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作者简介:

李健,男,硕士生,研究方向为土壤氮磷迁移转化.1220123971@qq.com;

曲植(通信作者),博士,副教授,主要从事土壤氮素循环生物学机理研究.zhiquzq@163.com

中图分类号:X511

文献标识码:A

DOI:10.13878/j.cnki.jnuist.2022.04.011

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目录contents

    摘要

    水稻是我国第一大粮食作物,稻田特有的淹水环境为反硝化作用的发生提供了必要条件,而反硝化作用造成的氮素平均利用率低、温室气体排放等问题日趋严重.反硝化作用作为微生物驱动的生物学过程,自身受到多种因素的影响.为揭示pH、有机碳源等关键限制因子对水稻土反硝化菌的影响,本研究以两种初始pH不同的碱性和酸性水稻土作为研究对象,通过室内泥浆厌氧培养试验,分别基于DNA和RNA水平分析了反硝化关键功能基因(nirK/SnosZ )丰度变化规律,以期揭示外源添加有机碳源(葡萄糖)对不同pH水稻土中反硝化微生物功能活性及潜势的影响.结果表明:1)外源添加葡萄糖会降低土壤pH,且pH降低程度随添加葡萄糖浓度的增加而增加;2)碱性水稻土中添加葡萄糖增强了反硝化作用;酸性水稻土中添加葡萄糖对反硝化作用的影响不显著;3)不同pH水稻土中nirKnirS的基因数量和表达量对添加葡萄糖的响应具有显著差异,其中nirK基因的响应程度相对更高;4)在酸性水稻土中,nosZ基因的数量和表达量随碳源浓度的升高而降低,而碱性水稻土添加低浓度葡萄糖后,碳源的刺激作用占主导地位,nosZ基因的数量和表达量均有所增加,添加高浓度葡萄糖后,碳源添加引起的土壤酸化对nosZ基因的数量和表达量均起到了抑制作用.本研究表明水稻土中外源有机碳的添加从碳源供应和酸化土壤两方面综合影响了反硝化微生物功能和活性,进而影响反硝化作用的发生和氧化亚氮的排放,研究结果为稻田外源有机物输入的环境效应分析提供理论依据.

    Abstract

    Rice is the largest grain crop in China,and its unique flooded paddy soil provides necessary condition for the occurrence of denitrification.However,the problems of nitrogen utilization decline and greenhouse gas emissions caused by denitrification have gained increasing concern.As a biological process driven by microorganisms,denitrification is affected by many factors such as soil pH and organic carbon sources.To reveal the effect of exogenous organic carbon on the functional activity and potential of denitrifying microorganisms in paddy soils with different pH values,this study added glucose to two paddy soils with different initial pH values and analyzed the abundance of key functional genes (nirK/S,nosZ ) for denitrification at DNA and RNA levels.The results showed that the glucose reduced soil pH,the degree of which rose with the increase of the glucose concentration.The added glucose also enhanced soil denitrification,which was observed only in alkaline paddy soil.The responses of number and expression of nirK and nirS genes to glucose addition were significantly different between the two soils with different pH values,and the response degree of nirK gene was relatively higher.In acidic paddy soil,the number and expression of nosZ gene decreased with the increase of carbon source concentration;while in alkaline paddy soil,low concentration glucose significantly stimulated the number and expression of nosZ gene,but high concentration glucose caused soil acidification,which then inhibited the number and expression of nosZ gene.This study shows that exogenous organic carbon source affects the function and activity of denitrifying microorganisms in paddy soil from aspects of carbon source supply and soil acidification,which in turn influences the occurrence of denitrification and subsequent nitrous oxide emission.

  • 0 引言

  • 水稻是我国第一大粮食作物,其产量约占全国粮食产量的1/3,截止2022年,我国栽培面积达到2 900万hm2[1].为提高作物产量,自20世纪70年代以来,我国农业生产中的氮肥施用量迅速增加.根据FAO的统计资料,平均每年增加约7.8×105 t.2008年耕地面积仅占世界7%的中国,消耗了3.3×107 t氮肥,占全球当年氮肥消耗量9.2×107 t的36%,有预测表明,我国的氮肥施用量还可能继续增加[2-3].目前,中国稻田的氮素平均利用率仅在30%~40%之间,而造成稻田氮素利用率低下的一个主要原因是稻田中发生反硝化作用导致氮素以气态形式流失[4-6].

  • 反硝化作用作为土壤中参与氮循环的重要一环,是农业上N2O排放的主要来源.反硝化作用是指反硝化微生物在厌氧条件下,将硝酸盐、亚硝酸盐逐步还原,最终将氮以一氧化氮(NO)、氧化亚氮(N2O)或分子态氮(N2)的形式释放的过程[7-8],它提高了农田生态系统中氮素流失的风险,并导致了严重的经济损失.

  • 反硝化过程是由微生物驱动的酶促反应过程,其反映速率和产物组成显著受到多种环境因素直接或间接的影响,如温度、pH、Eh、水分、含氧量、碳源类型、氮源类型、碳氮比、土壤质地、耕作方式及土地利用类型等.近年来,国内外众多学者围绕环境因子对反硝化作用的影响开展了一系列深入的研究.Tang等[9]通过向亚热带和温带森林土壤中添加N、P,发现pH值是反硝化微生物活性的主要控制因子;Tao等[10]通过有无施用有机肥对农田土壤反硝化微生物群落结构及N2O排放的试验中发现施加有机肥可显著提高土壤反硝化酶活性,增加反硝化过程相关功能基因的数量,并减少N2O排放量;王丽丽等[11]研究发现,生物反硝化系统中最好的电子供体是易于生物降解的有机物,其不仅可提高反硝化速率,还能够提升生物处理装置的能力和效率;王海涛等[12]、郑兰香等[13]发现土壤中C/N比越高,反硝化速率越强.Shan等[14]、Ryden等[15]、Bhandral等[16]研究也表明有机碳含量越高,其反硝化潜势也越大.这是由于反硝化作用是微生物在厌氧条件下进行的硝酸盐、亚硝酸盐的异养还原过程,需要碳源作为电子供体参与反应[17].淹水条件下微生物利用碳源厌氧发酵过程中产生的有机酸[18-19]、氢离子[20]、CO2等物质会降低土壤pH[21],而土壤pH是影响反硝化作用最主要也是最复杂的因素之一,可直接影响参加反硝化作用的反硝化的微生物群落结构和氮氧化物还原酶的活性[22-24].因此碳源是影响反硝化作用的关键因素之一,但是目前关于外加碳源的研究多见于对工农业污水脱氮处理,其对农业土壤尤其是稻田土壤中反硝化作用的影响机理研究较少,碳源添加对反硝化过程的影响机制研究鲜有报道.

