氮輸入對土壤甲烷產(chǎn)生、氧化和傳輸過程的影響及其機(jī)制

胡敏杰，仝川*，鄒芳芳

(1.福建師范大學(xué)濕潤亞熱帶生態(tài)-地理過程教育部重點實驗室，亞熱帶濕地研究中心，地理科學(xué)學(xué)院，福建 福州 350007；2.福建農(nóng)林大學(xué)安溪茶學(xué)院，福建 福州 350002)

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氮輸入對土壤甲烷產(chǎn)生、氧化和傳輸過程的影響及其機(jī)制

胡敏杰1，仝川1*，鄒芳芳2

(1.福建師范大學(xué)濕潤亞熱帶生態(tài)-地理過程教育部重點實驗室，亞熱帶濕地研究中心，地理科學(xué)學(xué)院，福建 福州 350007；2.福建農(nóng)林大學(xué)安溪茶學(xué)院，福建 福州 350002)

隨著人為氮輸入的增加，外源氮成為影響土壤甲烷產(chǎn)生、氧化和傳輸過程的重要因素。土壤甲烷排放受氮素有效性的調(diào)節(jié)，氮輸入會改變土壤初始環(huán)境和甲烷排放規(guī)律，最終影響甲烷排放量。綜述了氮輸入對土壤甲烷產(chǎn)生、氧化和傳輸過程的影響及機(jī)制。研究表明，1)氮輸入對甲烷排放通量的影響存在促進(jìn)、抑制和不顯著3種情況，這主要是甲烷產(chǎn)生、氧化和傳輸過程的變化引起的；2)氮輸入對甲烷產(chǎn)生過程的影響受產(chǎn)甲烷底物和產(chǎn)甲烷微生物活性的控制，氮輸入通過增加土壤有機(jī)碳的含量為甲烷產(chǎn)生提供了豐富的底物，同時底物理化性質(zhì)和植被覆蓋度的變化使得這種影響復(fù)雜化，氮輸入既可促進(jìn)又可抑制產(chǎn)甲烷菌的活性，并且這種作用受氮形態(tài)的影響；3)氮輸入對甲烷氧化過程的影響主要是通過刺激或抑制甲烷氧化菌的活性實現(xiàn)的，氮形態(tài)的不同也使得這種變化更為復(fù)雜；4)氮輸入對甲烷傳輸過程的影響主要受植物通氣組織的數(shù)量以及傳輸效率的控制，并且在不同生態(tài)系統(tǒng)這種控制作用差異較大。綜上所述，氮輸入對土壤甲烷產(chǎn)生、氧化和傳輸過程的影響及機(jī)制具有明顯的復(fù)雜性和不確定性，今后研究中應(yīng)綜合考慮氮輸入對甲烷排放關(guān)鍵過程的影響，并側(cè)重于探討氮輸入對相關(guān)微生物群落結(jié)構(gòu)、豐度和活性的影響，同時注重對各個生態(tài)系統(tǒng)的協(xié)同研究，確定氮輸入影響下各個生態(tài)系統(tǒng)對全球甲烷排放的貢獻(xiàn)率。

機(jī)制；甲烷產(chǎn)生；甲烷氧化；微生物；氮輸入

自工業(yè)革命以來，由于化石燃料的燃燒、牲畜的飼養(yǎng)以及水稻的栽培，全球甲烷排放通量已經(jīng)增加了2倍[1]。同時，由于甲烷吸收長波輻射的效率是CO2的20～30倍，有甲烷參與的化學(xué)過程也促進(jìn)了O3和CO2等的形成[2]，因此甲烷成為僅次于CO2的重要溫室氣體。相關(guān)研究已經(jīng)證實，土壤是大氣甲烷最重要的源或匯[3]。土壤中甲烷凈源或匯功能主要是由厭氧環(huán)境下產(chǎn)甲烷菌產(chǎn)生的甲烷和有氧環(huán)境下甲烷氧化菌引起的甲烷損耗間的平衡決定的[4]。其中，土壤中甲烷的產(chǎn)生主要有2個過程：1)微生物將有機(jī)化合物水解為CO2、H2和乙酸；2)厭氧條件下，產(chǎn)甲烷菌以H2作為H供體還原CO2形成CH4或?qū)⒁宜崦摷谆纬蒀H4[5-6]。而甲烷產(chǎn)生過程生產(chǎn)的甲烷有30%～90%在有氧條件下又被甲烷氧化菌氧化了[7]，并且最終排放通量還受傳輸過程的調(diào)節(jié)。因此，土壤甲烷排放是一個復(fù)雜的生物地球化學(xué)過程，凈甲烷通量是甲烷產(chǎn)生、氧化和傳輸過程綜合作用的結(jié)果[8]。

