Responses of soil respiration to changing precipitation regimes in an oak forest at a climate transitional zone

As the second largest carbon( C) flux between the atmosphere and terrestrial ecosystems,soil respiration remains one of the key sources of uncertainty while assessing terrestrial C cycling and sink strength. Changing precipitation patterns and its corresponding changes in soil water content are critical in regulating soil respiration. Hydrothermal conditions in the climatic transitional zone are more susceptible to changing precipitation patterns than other climatic zones.Determining the responses of soil respiration to changing precipitation regimes in the climatic transitional zone is favor to the improvement of precision of C cycling models. However,there is currently limited information on the response of soil CO_2emission to changing precipitation regimes in the climatic transitional zone. A field precipitation manipulation experiment was conducted at an oak( Quercus aliena) forest located at a climatic transitional zone( Baotianman),from subtropical to warm temperate,to examine the response of soil respiration and its temperature sensitivity to increased( + 50%) and decreased precipitation(-50%). Soil respiration,temperature,and moisture were measured weekly from July to November in 2013. The results showed that increased precipitation significantly elevated soil moisture by 8.92% but had no effect on soil temperature. Soil respiration was substantially enhanced by 80. 5% under increased precipitation treatment compared with that in the control plots. Temperature sensitivity of soil respiration under increased precipitation was significantly higher( 4.07) than that in control plots( 2.66). Soil respiration under increased precipitation showed negative correlations with soil moisture as well as soil temperature. Decreased precipitation substantially reduced soil moisture by 10.25% and tended to increased soil respiration. However,reduced precipitation showed little effect on the temperature sensitivity( 2.64) of soil respiration. Soil respiration under the decreased precipitation showed positive correlations with soil moisture and temperature. The results suggest that both increased and decreased precipitation can stimulate soil respiration with different extents. Changing precipitation patterns,therefore,may weaken soil C sequestration in forest ecosystems,and exert a positive feedback on atmosphere CO2 concentration at the climatic transitional zone from a subtropical to a warm temperate zone.