东北农区不同种植模式对土壤有机碳周转的影响及其机制

Northeast China is the most important maize and soybean production areas in China. Long-term continuous corn or soybean cropping led to the strong losses of soil organic carbon (SOC). Crop rotation has been confirmed to improve the soil fertility and increase crop yield. However, our mechanistic understanding of the effects of crop rotation on SOC, especially in subsoil remains incomplete.The effect of cropping systems on SOC stock within depth were studied based on long-term field experiment about bare fallow, maize or soybean continuous cropping, and maize-soybean rotation. 13C pulse labeling methods were used to determine the allocation and dynamics of new assimilates among pools within the plant-soil systems and evaluate amounts of C transferred to belowground and rhizodeposition. The incorporation of rhizo-C into specific microbial groups was determined by 13C in phospholipid fatty acids (PLFAs). We applied dual 13C and 14C isotopic labeling to partition soil CO2 efflux and C pools into three sources: SOC, roots and rhizodeposition. This study provides a better understanding of the interaction effects of three sources, and the stability and turnover of SOC under different cropping systems. Overall, this project will provide theoretical support for understanding carbon cycling in agro-ecosystems, optimizing maize and soybean cropping patterns in Northeast China, and enhancing the comprehensive function of cropland.

东北农区是我国玉米和大豆主产区，受长期连作的影响，农田土壤有机质流失严重。大豆→玉米轮作代替玉米或大豆连作被证实能够有效提高土壤肥力，增加作物产量。然而，该模式下土壤有机碳分布特征及碳周转机制尚缺乏系统研究。本研究以休闲、玉米连作、大豆连作和大豆→玉米轮作模式为研究对象，通过大田长期定位田间试验和室内盆栽（培养）试验相结合的方式，辅以静态箱-气象色谱技术、13C和14C同位素示踪技术、13C-PLFA等技术，分析不同种植模式对土壤有机碳周转的影响，探索其关键过程的调控机制。以期明确不同种植模式下土壤有机碳贮存及矿化特征，揭示作物光合同化碳向地下的转移与根际激发效应，探明作物根系以及根际沉积碳对土壤有机碳固持的影响，阐明土壤微生物群落结构对碳周转的贡献。本研究可为深入认识农田碳循环过程、优化东北地区种植模式、提升农田综合功能提供理论支撑。

东北地区是我国最重要的粮食主产区之一，然而由于黑土过度开垦及不合理的种植和耕作方式，导致土壤生产力下降，资源利用率降低的趋势。加强大豆→玉米轮作系统中土壤有机碳转化特征及机制研究，可为东北地区优化种植模式，发展作物可持续生产提供理论依据。本项目利用大田试验，将13C同位素标记技术，qPCR荧光定量技术及静态箱-气象色谱法相结合，研究不同模式下光合同化碳向土壤不同碳库的转移和根际激发效应，土壤温室气体排放特征及其微生物学机制。主要结果如下：（1）轮作与施肥互作显著提高了玉米和大豆的产量（P＜0.05）。从产量构成因素来看，不论施肥与否，轮作显著增加了玉米和大豆的百粒重；（2）轮作和施肥互作促进了玉米和大豆土壤有机碳含量的积累。施肥与不施肥处理下轮作均显著提高了0-20厘米的玉米颗粒有机碳含量；玉米和大豆土壤团聚体组成均以微团聚体< 53 μm和53-250μm为主，微团聚体53-250 μm和< 53 μm中的有机碳含量大于细大团聚体250-2000μm和大团聚体＞2000μm中的有机碳含量；（3）施肥与不施肥处理下，与连作相比，两年轮作玉米和大豆的N2O累积排放量高于连作。轮作和施肥互作处理土壤CH4净吸收量显著高于不施肥和连作处理（P<0.05），土壤CO2累积排放量以SC+N处理最高，两年平均达到5615.7kg/ha；轮作和施肥显著提高了土壤壤nirK，nirS和nosZ基因拷贝数，且各处理nirS基因的拷贝数大于nirK （4）与连作相比，轮作玉米输入到地下的总碳量提高16.07%，且输入到根部和有机碳的的碳量为2.9，高于连作玉米，连作玉米的根际激发效应为80.19%，而轮作玉米的根际激发效应为121.23%，说明轮作促进了根际沉积物的分解，促进了有机碳的分解。总之，轮作和施肥通过调节影响土壤碳转化的各个因素促进了土壤有机碳的积累，增加了作物产量。