热带地区水稻-辣椒轮作土壤CH4和N2O排放对水肥管理的响应及微生物机制研究

Methane (CH4) and nitrous oxide (N2O) are two important greenhouse gases in the atmosphere and rice paddy ecosystem is considered as one of their major sources. Fertilization and water management are two common agricultural practices. So far the effect of fertilization and water management on CH4 and N2O emissions still hasn’t been consistent in rice paddy ecosystem. Due to the distinct characteristics of parent material and climate condition, soil properties in tropical region are quite different to those in other regional soils. The cultivation of rice and vegetable is a common rotation system in tropical region. However, the responses of CH4 and N2O emission in such rotation soils are rarely studied. Therefore, in this study, a field experiment was conducted to investigate the effect of fertilization and water management on CH4 and N2O emissions in tropical region under rice-pepper rotation. A double 15N-labelled NH4NO3 experiment was conducted in the laboratory to quantify the contribution of autotrophic nitrification, heterotrophic nitrification and denitrification to N2O emission and their responses to fertilization and water management. In addition, the community structure and abundances of methanogenic bacteria, CH4 oxidizing bacteria, ammonia oxidizing archaea, ammonia oxidizing bacteria and denitrifier were measured by fluorescent quantified PCR and DGEE to investigate the microbial mechanisms of the responses of CH4 and N2O emissions to fertilization and water management under rice-pepper rotation. The final objective of the present study was to make scientific reference for tropical region to make suitable fertilization and water management practices to increase soil carbon sequestration and to reduce greenhouse gas emissions in rice paddy ecosystem.

CH4和N2O是大气中两种重要的温室气体，稻田被认为是其主要的排放源。作为两种常见的农业措施，施肥和水分管理对稻田CH4和N2O排放的影响尚未形成统一的认识。热带地区因其母质和气候等条件的特殊性，使得其土壤性质有别于其它地带性土壤。稻-菜轮作是热带地区常见的种植模式，然而关于该模式下土壤CH4和N2O排放对水肥的响应研究目前还鲜有报道。为此，本项目拟开展田间观测试验研究水肥管理对热带地区水稻-辣椒轮作土壤CH4和N2O排放的影响；采用15NH4NO3和NH415NO3双标记法研究自养硝化、异养硝化和反硝化作用对N2O排放的贡献及对水肥管理的响应；利用荧光定量PCR和DGGE技术，测定CH4菌、CH4氧化菌、氨氧化古菌、氨氧化细菌以及反硝化细菌的群落结构与丰度，探讨水稻-辣椒轮作土壤CH4和N2O的排放对水肥管理响应的微生物机制。最终为热带地区制定合理的固碳减排的水肥管理措施提供科学依据。

CH4和N2O是稻田生态系统中重要的温室气体，易受灌溉和施肥的影响。海南常年高温多雨使得土壤呈现有机质分解快、铁铝氧化物含量高和耕作层薄等特点。稻菜轮作是热带地区常见的种植模式，关于该模式下土壤CH4和N2O排放对水肥管理的响应规律及微生物学机制研究尚不明确。为此，本项目采用田间观测与室内培养法系统探讨4种施肥（PK、NPKM+NPK和M）和2种灌溉（长期淹水（F）和常规灌溉（D））对稻菜轮作土壤CH4和N2O排放的影响及其微生物学机制。主要研究结果如下：. （1）双季间水分管理对CH4排放量无显著影响，但常规灌溉 N2O排放高于长期淹水。早稻季F-NPK+M和F-M处理土壤CH4排放量均显著高于NPK处理，但两者之间无显著性差异，NPK+M显著减少辣椒季N2O排放。CH4排放主要集中在早稻种植中后期和晚稻种植前中期，而N2O排放主要集中在辣椒季。稻菜轮作系统N2O排放系数为：辣椒季>早稻季>晚稻季。水稻季N2O排放与AOA、AOB、nirK和nirS基因拷贝数呈负相关，但与nosZ基因拷贝数呈正相关；辣椒季N2O排放与nirS基因拷贝数呈极显著负相关。. （2）与NPK相比，NPK+M处理未显著提升早晚稻和辣椒产量，但显著降低了早稻季常规灌溉下GWP值和辣椒季的GWP值和GHGI值。. （3）水肥管理对稻菜轮作碳氮转化土壤酶活性的影响未表现出一致的规律。例如，长期淹水条件下早稻季四种施肥处理的蔗糖酶和纤维素酶无显著性差异，而常规灌溉条件下，M+NPK和M处理的蔗糖酶均显著低于NPK处理。辣椒季期间，NPK+M和M处理的蔗糖酶和葡萄糖苷酶活性均显著高于NPK处理。. （4）常规灌溉条件下2019年晚稻季和辣椒季均表现为NPK+M处理下土壤团聚体的MWD、GMD和R0.25值显著高于NPK处理，而分形维数显著低于NPK处理。2020年三种施氮肥处理显著增加土壤团聚体稳定性，但三者之间无显著性差异。. （5）施肥未显著提高稻菜轮作土壤有机碳含量，但NPK+M和M处理显著提高了易氧化有机碳和颗粒态有机碳含量。. 综合温室气体排放、作物产量和有机碳组分考虑，稻菜轮作模式下适合常规灌溉+有机无机配施的管理方式可达到固碳减排的目的。