人類活動(如化石燃料的燃燒、氮肥施用)以及生物固氮作用等輸入和積累的氮素隨地表徑流、干濕沉降等多種途徑進(jìn)入生態(tài)系統(tǒng)，已經(jīng)導(dǎo)致生態(tài)系統(tǒng)外源氮輸入的增加[9-10]。氮素是控制土壤生物反應(yīng)最重要的因子[11]。氮輸入會引起生態(tài)系統(tǒng)服務(wù)功能的變化，如改變了群落結(jié)構(gòu)，使水生生態(tài)系統(tǒng)富營養(yǎng)化等[12]。越來越多的證據(jù)表明，生態(tài)系統(tǒng)氮輸入改變了土壤微生物和植被的生理機(jī)能，直接影響溫室氣體的生產(chǎn)與消耗進(jìn)程[13]。氮輸入對土壤甲烷排放的影響可能有2個方面：1)以NH4+形式富集的氮可以通過土壤好氧微生物減少甲烷的消耗[14]；2)氮輸入通過增加產(chǎn)甲烷微生物所需有機(jī)碳的供給，可以提高甲烷的產(chǎn)生，但氮輸入也可以減緩產(chǎn)甲烷微生物的活性，最終降低或增加甲烷排放。由此可知，氮輸入對甲烷產(chǎn)生與氧化等生物化學(xué)過程的影響極其復(fù)雜，其方向和大小受生態(tài)系統(tǒng)類型、輸入氮的化學(xué)形態(tài)以及環(huán)境條件等的影響[15]。雖然氮輸入背景下，甲烷源/匯功能及其通量變化等已成為全球變化研究中的重要一環(huán)[16]，但其過程和機(jī)理還有許多不明晰之處。因此，全面梳理氮輸入對土壤甲烷排放關(guān)鍵過程的影響及機(jī)制，有助于了解甲烷排放通量對外源氮輸入的響應(yīng)，可為準(zhǔn)確估算全球甲烷排放，減少人類活動對氣候的影響提供策略支持。

1 氮輸入對甲烷排放通量的影響

目前關(guān)于氮輸入對甲烷產(chǎn)生過程的影響存在促進(jìn)、抑制和影響不顯著3種情況(表1)，這可能與輸入氮的形態(tài)、濃度以及土壤特性等的不同有關(guān)。Yao等[17]在水稻田的研究發(fā)現(xiàn)，輸入尿素降低了甲烷排放，而Zhang等[18]在相鄰區(qū)域水稻田的氮肥添加實驗則發(fā)現(xiàn)，甲烷排放通量隨氮肥輸入量的增加而升高。Liu和Greaver[15]運用Meta-analysis方法研究也發(fā)現(xiàn)，對草地、濕地、厭氧的農(nóng)業(yè)系統(tǒng)平均而言，氮輸入30～400 kg N/(hm2·a)，使甲烷排放通量顯著增加了95%。但Whalen和Reeburgh[19]的研究卻發(fā)現(xiàn)，森林土壤施氮后，其甲烷排放并沒有顯著變化，他們認(rèn)為這可能是森林土壤氮含量并未達(dá)到飽和。可見，外源氮輸入對甲烷排放具有復(fù)雜性和不確定性，這可能是甲烷產(chǎn)生、氧化和傳輸過程綜合影響的結(jié)果。

