冻融条件下农田土壤CO2排放对生物炭施用的响应机制

The change of soil aggregates and microbial community caused by freeze-thaw alternation leads to the increase of CO2 emission. The application of biochar not only enhances the stability of soil aggregates, but also changes the structure and abundance of microbial communities, thus affecting the process of CO2 emission. However, little information is available about the response mechanism of CO2 emission from farmland soil to biochar application under freeze-thaw condition. This study take the biochar derived from corn stalk and potato field soil as research objects. Laboratory simulation study was conducted in this research project to study the effect of biochar additon on the soil CO2 emissions and the fraction of soil organic carbon under freezing-thawing conditions. Meanwhile, the composition and stability of soil aggragate and the content of soil organic carbon in soil aggregate were also systematically analysed. The distribution characteristics of biochar in soil aggregates and its proportion in soil CO2 emission and organic carbon fractions were also studied by the technique of tracer δ13C. Thus, the relationship between the whereabouts of biochar in soil aggregates and soil carbon sequestration was analyzed. Meanwhile, the effects of biochar application on soil microbial community structure and abundance under freeze-thaw conditions were investigated by high-throughput sequencing analysis. Thus, the response mechanism of CO2 emission from farmland soil to biochar application under freeze-thaw condition were elucidated. The result of the study not only have enriched the mechanism of biochar application in soil carbon sequestration, but also provide data and theoretical support for the wide application of biochar in middle/high latitudes soils.

冻融交替造成土壤团聚体破碎、微生物丰度及活性的变化增加了CO2的排放量；生物炭施用在增强土壤团聚体稳定性的同时导致微生物群落结构及丰度发生改变，从而影响CO2的排放过程。然而，冻融条件下土壤CO2排放对生物炭施用的响应机制人们还不清楚。因此，本项目以玉米秸秆生物炭及马铃薯田土壤为研究对象，通过室内模拟试验，探究冻融条件下生物炭输入对土壤CO2排放的影响，并对土壤团聚体组成、稳定性及有机碳在团聚体中的分布特征进行分析，结合δ13C示踪技术，明确生物炭来源碳在CO2排放中的比例及其在团聚体中的分配特征，剖析冻融条件下生物炭在团聚体中的去向及其与土壤CO2排放的关系；同时，通过高通量测序分析技术探究冻融条件下生物炭输入对土壤微生物群落结构及丰度的影响。阐明冻融条件下农田土壤CO2排放对生物炭施用的响应机制。研究结果丰富了生物炭在农田土壤固碳的作用机制，为生物炭在中高纬度地区的应用提供理论依据。

冻融交替造成土壤团聚体破碎、微生物丰度及活性的变化增加了二氧化碳（CO2）的排放量；生物炭的输入会改变土壤团聚体组成、有机碳的分布特征及微生物群落结构及丰度，从而对土壤固碳减排具有重要的影响。然而，人们对冻融条件下土壤CO2排放对生物炭施用的响应机制尚不清楚。本文研究通过室内模拟试验探究了冻融条件下生物炭输入对土壤CO2排放的影响，并结合δ13C示踪技术和高通量测序分析技术系统分析了冻融条件下农田土壤CO2排放对生物炭施用的响应机制。研究结果表明（1）低温冻结作用增加了土壤CO2的排放速率，且随着冻融循环次数的增加，CO2排放速率呈现先增加后降低的趋势，生物炭输入降低了冻融条件下土壤CO2累积排放量的增加幅度；（2）低温冻融作用导致了土壤团聚体破碎，而生物炭输入可显著减少4.11%~7.74%的大团聚体破碎，从而增加了土壤团聚体稳定性，土壤平均重量直径（MWD）、几何平均直径（GMD）及水稳性团聚体（WR0.25）显著提高6.98%~16.54%；（3）生物炭的输入可显著增加各粒径土壤有机碳含量，且50%左右的生物炭主要富集在0.25~2 mm粒级，低温冻结使得0.25~2 mm粒级土壤中的生物炭进入更小粒级土壤中，多次冻融后0.053~0.25 mm土壤的生物炭分配比例显著增加；（5）生物炭输入增加了土壤微生物群落丰度和多样性，土壤微生物群落Chao1指数和Shannon指数平均增加了2.01%和3.37%；冻融条件下，生物炭对土壤微生物具有一定的保护作用，土壤Chao1指数和Shannon指数的下降幅度均较未添加生物炭处理较低。综上所述，低温冻融作用造成团聚体结构破碎及微生物的快速死亡，引起冻融期土壤CO2排放速率增加；而生物炭输入提高了土壤团聚体的稳定性和大团聚体中有机碳的分配，同时对土壤原有有机碳及微生物起到一定的保护作用，因此在冻融期间生物炭输入能够起到一定的固碳减排作用。本研究结果丰富了生物炭在农田土壤固碳的作用机制，为生物炭在中高纬度地区的应用提供理论依据。