  • 本研究通过室内水稻土泥浆厌氧培养试验,在不同本底pH水稻土中添加碳源培养,监测培养过程中土壤pH和无机氮浓度的变化,并基于DNA和RNA水平分别分析反硝化微生物编码亚硝酸盐还原酶的nirK/S和编码氧化亚氮还原酶的nosZ等功能基因丰度变化,旨在探究添加碳源对不同本底pH水稻土反硝化过程的调控机理,为提高氮素利用效率、温室气体减排提供理论支撑.

  • 1 材料方法

  • 1.1 样品采集

  • 供试水稻土分别采自天津市宝坻区王卜庄镇后张司马村(117.55°E,39.65°N)和广东省广州市萝岗区九龙镇洋田村(106.71°E,26.49°N).前者为多年种植单季稻土壤,以字母BD表示;后者为多年种植双季稻土壤,以字母GZ表示.在水稻落干期,采集稻田耕层0~20cm的土壤,拣去植物残体,自然风干,磨细,过1mm筛,避光保存,备用.供试土壤的理化性质如表1所示.

  • 表1 供试水稻土的理化性状

  • Table1 Physico-chemical properties of tested paddy soils

  • 1.2 培养试验

  • 1.2.1 风干土预培养

  • 分别取BD、GZ风干水稻土各1kg,调节其质量含水率至15%,于20℃恒温培养箱中好氧培养7d以恢复土壤微生物活性.

  • 1.2.2 泥浆厌氧培养试验

  • 试验设置:本试验选取两个因子,即土壤样品本底pH和外源添加有机碳(葡萄糖)浓度,其中土壤样品为酸性的GZ土壤和碱性的BD土壤;葡萄糖浓度设置3个水平,分别为0、25和100mmol·L-1,依次标记为CK、L和H(表2).

  • 淹水处理:取预培养土样3g置于10mL玻璃培养瓶中,加入1.5mL KNO3溶液作为氮源,再根据处理添加1.5mL相应浓度的葡萄糖溶液作为碳源,最终制成水土比为1∶1的泥浆.

  • 厌氧培养:淹水处理后,培养瓶加橡胶塞封口,以60mL·min-1的流速充入高纯氮气使瓶中N2交换循环至少20次,以去除瓶中的O2使其达到厌氧环境,后加铝盖密封,置于20℃恒温培养箱避光培养.

  • 表2 试验设置

  • Table2 Experiment design

  • 1.2.3 样品采集与保存

  • 分别于培养开始后的第0、0.5、1、2、3、4、5、6、7、9和11天采集土壤样品,直接用于土壤pH的测定;分别于培养开始后的第0小时、3小时、6小时、0.5天、1天、2天、3天、4天、5天、6天、7天、9天、11天,采集土壤样品置于2mL冻存管中,液氮冷冻后,-80℃保存,供提取土壤DNA和RNA使用;同时采集样品置于-20℃冰箱保存,以供土壤无机氮的测定.采集样品时先将培养瓶置于冰上预冷10min.

  • 1.3 土壤pH测定

  • 取泥浆样品摇匀后,采用pH计(MT-5000)依次对不同处理样品进行测定.

  • 1.4 土壤无机氮素含量测定

  • 取保存于-20℃的冷冻样品,解冻后取3g样品加入30mL 1mol·L-1的KCl溶液,震荡1h后过滤并收集滤液,利用流动分析仪测定样品中的NO-3-N、NO-2-N及NH+4-N含量.

  • 1.5 土壤总DNA的提取

  • 取0.5g-80℃冷冻保存的样品,使用DNA提取试剂盒(E.Z.N.A.® Soil DNA Kit,Omega Bio-tek)按照试剂盒说明书步骤提取土壤总DNA,提取的DNA样品分装后保存在-80℃(长期)低温冰箱中.

  • 1.6 土壤总RNA的提取和反转录

  • 取0.5g-80℃冷冻保存的样品,使用RNA提取试剂盒(E.Z.N.A.® Soil RNA Kit,Omega Bio-tek)按照试剂盒说明书步骤提取土壤总RNA,提取的RNA样品在确保没有gDNA后,使用RNA-cDNA反转录试剂盒(PrimeScript II 1st Strand cDNA Synthesis Kit,TaKaRa)将RNA反转录为cDNA,分装后保存在-80℃(长期)低温冰箱中.

  • 1.7 实时定量PCR扩增

  • 使用1.5小节和1.6小节中提取的DNA和cDNA为模板分别选取反硝化微生物亚硝酸盐还原酶(nirK/S)基因和氧化亚氮还原酶(nosZ)基因的对应引物对(表3)进行实时荧光定量PCR扩增,与已知浓度的含有各基因的标准质粒扩增结果比对,得到各样品中对应基因表达量.

  • 表3 使用的PCR扩增引物

  • Table3 Primer sequences of denitrifying genes used for qPCR

  • 1.8 数据分析

  • 数据方差分析和相关性分析用SPSS 20.0软件完成,采用单因素方差分析法区分样品间的显著性差异(One Way ANOVE,LSD检验);使用Origin 2021软件绘图.

