP and DP were significantly (P<0.05) and highly significantly (P<0.01) correlated with soil microbial biomass nitrogen (SMBN), respectively. It is suggested that SOC, nitrate content and SMBN were the most critical common factors controlling soil NP and DP in the karst area.