长期施用猪粪对红壤完全氨氧化菌基因丰度的影响

Effects of long-term pig manure applications on the abundance of comammox bacteria in an Ultisol

完全氨氧化菌(comammox Nitrospira)的发现对硝化微生物的研究提出了新的挑战。大量研究表明完全氨氧化菌在陆地生态系统中广泛分布,但其在农田土壤中的分布规律及其对长期施用粪肥的响应尚不清楚。研究了长期施用猪粪对农田红壤完全氨氧化菌、氨氧化古菌(AOA)和氨氧化细菌(AOB)功能基因(amoA)丰度的影响,及其与土壤净硝化速率的关系。结果表明:与不施肥的对照处理相比,猪粪施用显著提高土壤有机质和养分含量,且随着猪粪的施用量增加而增加。同时,施用中量和高量猪粪显著提升土壤净硝化速率,增幅分别达到317%和416%。所有处理中,完全氨氧化菌丰度以进化枝A为主,进化枝B丰度极低,大多为非特异性扩增产物,但进化枝A的amoA丰度均低于氨氧化古菌和氨氧化细菌。长期施用高量猪粪显著提升进化枝A的amoA基因丰度,表明存在喜好富营养环境的完全氨氧化菌,而有效磷是最主要的影响因子。相关性分析表明,进化枝A的amoA丰度与净硝化速率呈显著正相关(P<0.01),而氨氧化古菌和氨氧化细菌则没有,表明进化枝A可能在长期施用粪肥的农田红壤硝化过程中发挥重要功能。综上所述,长期施用粪肥显著提高农田红壤养分含量和完全氨氧化菌进化枝A的amoA丰度,进化枝A可能在农田红壤硝化过程中扮演重要角色。

The discovery of comammox Nitrospira challenged the conventional concept of two-step nitrification,which was thought to be performed by two distinct microorganisms,and opened up new avenues to study the relative contribution of different ammonia oxidizers to nitrification.Numerous studies have shown that comammox Nitrospira distributed widely in terrestrial ecosystems,however,their distribution in agricultural soils and how they responded to manure application remained largely unknown.In this study,we collected the soil samples from a long-term field experiment established 18 years ago at Yingtan Red Soil Ecology Experimental Station,Jiangxi,China.We determined the abundances of amoA genes of ammonia-oxidizing bacteria(AOB),archaea(AOA)and comammox Nitrospira using real-time quantitative PCR.The results showed that,compared with none fertilized control,long-term applications of pig manure significantly increased soil organic matter and nutrient contents,which increased with the increasing application rates of pig manure.Moreover,the long-term applications of medium and high rates of pig manure significantly increased soil net nitrification rates by 317%and 416%,respectively.In all the treatments,the abundance of comammox Nitrospira clade B was very low,which could be resulted from non-specific amplification products.Comammox Nitrospira clade A were detected in all the treatments,although their abundances were lower than those of AOA and AOB.The pig manure application significantly increased the abundance of comammox Nitrospira clade A amoA gene,indicating that the comammox Nitrospira in soils were not necessarily oligotrophic.Available phosphorus was a primary factor controlling the abundance of comammox Nitrospira clade A.The Pearson correlation analysis showed that the abundance of comammox Nitrospira clade A was positively correlated with the net nitrification rate,but that of AOA and AOB did not,indicating that comammox Nitrospira clade A might play an important role in nitrification of the soils under long-term applications of pig manure.In conclusion,this study suggests that long-term applications of pig manure increased the abundance of comammox Nitrospira clade A,which might play a critical role in nitrification of the arable Ultisols.