  • 2 结果与分析

  • 2.1 葡萄糖添加对水稻土pH的影响

  • BD(宝坻水稻土)在未添加葡萄糖的情况下,其pH几乎没有发生变化;而在添加葡萄糖后的2d内土壤pH值显著下降,后趋于稳定,并呈现外源添加葡萄糖浓度越高,pH降低幅度越大的特点.在低葡萄糖处理条件下,土壤pH值在2d内由7.78下降至6.24;而在高葡萄糖处理条件下,土壤pH值在2d内由7.77下降至6.08,之后仍存在缓慢降低,3d后基本稳定(图1a).GZ(广州水稻土)在未添加葡萄糖的情况下,其pH值随培养时间延长而缓慢上升,在整个培养期间由初始的4.51上升至6.42,增幅达1.91个单位.其中低葡萄糖添加处理,pH随培养时间呈现先升高后降低再升高的缓慢变化趋势,培养结束时pH上升1个单位;而高葡萄糖添加处理,pH随培养时间呈现先上升后下降的变化趋势,其中培养5d后pH最高为5.23,培养结束时pH上升0.22个单位,说明添加外源葡萄糖可减小土壤pH上升幅度,尤其是在高浓度葡萄糖处理条件下更为显著(图1b).

  • 2.2 葡萄糖添加对水稻土无机氮含量的影响

  • 培养过程中,各处理的NO-3均被完全消耗,并产生一定量的NO-2累积.BD土壤在未添加葡萄糖条件下, NO-3于第9d被完全消耗, NO-2浓度的峰值出现于第2天,并于第9天被完全转化(图2a);在添加葡萄糖培养后, NO-3于第2天被完全消耗, NO-2浓度的峰值出现于第1天,并于第2天被完全转化,由此说明葡萄糖的添加加速了NO-3的消耗及NO-2的累积(图2c、e).GZ土壤在培养过程中,所有处理的NO-3均于培养5d后消耗殆尽, NO-2浓度的峰值均出现在培养3d后,并于培养5d后被完全转化(图2b、d、f).

  • 图1 土壤pH变化

  • Fig.1 Changes in soil pH

  • NH+4浓度在未添加葡萄糖时均随时间的延长而缓慢增加,并在酸性土壤中表现更为明显.在BD土壤中,至培养结束时NH+4浓度增加了1.35mmol/g(soil),同比增加58.44%;而在GZ土壤中,至培养结束NH+4浓度增加5.52mmol/g(soil),同比增加388.73%.当向土壤中添加葡萄糖时, NH+4浓度均存在明显的降低过程.BD土壤在添加葡萄糖培养后, NH+4浓度在第1~2天内迅速降低,于2d后消耗殆尽,其中在低葡萄糖添加处理下, NH+4浓度于培养3d后开始缓慢回升,培养结束时已达初始水平(图2c);而在高葡萄糖添加处理下, NH+4浓度于培养7d后开始缓慢回升,培养结束时NH+4浓度较初始值减少1.14mmol/g soil,同比减少47.30%(图2e).GZ土壤在添加葡萄糖培养后,前期NH+4浓度同样缓慢上升,在第5~7天内迅速降低,于7d后消耗殆尽,其中在低葡萄糖添加处理下,NH+4浓度于培养7d后开始迅速回升,培养结束时NH+4浓度较初始值增加1.37mmol/g soil,同比增加93.20%(图2d);而在高葡萄糖添加处理中, NH+4浓度于培养结束时仍未出现明显回升现象, NH+4浓度较初始值减少1.30mmol/g soil,同比下降86.09%(图2f).

  • 图2 无机氮浓度变化

  • Fig.2 Changes in inorganic nitrogen content

  • 2.3 葡萄糖添加对土壤中反硝化功能基因数量的影响

  • BD水稻土在未添加葡萄糖的培养过程中nirK基因拷贝数几乎没有变化,而添加葡萄糖处理使得nirK基因拷贝数发生显著变化,其中在低葡萄糖处理下,nirK基因拷贝数整体上随时间呈现出先增后减的趋势,分别于培养3d和7d时达到峰值,最大值为6.46×107 copies/g(soil);而在高葡萄糖处理下,nirK基因拷贝数变化幅度更大,分别于第4d和6d时达到峰值,其最大值为1.17×108 copies/g(soil);之后nirK基因拷贝数均下降至初始水平(图3a).GZ水稻土在不同浓度葡萄糖添加下整体上均呈现下降趋势,其中无葡萄糖添加处理的降幅最大,为53.82%,低葡萄糖添加处理和高葡萄糖添加处理分别下降23.54%、41.89%(图3b).

  • BD水稻土在未添加葡萄糖的培养过程中nirS基因拷贝数在第6d达到最低值,于第9d达到峰值,整体上呈现缓慢上升的趋势.在葡萄糖添加下,nirS基因拷贝数变化显著,其中低葡萄糖添加使得nirS基因拷贝数于第3~7天均处于较高水平,7天时存在最大值为1.77×109 copies/g(soil),随后nirS基因拷贝数迅速下降,9d后达到最低,为2.08×108 copies/g(soil);而高葡萄糖添加使得在第5d后存在明显峰值,为1.59×109 copies/g(soil),其余阶段nirS基因拷贝数均与培养初期水平相当(图3c).GZ水稻土在高葡萄糖添加下nirS基因拷贝数整体水平较其他两个处理稍高,其余各处理nirS基因拷贝数在整体上均呈现下降趋势,其中无葡萄糖添加处理的降幅最大,为50.36%,低葡萄糖添加处理和高葡萄糖添加处理分别下降42.86%、38.93%(图3d).

