施氮对土壤有机碳转化过程、机制影响的C-14示踪研究

Soil organic carbon (SOC) holds more than twice as much C as either the atmosphere or terrestrial vegetation,and plays crucial role in the global C cycling. Storage change, transformation and stabilization mechanisms of SOC are presently the research "hotspot". Agricultural SOC stock of China has been changed dramatically in the last thirty years, mainly attributed to the change of cropland management (such as fertilization and cultivation) and climate warming, in which continuously increase application of synthetic N-fertilizer exerts a powerful influence. However, mechanisms of N-fertilizer on transformation of SOC and the potential contribution of N-fertilization to the change of agricultural SOC are still obscure. In the present project, response of SOC and its components to N-fertilizer will be investigated by means of 14C tracer, including: 1) Synthesis of uniformly and specifically labeled SOC; 2) Mineralization, transformation and residue distribution of 14C-SOC as affected by N-fertilizer in soils; 3) Effects of N-fertilizer on microbial activity and community related to transformation of SOC; 4) Establishing quantitative relationship between N-fertilizer application and SOC stock change. Results of this investigation are not only helpful to elucidate the potential contribution of N-fertilizer application to agricultural SOC change, but also have crucial implications for deeply understanding the transformation mechanisms of SOC.

土壤有机碳(SOC)是全球碳循环过程中的重要碳库，其储量变化和转化机制是当前国际研究的热点。过去三十年，我国农田SOC含量发生了很大变化，且不同地区土壤之间存在较大差异。此间，氮肥施加持续增长对农田SOC含量变化的影响和潜在贡献不容忽视，然而有关施氮对SOC转化过程的影响及其相关机制目前尚不清楚。本申请拟采用C-14同位素示踪技术研究氮肥施加对我国典型农田SOC转化过程的影响及相关机制，包括：1)SOC及其组分的C-14全标记和选择性标记制备；2)氮肥施加对SOC及其组分土壤中矿化、降解、赋存形态及归趋的影响；3)施氮引起的微生物群落和活性改变与SOC及其组分转化之间的关系；4)氮肥施加与农田SOC变化之间的潜在定量关系。研究结果对于揭示氮肥施加对我国农田SOC含量变化的潜在贡献，全面掌握我国农田SOC的转化和变化规律具有重要的理论和现实意义。

土壤有机碳(SOC)是全球变化过程中大气CO2的重要源和汇，其储量变化和转化机制是国际研究热点。农田是我国土地利用的主要形式，过去三十年，我国农田SOC含量发生了很大变化且呈现出且明显的地区差异，此间，氮肥施加的持续增长对SOC的影响不容忽视，但氮肥施加对农田SOC转化的影响机制及其对SOC含量变化的贡献还不清楚。为此，本课题以过去三十年SOC变化比较典型的农田土壤（潮土、黑土和乌栅土）为研究对象，采用14C示踪技术详细研究了氮肥施加对农田SOC转化的影响及其相关机制。研究结果发现，三种土壤中活性和中性SOC组分对施氮的响应不敏感且不同土壤间无明显差异，而稳定性SOC组分（蛋白和芳香组分）对施氮的响应表现出了明显土壤特异性的特点，并与过去三十年这三种土壤中土壤SOC的变化趋势是一致的，表明稳定性有机碳组分对施氮的响应很大程度上决定了农田土壤有机碳的变化趋势。利用高通量测序对土壤微生物群落和结构进行分析发现，潮土中施氮导致了微生物群落的明显分异，而黑土和乌栅土中，施氮并未引起微生物群落的明显分异，在门水平上，潮土、黑土和乌栅土中，施氮均显著改变了某些特定微生物种的变化，这很可能是导致稳定性土壤有机碳组分对施氮的响应在三种土壤上表现出了土壤特异性特点的原因。上述研究结果对于深入理解氮肥施氮导致的我国农田SOC的变化规律具有重要的理论和现实意义。