Effects of temperature on soil nitrogen mineralization in different pH paddy soils under anaerobic condition

Nitrogen mineralization has been one of the most important links of nitrogen cycle in soil ecosystems. Temperature and pH are important environmental factors influencing nitrogen mineralization. In this study, two paddy soils with different pH values were used to anaerobically incubate at four different temperatures - 15 ℃, 25 ℃, 37 ℃ and 50 ℃. Using the first order reaction kinetics equation in combination with the effective accumulated temperature equation, mineralization parameters such as soil nitrogen mineralization potential (N_O), mineralization rate (k), mineralization degree (k_a) and potential/total nitrogen mineralization rate (N_O/Tot.N) were analyzed in order to determine the impact of temperature on soil nitrogen mineralization under anaerobic condition. The results showed that soil nitrogen mineralization potential (N_O) of two paddy soils increased with increasing temperature. The changes in k and ka depended on temperature degrees of soils with different nitrogen mineralization potentials. At 15-37 ℃, soil k and ka increased with increasing temperature. However, the differences between every two soils were not significant at the same temperature. Then within 37-50 ℃, the changes in soil k and ka grew significantly (P < 0.01) different with increasing temperatures in different soils. It suggested that at high temperatures, the effect of temperature on the mineralization of different paddy soils changed greatly. N_O/Tot. N increased with increasing temperatures, suggesting that the quality of organic nitrogen improved at higher temperatures. Correlation analysis showed a positive correlation between temperature and mineralization parameters within the range of 15-37 ℃. Within the range of 37-50 ℃, the correlation decreased and some even became negative. The pH values did not fluctuate or change with the mineralization parameters. This implied that under anaerobic condition, theresponse of nitrogen mineralization of soils with different pH was similar to temperature within low to medium temperatures, but was significantly different at high temperatures.