生物炭施用引起的地表反照率变化对农业土壤呼吸作用及其环境效应的影响

Surface albedo is an important bio-geochemical driver that causes changes in land-atmospheric system. Soil respiration is an essential bio- geochemical process that closely relates to climate change. It is of tremendous significance and far-reaching influence to expand the quantitative research, which is still very meager nowadays, in how biochar application causes the change of surface albedo in farmland and how it affects soil respiration. The current project is to investigate how the change of surface albedo that is caused by biochar application influences the soil properties and its connection with soil respiration, to probe into the temperature sensitivity of soil respiration among different organic carbon fractions in the biochar-soil system, as well as to ascertain the influence of surface albedo on carbon isotopic signatures in biochar-soil system, to discern the sources of soil respiration, and to shed light on soil carbon balance, through experimental methods such as the preparation of biochar, field experiments and monitoring, laboratory incubation, carbon isotopic tracer techniques, soil-plant chemical analysis, and the instruments for precise analysis. Innovations in the current project: the research results, which are based on the change in surface albedo that is caused by biochar application in soils, through combining approaches of observation of meteorological factors and carbon isotope technique，can amplify the feedback information for land-atmospheric system from soil respiration process that closely relates to the influence of bichar application on the change of surface albedo, which will largely extend our knowledge with multi-angle in the influence of biochar-soil system on regional climate change, in order to be objective when evaluating how biochar can mitigate global warming.

地表反照率是影响地球气候系统变化的重要生物地球化学驱动因子，土壤呼吸是与气候变化密切相关的重要生物地球化学过程。生物炭引起农业土壤地表反照率变化、及其对土壤呼吸的影响和环境效应的量化研究还很缺乏，因此开展此项研究十分必要且意义深远。本项目通过生物炭制备、田间试验与监测、室内培养、碳同位素示踪、常规分析、精密仪器测试等技术手段，研究生物炭引起的地表反照率变化对土壤功能性状的影响及其与土壤呼吸的耦合作用，探求生物炭-土壤系统不同碳组分的呼吸敏感性，明确地表反照率变化对生物炭-土壤系统呼吸碳同位素组成的影响，辨析土壤呼吸来源，揭示碳动态。项目创新点：以生物炭引起地表反照率变化为切入点，结合气象观测与碳同位素技术，所获结果可充实与生物炭影响下地表反照率变化相关联的土壤呼吸过程对地球-气候系统的反馈信息，有助于多角度认识生物炭-土壤系统对区域气候变化的影响，客观评价生物炭抵御气候变化的作用。

生物炭输入土壤会导致地表颜色加深和粗糙度增加，进而引起地表反照率下降。地表反照率是地表能量平衡研究中的重要参数，地表反照率的降低可能会引起土壤温度上升及土壤呼吸作用增强，继而导致土壤有机质分解速度加快、CO2释放量增加。因此，探究生物炭介导的地表反照率变化与土壤呼吸作用间的关系及其环境效应，具有理论和实践意义。.通过田间试验与观测、样品采集与分析等方法和手段，考察了不同条件下农田地表反照率在不同时间尺度上的变化特征及其影响因素，探讨了地表反照率、土壤温湿度等因子变化与土壤呼吸过程的耦合作用程度，研究了生物炭影响下土壤呼吸温度敏感性以及土壤碳、氮组分的响应性变化。其次，借助室内模拟实验和碳同位素技术，比较了玉米秸秆及其生物炭对土壤CO2释放的影响和碳汇效应。.研究结果显示，生物炭输入可依地表条件和生物炭用量的差异在不同程度上降低农田地表反照率，最高降幅可达44.5%，但其降低效应可为作物种植及作物冠层结构的发展所减弱或掩盖。随作物生长盛期的到来及地表覆盖度的增加，生物炭介导的土壤N2O排放的增加效应亦因作物氮素吸收增加致土壤铵态氮和硝态氮含量减少而得以有效抑制。结果还揭示了生物炭在输入初期可显著增加土壤CO2释放量，但其增幅随时间逐渐收窄，生物炭导致的CO2排放增量主要来自生物炭-土壤体系中的水溶性有机碳，且生物炭是其主要贡献者。相关分析结果支持生物炭输入导致的地表反照率下降未对土壤呼吸产生直接影响的结论，而且生物炭可使土壤呼吸温度敏感性Q10值降低，46.0%的最大降幅发生在较高生物炭用量下的冬小麦生长季。室内培养实验及其土壤-生物炭系统样品的碳同位素分析数据显示，玉米秸秆生物炭输入土壤较玉米秸秆还田更不易矿化、其中的碳稳定性更强，这进一步印证了在一个较长时间尺度内生物炭的碳汇功能。.研究结果充实了与地表反照率相关联的土壤呼吸过程对地球—气候系统的反馈信息，对多角度认识生物炭于土壤有机碳源/汇效应的贡献提供了基础数据和支撑。