不同酸碱性紫色土的硝化活性及微生物群落组成

Nitrification Activity and Microbial Community Structure in Purple Soils with Different pH

为研究紫色土中的硝化作用、总微生物和硝化微生物的群落结构,以重庆永川的酸性紫色土(p H=5.3)和中性紫色土(p H=7.2)以及四川盐亭的石灰性紫色土(p H=8.5)为研究对象,采用稳定性同位素标记技术进行培养实验,并通过Miseq测序对三种紫色土微生物群落结构进行分析。每种土样共设有三种处理,包括^(13)CO_2标记处理、^(12)CO_2对照处理和^(13)CO_2+C_2H_2对照处理。结果表明,中性紫色土(p H=7.2)和石灰性紫色土(p H=8.5)经过56 d的培养后发生了强烈的硝化作用,而酸性紫色土(p H=5.3)中未发生明显的硝化作用,并且硝化作用类型都以自养硝化为主。三种紫色土中都存在着变形菌门(Proteobacteria)、酸杆菌门(Acidobacteria)、厚壁菌门(Firmicutes)、绿弯菌门(Chloroflexi)、放线菌门(Actinobacteria)、拟杆菌门(Bacteroidetes)和芽单胞菌门(Gemmatimonadetes),其中变形菌门在三种紫色土中都大约占有20%的比例。中性紫色土和石灰性紫色土各处理中硝化螺旋菌门(Nitrospirae)百分比大于酸性紫色土各处理。三种紫色土各处理中的氨氧化细菌(Ammonia-oxidizing bacteria,AOB)主要以亚硝化螺菌属(Nitrosospira)为主,亚硝酸氧化细菌(Nitrite-oxidizing bacteria,NOB)主要以硝化螺菌属(Nitrospira)为主。且NOB/AOB的值在三种紫色土各处理中最高可达到13,这意味着全程氨氧化细菌(Comammox)可能在紫色土的硝化作用中占据重要贡献。

【Objective】Nitrogen recycle is an important process in soil ecosystem,and soil microorganisms play a key role in the processes of nitrogen transformation.Nitrification is the process of soil microbe oxidizing ammonia into nitrate,involving ammonia-oxidizing bacteria（AOB）and nitriteoxidizing bacteria（NOB）,sequentially.But now,discovery of the microorganisms（Comammox）that can complete ammonia oxidization raised a number of fundamental questions.Purple soils is mainly distributed in the subtropical areas of China,particularly in Sichuan Basin,playing a very important role in agricultural production of the country.By p H and carbonate content,they can be divided into acidic,neutral and calcareous purple soils.Soil p H is an important factor not only affecting soil nitrification,but also influencing nitrification microorganisms in population and community structure.So what are the differences between purple soils different in p H in nitrification and nitrifying microbial community？These scientific questions need to be answered.【Method】Samples of purple soils different in p H,i.e.acidic purple soil（p H=5.3）and neutral purple soil（p H=7.2）in Yongchuan of Chongqing and calcareous purple soil（p H=8.5）in Yanting of Sichuan were collected for in-lab incubation to explore nitrification,soil microoganisms and community structures of nitrifying microorganisms in the soils,using the stable isotope probing technique and Miseq sequencing.The incubation experiment was designed to have three treatmentsfor each soil sample,including ^13CO2 labeling,^12CO2control and ^13CO2＋C2H2 control.Soil samples were cultured in a incubator at28℃for 56 days,during which 100 mg kg^-1urea-N and corresponding volume of gas was applied every week.Samples at D0 and D56 were analyzed with the Miseq sequencing technique.【Result】Intense nitrification,dominantly autotrophic nitrification,was observed in both neutral purple soil（p H=7.2）and calcareous purple soil（p H=8.5）,but not in acid purple soil（p H=5.3）.In all the three types of purple soils,bacteria of Proteobacteria,Acidobacteria,Firmicutes,Chloroflexi,Actinobacteria,Bacteroidetes and Gemmatimonadetes were detected,but varied in proportion.Bacteria of Proteobacteria accounted for about20%of the total in all the three purple soils.In addition,Planctomycetes was detected in acidic purple soil.In the neutral purple soil and calcareous purple soil,Armatimonadetes and Verrucomicrobia were detected.NOB/AOB ratio reached as high as 13 in all the three purple soils,which means that the Comammox may play an important role in the process of nitrification in purple soils.【Conclusion】In a word,the nitrification in the purple soils was mainly of the autotrophic type.Bacteria of Proteobacteria,Acidobacteria,Firmicutes,Chloroflexi,Actinobacteria,Bacteroidetes and Gemmatimonadetes were detected in all the three types of purple soils.Distribution of the soil microbial community varied with the soil.Nitrosospira and Nitrospira was the numerically dominant genus of ammonia-oxidizing bacteria（AOB）and nitrite-oxidizing bacteria（NOB）,respectively,in the three purple soils.NOB was higher than AOB in relative abundance.All these findings may serve as scientific basis for further study of nitrification in purple soils.