表1 氮輸入對土壤甲烷排放通量影響

2 氮輸入對甲烷產(chǎn)生的影響及機(jī)理

2.1 土壤產(chǎn)甲烷底物對甲烷產(chǎn)生的影響

甲烷產(chǎn)生是甲烷排放的先決條件。土壤中甲烷的產(chǎn)生是在厭氧條件下由產(chǎn)甲烷菌作用于產(chǎn)甲烷底物的產(chǎn)物，有機(jī)底物是產(chǎn)甲烷菌唯一的C源和能量來源。底物量的豐富程度直接決定了土壤微生物和酶的活性以及功能的發(fā)揮。土壤中產(chǎn)甲烷底物一般由土壤中固有的有機(jī)物質(zhì)以及生物殘留或由外源輸入的有機(jī)物質(zhì)構(gòu)成[25]。大多數(shù)研究認(rèn)為，外源氮輸入增加了土壤中氮素的有效性，這就相應(yīng)地提高了植被的生產(chǎn)力和產(chǎn)甲烷菌所需有機(jī)底物的有效性[26]，使得產(chǎn)甲烷微生物具有更多可利用的底物，促進(jìn)甲烷的產(chǎn)生。如Zhang等[27]對泥炭沼澤的研究發(fā)現(xiàn)，大氣氮沉降增加了泥炭土壤氮的有效性，這會提高初級生產(chǎn)力和礦化速率，從而促進(jìn)甲烷等溫室氣體的排放。Darby和Turner[28]也認(rèn)為氮輸入增加了地上和地下生物量，相應(yīng)地輸入到土壤中的植被枯落物增加，提高了土壤中的有機(jī)碳含量。一般而言，具有較高初始C∶N的底物，其分解速率會隨著氮的增加而增高，在微生物作用下形成有機(jī)物質(zhì)，從而為甲烷產(chǎn)生提供更多的有機(jī)底物[29]。Aronson和Helliker[14]對非濕地(non-wetland)土壤的研究也發(fā)現(xiàn)，高氮處理下凈甲烷排放率明顯增加，他們認(rèn)為這是因為高氮輸入刺激了許多微生物過程，提高了分解速率，間接地為甲烷產(chǎn)生提供所需底物。氮輸入引起的土壤有機(jī)質(zhì)本身、新鮮的植物枯落物以及根系分泌物等的增加，也為土壤甲烷產(chǎn)生提供了豐富的底物[30]。此外，短期的氮輸入刺激了土壤微生物的活性，導(dǎo)致根系分泌物的快速分解，也促進(jìn)了土壤有機(jī)質(zhì)的分解。在受氮限制環(huán)境中，氮輸入還可以通過減輕氮的限制作用，刺激土壤有機(jī)底物的產(chǎn)生[31]。但是也有研究認(rèn)為，氮輸入雖然可以通過C底物供應(yīng)的增加[32]而促進(jìn)了土壤微生物活性，但也可通過增加土壤毒害作用而抑制了微生物活性[33]。Pregitzer等[34]發(fā)現(xiàn)，長期的氮輸入增加了植被的死亡率，他們認(rèn)為這可能是因為氮輸入增加了土壤酸性。同時，氮輸入對底物的影響還與植被覆蓋率有關(guān)。Granberg等[35]在一個貧瘠的瑞典沼澤地研究發(fā)現(xiàn)，氮輸入增加了莎草(Cyperusrotundus)的覆蓋率，但減少了甲烷的排放。這可能表明在莎草豐富的泥炭土壤中，根的分布和C的分配可能改變了，這間接地減少了產(chǎn)甲烷菌的底物有效性，降低了莎草控制甲烷釋放的能力。此外，在硝態(tài)氮還原過程中，其底物利用熱量的效率明顯優(yōu)于甲烷產(chǎn)生過程，導(dǎo)致產(chǎn)甲烷底物濃度下降到產(chǎn)甲烷菌無法利用的程度，抑制了甲烷的生成[36]。

