Interactive effects of nitrogen forms and temperature on soil organic carbon decomposition in the coastal wetland of the Yellow River Delta, China

Nitrogen (N) is a limiting nutrient in many terrestrial ecosystems. Many studies concentrated on the relationships between the amount of N deposition and soil organic carbon (SOC) dynamics. However, few studies are dedicated to differentiate the influence of inorganic and organic N deposition on SOC decomposition. In addition, the interactive effect of different forms of N and temperature on SOC decomposition is still unknown. A short-term incubation experiment was conducted to determine the interactive of N addition (nitrate, ammonium and organic N) and temperature on SOC decomposition in the coastal wetland of the Yellow River Delta, China. The results showed that increased temperature had a positive effect on SOC decomposition (P < 0.05). Both ammonium and organic N additions accelerated SOC decomposition at the initial phase of incubation (P < 0.05), while organic N produced larger and positive effects on SOC decomposition than ammonium at high level of N addition in the initial stage of incubation (P < 0.05). Furthermore, the interactive effect of N additions (i.e. two level of nitrate and organic N additions and a high level of ammonium addition) and temperature on SOC decomposition was mainly an additive effect due to the neutral effect of such N additions on the Q10 value of SOC decomposition. However, a low level of ammonium addition and temperature produced an antagonistic effect on SOC decomposition. This may be attributed to the decreased Q10 value of SOC decomposition at a low level of ammonium addition (P < 0.05). This indicates that short-term SOC decomposition under simultaneous influence of temperature and a low level of ammonium addition may be overestimated based on their single effects. Our results also highlight the importance of differentiating the effects of organic and inorganic N additions on SOC decomposition.