  • BD水稻土在未添加葡萄糖时,nosZ基因呈现出先增加随后缓慢下降趋于稳定的规律,其中于第2天达到峰值1.04×109copies/g(soil);在低葡萄糖处理下,nosZ基因拷贝数变化显著,于第4~7d均维持在较高水平,最大值为1.58×109 copies/g(soil),之后迅速降低,第9天达到最低,为2.59×108 copies/g(soil);在高葡萄糖处理下,nosZ基因变化相对平缓,于第5天存在较小峰值,为9.59×108 copies/g(soil)(图3e).GZ水稻土在未添加葡萄糖的培养过程中nosZ基因拷贝数整体水平较其他两个处理稍高,呈现先减后增的趋势.葡萄糖添加使得nosZ基因拷贝数整体上均呈现下降趋势,低葡萄糖添加处理和高葡萄糖添加处理分别下降68.46%、66.47%(图3f).

  • 2.4 葡萄糖添加对各功能基因转录本数量的影响

  • BD水稻土在不同浓度葡萄糖添加下,nirK基因转录本数量均出现明显变动,并且均于培养第6天出现峰值,但低葡萄糖处理的峰值明显要高.此外在整个培养过程中,低葡萄糖处理nirK基因转录本数量变动也更为明显,于培养第3天后较先出现最高峰,其nirK基因转录本的最大值为2.95×105 copies/g(soil),显著高于未添加葡萄糖处理的4.12×104 copies/g(soil)和高葡萄糖添加处理的5.93×104 copies/g(soil)(图4a).GZ水稻土在无葡萄糖和低葡萄糖添加下,nirK基因转录本数量变动不大,且整体水平高于高葡萄糖添加处理.在高葡萄糖添加下,nirK基因转录本数量随培养时间在缓慢下降,至培养结束nirK基因转录本数量减少1.10×104 copies/g(soil),同比降低71.21%(图4b).

  • BD水稻土在未添加葡萄糖和低葡萄糖添加下,nirS基因转录本数量明显高于高葡萄添加处理,并且均于培养第3天出现峰值,但低葡萄糖处理的峰值更高,而高葡萄糖添加下nirS基因转录本数量没有明显变化.此外低葡萄糖处理中nirS基因转录本数量于培养5天后出现第2个峰值,其nirS基因转录本的最大值为4.10×107 copies/g(soil),显著高于无葡萄糖处理的2.51×107 copies/g(soil)和高葡萄糖处理的8.32×106 copies/g(soil)(图4c).在GZ水稻土培养过程中,各个处理nirS基因转录本数量于培养前2d内均出现不同程度的降低,其中高葡萄糖添加处理下降98.08%,显著高于其余两个处理.至培养结束时,葡萄糖的添加未使得nirS基因转录本数量发生明显改变,而在未添加葡萄糖时,nirS基因转录本数量于培养第9天开始出现明显上升的现象(图4d).

  • 图3 功能基因拷贝数变化

  • Fig.3 Changes in copy number of functional genes

  • BD水稻土在低葡萄糖添加下,nosZ基因转录本数量整体要高于其余两个处理,而未添加葡萄糖时,nosZ基因转录本数无明显变化;而添加葡萄糖处理中nosZ基因转录本数均于1d后出现峰值,且低葡萄糖添加处理的峰值为4.36×107 copies/g(soil)明显高于高葡萄糖添加处理的2.04×107 copies/g(soil)(图4e).对于GZ水稻土而言,培养前期各个处理中nosZ基因转录本数量均无明显变化.在未添加葡萄糖处理中,nosZ基因转录本数量于培养6d后迅速上升,至培养结束时增长1.74倍;在低葡萄糖添加处理中,nosZ基因转录本数量于培养6d后出现较小峰值;在高葡萄糖处理中,nosZ基因转录本数量整体变化不明显(图4f).

  • 图4 基因转录本数量变化

  • Fig.4 Changes in number of gene transcripts

  • 3 讨论

  • 土壤碳源对微生物活性具有重要的影响,反硝化微生物在同化NO-3的过程中需要碳源提供电子.原始土壤条件下,BD水稻土的有机质含量以及NO-3-N含量均小于GZ水稻土,无外源碳加入时,BD水稻土的NO-3的转化速率较低.

  • 葡萄糖的添加加速了BD土NO-3的消耗及NO-2的累积,而对GZ土的影响并不显著(图2).这是由于葡萄糖作为一种易分解的碳源,它为异氧微生物提供所需碳源的同时,还为NO-3的还原了提供电子,因而加速了NO-3的消耗及NO-2的累积过程[25-26].从GZ土的所有处理来看,NO-3均于培养5d后消耗殆尽,NO-2浓度的峰值均出现在培养3d后,并于培养5d后被完全转化,这主要是GZ水稻土培养前3d内pH值均低于5,其酸性环境在一定程度上限制了反硝化微生物的活性,因而添加碳源对氮素转化无明显效果.诸多研究也表明反硝化微生物更适宜在中性或微碱性的环境下生存,pH过低(≤5)反硝化作用会进行的较为缓慢[12,27],此外封克[28]的研究表明,在提供有效碳源时,酸性条件最不利于NO-3的还原.

  • 试验结果发现,在淹水培养过程中, NH+4浓度逐渐上升.这种现象可能是多方面因素造成的,首先是矿化作用,土壤有机态氮在微生物作用下转化为无机态氮(NH+4-N),使得NH+4浓度升高;再有可能是发生异化还原成铵作用(Dissimilatory Nitrate Reduction to Ammonium,DNRA),微生物在厌氧条件下将NO-3还原为NH+4,导致NH+4浓度上升.另有研究表明,同样是NO-3的还原过程,反硝化过程要比DNRA更容易发生[29],但是在NO-3浓度极低和更强的还原势下,即高的C与NO-3比条件下,DNRA比反硝化作用更容易发生[30-31],因此也不排除在高葡萄添加处理中,有DNRA发生的可能.

