Effects of experimental warming on soil respiration and biomass in Quercus variabilis Blume and Pinus densiflora Sieb. et Zucc. seedlings

Key message In the open-field warming experiment using infrared heaters, 3 °C warming affected soil respiration more in the deciduous Quercus variabilis Blume plot than in the evergreen Pinus densiflora Sieb. et Zucc. plot, but did not affect the plant biomass in either species. Context Understanding the species-specific responses of belowground carbon processes to warming is essential for the accurate prediction of forest carbon cycles in ecosystems affected by future climate change. Aims This study aimed to investigate the effect of experimental warming on soil CO 2 efflux, soil-air CO 2 concentration, and plant biomass for two taxonomically different temperate tree species. Methods Experimental warming was conducted in an open-field planted with Q. variabilis and P. densiflora seedlings. Infrared heaters increased the air temperature by 3 °C in the warmed plots compared with the air temperature in the control plots over a 2-year period. Results The increase in air and soil temperature stimulated soil CO 2 efflux by 29 and 22 % for the Q. variabilis and P. densiflora plots, respectively. Seasonal variation in the warming effect on soil CO 2 efflux was species-specific. Soil CO 2 efflux was also positively related to both soil temperature and soil water content. The soil moisture deficit decreased the difference in soil CO 2 efflux between the control and warmed plots. Warming did not affect soil CO 2 concentration and plant biomass in either species; however, the mean soil CO 2 concentration was positively correlated with root and total biomass. Conclusion Warming increased soil CO 2 efflux in both Q. variabilis and P. densiflora plots, while the increase showed remarkable seasonal variations and different magnitudes for the two species.