The different temperature sensitivity of gross N transformations between the coniferous and broad-leaved forests in subtropical China

An isotopes (N-15) tracing study was conducted under laboratory conditions to evaluate the effects of temperature changes (5-35 degrees C) on gross nitrogen (N) transformations in two contrasting soils of subtropical broad-leaved forest (BF) and coniferous forest (CF). With increasing temperature in BF soils, gross N immobilization rates increased to a lesser extent than gross N mineralization rates, which resulted in an increase in net N mineralization. By contrast, in the CF soils, the equally proportional increase in gross N mineralization and immobilization that occurred at 5-25 degrees C led to a lack of change in net N mineralization in response to temperature, whereas increasing the temperature from 25 to 35 degrees C resulted in a greater increase in the gross N mineralization rate than in the gross N immobilization rate, thereby increasing net N mineralization. The temperature sensitivity of gross nitrification was observed in the BF soils but not in the CF soils. The same temperature sensitivity of gross N mineralization and immobilization rates in the CF soils at temperatures below 25 degrees C, combined with negligible nitrification rates, suggests that the N available for plants and microbial growth, and the loss by nitrate (NO3-) leaching, is probably low in the CFs.