氮肥水平对稻田细菌群落及N2O排放的影响

作为土壤氮素转化的驱动者,微生物群落结构关系着稻田氮素利用及温室气体N_2O排放等问题。本研究分别基于高通量测序和荧光定量PCR技术,分析了不同氮肥水平CK(不施氮)、N(施N 180 kg·hm-2)、2/3N(施N 120 kg·hm-2)、1/3N(施N 60 kg·hm-2)]下稻田细菌群落及硝化反硝化关键微生物功能基因丰度的变化。结果显示:氮肥水平提高增加了稻田细菌物种丰富度Chao1指数和群落多样性Shannon指数,改变了细菌群落组成,其中与硝化作用相关的硝化螺菌门Nitrospirae和嗜酸的醋杆菌门Acidobacteria的相对丰度随氮肥水平提高而增加,但甲烷氧化菌Methylosinus的相对丰度随氮肥水平提高而降低。氮肥水平对稻田硝化作用关键微生物氨氧化细菌amo A基因丰度的影响较大,0~5 cm和10~20 cm深度土层中的amo A基因丰度均随氮肥用量增加而提高;反硝化作用关键微生物功能基因nir S、qno B和nos Z的丰度在不施肥处理(CK)中显著低于施肥处理(1/3N、2/3N和N)(P0.05),但1/3N、2/3N和N处理的稻田nir S基因丰度没有明显差异;0~5 cm土层中qno B和nos Z基因丰度存在随氮肥水平提高而增加的趋势,10~20 cm土层中nos Z基因丰度在2/3N和N处理下显著高于1/3N处理(P0.05)。N处理的稻田N_2O排放通量显著高于2/3N及1/3N处理(P0.05),后者又显著高于CK处理(P0.05)。相关分析结果表明稻田N_2O排放通量与0~5 cm土层中硝化螺菌门Nitrospirae相对丰度及10~20 cm土层中amo A基因丰度存在显著相关性(P0.05,n=10)。综上所述,氮肥水平提高增加了稻田细菌群落多样性,促进了稻田N_2O排放,且本研究稻田中硝化作用微生物群落及丰度变化与稻田N_2O排放的关系更为密切。

Effect of nitrogen fertilizer level on bacterial community and N2O emission in paddy soil

Microbial community structures are relevant for the utilization of nitrogen (N) and the emission of nitrous oxide (N₂O) in paddy soils. Nitrification and denitrification are the main ways to produce N₂O in soils and nitrification bacteria and denitrifying bacteria respectively drive the processes of nitrification and denitrification. In this study, changes in bacterial communities and the abundance of nitrification bacteria or denitrifying bacteria under different nitrogen fertilizer levelsCK (no N fertilization), 1/3N (N application of 60 kg·hm^-2), 2/3N (N application of 120 kg·hm^-2) and N (N application of 180 kg·hm^-2] in paddy soils were analyzed respectively by high-throughput sequencing and real-time PCR. The analysis in abundance of nitrification bacteria or denitrifying bacteria was based on ammonia-oxidizing bacterial amoA gene and denitrifying bacterial nirS gene or qnoB gene or nosZ gene. The results showed that increase in application of nitrogen fertilizer enhanced Chao1 index and Shannon diversity index of bacterial communities and changed the composition of bacterial communities in paddy soil. The relative abundance of Nitrospirae and Acidobacteria increased with improvement of nitrogen fertilizers, while that of Methylosinus decreased with improvement of nitrogen fertilizers in paddy soils. There was greater impact of increased use of nitrogen fertilizer on the abundance of amoA gene in paddy soils. The abundance of amoA gene increased with increasing nitrogen application in the 0-5 cm or 10-20 cm depths of soil. The abundances of nirS gene, qnoB gene and nosZ gene in no-fertilizer soil (CK) were significantly lower than those in fertilizer soils (1/3N, 2/3N and N) (P<0.05). There was no significant difference in the abundance of nirS gene among 1/3N, 2/3N and N treatments. However, there was an increasing tendency in the abundance of qnoB gene and nosZ gene with increasing application of nitrogen fertilizer in the 0-5 cm depth of soil. The abundance of nosZ gene in the 10-20 cm depth of soil under both 2/3N and N treatments were significantly higher than that in 1/3N treatment (P<0.05). At the same time, the emission of N₂O under N treatment was significantly higher than that under 2/3N or 1/3N treatment (P<0.05), and the latter two were also higher than that under CK (P<0.05). Correlation analysis showed that the emission of N₂O was markedly correlated with the relative abundance of Nitrospirae in the 0-5 cm depth of soil and the abundance of amoA gene in the 10-20 cm depth of soil (P<0.05, n=10). In summary, increasing nitrogen application improved the diversity of bacterial communities and the emission of N₂O in the studied paddy soils. Also there was a closer correlation between changes in abundance of nitrification bacteria and the emission of N₂O. The results suggested that the influence of nitrification bacteria on the emission of N₂O in the studied paddy soils was greater than that of denitrifying bacteria.