南方典型土壤有机碳组分对碳投入的响应和产量的作用及机制

Soil total organic carbon density at steady state was recently found to show linear and slowly non-linear positive responses to carbon input for red soil with higher carbon saturation deficit (CSD) and paddy soil with lower CSD, respectively. And, similar responses were also observed for crop yield to soil total organic C content on the two soils. However, response of soil organic C fractions to C input and mechanisms by which the crop yield increased with soil total organic C content are still unclear. Therefore, this project aims 1) to understand response patterns of soil organic C fractions to C input for the two soils, by using soil organic C physical-chemical fractionation method, based on the long-term field experiments on straw return rate; 2) to test saturation behavior of soil organic C fractions, by using incubation experiment and 13C-tracing technique; 3) to quantify relative correlations between soil organic C fractions and soil fertility factors of nutrients and structure etc. and their relative contributions to crop yield, under fertilization and non-fertilization conditions, by canonical correspondence analysis (CCA)-based variation partitioning analysis (VPA), and to in turn clarify mechanisms by which the crop yield increased with soil total organic C content. Results will contribute to better understand accumulation process and ecological functioning of soil organic carbon, and also will provide scientific basis for soil fertility-increasing strategy in typical agoecosystems of south China.

近期在碳饱和空隙较大的红壤和较小的水稻土上研究发现，土壤总有机碳平衡密度随碳投入的增加，分别呈线性和曲线缓慢的上升趋势，作物产量和土壤总碳含量间亦有类似关系。然而,关于土壤各组分有机碳对碳投入的响应特征，以及土壤有机碳提升的增产机制，尚缺乏深入研究。因此，本项目拟以秸秆还田定位试验为依托，运用土壤有机碳物理-化学联合分组等方法，揭示红壤、水稻土各组分有机碳平衡密度对碳投入的响应特征；通过室内培养实验和13C示踪等手段，验证土壤各组分有机碳的饱和行为；分别在施肥与不施肥条件下，采用基于典范对应分析的方差分解分析等方法，定量评价土壤各组分有机碳和养分、结构等肥力因子间的相对密切关系，以及分别对产量影响的相对贡献，阐明特定条件下红壤、水稻土有机碳提升的增产机制和主导因子。研究结果将为深入认识土壤有机碳的蓄积过程和生态功能提供理论基础，为南方典型农田土壤肥力的定向培育提供科学依据。

本项目针对土壤各组分有机碳对碳投入的响应特征，及土壤有机碳提升的增产机制尚不明确的科学问题，以我国南方红壤和水稻土的长期施肥试验为基础，采取长期定位试验和室内培养实验相结合的方法，运用土壤有机碳物理-化学联合分组等方法，研究揭示红壤、水稻土各组分有机碳平衡密度对施肥驱动碳投入的响应特征，以及综合分析与产量间关联，阐明红壤、水稻土有机碳提升的增产机制。.主要研究结果：（１）土壤有机碳不同组分对施肥驱动碳投入的响应在红壤与水稻土敏感不同。红壤中，有机碳各组分中的物理保护组分含量较少仅为6%，其余组分相当。与对照相比，化肥、化肥加秸秆处理主要提高有机碳的非活性碳组分，其含量分别较对照高67%和75%，而化肥加有机肥处理以提高其活性组分为主，较对照高55%；水稻土有机碳组分中，以游离活性有机碳为主占53%。仅施用化肥条件下，各组分无明显变化，而化肥配合施有机肥下活性及非活性组分均有提高，较对照分别提高31%和10%。有机培肥显著提高了土壤总有机碳及各组分有机碳密度。.（2）农田土壤有机质提升显著促进了作物增产，土壤有机质含量与产量呈极显著的正相关。红壤上有机质提升对作物增产的潜力大于水稻土。土壤有机质提升也显著改善旱地作物的稳产性，土壤有机质每提升1 gC/kg，玉米、小麦的产量可持续性指数提高5%，而变异系数下降；而水田有机质提升对其稳产性影响不明显。.研究结果可为深入认识土壤有机碳的蓄积过程和生态功能提供理论基础，为南方典型农田土壤肥力的定向培育提供科学依据。