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 deciduousQuercus variabilisBlume plot than in the evergreenPinus densifloraSieb. 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 CO₂ efflux, soil-air CO₂ 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 CO₂ efflux by 29 and 22 % for the Q. variabilis and P. densiflora plots, respectively. Seasonal variation in the warming effect on soil CO₂ efflux was species-specific. Soil CO₂ efflux was also positively related to both soil temperature and soil water content. The soil moisture deficit decreased the difference in soil CO₂ efflux between the control and warmed plots. Warming did not affect soil CO₂ concentration and plant biomass in either species; however, the mean soil CO₂ concentration was positively correlated with root and total biomass. Conclusion: Warming increased soil CO₂ efflux in both Q. variabilis and P. densiflora plots, while the increase showed remarkable seasonal variations and different magnitudes for the two species.