2.2 土壤產(chǎn)甲烷微生物活性變化對甲烷產(chǎn)生的影響

甲烷是在土壤中由產(chǎn)甲烷微生物通過有機(jī)分解而生產(chǎn)。氮輸入對土壤產(chǎn)甲烷微生物活性的影響較為復(fù)雜，一般認(rèn)為有促進(jìn)和抑制兩種作用[37]。Bodelier等[38]認(rèn)為，硝酸鹽減少了產(chǎn)甲烷作用，因為當(dāng)微生物在厭氧環(huán)境下氧化有機(jī)底物(如乙酸)時，可以使用硝酸鹽作為電子受體，而產(chǎn)甲烷菌無法與這些硝酸鹽還原劑競爭底物，使得甲烷產(chǎn)生減少。由于氮輸入促進(jìn)了生態(tài)系統(tǒng)的新陳代謝過程，微生物隨著新陳代謝作用獲得了更多的能量，這也將減緩產(chǎn)甲烷微生物的活性[39]。但Siciliano等[40]則認(rèn)為，甲烷的產(chǎn)生主要取決于產(chǎn)甲烷菌的活性，在氮富集環(huán)境下，更高的枯落物輸入減緩了C對微生物的限制作用，提高了產(chǎn)甲烷菌的活性，從而產(chǎn)生了更多的甲烷。不同形態(tài)氮的影響也是不一致的，如(NH4)2SO4添加下甲烷的排放就明顯低于尿素，這是因為SO42-作為有機(jī)質(zhì)氧化的電子受體，通過與產(chǎn)甲烷菌競爭產(chǎn)甲烷底物而抑制甲烷的產(chǎn)生[41]。而NaNO3對排放的影響取決于硝酸鹽含量的多少，當(dāng)NO3-含量高時會抑制甲烷的產(chǎn)生，反之則促進(jìn)了甲烷的產(chǎn)生。也有研究認(rèn)為，氮輸入引起的土壤產(chǎn)甲烷菌pH值的變化以及H2S的毒害作用等也抑制了產(chǎn)甲烷菌的活性，減少了甲烷的產(chǎn)生[42]。

3 氮輸入對甲烷氧化的影響及機(jī)理

3.1 不同氮形態(tài)對甲烷氧化的影響及機(jī)理

輸入氮化學(xué)形態(tài)和水平的不同對甲烷氧化過程的影響是不同的[43]。甲烷氧化菌在低滲透壓下具有最佳的氧化活性，氮肥(如KNO3，NH4Cl，NH4NO3)通過增加滲透壓，已經(jīng)展示對甲烷氧化菌活性的抑制作用[44]。Crill等[45]通過不同氮肥的施加實驗發(fā)現(xiàn)，NH4Cl對甲烷氧化的抑制作用明顯高于KNO3，這是因為NH4+是甲烷氧化的競爭性抑制劑，通過與甲烷單氧酶的競爭，減少了甲烷的氧化。而尿素的抑制作用更弱，這主要是因為輸入的尿素需要經(jīng)過土壤微生物的分解后才能緩慢釋放氮素。銨鹽對甲烷氧化的抑制作用在多種土壤類型中都得到證實[46-47]，這種抑制機(jī)制非常復(fù)雜，不僅包括由NH4+引起的甲烷單氧酶、氨氧化菌以及甲烷氧化菌間的競爭性抑制作用，也包括由NH4+氧化引起的羥胺和亞硝酸鹽間的非競爭性抑制作用。此外，由于甲烷單氧酶對底物的競爭以及銨鹽氧化產(chǎn)生的亞硝酸鹽的毒害作用也抑制了甲烷的氧化[48]，各離子的毒害作用依次為[49]：NH4+

