楊　杉，吳勝軍，蔡延江，周文佐，朱同彬，王　雨，黃　平,*

1 中國(guó)科學(xué)院水庫(kù)水環(huán)境重點(diǎn)實(shí)驗(yàn)室，中國(guó)科學(xué)院重慶綠色智能技術(shù)研究院，重慶　400714

2 西南大學(xué)地理科學(xué)學(xué)院，重慶　400715

3 中國(guó)科學(xué)院水利部成都山地災(zāi)害與環(huán)境研究所中國(guó)科學(xué)院山地表生過(guò)程與生態(tài)調(diào)控重點(diǎn)實(shí)驗(yàn)室，成都　610041

4 南京師范大學(xué)地理科學(xué)學(xué)院，南京　210046

硝態(tài)氮異化還原機(jī)制及其主導(dǎo)因素研究進(jìn)展

楊杉1,2，吳勝軍1，蔡延江3，周文佐2，朱同彬4，王雨1，黃平1,*

1 中國(guó)科學(xué)院水庫(kù)水環(huán)境重點(diǎn)實(shí)驗(yàn)室，中國(guó)科學(xué)院重慶綠色智能技術(shù)研究院，重慶400714

2 西南大學(xué)地理科學(xué)學(xué)院，重慶400715

3 中國(guó)科學(xué)院水利部成都山地災(zāi)害與環(huán)境研究所中國(guó)科學(xué)院山地表生過(guò)程與生態(tài)調(diào)控重點(diǎn)實(shí)驗(yàn)室，成都610041

4 南京師范大學(xué)地理科學(xué)學(xué)院，南京210046

摘要:硝態(tài)氮)異化還原過(guò)程通常包含反硝化和異化還原為銨(DNRA)兩個(gè)方面，是土壤氮素轉(zhuǎn)化的重要途徑，其強(qiáng)度大小直接影響著硝態(tài)氮的利用和環(huán)境效應(yīng)(如淋溶和氮氧化物氣體排放)。反硝化和DNRA過(guò)程在反應(yīng)條件、產(chǎn)物和影響因素等方面常會(huì)呈現(xiàn)出協(xié)同與競(jìng)爭(zhēng)的交互作用機(jī)制。綜述了反硝化和DNRA過(guò)程的研究進(jìn)展及其二者協(xié)同競(jìng)爭(zhēng)的作用機(jī)理，并闡述了在、pH、有效C、氧化還原電位(Eh)等環(huán)境條件和土壤微生物對(duì)其發(fā)生強(qiáng)度和產(chǎn)物的影響，提出了今后應(yīng)在產(chǎn)生機(jī)理、土壤環(huán)境因素、微生物學(xué)過(guò)程以及與其他氮素轉(zhuǎn)化過(guò)程耦聯(lián)作用等方面亟需深入研究，以期增進(jìn)對(duì)氮素循環(huán)過(guò)程的認(rèn)識(shí)以及為加強(qiáng)氮素管理利用提供依據(jù)。

關(guān)鍵詞：硝態(tài)氮異化還原；反硝化；硝態(tài)氮異化還原成銨(DNRA)；N2O；協(xié)同競(jìng)爭(zhēng)機(jī)制

1硝態(tài)氮異化還原的機(jī)理過(guò)程

(4)時(shí)間進(jìn)程不同在條件適宜的情況下，土壤反硝化速度較快，1—2 d就可全部完成；DNRA過(guò)程一般要在2—5 d之后才發(fā)生[1, 24]。但為何出現(xiàn)DNRA過(guò)程相對(duì)滯后的現(xiàn)象，其機(jī)制目前尚不清楚[1]。

圖1　硝態(tài)氮異化還原過(guò)程及其主要機(jī)理Fig.1　The scheme of dissimilatory nitrate reduction process and its main mechanisms(Nar,Nor,Nos,dNir,dnra-Nir表示參與硝態(tài)氮異化還原過(guò)程的還原酶；narG /napA,nirB/nirC/cysG, nirK/nirS,norC/norB,nosZ/nosR/nosD-FYL表示參與硝態(tài)氮異化還原過(guò)程的還原酶所對(duì)應(yīng)的功能基因

2硝態(tài)氮異化還原的協(xié)同競(jìng)爭(zhēng)機(jī)制

3硝態(tài)氮異化還原過(guò)程主導(dǎo)因素及其對(duì)協(xié)同與競(jìng)爭(zhēng)的調(diào)節(jié)機(jī)制

3.1土壤環(huán)境條件

3.1.2氧化還原電位(Eh)

