旱地土壤反硝化厌氧甲烷氧化菌的垂向分布特性与活性分析

在厌氧条件下,以亚硝酸盐作为电子受体将甲烷氧化的反硝化厌氧甲烷氧化反应(nitrite-dependent anaerobic methane-oxidizing,n-damo)的发现,彻底颠覆了人们对甲烷循环的传统理解.通过分子生物学方法及13C和15N稳定同位素示踪技术,对河北省北澧河附近的旱地农田土壤(0~1 m)中n-damo菌的群落结构、丰度和活性进行了研究,深入探究了n-damo菌的亚硝酸盐底物来源.结果显示,n-damo菌更多存在于旱地浅层土壤中,并且随季节变化分布在不同深度的土壤中.针对其pmo A基因的系统发育分析显示,旱地土壤中n-damo菌的群落结构具有明显的空间异质性,来自土壤0~20 cm和40~60 cm土层的序列完全分开,处于系统发育树不同分枝.针对其16S rRNA基因的实时荧光定量PCR结果显示,n-damo菌丰度随土壤深度的增加而降低,夏季丰度(1.44×10~4~1.02×10~5copies·g~(-1))低于冬季(3.66×104~2.67×105copies·g-1).在浅层土壤(0~20 cm)中,硝化反应和反硝化反应共同为n-damo菌提供亚硝酸盐底物来源;而在深层土壤(60~80 cm)中,亚硝酸盐底物主要来源于硝化反应.n-damo菌的活性(0.18 nmol·g~(-1)·d~(-1),以CO_2计)只能在夏季表层土壤(0~20 cm)中检测到,其余深度均未检测到其活性.在旱地农田土壤中,反硝化厌氧甲烷氧化菌对农田碳循环的影响可能不大.

Vertical distribution characteristics and activity analysis of nitrite-dependent anaerobic methane oxidation in an agricultural upland soil core

The discovery of nitrite-dependent anaerobic methane oxidation (n-damo) with nitrite as the electron acceptor has changed the understanding about methane oxidation. In this study, the unique distribution characteristics and activity of n-damo bacteria were investigated in upland soil cores (1 m depth) from an agricultural upland at the Beili River in Hebei Province, China. Meanwhile, nitrite source for n-damo bacteria was also studied. Evidence was obtained using molecular biology methods and isotope-tracing technique. Results showed that n-damo bacteria were detected only in the shallow upland soil and distributed at various depths in different seasons. Phylogenetic analysis of pmoA genes showed apparent spatial heterogeneity of n-damo bacteria, and the sequences from 0~20 cm and 40~60 cm were completely separated in different branches of the phylogenetic tree. The abundance of n-damo bacteria decreased with soil depths, and the abundance in summer (1.44×10⁴~1.02×10⁵ copies·g^-1) was lower that in winter (3.66×10⁴~2.67×10⁵copies·g^-1). In this study, we found that the NO₂^- source for n-damo process came from both nitrification and denitrification processes in surface soils (0~20 cm), while in deep soils (60~80 cm) it mainly came from the nitrification process. Moreover, the n-damo activity (0.18 nmol CO₂·g^-1·h^-1) was only observed in surface soil (0~20 cm), and activity at other depths could not be detected. The influence of n-damo bacteria in the agricultural upland soil may be limited.