The temperate steppe in northern
Results/Conclusions In Case Study I, all ecosystem C fluxes including NEE, GEP, ecosystem, soil and microbial respiration showed negative responses to experimental warming simulated with infrared heaters, but positive responses to increased precipitation since 2005. The effects of increasing temperature and precipitation were additive. The observations were in agreement with the expectations that climate warming may have negative impacts on the semiarid steppe because water is the predominant limiting factor in the ecosystem and warming may exacerbate water limitation. In Case Study II, warming and N addition treatments were conducted along a precipitation gradient from meadow steppe in the east (MAP 455 mm), typical steppe in the middle (MAP 385 mm), and desert steppe in the west (MAP 310 mm) since April 2006. The sensitivity of ecosystem C cycling and plant diversity to warming was site dependent irrespective of their positive response to N addition. In Case Study III, a warming experiment with four treatments, i.e., control, day warming (6:00am-6:00pm), night warming (6:00pm-6:00am), and diurnal warming (24 hours), has been conducted for 3 years since 2006 in the typical steppe to address possible roles of asymmetrical diurnal warming occurring widely across the world in regulating ecosystem C sequestration. We found that night warming increased nighttime plant respiration and carbohydrate depletion, stimulated plant photosynthesis in the second day in return, which over-compensated for the carbon loss via respiration and thus enhanced ecosystem C sequestration. Our findings will facilitate model simulation and projection of climate-carbon feedbacks.