  • 在添加葡萄糖培养中期, NH+4浓度均存在明显的降低过程,并且在高pH水稻土中该过程明显提前于低pH水稻土(图2).NH+4浓度的降低这主要是由于碳源添加,导致土壤中C/N比增加,加速微生物利用NH+4进行同化作用,使得NH+4浓度降低;随着葡萄糖的减少,C/N比降低, NH+4的产生量逐渐大于消耗量, NH+4浓度再次升高.高pH水稻土中该过程发生早,主要是NO-3消耗速度快,在有碳源剩余的情况下,微生物会迅速利用产生的NH+4,这也是高葡萄糖添加处理中,NH+4浓度回升延迟的原因.而在低pH水稻土中,由于pH的限制,碳源添加对微生物活性的刺激作用较弱,微生物活性较低,对NH+4的利用较慢.

  • nirK基因和nirS基因分别编码的两种形式的NIR均存在于细胞膜外周质中,功能上未见任何区别,但到目前为止尚未发现任何一种微生物同时具有这两种形态的NIR.所以添加碳源培养过程中两类具有不同功能基因的微生物之间存在怎样的关系,是我们关注的重要问题.添加碳源对基于DNA水平的nirSnirK的基因数量均呈现相对促进状态,而对基于RNA水平的nirSnirK基因的表达量均呈现相对抑制状态.这是由于添加碳源,促进了微生物生长,菌体数量增多,从而反硝化功能基因数量相对增多.但是添加碳源后,引起土壤pH在培养过程中发生较大幅度变化,特别是高葡萄糖添加处理中,两种水稻土的pH均与对照相差2个单位,从而对反硝化功能基因nirKnirS的转录造成了影响.通过建立两种功能基因数量及表达量的比值随培养时间的动态对比(图5)发现,相较于对照处理添加碳源培养过程中,nirSnirK的基因数量比值在降低,因此推断碳源的加入更有利于促进编码nirK基因的微生物生长.而GZ水稻土中,低葡萄糖添加处理下表现更为明显,主要是由于高葡萄糖添加处理下,pH降低不利于微生物生存.此外在BD水稻土上,相较于对照处理添加碳源培养过程中,nirSnirK的基因表达量比值在降低,并且碳源浓度越高,降低程度越显著.在BD水稻土上,添加碳源培养过程中NO-2的累积速度更快(于培养1d后出现峰值,而对照于培养3d左右出现峰值),所以推测快速累积的NO-2对具有nirK功能基因的微生物刺激作用更强,更易促进nirK的转录,再加上碳源导致的DNA水平比值的降低,所以存在RNA水平上比值降低的现象.而在GZ水稻土中,不同处理中NO-2浓度变化差异不大,再加上高葡萄糖添加处理下,pH过低不利于反硝化功能基因的表达[32],所以整体现象不明显.因此通过已有现象可以推断,相比于具有nirS,nirK基因数量和表达量对于外界环境变化的响应程度相对更高.对于外界条件的改变表现的相对更敏感,响应程度更高.

  • nosZ基因编码的氧化亚氮还原酶(N2OR)是目前已知的唯一能将N2O还原为N2的生物酶,当nosZ基因数量和表达量受到不利条件的抑制时,就会导致温室气体N2O的大量累积.在本试验中,酸性土壤(GZ)经过碳源添加处理后,nosZ基因数量和表达量收到了抑制作用,且碳源浓度越高,抑制作用越强;碱性土壤(BD)经低葡萄糖处理后促进了nosZ基因数量和表达量,但是高葡萄糖处理下却抑制了nosZ基因的表达,这主要是由于在酸性土壤中,由于本身pH很低,加入葡萄糖后使得土壤pH再次下降,从而出现nosZ基因的表达受抑制.这与朱永官等[27]、潘亚男等[32]、Qu等[33]研究结果一致,即从基因角度来说,相应编码基因的表达更易受到土壤pH的影响,低pH会影响到生物体产生功能性N2O还原酶的能力,当土壤pH<7时反硝化酶nosZ活性逐渐减小;在碱性土壤中,低浓度葡萄糖作为碳源进入土壤中,激发了反硝化微生物的功能活性;而高浓度葡萄糖进入土壤所带来的土壤酸化反而抑制了反硝化微生物的活性,这与封克等[28]的研究结果一致,即碱性旱地土壤在有碳源加入的情况下,最有利于N2O还原为N2的土壤pH为6.92,当添加高浓度葡萄糖时,土壤将低于这个最适pH,所以反而抑制了nosZ基因的表达.

  • 图5 nirS/nirK比值变化

  • Fig.5 Changes in nirS/nirK ratio

  • 4 结论

  • 本研究揭示了反硝化微生物对碳源添加的敏感性,葡萄糖添加可以从提供碳源和降低土壤pH两个方面,直接或间接的影响水稻土反硝化过程:1)高pH土壤上添加碳源增强了反硝化作用;低pH土壤上添加碳源对反硝化过程的促进作用不明显.2)不同本底pH的土壤中nirKnirS基因数量和表达量对加入碳源引起的pH变化的响应具有显著差异,其中nirK基因数量和表达量对于外界环境变化的响应程度相对更高.3)在低pH土壤上,碳源添加对nosZ基因数量和表达量存在抑制作用,且碳源浓度越高抑制作用越强;在高pH土壤上,低葡萄糖处理下,碳源的刺激作用占主导地位;高葡萄糖处理下,碳源引起的pH变化的抑制作用占主导.本研究有助于理解稻田外源有机物输入对土壤反硝化过程的影响机制,为稻田氧化亚氮减排措施的实施与评估提供理论依据.

