【作者】 周萍；

【导师】 潘根兴；

【作者基本信息】 南京农业大学 ， 土壤学， 2009， 博士

【副题名】基于长期试验及跨地域统计分析

【摘要】 农业土壤固碳作为《京都协议书》认可的固碳措施之一,对稳定生产力和应对气候变化具有双赢的积极效应。国际农业土壤固碳研究也一直十分活跃。目前对土壤固碳的容量及库间的分配、转化与稳定已经积累了大量的研究资料和认识,并随着现代有机质分析技术的发展已经深入到分子水平的固碳机理研究。目前关于不同农业管理措施下土壤有机碳及其组分的分布已有较多的研究报道,而稻田土壤作为我国特色的耕作土壤,其固碳潜力较大,固碳效应明显,在我国应对气候变化中具有举足轻重的作用。因此,阐明稻田土壤固碳的机理对于发展增产和减排共赢的稻作农业技术,增强稻作农业应对气候变化的能力具有重要意义。本研究以我国南方典型稻田土壤为对象,采用典型系统解剖和跨地域统计分析,研究长期试验体系中不同施肥管理下土壤有机碳含量变化及其团聚体有机碳组分分配的变化,并以活性有机碳组分-颗粒有机碳为代表,解剖稻田土壤有机质积累中有机碳组分的化学稳定机制,以阐明有机碳变化与环境因素、作物生产的关系,揭示有机碳积累中不同组分的转化特点,诠释稻田土壤有机碳固定中物理保护-化学结合和稳定的作用,充实稻田土壤有机碳固定机制的认识。并在此基础上通过试验探讨有机碳固定的途径和方法,为国家发展可持续稻作农业和固碳减排技术提供依据。主要研究结果如下：一、颗粒有机碳的积累是指示稻田土壤固碳的敏感性指标以太湖地区黄泥土为例,研究了长期不同施肥下颗粒有机碳(POC)的含量变化。结果表明：本体土壤(bulk soil)中TOC和POC的深度分布均符合幂函数方程(Y=aX-b)。不同的施肥处理主要影响耕层土壤的TOC和POC含量及其分配比例,而并未改变其深度分布格局。有机无机肥配施下由于有机物质的输入其TOC和POC含量显著高于其它处理。另外,太湖地区黄泥土的水稳性团聚体(WSAs)组成以>2 mm和2-0.25 mm粒径为主,施肥下>2 mm粒径的WSAs显著增加,并伴随2-0.25 mm粒径的明显减少。POC主要存在于>2 mm粒径的WSAs中,并随着团聚体粒径的减小而明显减少。>2 mm粒径WSAs中的POC对施肥的响应较为敏感,以化肥与秸秆配施下该粒径的POC积累最为明显。而化肥与猪粪配施则显著增加了2-0.25 mm和0.25-0.053 mm粒径的POC含量。土壤不同层次WSAs中POC的来源不同,在0-5 cm表层可能主要来源于作物生物量的输入,而在5-15 cm土层则可能跟外源有机物的施入有关。二、稻田土壤固碳存在着粗团聚体的物理保护及氧化铁的化学结合机制在本课题组对长期试验下紫泥田、红泥砂田和太湖地区黄泥土团聚体颗粒组SOC及其键合形态分析数据的基础上,运用跨区域分析探讨稻田土壤固碳的团聚体物理保护和氧化铁化学结合机制。结果表明：直径为2000-200μm的粗团聚体作为新增有机碳的主要载体,随长期不同耕作和施肥的变化最为强烈,其中又以红泥砂田的有机碳(sOC)变化最为明显,说明其良好管理下的有机碳累积效应最为显著。统计分析表明,本体土壤SOC积累量与2000-200μm粗团聚体SOC积累量之间的关系可用抛物线方程拟合(R2=0.95,n=8)。长期试验下粗团聚体对新固定有机碳的物理保护可能存在某种饱和机理。计算表明,供试稻田土壤的粗团聚体物理保护在长期试验期内还未达到其饱和限。同时,红泥砂田的粗团聚体保护作用最强,仍然具有明显的固碳潜力.直径为2000-200μm粗团聚体中的钙键合态有机碳(Ca-SOC)和铁铝键合态有机碳(Fe(Al)-SOC)对长期不同耕作和施肥的响应最为敏感,良好的耕作施肥下稻田土壤SOC的积累主要表现为Fe(Al)-SOC的增加。氧化铁铝的含量与SOC之间存在一定的依变关系,说明这些土壤发生的无机组成分在有机碳的保护与稳定中发挥着重要的作用,并且以红泥砂田粗团聚体中的氧化铁铝对有机碳的保护作用最强。因此,团聚体更新中物理保护的有机碳在细团聚体形成中进一步与氧化铁铝的键合可能是这些稻田土壤有机碳稳定的重要机制。三、有机质分子结构稳定是稻田土壤颗粒有机碳稳定积累的重要化学稳定机制采用固体交叉极化魔角自旋13C核磁共振(CPMAS 13C-NMR)波谱技术对长期不同施肥下红泥砂田和太湖地区黄泥土POC的化学结构特征进行了研究,以揭示稻田土壤固碳的化学稳定机制。结果表明,本体土壤和WSAs中POC的结构组成相似,主要以烷氧C为主,其次为烷基C和芳香C。施肥改变了本体土壤POC各类C原子的相对含量,化肥配施有机肥下烷氧c明显降低,伴随芳香C和酚基C不同程度的增加,使得芳香度和疏水性增强,表明POC的稳定性增强；而单施化肥下烷氧C最高,烷基C和芳香C均最低,导致芳香度和疏水性降低,从而POC的稳定性减弱。施肥还改变了太湖地区黄泥土WSAs中POC不同C原子的相对含量,使得POC对团聚体的稳定性作用发生变化。而红泥砂田WSAs中POC各类C原子的分配并未明显受到施肥的影响。而运用热裂解气相质谱(Pyr-TMAH-GC/MS)技术对太湖地区黄泥土POC的结构特征进行的进一步研究表明,各施肥处理下POC的热裂解产物主要以脂肪族化合物和木质素类化合物为主。脂肪族化合物主要为C8-C30脂肪酸酯(FAMEs),且大多为偶数碳结构。施肥改变了各裂解产物在本体土壤和WSAs中的分布,从而使得不同施肥处理下各类化合物对POC稳定性的贡献出现了差异。化肥配施猪粪下木质素类化合物以及微生物源的脂肪族化合物均贡献于本体土壤POC的积累与稳定,而化肥配施秸秆下本体土壤POC的化学稳定性主要归因于高等植物源和微生物源脂肪族化合物的共同贡献。化肥配施有机肥下WSAs中较高的POC主要归因于植物源有机质的分解贡献而非微生物本身。本研究揭示了化肥配施有机肥下POC的疏水性组分在提高其化学抗性和稳定性中的重要作用。四、合理的施肥措施促进稻田土壤作物碳同化和与土壤碳固定效应在稻田土壤内部有机碳固定机制研究的基础上,为了进一步探讨稻田土壤固碳的土壤-作物系统关系,以太湖地区黄泥土的长期肥料定位试验为典型案例,分析了不同施肥处理对作物碳同化及土壤碳固定的影响。结果表明,施肥对水稻产量有显著影响,尤其以有机无机肥配施处理水稻产量显著最高且最为稳定。施肥显著提高了耕层土壤碳密度,固碳速率以有机无机肥配施处理显著高于单施化肥处理。相关性分析表明,土壤固碳速率与作物输入碳+有机肥源碳的总输入量呈显著的线性正相关关系。这提示土壤有机碳积累主要与作物产量有关,而并非依变于有机肥源碳输入。因此,与作物产量直接关联的作物碳输入的增加是提高土壤碳固定的重要途径。肥料N素对水稻碳同化和土壤碳固定的效应均为化肥配施有机肥处理显著高于单施化肥处理。这揭示化肥配施有机肥是提高与稳定稻田生产力和促进土壤固碳与温室气体减排的双赢措施。五、外源碳输入贡献于稻田土壤的有效固碳,但因土壤类型而异在对太湖地区黄泥土施肥下作物碳同化与土壤碳固定案例分析的基础上,通过收集我国南方4种典型稻田土壤(紫泥田、红泥砂田、太湖地区黄泥土和青紫泥)长期不同施肥下的土壤有机碳及作物产量的年际数据,进一步分析不同类型稻田土壤固碳的土壤-作物关联机制。结果表明：不同施肥处理下的土壤年均固碳量线性依存于年均碳输入增量,施肥措施主要通过增加外源碳输入来促进土壤的有效固碳,单位碳输入增加下以紫泥田和红泥砂田的年均固碳量相对较高。良好施肥下的饱和固碳量以红泥砂田的明显最高,其次为青紫泥。统计分析表明,施肥下不同类型稻田土壤的固碳效率(碳输入增量与土壤固碳的线性关系斜率)主要受到初始有机碳水平的控制,而与黏粒之间的相关性并不明显。不同类型稻田土壤的饱和固碳量与游离氧化铁以及降水量之间有着密切的正相关关系。可见,稻田土壤中活跃的氧化铁对土壤碳储量的提高起着积极的促进作用,而黏粒并非土壤固碳的控制因子。施肥下稻田土壤的有效固碳还促进了肥料N素的农学效率。气候可能是影响稻田土壤碳储量变化的另一主导因子。六、稻田土壤氧化铁可有效辅助农业固碳减排.在固碳机理研究的基础上,通过选取水稻秸秆、猪粪、污泥和颗粒有机肥,添加氧化铁后分别进行室内好气培养(25℃)和田间填埋矿化(夏季),以探索农业固碳减排的技术途径。结果表明：好气培养条件下,氧化铁明显降低了水稻秸秆、猪粪、污泥和颗粒有机肥的C02释放速率,整个培养期间的C02累积释放量分别由未添加氧化铁的10934.45、5426.12、5288.43和794.90 mg C02-C kg-1降低为添加氧化铁的125.47、1535.15、1473.36和498.72 mg C02-C kg-1,以水稻秸秆的效果最为显著。