3.2 土壤甲烷氧化微生物活性變化對甲烷氧化的影響

在有氧土壤表層，好氧的甲烷氧化菌能夠消耗超過90%的產(chǎn)生于深層厭氧層的甲烷[14]。甲烷氧化菌的活性既能被氮激活，又可被氮抑制。根據(jù)生理學(xué)、形態(tài)學(xué)特征，可將甲烷氧化菌分為兩類，即Ⅰ型(Type Ⅰ)甲烷氧化菌和Ⅱ型(Type Ⅱ)甲烷氧化菌[55]。研究發(fā)現(xiàn)，氮輸入刺激了濱海濕地土壤甲烷的氧化，因為此處甲烷氧化菌群落主要以Ⅰ型甲烷氧化菌為主導(dǎo)[56]。相反，氮輸入抑制了森林[57]和農(nóng)業(yè)[58]土壤Ⅱ型甲烷氧化菌活性。氮對不同類型甲烷氧化菌的抑制/促進(jìn)作用是因為不同類型甲烷氧化菌間的競爭，在氮富集條件下Ⅱ型甲烷氧化菌固定分子態(tài)氮的能力更強(qiáng)，從而降低了它們對銨鹽和硝酸鹽的需求，導(dǎo)致Ⅰ型甲烷氧化菌在競爭中占有優(yōu)勢[59]。不同環(huán)境下，Ⅰ型和Ⅱ型甲烷氧化菌所起作用也是不一樣的，Ⅰ型甲烷氧化菌喜好相對穩(wěn)定的環(huán)境，而Ⅱ型甲烷氧化菌則常產(chǎn)生于波動強(qiáng)烈的環(huán)境下(如水稻土)[60]。大多數(shù)研究認(rèn)為，氮輸入抑制了甲烷的氧化活性。Gupta等[61]研究發(fā)現(xiàn)，在濕地土壤中專性好氧型甲烷氧化菌可以使用分子氧將甲烷氧化成CO2和細(xì)胞碳，在土壤表層和植物氧釋放的根際這些微生物最為活躍，從而限制甚至抑制甲烷氧化菌活性。Shukla 等[62]認(rèn)為，銨鹽對甲烷氧化的抑制作用在一定程度上可以解釋為是離子或鹽的影響，陽離子的添加引起的土壤氨的生理鹽脅迫和離子交換都可能引起土壤甲烷氧化的下降，而氨氧化代謝產(chǎn)生的硝酸鹽和亞硝酸鹽對產(chǎn)甲烷菌的毒害作用是其他可能的原因。由于好氧甲烷氧化的控制與氧氣和甲烷有關(guān)，因此最大的甲烷氧化率往往發(fā)生在最適宜甲烷氧化菌生存的地方[63]。此外，由于甲烷和氨具有相似的基因結(jié)構(gòu)，當(dāng)土壤中具有豐富的銨態(tài)氮時，甲烷氧化菌的氧化底物會從甲烷轉(zhuǎn)換為氨氣[64]。但這種轉(zhuǎn)換僅僅發(fā)生在氨氣濃度顯著高于甲烷的土壤中[65]。

相反，氮輸入也會促進(jìn)甲烷氧化。由于硝化細(xì)菌同樣可以氧化消耗甲烷，氮輸入刺激了硝化細(xì)菌的生長，從而促進(jìn)了土壤對甲烷的氧化吸收[66]。也有研究顯示，氮輸入沒有顯著影響濱海濕地甲烷氧化能力和甲烷通量，這是因為雖然氮輸入影響了甲烷氧化菌群落結(jié)構(gòu)，但并沒有干擾甲烷氧化菌群落的整體活性。關(guān)于甲烷氧化菌對N的耐受性在其他土壤類型中也得到相似的結(jié)論[67]。較高的甲烷有效性也會抵消由銨鹽以及其他物理化學(xué)和生物機(jī)制(pH的變化、土壤水勢、離子吸附、中間體的毒害作用等)引起的對甲烷氧化的競爭抑制作用[68]。氮輸入時間的長短也影響了甲烷氧化作用，因為自然狀態(tài)下氮素首先輸入到土壤表層，由于受土層的阻隔，氮輸入初期對土壤吸收甲烷的影響較弱。此外，分類結(jié)構(gòu)和微生物群落活性的變化引起的甲烷氧化和氮周轉(zhuǎn)過程的變化是其他可能的原因[69]。

4 氮輸入對甲烷傳輸?shù)挠绊懠皺C(jī)理

在評估氮輸入對甲烷排放的影響時，具有通氣組織的植物(如維管束植物)對甲烷排放的影響是研究的重點。已有研究顯示，土壤或植物根部產(chǎn)生的甲烷有很大部分是通過植物體傳輸?shù)酱髿庵械模鋫鬏斄考s占甲烷傳輸總量的50%～90%[70]。雖然植物傳輸通常是讓土壤中的甲烷通過體內(nèi)的通氣組織進(jìn)入大氣，但不同類型植物采取的甲烷傳輸機(jī)制是不同的，主要有對流傳輸和擴(kuò)散傳輸兩種。一般而言，對流傳輸機(jī)制植物的甲烷輸送效率要高于擴(kuò)散傳輸機(jī)制的植物[71]。植物通氣組織的數(shù)量以及傳輸效率顯著影響著甲烷的排放。Saarnio和Silvola[72]在泥炭沼澤的研究發(fā)現(xiàn)，最高的甲烷排放一般是與維管束植物有關(guān)，因為維管束植物擁有發(fā)達(dá)的通氣組織，甲烷分子通過植物的通氣組織傳輸?shù)酱髿庵?，可避免土壤甲烷氧化微生物的氧化作用。但發(fā)達(dá)的通氣組織也可以在植物根部形成好氧區(qū)域，大氣中的氧氣通過植株的通氣組織進(jìn)入根部，從而加速甲烷的氧化[73]。由此可見，植物體對甲烷的傳輸過程具有復(fù)雜性和不確定性。一般而言，植物體傳輸甲烷的效率主要與溫度[74-75]、濕度[76]、通氣組織[77]以及生長期[78]等有關(guān)，濕度越低，溫度、風(fēng)速越高，通氣組織越多都將提高植物體傳輸甲烷的能力。土壤甲烷排放也與植被物種構(gòu)成有關(guān)。Bubier[79]研究了苔蘚植物物種與甲烷通量間的關(guān)系發(fā)現(xiàn)，Sphagnumfuscum表層的甲烷通量低于S.angustifolium占優(yōu)勢的區(qū)域，而Myliaanomala覆被的區(qū)域其甲烷通量更高。Tong等[80]對閩江河口濕地的研究也表明，單株植物甲烷傳輸能力是不同的。