  • 参考文献

    • [1] 国家统计局工业统计司.中国工业统计年鉴:2020[M].北京:中国统计出版社,2020

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    • [4] Fraser P E,Rand R P,Deber C M.Bilayer-stabilizing properties of myelin basic protein in dioleoylphosphatidylethanolamine systems[J].Biochimica et Biophysica Acta:Biomembranes,1989,983(1):23-29

    • [5] 李晓波,马兰,马舒坦,等.稻田反硝化速率测定方法研究进展[J].土壤,2021,53(6):1107-1114;LI Xiaobo,MA Lan,MA Shutan,et al.Methods for measuring denitrification in flooded rice paddies:a review[J].Soils,2021,53(6):1107-1114

    • [6] 李帅,卫琦,徐俊增,等.水肥一体化条件下控灌稻田土壤氮素及水稻生长特性研究[J].灌溉排水学报,2021,40(10):79-86;LI Shuai,WEI Qi,XU Junzeng,et al.Improving nitrogen use efficiency and growth of paddy rice using controlled fertigation[J].Journal of Irrigation and Drainage,2021,40(10):79-86

    • [7] Zumft W G.Cell biology and molecular basis of denitrification[J].Microbiology and Molecular Biology Reviews:MMBR,1997,61(4):533-616

    • [8] 宋雅琦,王玲,李昆,等.土壤微生物还原N2O机制及其研究进展[J].环境科学与技术,2019,42(9):82-90;SONG Yaqi,WANG Ling,LI Kun,et al.The mechanism and research progress of soil microorganism reducing N2O[J].Environmental Science & Technology,2019,42(9):82-90

    • [9] Tang Y Q,Yu G R,Zhang X Y,et al.Environmental variables better explain changes in potential nitrification and denitrification activities than microbial properties in fertilized forest soils[J].Science of the Total Environment,2019,647:653-662

    • [10] Tao R,Wakelin S A,Liang Y C,et al.Nitrous oxide emission and denitrifier communities in drip-irrigated calcareous soil as affected by chemical and organic fertilizers[J].Science of the Total Environment,2018,612:739-749

    • [11] 王丽丽,赵林,谭欣,等.不同碳源及其碳氮比对反硝化过程的影响[J].环境保护科学,2004,30(1):15-18;WANG Lili,ZHAO Lin,TAN Xin,et al.Influence of different carbon source and ratio of carbon and nitrogen for water denitrification[J].Environmental Protection Science,2004,30(1):15-18

    • [12] 王海涛,郑天凌,杨小茹.土壤反硝化的分子生态学研究进展及其影响因素[J].农业环境科学学报,2013,32(10):1915-1924;WANG Haitao,ZHENG Tianling,YANG Xiaoru.Molecular ecology research progress for soil denitrification and research status for its influencing factors[J].Journal of Agro-Environment Science,2013,32(10):1915-1924

    • [13] 郑兰香,鞠兴华.温度和C/N比对生物膜反硝化速率的影响[J].工业安全与环保,2006,32(10):13-15;ZHENG Lanxiang,JU Xinghua.The effect of temperature and C/N ratio on biofilm denitrification rate[J].Industrial Safety and Environmental Protection,2006,32(10):13-15

    • [14] Shan J,Yang P P,Shang X X,et al.Anaerobic ammonium oxidation and denitrification in a paddy soil as affected by temperature,pH,organic carbon,and substrates[J].Biology and Fertility of Soils,2018,54(3):341-348

    • [15] Ryden J C.Gaseous losses of nitrogen from grassland[M].Springer Netherlands,1986

    • [16] Bhandral R,Bolan N S,Saggar S,et al.Nitrogen transformation and nitrous oxide emissions from various types of farm effluents[J].Nutrient Cycling in Agroecosystems,2007,79(2):193-208

    • [17] Saggar S,Jha N,Deslippe J,et al.Denitrification and N2O:N2 production in temperate grasslands:processes,measurements,modelling and mitigating negative impacts[J].Science of the Total Environment,2013,465:173-195

    • [18] Sugaya K,Tusé D,Jones J L.Production of acetic acid by Clostridium thermoaceticum in batch and continuous fermentations[J].Biotechnology and Bioengineering,1986,28(5):678-683

    • [19] Deiglmayr K,Philippot L,Hartwig U A,et al.Structure and activity of the nitrate-reducing community in the rhizosphere of Lolium perenne and Trifolium repens under long-term elevated atmospheric pCO2[J].FEMS Microbiology Ecology,2004,49(3):445-454

    • [20] Cai Y J,Wang X D,Tian L L,et al.The impact of excretal returns from yak and Tibetan sheep dung on nitrous oxide emissions in an alpine steppe on the Qinghai-Tibetan Plateau[J].Soil Biology and Biochemistry,2014,76:90-99

    • [21] 贾蓉.不同碳源模式下水稻土中脱氢酶活性与微生物铁还原的关系[D].杨凌:西北农林科技大学,2012;JIA Rong.Relationship between dehydrogenase activity and microbial iron reduction with different carbon sources in paddy soil[D].Yangling:Northwest A & F University,2012

    • [22] Cuhel J,Simek M,Laughlin R J,et al.Insights into the effect of soil pH on N2O and N2 emissions and denitrifier community size and activity[J].Applied and Environmental Microbiology,2010,76(6):1870-1878

    • [23] ŠImek M,Cooper J E.The influence of soil pH on denitrification:progress towards the understanding of this interaction over the last 50 years[J].European Journal of Soil Science,2002,53(3):345-354

    • [24] Liu B B,Mørkved P T,Frostegård Å,et al.Denitrification gene pools,transcription and kinetics of NO,N2O and N2 production as affected by soil pH[J].FEMS Microbiology Ecology,2010,72(3):407-417

    • [25] Granli T.The experimental basis,nitrous oxide from agriculture[J].Nor J Agric Sci,1994,12:22-29

