Temperature Sensitivity Of Soil Organic Carbon Mineralization In Temperate Forests In Northeast China

Global warming is expected to increase atmospheric CO2 concentrations by accelerating SOM decomposition,resulting in a positive feedback between the global C cycle and climate warming(Jones et al.,2003,IPCC,2013).The magnitude of this feedback depends on the temperature sensitivity of SOC decomposition.Therefore,under the projected global warming,the temperature sensitivity of SOC mineralization(Q10)would largely regulate the feedback between global climate change and carbon cycle.However,the response of soil Q10 to projected warming and its regulatory mechanisms remains poorly understood.In the present study,natural Broad-leaved Korean pine mixed forests along a latitudinal gradient from Northeast China were selected.Using short-term incubation experiment,the correlations between mean annual temperature(MAT)and the temperature sensitivity of SOC decomposition was investigated,and the seasonal pattern of such correlation was studied.Using lab-based 365-day incubation experiment,the long-term response of soil Q10 to elevated temperature was evaluated.Further,the biotic and abiotic factors driving the soil Q10 were revealed.In particular,soil microbial community structure and functional gene composition were analyzed by Illumina Mi Seq sequencing platform and quantitative-PCR method,respectively,and their linkages with temperature response of SOC decomposition were evaluated.The main results and conclusions are as follows:Short-term incubation showed that soil Q10 increased with increasing MAT in broad-leaved Korean pine forests in Northeast China.The soil Q10 was influenced by climate,soil carbon quality and availability,soil microbial community composition and function.Sites with higher MAT was characterized by low recalcitrant carbon content,high carbon quality,low carbon availability,high abundance of copiotrophic bacterial taxa,and high abundance of labile carbon degradation genes,which attribute to higher soil Q10 in warm sites.The relationship between soil Q10 and MAT was influenced by sampling season.In specific,there was no significant relationship between Q10 and MAT in summer,whereas soil Q10 was positively correlated with MAT in spring and autumn.The driving factors of soil Q10 are quite different in different sampling seasons.In summer days,because of the small difference in temperature among sampling sites,the soil Q10 was indirectly influenced by average seasonal temperature through changing soil carbon quality.In spring and autumn,the soil Q10 was directly influenced by average seasonal temperature due to the great difference in temperature between the northern and southern sites.Besides,the average seasonal temperature can indirectly influence the soil Q10 through changing soil carbon quality and availability,soil microbial community composition and functional gene.The long-term lab-based incubation experiment verified that soil Q10 in central and southern sites was higher than that in northern sites.Based on the fitted two-pool carbon decomposition model,the soil Q10 is mainly ascribed to the decomposition of recalcitrant carbon pool in the central and southern sites.However,in the northern site,the changes of soil Q10 are dependent on the decomposition of labile carbon pool.This result is consistent with the “carbon quality-temperature” hypothesis.During the incubation experiment,the soil Q10 in the central and southern sites had a pulse effect at 40-day,which mainly caused by the mineralization of relative recalcitrant carbon pool.Soil Q10 in the northern site decreased in the early stage and then gradually increased with the incubation time.The SOC mineralization was documented by labile carbon decomposition at the early incubation stage,whereas was dominated by recalcitrant carbon decomposition at the later stage.In the early stage of incubation,the soil microbial community was dominated by copiotrophic microbial taxa and labile-carbon degradation,and was subsequently replaced by oligotrophic microbial group and recalcitrant-carbon degradation at the later incubation stage.According to the results obtained in this research,we project that increased temperature would decrease the ratio of coniferous to broadleaf trees(NRCB),increase the soil carbon quality,but decrease the soil carbon availability,increase the ratio of copiotrophic/oligotrophic microbial taxa,the ratio of labile/recalcitrant carbon degradation potential,and thus,increase soil Q10.From the long-term perspective,climate warming would increase the contribution of recalcitrant carbon pool to the increased SOC mineralization,and ultimately increased soil Q10.The present study has profound implications on the prediction of SOC mineralization potential in temperate mixed forest under the future scenarios of warming,and would provide basic knowledge for improving global carbon cycling model from perspective of soil microbial ecology.