一般而言，氮輸入促進(jìn)了植物的生長，相應(yīng)地也增加了植物的通氣組織數(shù)量[81]，這種影響在濕地生態(tài)系統(tǒng)中表現(xiàn)得尤為明顯[82]。維管束植物在將C分配到產(chǎn)甲烷區(qū)中也有重要作用[83]。由此可見，植物群落與甲烷排放間存在密切的關(guān)系，氮輸入通過促進(jìn)植物生產(chǎn)力和生物量，影響了甲烷的排放。通常濕地植物都具有發(fā)達(dá)的通氣組織，而干旱及營養(yǎng)元素貧瘠的區(qū)域具有通氣組織的植物較少，這就使得濕地生態(tài)系統(tǒng)成為甲烷的重要排放源。此外，植物的生理活動也影響了底物質(zhì)量和氧化劑數(shù)量等調(diào)控甲烷氧化的因素，控制甲烷排放。

5 研究不足與展望

甲烷排放是甲烷產(chǎn)生、氧化和傳輸過程的最終表現(xiàn)，外源氮的輸入使得這些過程更加復(fù)雜、多變。綜上所述，國內(nèi)外相關(guān)學(xué)者已就氮輸入對甲烷產(chǎn)生、氧化和傳輸過程及其機(jī)理進(jìn)行了較為深入的研究，對甲烷產(chǎn)生與氧化的微生物過程也有了初步的描述，但在機(jī)理的探究上還存在許多不確定性，目前研究中尚存在以下問題和不足：

1)關(guān)于氮輸入對甲烷排放的影響因素和機(jī)理的探究尚顯不足，尤其是氮輸入對土壤微生物以及酶的活性等方面的研究較少，難以從根源解釋相關(guān)問題。同時，關(guān)于氮與其他因素之間的耦合研究也較欠缺。

2)現(xiàn)有研究多為短期的、小區(qū)域的研究，缺乏長期、連續(xù)以及多區(qū)域協(xié)同研究，難以保證數(shù)據(jù)的準(zhǔn)確性、連續(xù)性和可比性?，F(xiàn)有研究多局限于單一生態(tài)系統(tǒng)的研究，缺乏多生態(tài)系統(tǒng)間的綜合研究，導(dǎo)致研究結(jié)論缺乏普適性。此外，目前關(guān)于氮輸入對甲烷排放影響的爭議在很大程度上源于測定方法的差異，缺乏標(biāo)準(zhǔn)的測定方法和體系。

3)氮輸入對土壤甲烷排放通量的影響，勢必會對全球變暖潛力產(chǎn)生促進(jìn)作用，但目前相關(guān)組織和機(jī)構(gòu)對全球變暖的評估和估算中卻沒有著重考慮這一因素，這不利于對全球變暖的控制和調(diào)節(jié)。