田间填埋条件下,除了颗粒有机肥的有机碳降解速率基本未受氧化铁影响外,其余三种有机物料在每一取样阶段的有机碳降解速率均受到了氧化铁的有效抑制。填埋90天后,水稻秸秆、猪粪和污泥的有机碳降解速率分别由未添加氧化铁的34.06%、14.91%和19.90%,降低为添加氧化铁的24.25%、9.45%和14.24%,也以水稻秸秆的效果最为明显。可见,无论是室内好气培养还是田间填埋矿化,氧化铁均表现出对有机物料矿化降解的有效抑制作用,具有明显的有机碳回持能力。综上所述,稻田土壤有机碳的固定机制主要表现为团聚体物理保护、氧化铁化学结合和分子结构化学稳定的共同作用,从而构成稻田土壤特色的固碳机理。而黏粒保护理论并不足以解释普遍观察到的稻田土壤有机碳快速积累的原因。并且,这种固定的有机碳主要来源于外源碳输入的贡献,但是这种贡献也因土壤类型和土壤组成分的不同而异,进而影响到稻田土壤固碳的饱和趋势。外源碳输入贡献与稻田土壤内在的有机碳固定机制相辅相成,共同促进稻田土壤碳储量和固碳潜力的提高。今后还需加强对较大区域尺度和气候背景下的有机碳固定机制的研究,以区分不同的固碳机制在不同类型土壤中的相对重要性和相对贡献,并探讨气候在农业土壤固碳中的作用。另外,加强固碳机制基础上固碳技术的开发研究,以寻求快速有效的固碳方法与途径。更多还原

【Abstract】 Soil carbon sequestration in agriculture was supposed by the Kyoto Protocol as a ratified and important strategy in carbon sequestration and mitigation. It suggests a win-win effect on sustainning crop production and replying climatic change. Much more attention had been paid on agricultural soil carbon sequestration. It has been understood sufficiently on the capacity of soil carbon sequestration and distribution, translation and stabilization in carbon stock. For the last decades, molecular level of carbon sequestration is being focused on along with the reent developments in the structural characterization of organic matter components. In China, the content variation and distribution of SOC and its components under different agricultural managements have been studied sufficiently. As a unique type of anthropogenic soil, paddy soil has been extensively observed with distinctive trend and large potential of carbon sequestration, it was crucial for replying to climatic change. Thus, it is of vital importance to elucidate the C sequestration fate in paddy sois for developing the win-win technique of C enhancement and crop productivity in rice field and for enhancing the capacity of rice field answering to the climatic change. In this study, the content change of SOC in bulk soil and aggregates of typical paddy soils from South China under long-term agro-ecosystem experiments were conducted with typical and cross-site analysis, particularly, the molecular information on the composition of particulate organic carbon (POC) was elucidated to indicate the relationship of SOC change with environment and crop production, to annotate the physical protection, chemical binding and stabilization involved in soil C sequestration and to enrich the understanding about soil C sequestration fates in paddy soils. The approach and method of soil C sequestration was further explored in order to provide a foundation for the national development of sustanabal rice farming and C sequestration and mitigation technique. The main results are as follows:1. Accumulation of particulate organic carbon sensitively indicated soil C sequestration in paddy soilsVariations of total organic carbon (TOC) and particulate organic carbon (POC) in bulk soil and water-stable aggregates from Tai Lake paddy soil under long-term different fertilizations were conducted. It showed that the depth distribution of both TOC and POC fitted best to power function equations. Different fertilization practices tended to affect not the depth distribution of TOC and POC but the content in topsoil, being the highest under the treatment of chemical fertilizer plus organic fertilizer.In addition, the water stable-aggregates (WSAs) in Tai Lake paddy soil were dominated by the size fraction of>2 mm and 2-0.25 mm. However, the size fraction of>2 mm was increased and that of 2-0.25 mm decreased under