紫云英与油菜混播对稻田土壤N2O排放及相关功能基因丰度的影响

Effects of the Mixted-cropping of Chinese Milk Vetch and Rape on Soil Nitrous Oxide Emission and Abundance of Related Functional Genes in Paddy Fields

【目的】探究绿肥混播对稻田土壤N_(2)O的减排效果和机制,筛选既高产稳产,又减排的适合南方双季稻区发展应用的绿肥混播种植模式。【方法】比较不同紫云英与油菜混播比例(单播紫云英(CK1)、单播油菜(CK2))、3/4紫云英+1/4油菜(3/4M+1/4R)、1/2紫云英+1/2油菜(1/2M+1/2R)、1/4紫云英+3/4油菜(1/4M+3/4R)对稻田N_(2)O排放规律及相关功能基因的影响。【结果】(1)作物种类影响N_(2)O排放。各处理的N_(2)O排放规律基本一致,其中冬作季N_(2)O排放主要集中在冬季绿肥的盛花期,早晚稻季主要集中在水稻的分蘖、灌浆和成熟期。总体来看,稻田N_(2)O排放主要集中在水稻季,早稻季的N_(2)O排放量低于晚稻季;2018年稻田N_(2)O排放通量总体比2019年高。(2)各处理的早稻N_(2)O累积排放量差异均不显著。连续两年单播处理的N_(2)O累积排放量低于混播各处理,其中2019年处理CK1最低,处理3/4M+1/4R的N_(2)O周年累积排放量在各混播处理中最低。(3)整体来看,晚稻土壤的amo A-AOA和amoA-AOB基因拷贝数比早稻要高,amo A-AOA基因拷贝数比amo A-AOB高1—2个数量级。晚稻的土壤nirS、nirK、nosZ基因拷贝数比早稻要高,其中nir S基因拷贝数比nir K和nosZ高1—2个数量级。紫云英与油菜混播提高了土壤amo A-AOA和amoA-AOB基因丰度,amoA-AOA基因为优势功能基因,而且提高了土壤nirS、nirK、nosZ基因丰度,nirS基因占主导地位。反硝化基因拷贝数比硝化基因拷贝数高1—3个数量级,反硝化作用对N_(2)O排放贡献更大。【结论】"3/4紫云英+1/4油菜-早稻-晚稻"种植模式在保证高产和高肥力的情况下,N_(2)O排放量相对较低,是较理想的种植模式。

【Objective】The aim of this study was to determine how a green manure mixted-cropping affected nitrous oxide(N_(2)O)emissions from soil and the abundance of related functional genes in paddy field soil.The ultimate aim of this research was to identify a green manure mixted-cropping that had high and stable yields and reduces emissions,and was suitable for cultivation in the double-rice areas of southern China.【Method】The effects of mixted-cropping of Chinese milk vetch and rape at different ratios(single Chinese milk vetch,single rape,3/4 Chinese milk vetch+1/4 rape,1/2 Chinese milk vetch+1/2 rape,and 1/4 Chinese milk vetch+3/4 rape)on N_(2)O emissions and the abundance of related functional genes in paddy field soil were determined and compared.【Result】(1)The crop species affected N_(2)O emissions.The N_(2)O emissions were similar among the different treatments.Among them the N_(2)O emissions from winter crop soil were mainly concentrated at its flowering stage,and those during the rice growing period were concentrated at the tillering,filling,and maturity stages of early and late rice crops.On the whole,the N_(2)O emissions from paddy fields were lower N_(2)O in the early rice season than that in the late rice season.The overall N_(2)O emissions flux in the paddy fields was higher in 2018 than that in 2019.(2)There was no significant difference in N_(2)O cumulative emission of early rice under different treatments.The cumulative N_(2)O emissions from a single seeding treatment were lower than those from mixed treatments over two consecutive years.The annual cumulative N_(2)O emissions were lowest under CK1 in 2019.Among all the mixed treatments,the 3/4 Chinese milk vetch+1/4 rape treatment had the lowest annual cumulative N_(2)O emissions.(3)In general,the copy number of amo A-AOA and amoA-AOB genes was higher in the soil of late rice than that in the soil of early rice,and the copy number of AmoA-AOA was up to two orders of magnitude higher in late rice soil than in early rice soil.The copy numbers of nirS,nir K and nos Z were higher in the soil of late rice crops than that in the soil of early rice crops,and the copy number of nir S was up to two orders of magnitude higher than those of nirK and nos Z in late rice soil.The mixted-cropping of Chinese milk vetch and rape increased the abundance amo A-AOA and amo A-AOB genes in soil,and amo A-AOA was the dominant functional gene.It also increased the abundance of nir S,nir K and nos Z genes in soil,and nir S gene was the dominant gene.The copy number of genes related to denitrification was one to three orders of magnitude higher than the copy number of genes related to nitrification,indicating that denitrification made a larger contribution to N_(2)O emissions.【Conclusion】Overall,the 3/4 Chinese milk vetch+1/4 rape-early rice-late rice was the best mixed planting system,because it had the best combination of low N_(2)O emissions as well as high yield and high fertility.