    • [26] 封克,殷士学,钱晓晴,等.矿物固铵能力对铵离子在土壤中转化过程的影响Ⅰ:不同矿物类型土壤、不同C/N和K+的存在对铵转化过程的影响[J].江苏农学院学报,1994,15(2):39-44;FENG Ke,YIN Shixue,QIAN Xiaoqing,et al.Effect of ammonium fixation capacity on transformation of NH+4 in soils Ⅰ:effect of different C/N ratios and presence of K+ on transformation of NH+4 in soils[J].Journal of Jiangsu Agricultural College,1994,15(2):39-44

    • [27] 朱永官,王晓辉,杨小茹,等.农田土壤N2O产生的关键微生物过程及减排措施[J].环境科学,2014,35(2):792-800;ZHU Yongguan,WANG Xiaohui,YANG Xiaoru,et al.Key microbial processes in nitrous oxide emissions of agricultural soil and mitigation strategies[J].Environmental Science,2014,35(2):792-800

    • [28] 封克,王子波,王小治,等.土壤pH对硝酸根还原过程中N2O产生的影响[J].土壤学报,2004,41(1):81-86;FENG Ke,WANG Zibo,WANG Xiaozhi,et al.Effect of soil pH on N2O production in nitrate reduction[J].Acta Pedologica Sinica,2004,41(1):81-86

    • [29] 贺纪正,张丽梅.土壤氮素转化的关键微生物过程及机制[J].微生物学通报,2013,40(1):98-108;HE Jizheng,ZHANG Limei.Key processes and microbial mechanisms of soil nitrogen transformation[J].Microbiology China,2013,40(1):98-108

    • [30] Tiedje J M,Simkins S,Groffman P M.Perspectives on measurement of denitrification in the field including recommended protocols for acetylene based methods[J].Plant and Soil,1989,115(2):261-284

    • [31] Rütting T,Huygens D,Staelens J,et al.Advances in 15N-tracing experiments:new labelling and data analysis approaches[J].Biochemical Society Transactions,2011,39(1):279-283

    • [32] 潘亚男,王娅静,曹文超,等.土壤pH影响氧化亚氮(N2O)排放的研究进展[J].安徽农学通报,2017,23(15):19-24,99;PAN Yanan,WANG Yajing,CAO Wenchao,et al.A review of the influence of soil pH on nitrous oxide(N2O)emission[J].Anhui Agricultural Science Bulletin,2017,23(15):19-24,99

    • [33] Qu Z,Wang J G,Almøy T,et al.Excessive use of nitrogen in Chinese agriculture results in high N2O/(N2O+N2)product ratio of denitrification,primarily due to acidification of the soils[J].Global Change Biology,2014,20(5):1685-1698

  • 参考文献

    • [1] 国家统计局工业统计司.中国工业统计年鉴:2020[M].北京:中国统计出版社,2020

    • [2] 沈仁芳,孙波,施卫明,等.地上-地下生物协同调控与养分高效利用[J].中国科学院院刊,2017,32(6):566-574;SHEN Renfang,SUN Bo,SHI Weiming,et al.Interactions between above-and below-ground organisms for nutrient-efficient utilization[J].Bulletin of Chinese Academy of Sciences,2017,32(6):566-574

    • [3] 王荣萍,余炜敏,李淑仪,等.华南地区主要蔬菜氮肥肥料利用率研究[J].中国农学通报,2016,32(25):34-39;WANG Rongping,YU Weimin,LI Shuyi,et al.Nitrogen use efficiencies of main vegetables in South China[J].Chinese Agricultural Science Bulletin,2016,32(25):34-39

    • [4] Fraser P E,Rand R P,Deber C M.Bilayer-stabilizing properties of myelin basic protein in dioleoylphosphatidylethanolamine systems[J].Biochimica et Biophysica Acta:Biomembranes,1989,983(1):23-29

    • [5] 李晓波,马兰,马舒坦,等.稻田反硝化速率测定方法研究进展[J].土壤,2021,53(6):1107-1114;LI Xiaobo,MA Lan,MA Shutan,et al.Methods for measuring denitrification in flooded rice paddies:a review[J].Soils,2021,53(6):1107-1114

    • [6] 李帅,卫琦,徐俊增,等.水肥一体化条件下控灌稻田土壤氮素及水稻生长特性研究[J].灌溉排水学报,2021,40(10):79-86;LI Shuai,WEI Qi,XU Junzeng,et al.Improving nitrogen use efficiency and growth of paddy rice using controlled fertigation[J].Journal of Irrigation and Drainage,2021,40(10):79-86

    • [7] Zumft W G.Cell biology and molecular basis of denitrification[J].Microbiology and Molecular Biology Reviews:MMBR,1997,61(4):533-616

    • [8] 宋雅琦,王玲,李昆,等.土壤微生物还原N2O机制及其研究进展[J].环境科学与技术,2019,42(9):82-90;SONG Yaqi,WANG Ling,LI Kun,et al.The mechanism and research progress of soil microorganism reducing N2O[J].Environmental Science & Technology,2019,42(9):82-90

    • [9] Tang Y Q,Yu G R,Zhang X Y,et al.Environmental variables better explain changes in potential nitrification and denitrification activities than microbial properties in fertilized forest soils[J].Science of the Total Environment,2019,647:653-662

    • [10] Tao R,Wakelin S A,Liang Y C,et al.Nitrous oxide emission and denitrifier communities in drip-irrigated calcareous soil as affected by chemical and organic fertilizers[J].Science of the Total Environment,2018,612:739-749

    • [11] 王丽丽,赵林,谭欣,等.不同碳源及其碳氮比对反硝化过程的影响[J].环境保护科学,2004,30(1):15-18;WANG Lili,ZHAO Lin,TAN Xin,et al.Influence of different carbon source and ratio of carbon and nitrogen for water denitrification[J].Environmental Protection Science,2004,30(1):15-18

    • [12] 王海涛,郑天凌,杨小茹.土壤反硝化的分子生态学研究进展及其影响因素[J].农业环境科学学报,2013,32(10):1915-1924;WANG Haitao,ZHENG Tianling,YANG Xiaoru.Molecular ecology research progress for soil denitrification and research status for its influencing factors[J].Journal of Agro-Environment Science,2013,32(10):1915-1924