氧化還原電位(Eh)能間接地反映土壤的含氧狀態(tài)，從而影響硝態(tài)氮異化還原過(guò)程，其主要取決于土壤中的氧分壓或溶解態(tài)氧的濃度[17]。Eh通過(guò)氧分壓來(lái)調(diào)控硝態(tài)氮異化還原過(guò)程，氧化和還原條件均能進(jìn)行反硝化作用[34, 37]，但相較于還原條件，在氧化條件下反硝化速率明顯降低[37]；而強(qiáng)還原性會(huì)更有利于DNRA過(guò)程的發(fā)生[1, 18, 38]。Eh<300 mV 的厭氧條件是反硝化進(jìn)行的必要條件；若Eh較高，氧分壓就會(huì)成為反硝化作用的主要限制因子[1, 37]。也有研究表明，還原性較弱的環(huán)境中也能進(jìn)行DNRA過(guò)程[12, 39]，Pseudomonasputrefaciens在Eh為0mv時(shí)能進(jìn)行DNRA過(guò)程，而Eh為-100mV時(shí)受到極大抑制[1]。此外，Eh還能決定硝態(tài)氮異化還原的途徑[34]，通過(guò)對(duì)兩個(gè)過(guò)程產(chǎn)生條件的比較，DNRA過(guò)程對(duì)氧分壓變化較不敏感[39- 40]。當(dāng)氧分壓從0升高到2%的過(guò)程中，反硝化均呈現(xiàn)降低的趨勢(shì)。但DNRA過(guò)程則呈現(xiàn)不同的趨勢(shì)，當(dāng)氧分壓為0—0.5%時(shí)，DNRA過(guò)程顯著增加；為0.5%—1%時(shí)，DNRA過(guò)程沒有變化；繼續(xù)上升到1%—2%時(shí)，DNRA的強(qiáng)度減小[40]。這些研究結(jié)果為通過(guò)調(diào)控氧化還原狀況有效管理氮素轉(zhuǎn)化與利用提供了重要依據(jù)。

3.1.3土壤pH

3.1.4有效C

3.2土壤微生物

土壤微生物在其新陳代謝過(guò)程中能對(duì)有機(jī)質(zhì)進(jìn)行分解、轉(zhuǎn)化，是硝態(tài)氮異化還原過(guò)程的參與者。

3.2.1硝態(tài)氮異化還原過(guò)程土壤微生物

土壤微生物的種類、數(shù)量、種群結(jié)構(gòu)與時(shí)空動(dòng)態(tài)變化等都會(huì)對(duì)硝態(tài)氮異化還原過(guò)程有一定的影響。硝態(tài)氮異化還原微生物是一個(gè)大的生理類群，而反硝化和DNRA過(guò)程存在著不同的微生物類型(表1)。

表1　硝態(tài)氮異化還原過(guò)程的微生物類型

細(xì)菌功能基因是影響硝態(tài)氮異化還原過(guò)程動(dòng)態(tài)變化及產(chǎn)物組成的關(guān)鍵因子，故借助編碼硝態(tài)氮異化還原過(guò)程關(guān)鍵基因的菌群是研究硝態(tài)氮異化還原過(guò)程微生物的重要方法。研究表明，土壤反硝化菌中，nosZ基因最為穩(wěn)定，不易受到環(huán)境影響；nirK基因?qū)Νh(huán)境因子的響應(yīng)比nirS基因敏感[33]。分別施用有機(jī)肥和無(wú)機(jī)氮肥，土壤narG基因的優(yōu)勢(shì)種群有明顯差異(無(wú)機(jī)肥處理含優(yōu)勢(shì)種群EU873052，有機(jī)肥處理則沒有)[32]。

3.2.2影響硝態(tài)氮異化還原過(guò)程土壤微生物多樣性的因素

硝態(tài)氮異化還原過(guò)程的影響因素較多，且影響作用并不是單一的，而是交互聯(lián)系作用的。除以上幾種主導(dǎo)因素外，土壤質(zhì)地[35]、土壤含水量[35]和土壤溫度[7, 44]等土壤環(huán)境的其他因素也會(huì)對(duì)硝態(tài)氮異化還原過(guò)程產(chǎn)生影響。在對(duì)不同土壤質(zhì)地與硝態(tài)氮異化還原關(guān)系的研究中，與粘土相比，砂土的DNRA過(guò)程速率低，N2O的排放量少[35]。這主要是由于粘土所含的土壤水分多，厭氧環(huán)境較適宜硝態(tài)氮異化還原過(guò)程的發(fā)生[35]。

