Shift in the rhizosphere microbial communities between growing- and low-temperature dormant seasons in a northern hardwood forest

北方広葉樹林における休眠期と成長期の根圏微生物の違い

中山 理智  ; 舘野 隆之輔*

Nakayama, Masataka; Tateno, Ryunosuke*

植物細根の周辺土壌(根圏)の微生物は根滲出物や根との共生によって非根圏の微生物とは異なっており、植物の生育に重要な役割を担っている。しかし、特に冷温帯林の植物の休眠期に関して、根圏微生物の季節的な変動は不明である。我々は根圏の微生物群集を冷温帯の落葉広葉樹林において、休眠期の開始時、終了時そして成長期において調査した。外生菌根菌の相対優占度は成長期には根圏で高かったが、休眠期はその違いが不明瞭であり、共生している植物からの炭素供給の季節性が重要であることが示唆された。一方で、主に細菌から構成される根圏の主要な小グループは季節的な変動をせず、pHや含水率などの物理化学性に強く影響されていた。これらの結果は、根圏の真菌、細菌群集は植物の休眠期に対して異なる適応をしており、微生物同士および微生物と植物根との関係性が根圏において季節的に異なることを示唆するものである。

Microbial communities within the soil surrounding plant roots (rhizosphere) are distinct from those in the non-rhizosphere soil because of root exudation and symbiosis with plant roots and play important roles in plant growth. However, seasonal variations in these rhizosphere microbial communities are not well known, especially during the plant's dormant season in cool temperate forests. We investigated the rhizosphere microbial communities in a cool-temperate deciduous broad-leaved forest at the growing season (mid-summer) and at the beginning and end of the plant's dormant season (early winter and early spring) using metabarcoding of prokaryotic 16S rRNA genes and fungal ITS region, microbial functional prediction, and co-occurrence network analysis. The rhizosphere dominant prokaryotic subgroup (occupying 19.4 3.2% of relative read counts) had non-significant seasonal fluctuations, and their relative read counts were correlated with physicochemical properties, including pH and water content. In contrast, the relative read count of ectomycorrhizal fungi was 1.4 times higher in the rhizosphere than that in the bulk soil in mid-summer. However, the relative read counts of ectomycorrhizal fungi within rhizospheres in winter and spring (28.5 18.9% and 20.8 13.8%, respectively) were similar to that in bulk soil (25.8 18.7% and 22.4 17.1%, respectively). Ectomycorrhizal fungi reduced their occupancy within the rhizosphere during the plant's dormant seasons, whereas rhizosphere-dominant prokaryotic communities were stable during the seasonal change, implying the importance of prokaryotic rather than ectomycorrhizal fungal communities in the processes occurring within the rhizosphere during dormant seasons.