亚热带低粘粒森林土壤微生物利用DOC产生残体碳的过程研究

探明森林土壤有机碳的积累机制是增加土壤碳汇的重要理论基础。前期结果发现在粘粒含量仅10%、土壤有机碳含量约2%的亚热带森林土壤中微生物残体碳占比高达50%，且外源输入土壤的可溶性有机碳(DOC)通量大。在粘粒含量如此低、保碳能力差的森林土壤中，有机碳积累的可能机制是什么？基于前期结果，本项目推测，和高粘粒土壤相比，低粘粒土壤对大量外源输入DOC的结合较弱，微生物摄取DOC的量大、效率高，产生残体碳占总有机碳的比例大。为验证这些推测，本项目拟通过野外长期监测实验，定量DOC输入不同粘粒含量土壤后被淋溶、微生物矿化、转化成残体碳的量；并在室内利用13C和18O同位素分别测定微生物对DOC的利用效率和周转速率,以共同指征低粘粒土壤微生物利用DOC合成残体碳的效率。项目的预期成果可为制定高碳汇森林经营管理措施提供新的理论依据，亦可为揭示亚热带低粘粒森林土壤有机碳的累积机制提供新的研究思路。

Unraveling forest soil organic carbon (SOC) accumulation mechanism is the theoretical basis of increasing soil carbon sink. My previous results showed that in the subtropical forest soil with clay content of only 10% and SOC content of only 2%, the contribution of microbial necromass carbon to total SOC was as high as 50%, and the input of dissolved organic carbon (DOC) was substantial. What are the possible SOC accumulation mechanisms in forest soil with such a low clay content and less carbon holding capacity? Based on my preliminary results, this project presumes that compared with high-clay soil, low-clay soil is weak in binding DOC, and soil microbes within can uptake DOC enormously and efficiently, and produce large quantities of microbial necromass carbon and contribute to total SOC. To test these presumptions, this project will conduct a long term in-situ field experiment to monitor DOC leaching, mineralization, and transformation to microbial necromass carbon in soils with different soil clay content, and utilize isotope carbon 13 and oxygen 18 to investigate microbial carbon use efficiency and growth rate following DOC addition to finally evaluate the microbial synthesis efficiency of necromass carbon. Results of this project could provide a new theoretical basis for formulating better forest management practices to increase carbon sequestration and new ideas of revealing the SOC accumulation mechanisms in subtropical low-clay forest soil.