4研究展望

以往對(duì)硝態(tài)氮異化還原過(guò)程的研究主要集中于反硝化，但由于DNRA過(guò)程生成了有效性高且淋溶性較差的銨態(tài)氮，進(jìn)而增強(qiáng)土壤氮的可利用性，近年來(lái)關(guān)于DNRA過(guò)程的研究逐漸受到了充分重視。目前，DNRA過(guò)程的研究對(duì)象多為海水或淡水沉積物[10, 18]，而對(duì)陸地土壤研究較少，已有的研究也主要集中于森林和農(nóng)田等土壤，且多為室內(nèi)培養(yǎng)結(jié)果[15, 25]，自然生境中的硝態(tài)氮異化還原狀況還未知。在全球變化的背景下，有必要對(duì)不同氣候、土壤和耕作施肥制度下的硝態(tài)氮異化還原強(qiáng)度深入研究。鑒于硝態(tài)氮異化還原過(guò)程研究中存在影響因素多、時(shí)空變異大、測(cè)定難度大等限制條件，今后應(yīng)亟需加強(qiáng)以下幾個(gè)方面的研究。

(2)加強(qiáng)土壤環(huán)境因素對(duì)硝態(tài)氮異化還原過(guò)程反饋機(jī)制的研究。硝態(tài)氮異化還原過(guò)程的研究多數(shù)局限在對(duì)單一土壤環(huán)境因素的控制或模擬，而主導(dǎo)硝態(tài)氮異化還原過(guò)程的土壤環(huán)境因素有很多，存在復(fù)雜的交互作用，且不同生境下各因子的影響強(qiáng)度差異較大。如不同海拔高度、不同立地條件，土壤水熱條件和有機(jī)C庫(kù)有所不同，勢(shì)必影響到硝態(tài)氮異化還原的強(qiáng)度。決定土壤中反硝化和DNRA過(guò)程平衡的環(huán)境因素亦未見報(bào)道。此外，在硝態(tài)氮異化還原過(guò)程對(duì)環(huán)境因子的響應(yīng)研究中，探討如何選擇并調(diào)節(jié)土壤環(huán)境因子參數(shù)。同時(shí)，考慮在土壤環(huán)境因子復(fù)合影響下，土壤氮素和其他土壤元素之間的綜合效應(yīng)，明確土壤氮素閾值，提高氮肥利用率的同時(shí)，確保土壤的其他養(yǎng)分的固持。諸如，若Eh<200 mV，土壤中的鐵錳化合物會(huì)被還原為不同價(jià)態(tài)的錳、硫、鐵，土壤出現(xiàn)潛育化，導(dǎo)致O2分壓減小，影響土壤中的氮素形態(tài)及供應(yīng)情況[17]；硝態(tài)氮異化還原過(guò)程能在此范圍中發(fā)生，如何協(xié)調(diào)各土壤養(yǎng)分固持與供給平衡，以獲得最高產(chǎn)量或最大收益時(shí)最佳氮素投入量，保持土壤優(yōu)良性狀，利于作物生長(zhǎng)。

(3)加強(qiáng)硝態(tài)氮異化還原過(guò)程的微生物學(xué)過(guò)程的研究。當(dāng)前，參與硝態(tài)氮還原的微生物中，反硝化菌的數(shù)量、區(qū)系組成及其活性報(bào)道較多[3]，而對(duì)于DNRA菌組成和數(shù)量等的研究較少，但已越來(lái)越受到研究者們的關(guān)注。土壤環(huán)境和農(nóng)業(yè)措施，能夠影響土壤中微生物的活性、豐度及群落組成。研究不同生態(tài)系統(tǒng)土壤微生物量及活性對(duì)反硝化和DNRA兩個(gè)過(guò)程的影響，對(duì)于完善土壤氮素內(nèi)循環(huán)機(jī)制，提高土壤肥力，具有十分重要的作用。對(duì)于滿足反硝化和DNRA雙重性質(zhì)的細(xì)菌，今后可在同一個(gè)細(xì)胞中開展反硝化與DNRA競(jìng)爭(zhēng)機(jī)理的研究[3]。同時(shí)，考慮厭氧氨氧化細(xì)菌對(duì)硝態(tài)氮異化還原過(guò)程的影響。研究表明，厭氧氨氧化菌能同時(shí)表現(xiàn)出反硝化和厭氧氨氧化的能力，兩個(gè)反應(yīng)可在同一種微生物體內(nèi)進(jìn)行[46- 47]。

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The synergetic and competitive mechanism andthe dominant factors of dissimilatory nitrate reduction processes: a review

YANG Shan1, 2, WU Shengjun1, CAI Yanjiang3, ZHOU Wenzuo2, ZHU Tongbin4, WANG Yu1, HUANG Ping1,*

1KeyLaboratoryofReservoirAquaticEnvironment,ChongqingInstituteofGreenandIntelligentTechnology,ChineseAcademyofScience,Chongqing400714,China2SchoolofGeographyScience,SouthwestUniversity,Chongqing400715,China3InstituteofMountainHazardsandEnvironment,ChineseAcademyofSciencesandMinistryofWaterResources;KeyLaboratoryofMountainEnvironmentEvolvementandRegulation,ChineseAcademyofSciences,Chengdu610041,China4CollegeofGeographyScience,NanjingNormalUniversity,Nanjing210046,China

