酸性土壤（pH<5.5）在我國分布面積廣泛,，是我國熱帶亞熱帶糧食和經(jīng)濟(jì)作物的重要產(chǎn)地,。一直以來,，氨氧化細(xì)菌（AOB）被認(rèn)為是土壤硝化作用的主要驅(qū)動(dòng)者,，但在多數(shù)酸性土壤中檢測(cè)不到AOB,，或發(fā)現(xiàn)AOB的存在與硝化作用無關(guān),，酸性土壤硝化作用的機(jī)理一直不夠清楚,。
中國科學(xué)院生態(tài)環(huán)境研究中心賀紀(jì)正研究員課題組于2007年在Environmental Microbiology上首次報(bào)道了酸性土壤中存在大量氨氧化古菌（AOA）,，且AOA的數(shù)量與土壤硝化潛勢(shì)呈顯著正相關(guān)關(guān)系，該成果在國際上引起關(guān)注,，被SCI期刊廣泛引用,。最近，他們利用穩(wěn)定性同位素探針技術(shù)（SIP）,，結(jié)合經(jīng)典的分子生態(tài)學(xué)手段,，對(duì)我國強(qiáng)酸性土壤中的硝化作用機(jī)理開展了深入研究。
根據(jù)氨氧化微生物氧化氨時(shí)進(jìn)行化能自養(yǎng)生長(zhǎng)固定CO2為碳源的牲征,，研究人員在實(shí)驗(yàn)室微宇宙培養(yǎng)條件下,，分別用13C-CO2和12C-CO2對(duì)酸性土壤進(jìn)行標(biāo)記培養(yǎng)，通過密度梯度超速離心,，將結(jié)合了13C和12C的微生物DNA加以分離,，并對(duì)這些DNA進(jìn)行分子生物學(xué)分析，發(fā)現(xiàn)屬于奇古菌門(Thaumarchaeota)中的氨氧化古菌(AOA)能固定13CO2,，且其豐度變化與活躍的氨氧化速率呈顯著正相關(guān),。在代表微生物多樣性組成的DGGE指紋圖譜上，兩個(gè)AOA類群在培養(yǎng)后顯著增加,，而相應(yīng)的氨氧化細(xì)菌則變化不明顯,，表明AOA是該酸性土壤硝化作用的主要貢獻(xiàn)者。
這一發(fā)現(xiàn)為AOA在酸性土壤硝化作用中發(fā)揮主導(dǎo)作用提供了直觀證據(jù),，為重新認(rèn)識(shí)酸性土壤中的硝化作用機(jī)理提供了重要參考,。
該研究成果發(fā)表于5月出版的國際微生物生態(tài)學(xué)會(huì)會(huì)刊The ISME Journal上(Ammonia-oxidizing archaea have more important role than ammonia-oxidizing bacteria in ammonia oxidation of strongly acidic soils. The ISME J, 6(5): 1032-1045)。奇古菌門是最近定義的一個(gè)新的古菌類群,，賀紀(jì)正等在最近一期的中文期刊《微生物學(xué)報(bào)》上對(duì)奇古菌門也作了專門介紹（張麗梅和賀紀(jì)正,，2012，52：411-421）,。（生物谷Bioon.com）
doi:10.1038/ismej.2011.168
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Ammonia-oxidizing archaea have more important role than ammonia-oxidizing bacteria in ammonia oxidation of strongly acidic soils
Li-Mei Zhang1,3, Hang-Wei Hu1,2,3, Ju-Pei Shen1 and Ji-Zheng He1
Increasing evidence demonstrated the involvement of ammonia-oxidizing archaea (AOA) in the global nitrogen cycle, but the relative contributions of AOA and ammonia-oxidizing bacteria (AOB) to ammonia oxidation are still in debate. Previous studies suggest that AOA would be more adapted to ammonia-limited oligotrophic conditions, which seems to be favored by protonation of ammonia, turning into ammonium in low-pH environments. Here, we investigated the autotrophic nitrification activity of AOA and AOB in five strongly acidic soils (pH<4.50) during microcosm incubation for 30 days. Significantly positive correlations between nitrate concentration and amoA gene abundance of AOA, but not of AOB, were observed during the active nitrification. 13CO2-DNA-stable isotope probing results showed significant assimilation of 13C-labeled carbon source into the amoA gene of AOA, but not of AOB, in one of the selected soil samples. High levels of thaumarchaeal amoA gene abundance were observed during the active nitrification, coupled with increasing intensity of two denaturing gradient gel electrophoresis bands for specific thaumarchaeal community. Addition of the nitrification inhibitor dicyandiamide (DCD) completely inhibited the nitrification activity and CO2 fixation by AOA, accompanied by decreasing thaumarchaeal amoA gene abundance. Bacterial amoA gene abundance decreased in all microcosms irrespective of DCD addition, and mostly showed no correlation with nitrate concentrations. Phylogenetic analysis of thaumarchaeal amoA gene and 16S rRNA gene revealed active 13CO2-labeled AOA belonged to groups 1.1a-associated and 1.1b. Taken together, these results provided strong evidence that AOA have a more important role than AOB in autotrophic ammonia oxidation in strongly acidic soils.
