Soil gross nitrogen transformations along the Northeast China Transect (NECT) and their response to simulated rainfall events.

Climate changes are predicted to increase extreme rainfall events in semiarid and arid region in Northern Hemisphere. Nutrient cycles will be affected by the precipitation changes but so far only very little is known how soil N transformations may respond. Here we investigated gross soil N transformation rates and their response to simulated rainfall events across Northeast China Transect (NECT). The results showed that gross N mineralisation rate, nitrification rate and nitrification to mineralisation ratio significantly increased as the humidity index decreased along NECT, resulting in NO3(-) as the predominant inorganic N form. These characteristics could increase the risk of NO3(-) losses but at the same time reduce the risk of N losses via volatilization in the semiarid and arid region. The soil-plant ecosystems have developed effective N conservation strategies in the long term with respect to the prevailing climate in arid region. However, compared to humid soils more dramatic changes of soil N transformation rates are likely to occur in arid soils, after sudden soil moisture increases. Soil N conservation mechanisms in arid regions were drastically affected when the heavy rainfall frequently occurred. Arid ecosystems are expected to be more vulnerable than humid ecosystems in response to extreme rainfall events.