fertilization treatments compared to that under no fertilization. POC was found to accumulate in the WSAs of>2 mm fraction and to decrese sharply with the decreasing size. POC in>2 mm fraction was more sensitive to fertilization practices, being significantly higher under chemical fertilization plus straw return, while POC in those of 2-0.25 mm and 0.25-0.053 mm size was slightly higher under chemical fertilization plus pig manure. Regression coefficients showed a possible source of POC in WSAs from increased crop biomass in topsoil (0-5 cm) and from organic matter applied in sub-surface layer (5-15 cm).2. Physical protection in coarse aggregates and chemical binding of ferric oxide contributed to soil C sequestration in paddy soilsIn order to elucidate the physical protection and chemical binding of soil C sequestration, the content of SOC and its binding forms in size fractions of micro-aggregates from purple paddy soil, red paddy soil and Tai Lake paddy soil was discussed with cross-site analysis. It showed that the newly accumulated SOC found its fate mainly in the coarse fraction of 2000-200μm in active response to tillage and fertilization treatments. Of the three studied paddy soils, SOC in red paddy soil exhibited the most intense response to fertilizations, exerting a most prominent trend of SOC accumulation under well management practices. Furthermore, statistic analysis indicated significant parabola relationship between SOC accumulation in bulk soil and in 2000-200μm coarse fractions. Therefore, it is inferred that accumulation of young SOC in topsoil may reach a saturation controlled by the physical protection in the coarse particle-size fraction. However, the maximum protection capacity by the coarse aggregates of the three tested paddy soils had not yet realized, still possessing an obvious potential of carbon sequestration.Calcium bound SOC (Ca-SOC) and iron/aluminum oxyhydrates-bound SOC (Fe(Al)-SOC) in coarse aggregates of 2000-200μm showed the most sensitive response to long- term tillage and fertilization practices. The SOC accumulation in paddy soils under good management practices was represented mostly as increase in Fe(Al)-SOC. Fe/Al oxyhydrates in coarse aggregates from the red paddy soil showed the most intensive chemical protection of SOC. Thus, chemical protection of SOC physically protected in coarse fractions by binding with Fe/Al oxyhydrates during micro-aggregate turnover was supposed as a prevailing mechanism of SOC sequestration in these paddy soils.3. Molecular stabilization of organic matter composition was a fate of particulate organic carbonr sequestration in paddy soilsThe combination of solid state CPMAS 13C-NMR and TMAH thermochemolysis-GC/MS was conducted to investigate the supramolecular structure change of POC from Tai Lake paddy soil and red paddy soil. POC in both soils were composed basically of O-alkyl-C, Alkyl-C and Aromatic-C, with the former being dominating. Fertilization treatments modified the proportion of different C species from the bulk samples as the portion of O-alkyl-C was decreased and that of aromatic-C and phenolic-C increased under both organic fertilization and compound fertilization of organic and inorganic fertilizers, resulting in the high aromaticity and hydrophobicity of POC. It indicated the enhanced chemical recalcitrance and stability of POC under organic amendments. Whereas, increased portion of O-alkyl-C but decreased portion of alkyl-C and aromatic-C was observed under chemical fertilization only and it induced