Abstract：The nitrate ion ), an important form of inorganic soil nitrogen, is susceptible to reduction under anaerobic conditions, and its reduction consists of both assimilatory and dissimilatory processes. The dissimilatory nitrate reduction process—of great significance in nitrogen transformation—includes denitrification and dissimilatory nitrate reduction to ammonium (DNRA). Such reduction processes can directly affect the transformation of nitrates and the environmental consequences (such as leaching and N2O emission). During the processes of denitrification and DNRA, is utilized as a substrate, while N2O is generated synchronously. Nonetheless, there are significant differences between denitrification and DNRA, such as metabolic processes, the transformation mechanism, reductases, and the final products. For DNRA, the final product is ammonium ), which can continue to participate in other soil nitrogen transformation processes, such as crop uptake and nitrification. In agroecosystems, DNRA can consume 3.9%—25.4% of ; this process can decrease leaching and N2O emissions in comparison with denitrification.Both reducing pathways show a synergistic and competitive mechanism among the reaction conditions, products, and dominant regulators. The synergistic mechanism of denitrification and DNRA manifests itself as the similar suitable environmental conditions, the shared nitrate reductase (Nar), and an intermediate product (N2O), along with the similar soil parameters. Thus, according to the synergistic effect, the dissimilatory nitrate reduction process can be greatly enhanced without limiting factors such as the soil water regimen, temperature, and soil substrates. As for the competitive mechanism, it mainly involves competition for a substrate and energy supplies between denitrification and DNRA. In contrast, the direct competition for exists ubiquitouslybetween denitrification and DNRA. Nevertheless, regulation of soil parameters (such as available carbon,oxidation-reduction potential (Eh)) changes the concentration of accordingly; thus, the competition for between denitrification and DNRA should be rebalanced subsequently. Moreover, soil microorganisms that are related to denitrification and DNRA can compete for a carbon source for their growth and proliferation. The dissimilatory nitrate reduction process is influenced by a great number of factors, mainly environmental conditions and microorganisms. Sufficient soil and available carbon can significantly enhance the dissimilatory nitrate reduction process, whereas soil pH and Eh have their own suitable ranges for different dissimilatory nitrate reduction processes. The competition between denitrification and DNRA is regulated by these factors. With the changes in available carbon, soil pH, and Eh, the two pathways show different levels of activity. Bacteria can exist in the form of an advantageous microbial population during the dissimilatory nitrate reduction process. Nevertheless, different populations and genes are involved in denitrification and DNRA, and the diversity of soilmicroorganisms is in turn influenced by soil environmental factors. This review summarizes the synergistic and competitive mechanisms and the factors influencing denitrification and DNRA, for example, soil environmental conditions (soil , soil pH, available carbon and Eh) and microorganisms (population, diversity and genes). The mechanism of formation, soil environmental factors, microbiological processes, and the correlation with other nitrogen transformation processesurgently need further research on dissimilatory nitrate reduction processes. In DNRA, the mechanism of formation and analysis of N2O emissions, populations, diversity, and genes of a microorganism have not been established yet. In addition, the interactions of nitrogen transformation processes in soils—e.g., between denitrification and DNRA or between anaerobic ammonium oxidation and denitrification—should be investigated holistically. The knowledge about synergistic and competitive mechanisms and the factors influencing denitrification and DNRA should improve the understanding of the regulation of nitrogen transformation in soils; this knowledge is also necessary for the development of effective countermeasures and policies on soil nitrogen management.

Key Words:dissimilatorynitrate reduction process; denitrification; dissimilatory nitrate reduction to ammonium (DNRA); N2O; synergetic and competitive mechanism

基金項(xiàng)目:中國(guó)科學(xué)院西部行動(dòng)計(jì)劃項(xiàng)目(KZCX2-XB3-14); 重慶市基礎(chǔ)與前沿研究項(xiàng)目(cstc2013jcyjA0302);中國(guó)科學(xué)院水庫(kù)水環(huán)境重點(diǎn)實(shí)驗(yàn)室開放基金(RAE2014BA06B)

收稿日期:2014- 07- 18; 網(wǎng)絡(luò)出版日期:2015- 07- 22

DOI:10.5846/stxb201407181464

*通訊作者Corresponding author.E-mail: huangping@cigit.ac.cn

楊杉，吳勝軍，蔡延江，周文佐，朱同彬，王雨，黃平.硝態(tài)氮異化還原機(jī)制及其主導(dǎo)因素研究進(jìn)展.生態(tài)學(xué)報(bào),2016,36(5):1224- 1232.

Yang S, Wu S J, Cai Y J, Zhou W Z, Zhu T B, Wang Y, Huang P.The synergetic and competitive mechanism andthe dominant factors of dissimilatory nitrate reduction processes: a review.Acta Ecologica Sinica,2016,36(5):1224- 1232.