秸秆生物质炭对农田土壤有机碳保持作用及其机制

Biochar amendment of soils has been considered as the most promising measure to enhance soil organic carbon storage and reducing greenhouse gas emission from croplands. However, a critical issue has been raised if soil respiration and CO2 evolution increased after biochar application and a potential priming effect of soil organic matter decomposition. If priming and increased CO2 are valid then it is not mitigation of GHG emission. The proposed project will have an investigation of changes in soil respiration and organic matter decomposition after biochar amendment. We will use soils with contrasting physico-chemical properties and biochars of contrasting 13C stable isotope abundance; Meanwhile we will conduct experiments both of lab incubation and field monitoring under treatment of biochar with and without crop straw. Changes in contents of organic carbon and its fractions, in soil respiration activity as well as in 13C abundance will be traced for the samples from short term amended and long term amended soils. Soil respiration will be monitored with incubation jar method at laboratory and with static chamber method in field. Physico-chemical properties of soil will be analysed: pH (and Eh in rice soil), bulk density, aggregate size fractions . Carbon analysis works include organic carbon content and fractions of recalcitrance as well as molecular characterization using state of the art pyrolysis mass spectroscopy. Microbial community and structure will be analysed by both biochemical methods (microbial carbon, PLFA) and by molecular fingerprint methods of PCR-DGGE and sequencing for selected samples. The project is to answer the questions: (1) is priming effect significant and sustain over years after biochar amendment; (2) does biochar exert a role in stabilizing indigenous organic carbon in soils and thus in enhancing carbon sequestration; (3) does the biochar induced changes in soil respiration and organic matter decomposition varies with soil properties conditions and with experiment conditions, and reason. Finally, the study will provide a sound understanding of biochar effects on C cycling in croplands and the sustainability for mitigation of greenhouse gas emissions from croplands under biochar amendment.

生物质炭农田施用被认为是一种最具潜力的农业上固碳减排措施，但大量实验室研究提出了生物质炭添加土壤中可能存在对老碳分解的激发效应，这可能削弱其实际固碳减排潜力。本项目采用不同生物质原料热裂解生物质炭不同用量施用于稻田和旱地，通过实验室培养和田间实地监测试验，观察土壤呼吸变化和土壤碳库变化，结合有机质分子结构变化研究和微生物分子生态变化分析，研究生物质炭施用下生物质炭/土壤有机碳分解动态与对土壤老碳分解变化以及同位素组成变化。回答：1，生物质炭添加是否会导致对老碳分解的激发效应及其年际持续性；2，生物质炭是否具有对老碳的稳定性或可能促进土壤固碳作用；3，生物质炭对土壤碳循环影响在稻田和旱地间和实验室培养和田间试验间的差异性及其原因；最终为认识生物质炭的农田可持续固碳减排效应及其机理提供科学依据。

本项目围绕秸秆作为农业废弃物炭化处理后的生物质炭施用于农田对土壤有机碳的保持和稳定作用，采用文献整合分析、联网试验结果整合分析、以往单点施用农田的采样分析以及同种秸秆不同处理比较试验，分析秸秆生物质炭施用后土壤有机碳总量、微生物生物量碳（氮）、土壤呼吸（CO2和CH4）的变化规律，并采用有机质组成分子鉴定法、同位素丰度标记法、微生物活性群落分子探针法审视生物质炭施用下碳库的消长及其作物季/年际消长。主要结果和发现如下：（1）生物质炭施用农田普遍增加土壤有机碳库，并减缓土壤呼吸更新；（2）生物质炭的可提取活性组分，通过影响植物生长并进一步的植物碳输入而短期影响土壤呼吸，而不是活性有机碳本身；（3）生物质炭施用多年后增加的碳库短期多年稳定，生物质炭来源的有机碳和生物质炭施入后增加固定的新有机质是碳库持续增加的表现；（4）生物质炭施用的农田土壤中，可溶态和游离态有机质组分减少，稳定态或复杂杂环有机质增加，土壤微生物产生多苯环复杂基质适应性群落演替，伴随碳循环相关酶活性的改变，使表现出低碳代谢，减缓了碳更新，这是生物质炭进一步利于有机质保持的分子机理；（5）秸秆直接还田和秸秆厩肥的有机质分解快速，残留稳定于土壤在15%以下，大部分当季就呼吸消耗；相反，秸秆生物质炭增加的有机质可占土壤有机质的30%以上，持续多季稳定，极少产生呼吸排放。这种有机碳的稳定增加改善了土壤肥力和作物生产力，提高了氮素效率和降低了温室气体排放，促进了系统的生态功能。本研究也再次支持了生物质炭的有机碳稳定作用，提示这种作用与团聚体过程、有机质分子过程和微生物分子生态过程密切有关。其土壤-生物质炭相互作用过程尚需多年的定位研究。项目成果支撑了秸秆生物质炭产业化发展。