    • [13] 郑兰香,鞠兴华.温度和C/N比对生物膜反硝化速率的影响[J].工业安全与环保,2006,32(10):13-15;ZHENG Lanxiang,JU Xinghua.The effect of temperature and C/N ratio on biofilm denitrification rate[J].Industrial Safety and Environmental Protection,2006,32(10):13-15

    • [14] Shan J,Yang P P,Shang X X,et al.Anaerobic ammonium oxidation and denitrification in a paddy soil as affected by temperature,pH,organic carbon,and substrates[J].Biology and Fertility of Soils,2018,54(3):341-348

    • [15] Ryden J C.Gaseous losses of nitrogen from grassland[M].Springer Netherlands,1986

    • [16] Bhandral R,Bolan N S,Saggar S,et al.Nitrogen transformation and nitrous oxide emissions from various types of farm effluents[J].Nutrient Cycling in Agroecosystems,2007,79(2):193-208

    • [17] Saggar S,Jha N,Deslippe J,et al.Denitrification and N2O:N2 production in temperate grasslands:processes,measurements,modelling and mitigating negative impacts[J].Science of the Total Environment,2013,465:173-195

    • [18] Sugaya K,Tusé D,Jones J L.Production of acetic acid by Clostridium thermoaceticum in batch and continuous fermentations[J].Biotechnology and Bioengineering,1986,28(5):678-683

    • [19] Deiglmayr K,Philippot L,Hartwig U A,et al.Structure and activity of the nitrate-reducing community in the rhizosphere of Lolium perenne and Trifolium repens under long-term elevated atmospheric pCO2[J].FEMS Microbiology Ecology,2004,49(3):445-454

    • [20] Cai Y J,Wang X D,Tian L L,et al.The impact of excretal returns from yak and Tibetan sheep dung on nitrous oxide emissions in an alpine steppe on the Qinghai-Tibetan Plateau[J].Soil Biology and Biochemistry,2014,76:90-99

    • [21] 贾蓉.不同碳源模式下水稻土中脱氢酶活性与微生物铁还原的关系[D].杨凌:西北农林科技大学,2012;JIA Rong.Relationship between dehydrogenase activity and microbial iron reduction with different carbon sources in paddy soil[D].Yangling:Northwest A & F University,2012

    • [22] Cuhel J,Simek M,Laughlin R J,et al.Insights into the effect of soil pH on N2O and N2 emissions and denitrifier community size and activity[J].Applied and Environmental Microbiology,2010,76(6):1870-1878

    • [23] ŠImek M,Cooper J E.The influence of soil pH on denitrification:progress towards the understanding of this interaction over the last 50 years[J].European Journal of Soil Science,2002,53(3):345-354

    • [24] Liu B B,Mørkved P T,Frostegård Å,et al.Denitrification gene pools,transcription and kinetics of NO,N2O and N2 production as affected by soil pH[J].FEMS Microbiology Ecology,2010,72(3):407-417

    • [25] Granli T.The experimental basis,nitrous oxide from agriculture[J].Nor J Agric Sci,1994,12:22-29

    • [26] 封克,殷士学,钱晓晴,等.矿物固铵能力对铵离子在土壤中转化过程的影响Ⅰ:不同矿物类型土壤、不同C/N和K+的存在对铵转化过程的影响[J].江苏农学院学报,1994,15(2):39-44;FENG Ke,YIN Shixue,QIAN Xiaoqing,et al.Effect of ammonium fixation capacity on transformation of NH+4 in soils Ⅰ:effect of different C/N ratios and presence of K+ on transformation of NH+4 in soils[J].Journal of Jiangsu Agricultural College,1994,15(2):39-44

    • [27] 朱永官,王晓辉,杨小茹,等.农田土壤N2O产生的关键微生物过程及减排措施[J].环境科学,2014,35(2):792-800;ZHU Yongguan,WANG Xiaohui,YANG Xiaoru,et al.Key microbial processes in nitrous oxide emissions of agricultural soil and mitigation strategies[J].Environmental Science,2014,35(2):792-800

    • [28] 封克,王子波,王小治,等.土壤pH对硝酸根还原过程中N2O产生的影响[J].土壤学报,2004,41(1):81-86;FENG Ke,WANG Zibo,WANG Xiaozhi,et al.Effect of soil pH on N2O production in nitrate reduction[J].Acta Pedologica Sinica,2004,41(1):81-86

    • [29] 贺纪正,张丽梅.土壤氮素转化的关键微生物过程及机制[J].微生物学通报,2013,40(1):98-108;HE Jizheng,ZHANG Limei.Key processes and microbial mechanisms of soil nitrogen transformation[J].Microbiology China,2013,40(1):98-108

    • [30] Tiedje J M,Simkins S,Groffman P M.Perspectives on measurement of denitrification in the field including recommended protocols for acetylene based methods[J].Plant and Soil,1989,115(2):261-284

    • [31] Rütting T,Huygens D,Staelens J,et al.Advances in 15N-tracing experiments:new labelling and data analysis approaches[J].Biochemical Society Transactions,2011,39(1):279-283

    • [32] 潘亚男,王娅静,曹文超,等.土壤pH影响氧化亚氮(N2O)排放的研究进展[J].安徽农学通报,2017,23(15):19-24,99;PAN Yanan,WANG Yajing,CAO Wenchao,et al.A review of the influence of soil pH on nitrous oxide(N2O)emission[J].Anhui Agricultural Science Bulletin,2017,23(15):19-24,99

    • [33] Qu Z,Wang J G,Almøy T,et al.Excessive use of nitrogen in Chinese agriculture results in high N2O/(N2O+N2)product ratio of denitrification,primarily due to acidification of the soils[J].Global Change Biology,2014,20(5):1685-1698

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