典型农田土壤物理-化学稳定性碳组分对长期碳输入的响应机制

Soil organic carbon in arable land is crucial to ensure food security and climate change mitigation. The objectives of this project is to explore the mechanism in the response sensitivity of soil organic carbon and its fractions to carbon input, which varies in typical soil types and remains poorly understood. We will conduct our study based on the gradient of soil organic carbon content and carbon input resulted from various chemical and manure applications under four (three from upland and one from paddy) 20-3-years ongoing experiments.We will sample soils from the selected treatments and collect the kept soil samples every 8 to 10 years from the initial of the long-term experiments to now on. By using a combination of physical, chemical, and density fractionation techniques, as well as the 13C CP/MAS-NMR techniques, we will analysis the change of physical and chemical stabilized soil organic carbon fractions and its response to carbon input for the collected soils，and figure out the regulating factors. We will conduct indoor incubation experiments with labeled 13C isotope to reveal the response of soil microbial and the priming effect on soil organic carbon mineralization and decomposition with various carbon input types. Field incubation with natural abandence of 13C (C3/C4) will also be carried on to validate the response mechanism of physical and chemical stabilized organic carbon to carbon input from typical cropland soils. All the results will help to understand the interaction mechanism between organic carbon and soil minerals and offer theoretical basis for sustainable soil organic carbon management practices.

农田土壤有机碳对于保障粮食安全和减缓温室气体排放具有重要意义。本项目针对典型农田土壤碳积累与碳输入的响应关系存在差异而机制不明确这一问题，依托典型农田20-30年的长期定位试验，采用土壤碳的物理-化学联合分级手段，结合固体核磁共振技术，研究自起始年份至项目执行期间（每间隔8-10年）不同水平碳输入下土壤物理未保护、物理保护（团聚体）、化学保护（粘粉粒结合）和生物化学保护（未酸解）碳组分的演变特征及其与碳输入的响应关系；结合13C示踪室内模拟培养实验，阐明外源碳输入后土壤微生物的变化动态及其对土壤有机碳的激发效应，并利用C3/C4系统转化的自然丰度13C示踪的野外控制试验，阐明典型农田土壤各碳库组分对碳输入的响应过程与更新速率，揭示典型农田土壤物理-化学稳定性碳组分对碳输入的响应机制，研究结果将有助于理解农田土壤固碳过程与稳定机制，为筛选可持续的土壤有机碳管理措施提供科学依据。

土壤有机碳（碳）的积累取决于系统碳输入与输出的动态平衡。我国集约化管理模式下，提高农田土壤有机碳水平的主要途径是包括增加植物源或有机物料的碳输入。本项目针对典型农田土壤碳积累与碳输入的响应关系存在差异而机制不明确这一问题，依托典型农田20-30 年的长期定位试验，研究了土壤不同物理-化学保护碳组分与碳输入的响应关系与差异及其主控因素。结果表明，非保护态的颗粒有机碳和物理保护的团聚体是目前典型农田土壤有机碳积累的主要形态，这2个组分均与外源碳的输入显著正相关；但生化保护态、物理-化学、物理生化保护态及化学保护碳组分对外源碳输入无响应，可能已经达到平衡。多点位联网分析结果表明，土壤属性、气候、管理措施及其交互作用解释了不同保护形态的碳87%-91%的变异；核磁共振的结果表明，长期施肥明显降低了土壤有机碳芳香碳的相对含量，而增加了烷氧碳的相对含量。土壤碳各功能团的转化效率为烷氧碳 > 芳香碳 >烷基碳 > 羰基碳。联网分析结果表明，气候（年降雨，均温和年均有效积温）、土壤属性（C:N比，pH值、粘粒含量）和年均碳投入及其交互作用总共解释了土壤有机碳功能团转化效率86.06%的变异。长期碳输入主要是通过影响土壤C:N及pH值来影响土壤有机碳功能团组成；通过同位素示踪模拟试验进一步分析表明，单次和重复的碳输入均显著促进了不同肥力水平土壤大团聚中原有有机碳的矿化，而外源碳的积累主要发生在微团聚和粉黏粒组分中。表明长期碳输入条件下，外源碳主要在微团聚体和矿物结合态的固定，再通过团聚作用增加大团聚体数量而促进土壤总有机碳的积累，而矿物结合态碳容量主要由土壤质地决定。项目相关成果发表在《Science of Total Environment》、《Soil & Tillage Research》、《Journal of Environmental Management》和《植物营养与肥料学报》、《中国农业科学》等国内外知名期刊上发表论文15篇。研究结果有助于理解农田土壤的固碳过程与稳定机制，为可持续的土壤有机碳管理措施的筛选提供科学依据。