Short-term Effects of Night Warming and Nitrogen Addition on Soil Respiration of Subalpine Coniferous,Western Sichuan,China

Responses of soil respiration to experimental warming and nitrogen addition can provide insights into C source/sink functions of forest ecosystems in climates change.An infrared heater was used to determine the short-term effects of two levels of air temperature(ambient and warmed) combined with nitrogen addition(N,0 and 25 g m-2 a-1) on soil respiration in Picea asperata plots and Abies faxoniana plots.The results showed that the warming manipulation increased mean air temperature and soil temperature at 5 cm depth by 2.03℃ and 4.10 ℃,respectively.Soil respiration displayed strong seasonal and diurnal patterns.In general,simulated warming increased soil respiration,while nitrogen addition decreased the soil respiration of the two conifer plots during the whole experiment.However,the responses of soil respiration to experimental warming and nitrogen addition were strongly dependent on both tree species and seasons.Warming increased the carbon fluxes of soil total respiration by 22.30% and 8.82% in the unfertilized and fertilized P.asperata plots,and 4.85% and 4.45% in the unfertilized and fertilized A.faxoniana plots,respectively.Significant exponential relationships were found between the soil respiration rates and soil temperature at 5 cm depth.Warming and nitrogen addition both increased the Q 10 values in the two conifer plots,but Q 10 value was generally higher in P.asperata plots.Therefore,the soil respiration in P.asperata plots was more sensitive to temperature changes than A.faxoniana plots.As a result,the response differences to warming and nitrogen addition between tree species add more uncertainty and complexity in C sink/source dynamics in changing climate,and the underlying mechanism should be further studied.