Carbon and nitrogen storage in plant and soil as related to nitrogen and water amendment in a temperate steppe of northern China

We conducted a field-manipulated experiment to assess whether changes in precipitation and nitrogen (N) deposition alter ecosystem carbon (C) and N storage. Both C and N pools of plant and soil were monitored when urea-N (17.5 g N m⁻²) and water (increasing mean annual precipitation by 50%) were added to a temperate steppe. After 2 years of treatments, both N and water addition significantly increased soil inorganic N availability by 125% and 62% during the growing season. While water addition significantly increased ecosystem C storage by 6% and N storage by 8%, N addition showed significant effects on neither of them. There were no interactions between N and water addition to affect both total C and N storage in this ecosystem, though they did interact to affect several individual pools (e.g., aboveground biomass N pool, litter C, and N pool). Results from the present study indicate that water availability is more important than N availability for C sequestration and that increasing precipitation will favor C sequestration in this semi-arid grassland.