10:45 〜 12:15
[BBC02-P03] Methanogenic microbial communities living inside trees
キーワード：メタン、メタン生成古細菌、森林
Forest ecosystem has been recognized as a sink of atmospheric methane because the soil usually shows negative methane flux. However, recent studies have revealed that trees emit significant amounts of methane through the stems. These findings suggest the necessity of studies on the mechanisms of methane emission from trees. Previous studies showed that methanogenic archaea inhabit the inside of poplar trees. However, methanogenic microbial communities living inside trees other than poplar, that is the ubiquity of methanogenic archaea and their abundance and diversity, have not been reported yet. The present study investigated methanogenic microbial communities living inside seven tree species in a cold temperate mountain forest in Japan.
Wood core segments were obtained with an increment borer from the trunk of seven tree species, Cryptomeria japonica (Cj, Sugi), Quercus crispula (Qc, Mizunara), Fraxinus mandchurica (Fm, Yachidamo), Acer pictum (Ap, Itayakaede), Aesculus turbinata (At, Tochinoki), Magnolia obovata (Mo, Hoonoki), and Populus tremula var. sieboldii (Pt, Yamanarashi) in the Ashiu Experimental Forest of Kyoto University in July 2020 and September 2021. The core samples were divided into heartwood and sapwood prats depending on the color. Total DNA was extracted from the core samples, and then the abundance of methanogenic archaea was estimated by qPCR analysis of mcrA gene, encoding the alpha subunit of methyl-coenzyme M reductase. Amplicon sequencing analysis of 16S rRNA genes was carried out to reveal the diversity and composition of methanogenic microbial communities. Besides, the viable number of methanogenic archaea was also enumerated by the most probable number (MPN) method.
The mcrA gene was detected from all the samples irrespective of tree species and heartwoods/sapwoods. Although the variations in the copy numbers were large among the individuals (103–108 copies g-1 dry wood), some heartwood samples of Cj, Qc, Fm, and At contained more than 106 copies of mcrA g-1 dry wood. The MPN enumeration also demonstrated the inhabitation of methanogenic archaea inside the trees (max. 105 cells g-1 dry wood; Cj). Most of methanogenic archaeal 16S rRNA genes retrieved in the amplicon sequencing analysis were derived from Methanobacteriaceae. Bacilli, Clostridia, and Beta- and Gamma-proteobacteria were the predominant members in the trees, of which the relative abundance of Clostridia, Negativicutes, and Actinobacteria was higher in the heartwood than that in the sapwood. These results suggested that the inside of various trees is a common habitat for methanogenic microbial communities and a potential source of methane in the forest ecosystem.
Wood core segments were obtained with an increment borer from the trunk of seven tree species, Cryptomeria japonica (Cj, Sugi), Quercus crispula (Qc, Mizunara), Fraxinus mandchurica (Fm, Yachidamo), Acer pictum (Ap, Itayakaede), Aesculus turbinata (At, Tochinoki), Magnolia obovata (Mo, Hoonoki), and Populus tremula var. sieboldii (Pt, Yamanarashi) in the Ashiu Experimental Forest of Kyoto University in July 2020 and September 2021. The core samples were divided into heartwood and sapwood prats depending on the color. Total DNA was extracted from the core samples, and then the abundance of methanogenic archaea was estimated by qPCR analysis of mcrA gene, encoding the alpha subunit of methyl-coenzyme M reductase. Amplicon sequencing analysis of 16S rRNA genes was carried out to reveal the diversity and composition of methanogenic microbial communities. Besides, the viable number of methanogenic archaea was also enumerated by the most probable number (MPN) method.
The mcrA gene was detected from all the samples irrespective of tree species and heartwoods/sapwoods. Although the variations in the copy numbers were large among the individuals (103–108 copies g-1 dry wood), some heartwood samples of Cj, Qc, Fm, and At contained more than 106 copies of mcrA g-1 dry wood. The MPN enumeration also demonstrated the inhabitation of methanogenic archaea inside the trees (max. 105 cells g-1 dry wood; Cj). Most of methanogenic archaeal 16S rRNA genes retrieved in the amplicon sequencing analysis were derived from Methanobacteriaceae. Bacilli, Clostridia, and Beta- and Gamma-proteobacteria were the predominant members in the trees, of which the relative abundance of Clostridia, Negativicutes, and Actinobacteria was higher in the heartwood than that in the sapwood. These results suggested that the inside of various trees is a common habitat for methanogenic microbial communities and a potential source of methane in the forest ecosystem.