relatively low aromaticity and hydrophobicity and a more readily decomposable nature of POC. The water-stable aggregates also differed in relative proportion of each C species from Tai Lake paddy soils under different fertilization treatments, and it modified the interactive effect of POC on aggregates stability of the paddy soil, whereas those from red paddy soil were not affected by fertilizations.Furthermore, the supramolecular structure of POC from Tai Lake paddy soil showed thermochemolysis products dominated by aliphatic and lignin-derived compounds. The most abundant aliphatic compounds were C8-C30 fatty acid methyl esters (FAMEs) dominated by even-numbered carbon species, in which short chain FAMEs of microbial origin were prevalent. Fertilization systems induced an increased trend of aliphatic compounds and it was mainly attributed to organic matter of microbial origin under chemical fertilizer only and chemical fertilizer plus pig manure, suggesting increased microbial activity in these two treatments; whereas it was primarily attributed to that of higher plant origin, followed by microbial origin under chemical fertilizer plus crop straw. The C stabilization by molecular recalcitrance is supposed as a way to contribute to C sequestration in Chinese paddy soils under good managements.4. Good fertilizations promoted crop carbon assimilation and soil carbon sequestrationTaking an example of a long-term fertilization trial from Tai Lake paddy soil, the effect of fertilization treatments on soil C sequestration and crop C assimilation as indicated by grain yield was analized to elucidate the process of soil-crop ecosystem involved in soil C sequestration. The results were as follows:significant difference in mean rice yield was observed between the treatments, with higher and more stable yield of rice under the combination of organic and inorganic fertilizers. Fertilizations significantly increased the C storage of topsoil and it showed higher C sequestration rate under the combination of organic and inorganic fertilizers than under inorganic fertilizers only. Soil C sequestration rate was in proportional to the total input of crop biomass and organic fertilizer to the soil. This demonstrated a key role of enhanced biomass C input in soil C sequestration of the paddy. Moreover, effect of applied N both on rice C assimilation as indicated by grain yield and soil C sequestration turned stronger under combined fertilizations. This, in turn, evidenced a Win-Win effect of enhancing and stabilizing crop productivity and C sequestration and greenhouse gas mitigation as well by paddies.5. Carbon input contributes to soil carbon sequestration in paddy soils and it varied among soil types with particularly indigenous soil componentIn view of the influence of fertilization on crop C assimilation and soil C sequestration, four sites of long-term soil-agro-ecosystem experiments (purple paddy soil, red paddy soil, Tai lake paddy soil and gley paddy soil) under different fertilizations from South China was further investigated with cross-site analysis to elucidate the soil-crop cooperation involved in soil C sequestration. It showed that fertilization could promote soil C sequestration via increasing the C inpur since it suggested a good linear correlation between annual soil C sequestration and C input. The soil C sequestration efficiency (the slopes of linear correlation between soil C sequestration and C input) differed between different types of paddy soils and it was higher in purple paddy