生物炭对微生物介导土壤固碳作用的影响及其微观机制

Biochar amendment as an effective strategy to enhance soil carbon sequestration and to control soil pollution has attracted great concern internationally. Research on effects and mechanisms of biochar application on soil carbon sequestration mainly focus on structural stability of biochar, protection of soil aggregation, and priming effects on soil organic matter, while long-term effects and mechanisms mediated by microorganisms remain unclear. This study aims to verify influences of biochar amendment on soil autotrophic and heterotrophic microbial activity, on soil organic carbon mineralization and fixation, as well as the microbiological mechanisms underlying that. For doing so, the main focus of this study is on effects of biochar with various structures and characteristics on soil microbial community and on carbon sequestration. Based on stable isotope mixing model, contributions from soil organic matter mineralization and from biochar during the aging process to soil respiration are to be distinguished. Soil enzyme activities will be analyzed to investigate effects of biochar on soil organic carbon decomposition and on CO2 fixation. Using stable isotope probing coupled with molecular biological methods, i.e. DNA-SIP, community structures of soil heterotrophic and autotrophic microbes can be illustrated separately, and deep relations between community structure and biochar properties can be revealed. Conclusively, effects of biochar properties on soil organic matter mineralization, on CO2 fixation, on enzyme activities, and on soil microbial community structure are to be analyzed integratively, to reveal the microbiological mechanism of biochar induced soil carbon sequestration, which will provide pivotal evidences for the effects of biochar amendment on soil carbon sequestration.

生物炭在土壤固碳和污染控制中具有良好的应用潜力，引起国际极大关注。生物炭的固碳效应存在不确定性，研究主要集中于生物炭自身结构稳定性、土壤团聚体保护作用及有机质降解激活效应等，有关生物炭对微生物介导土壤固碳作用长期效应的影响及其机制尚未研究。本项目旨在探明生物炭对土壤自养与异氧微生物活性、微生物介导固碳的影响及微观机理，重点研究不同性质和结构生物炭对土壤微生物群落结构和固碳效应的影响。基于稳定碳同位素混合原理，研究生物炭老化过程对土壤有机质矿化的影响及对土壤呼吸的贡献率；采用酶活性表征方法，探讨生物炭对土壤有机质矿化和CO2固定作用的影响及机理；采用稳定同位素示踪结合分子生物学方法（DNA-SIP），深入研究生物炭对土壤异氧微生物和自养微生物群落结构影响及与生物炭结构之间的关系，从生物炭固碳过程-酶活性-土壤微生物群落结构，揭示生物炭增强土壤固碳的微生物学机制，为生物炭土壤固碳提供科学指导。

生物炭作为土壤改良剂被大量应用，对土壤有机碳稳定性的影响具有不确定性。生物炭固碳效应不仅与生物炭自身碳结构有关，更受到生物炭-微生物相互作用的调节。本研究合成分析了生物炭-微生物相互作用机制；总结了生物炭表面官能团与电子传递作用对土壤污染修复与土壤固碳的影响；利用稳定碳同位素混合模型，区分生物炭与土壤本底有机碳对土壤呼吸CO2释放量的贡献；利用基于土壤微生物DNA的高通量测序技术，揭示生物炭对土壤细菌与真菌群落结构的影响；冗余分析揭示生物炭通过调控土壤理化性质从而调控土壤微生物群落结构的驱动机制；利用16SrRNA基因作为分子标记物，预测土壤微生物功能。研究结果表明：生物炭的自身矿化率远低于生物质，生物炭与生物质对土壤本底有机碳的矿化均具有负向激发效应，与土壤微生物群落结构有关。生物炭维持稳定的土壤高pH值，对土壤微生物群落结构的干扰较小，几乎不改变土壤微生物参与的有机碳代谢过程；而生物质则通过提高土壤DOC、降低土壤pH值，促进了酸杆菌Acidobacteria等一类土壤微生物对生物质自身易降解有机碳组分的分解。生物炭对土壤微生物功能的影响主要体现在其主要富集次级代谢产物的合成与分解、多环芳烃PAH降解、电子传递等代谢过程。据此，我们提出生物炭-微生物相互作用影响土壤固碳的关键机制，即生物炭与生物质对土壤关键理化性质特别是土壤pH值与DOC含量的影响不同，从而造成土壤微生物活性、群落结构、代谢功能的差异，最终决定生物炭与生物质分解率的差异以及土壤本底有机碳的不同命运。主要学术贡献如下：（1）阐明了生物炭-微生物相互作用机制、生物炭表面官能团对土壤物质循环的关键作用、生物炭电子传递机制与环境效应；（2）阐明了生物炭-微生物相互作用对生物炭与土壤有机碳稳定性的影响机制；（3）利用双重体系共同评价生物炭吸附固定土壤多环芳烃进一步释放的环境风险，提出了生物炭作为连续体，在实际土壤污染修复过程中土壤有机质负载对其修复效率具有潜在的负面影响。