為此，未來可在以下幾方面進(jìn)行重點研究和探討： 1)加強(qiáng)對甲烷產(chǎn)生與氧化過程中微生物機(jī)制的研究，探討氮輸入對相關(guān)微生物群落結(jié)構(gòu)、豐度和活性的影響，明確微生物活動在甲烷產(chǎn)生與氧化過程中的地位與作用。 2)加強(qiáng)對多生態(tài)系統(tǒng)的整合研究，綜合研究氮輸入對濕地、森林和草地等生態(tài)系統(tǒng)甲烷排放通量及其關(guān)鍵過程的影響，為全面估算氮輸入對全球甲烷貢獻(xiàn)率提供參考和數(shù)據(jù)支持。 3)改進(jìn)研究方法，建立標(biāo)準(zhǔn)體系，注重室內(nèi)培養(yǎng)與野外原位實驗的結(jié)合，并利用最新手段(如穩(wěn)定同位素技術(shù)、高通量測序等)和機(jī)理模型，明晰氮輸入對甲烷產(chǎn)生與氧化過程中促進(jìn)/抑制作用的臨界值，以及甲烷產(chǎn)生與氧化過程對甲烷排放通量變化的貢獻(xiàn)，為全球甲烷減排提供依據(jù)。

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Effects of nitrogen input on CH4production, oxidation and transport in soils, and mechanisms: a review

HU Min-Jie1， TONG Chuan1*， ZOU Fang-Fang2

1.KeyLaboratoryofHumidSub-tropicalEco-geographicalProcessoftheMinistryofEducation,ResearchCentreofWetlandsinSubtropicalRegion,SchoolofGeographicalSciences,FujianNormalUniversity,Fuzhou350007,China; 2.AnxiTeaCollege,FujianAgricultureandForestryUniversity,Fuzhou350002,China

Methane is an important component of carbon output in anaerobic soil. Minor changes to the soil carbon cycle will cause significant changes in the metabolic processes involving methane, which in turn can be markedly affected by exogenous nitrogen input. With increase in anthropogenic nitrogen inputs, exogenous nitrogen becomes an important factor in soil methane production, oxidation, and transmission processes. Methane emissions are regulated by nitrogen availability. Nitrogen inputs can change the background environment and methane emission mechanisms in soil, and consequently influence methane emission fluxes. Research into effects of nitrogen input on CH4production and the mechanisms of N effects on oxidation and transport processes in soils are reviewed in this paper. The important findings in the literature are: 1) The effects of nitrogen input on CH4fluxes in soils can be positive, negative or neutral, due to the range of effects of added N on methane production, oxidation, and transport processes; 2) The effects of nitrogen input on methane production processes are controlled by methanogenic substrates and methanogenic microbial activities. Nitrogen input provides rich substrates for methane production by increasing soil organic carbon content. The changes in the physical and chemical properties of substrates and vegetation cover make this effect complicated. Nitrogen input can also either promote or inhibit the activity of methanogens, depending on the form of nitrogen supplied; 3) The effects of nitrogen input on methane oxidation processes mainly arise from stimulation or inhibition of the activities of methanotrophs; 4) The effects of nitrogen input on methane transport processes depend mostly on the number of aerenchyma vessels and on transport efficiencies, and the degree of dependence varied greatly in different ecosystems. Overall, the effects of nitrogen input on soil CH4production, oxidation, and transport process are complicated and the mechanisms are uncertain. Future research should focus on the effects of nitrogen input on the critical processes determining methane emissions, on investigation of the effects of nitrogen input on microbial community structures, abundance and activities, and on collaborative research in a range of ecosystems. The goal of future research should be to determine the contribution of various ecosystems to global methane emissions at specific levels of nitrogen input.

mechanisms; methane production; methane oxidation; microorganism; nitrogen input

10.11686/cyxb2014313

http://cyxb.lzu.edu.cn

2014-07-14；改回日期：2014-09-12

國家自然科學(xué)基金項目(41071148)，福建省教育廳項目(JA13469)，福建師范大學(xué)創(chuàng)新團(tuán)隊項目和福建師范大學(xué)地理科學(xué)學(xué)院研究生創(chuàng)新基金項目資助。

胡敏杰(1988-)，男，安徽合肥人，在讀博士。E-mail: mjhu0014@163.com *通訊作者Corresponding author. E-mail: tongch@fjnu.edu.cn

胡敏杰，仝川，鄒芳芳. 氮輸入對土壤甲烷產(chǎn)生、氧化和傳輸過程的影響及其機(jī)制. 草業(yè)學(xué)報, 2015, 24(6): 204-212.

Hu M J，Tong C，Zou F F. Effects of nitrogen input on CH4production, oxidation and transport in soils, and mechanisms: a review. Acta Prataculturae Sinica, 2015, 24(6): 204-212.