soil and red paddy soil. The saturated C sequestration under good fertilizations was distinctively higher in red paddy soil, followed by gley paddy soil. Statistic analysis indicated negative linear correlation of C sequestration efficiency with initial SOC content, whereas no correlation with the clay content. The saturated C sequestration represented distinctly positive linear correlation with free ferric oxide and annual precipitation in different types of paddy soils. Thus, the abundant ferric oxide promoted the increase of soil C stock, whereas clay exhibited no positive effect on C sequestration in paddy soils. Soil C sequestration also promoted the N efficiency on crop yields. Climate is supposed to be another drive index of soil C stock of paddy soils.6. Ferric oxide could effectively promote agricultural carbon sequestration and mitigationIn order to explore the approach and method of soil C sequestration, the effect of ferric oxide on reducing the mineralization of organic materials (rice straw, pig manure, sewage sludge and granule organic fertilizer) under aerobic incubation and field landfill conditions was explored and elucidated. The results showed that ferric oxide significantly decreased the C mineralization rate of organic materials at each incubation time, it resulted in a significant reduction of the cumulative evolution of CO2 from organic materials during the early incubation period of 23 days, from 10934.45,5426.12,5288.43 and 794.90 mg CO2-C kg-1 to 125.47,1535.15,1473.36 and 498.72 mg CO2-C kg-1 for rice straw, pig manure, sewage sludge and granule organic fertilizer respectively, being more distinct for rice straw. Under the field landfill condition, except for granule organic fertilizer, the organic carbon remained for rice straw, pig manure and sewage sludge, sampled and determined after 30, 60 and 90 days since the beginning of field landfill process, was distinctively higher in organic materials granulated with Fe oxyhydrates than in those granulated with deionized-water. The decomposition rate of organic materials during the entire 90 days of field landfill was reduced by ferric oxide from 34.06%,14.91%and 19.90%to 24.25%,9.45% and 14.24%for rice straw, pig manure and sewage sludge, respectively, being more distinct for rice straw. Both of aerobic incubation and field landfill indicated distinct effect of ferric oxide on reducing the C mineralization and decomposition in organic materials.Thus, the particular fate of soil C sequestration in paddy soils was involved in phycial protection of coarse aggregates, chemical binding of ferric oxides and molecular structure stabilization, while clay protection was not supposed to explain the distinct C accumulation in paddy soils. In addition, soil C accumulation was mainly originated from biological C input and it was different among soil types with particularly indigenous soil component, which could influence the saturation capacity of soil C sequestration. Soil C input and the sequestration fate inside the paddy soil supplemented each other and promoted together the soil C stock and sequestration potential. It still deserves more attention on soil C sequestration fate under large region scale and climate backgfound in order to distinguish the relative importance and contribution of single C sequestration fate in different soil types, and to probe the effect of climate on agricultural C sequestration. The method and approach of C sequestration also deserves more study based on the soil C sequestration fate.更多还原