稻田土壤N2O消纳能力及nosZ-I型功能种群应答机制

Consumption Capacity of N2O in Paddy Soil and the Response Mechanism of nosZ-I-containing Communities

稻田土壤长期的淹水厌氧环境有利于反硝化作用的进行,是导致N2O大量排放的重要原因之一.目前,关于稻田土壤N2O排放特征的相关研究已有不少,然而关于稻田土壤N2O的消纳能力及相关功能微生物的应答机制尚不明确.本研究以淹水水稻土原状土柱(0~5 cm)为研究对象,在土柱底部输入外源N2O气体,系统监测所添加外源N2O通过土柱的浓度及关键土壤因子的动态变化特征,以及分析nosZ-I型功能种群组成的演替规律,以期揭示淹水水稻土N2O的消纳能力及nosZ-I型功能种群的应答机制.结果表明,外源N2O输入后约97.39%扩散进入土柱,逸散出土表的N2O占0.72%~7.75%,达到排放高峰后被土壤继续消耗,培养192 h后外源N2O处理比对照多消耗67.10%N2O,N2O消耗速率提高144.2%.同时,NH+4-N、NO-3-N和DOC分别多消耗了19.65%、16.29%和8.41%.N2O输入192 h后nosZ-I的群落多样性没有显著差异,但是其种群组成发生显著改变:优势菌株OTU5004、OTU5065、OTU960和OTU1282(Proteobacteria)相对丰度显著提高,其中OTU5004菌株相对丰度比初始样和CK升高7.30%和4.63%,非优势菌株OTU5265(Azoarcus sp.)比初始样和CK升高0.33%和0.15%.上述结果表明,0~5 cm深度渍水水稻土壤具有很强的N2O消耗能力,外源N2O添加使N2O消耗速率明显加快,提高了淹水水稻土壤对N2O的消纳潜力,促进碳氮转化和nosZ-I群落组成变化,这将为降低大气N2O排放提供新的参考.

The long-term flooding anaerobic environment in paddy soils is conducive to denitrification,which is one of the most important reasons for N2O emissions.N2O can be transformed to nitrogen gas(N2)by bacteria and archaea containing nitrous oxide reductase(N2OR)encoded by the nosZ gene,which is the only known biological pathway of N2O consumption in soil.nosZ-I is known to be typical in denitrifying bacteria,which is one of the clades of the nosZ gene and is mainly possessed a Tat signal peptide motif.Although many researchers have studied N2O emission characteristics of paddy soil,the capacity of N2O consumption and the response mechanism of related functional microorganisms in paddy fields is not yet clear.To verify the effect of exogenous N2O on N2O consumption and nosZ-I gene,a pot trial experiment was performed under anaerobic conditions.We collected intact soil cores from flooding paddy fields at a 0-5 cm depth,and exogenous N2O gas was input through the bottom of flooding paddy soil cores.Meanwhile,a control treatment(CK)with no additional N2O gas was also performed.The dynamic characteristics of the added exogenous N2O concentration through the intact soil cores,the content of inorganic nitrogen,and DOC were systematically monitored.In addition,the change in the nosZ-I population diversity and community composition were investigated by high-throughput sequencing approaches,with the purpose of revealing the N2O uptake ability of flooded paddy soil and the response mechanism of the nosZ-I population.The results showed that 97.39%of exogenous N2O diffused into the soil cores,and only 0.72%-7.75%of exogenous N2O escaped from the soil surface.The N2O released in the headspace of soil cores could continue being absorbed and consumed by the flooding soil column.In addition,67.10%of the N2O escaped to the headspace was consumed in exogenous N2O treatment after 192 h of incubation,which was higher than that in CK treatment,and the N2O consumption rate increased by 144.2%than that in CK treatment.Meanwhile,the consumption of NH+4-N,NO-3-N,and DOC consumed during exogenous N2O addition treatment was 19.65%,16.29%,and 8.41%higher than that in CK treatment,respectively.However,the diversity of the nosZ-I gene community had no significant difference;the community composition of nosZ-I-containing bacteria changed significantly after 192 h when exogenous N2O was input.The abundances of OTU5004,OTU5065,OTU960,and OTU1282(Proteobacteria)significantly increased,which were the dominant bacterial strain of nosZ-I gene on the OTU level.Compared with the initial sample and CK,the abundance of the OTU5004 strain increased by 7.3%and 4.63%,and the abundance of the OTU5265 strain(Azoarcus sp.)increased by 0.33%and 0.15%,respectively.The result indicated that the flooding paddy soil column at the soil layer of 0-5 cm has a strong N2O absorption and consumption ability.In summary,compared with CK,the addition of exogenous N2O significantly accelerated the N2O consumption rate,improved the consumption potential of flooding paddy soil column,promoted carbon and nitrogen conversion,and changed nosZ-I community composition.These results would provide a new reference for reducing atmospheric N2O emissions.