[A-HW18] Material transportation and cycling at the land-sea interface: from headwaters to the ocean

[AHW18-07] Changes in microbial community structure related to biodegradation of eelgrass (Zostera marina)

*Md Mehedi Iqbal¹, Masahiko Nishimura¹, Yuya Tsukamoto¹, Susumu Yoshizawa^1,2 (1.Atmosphere and Ocean Research Institute, The University of Tokyo , 2.Department of Natural Environmental Studies, Graduate School of Frontier Sciences, The University of Tokyo)

Keywords:Zostera marina (eelgrass), 16S rRNA, microcosm, decomposition, carbon and nitrogen content

Seagrass meadows produce organic carbon and deposit it on the seabed through the decaying process. Microbial activity is closely related to the process of seagrass death and collapse. We investigated the microbial community structure of eelgrass (Zostera marina) during the eelgrass decomposition process by using a microcosm containing raw seawater and excised leaves collected from a Z. marina bed in Futtsu, Chiba Pref., Japan. Microbial communities of the test containers were monitored over 180 days, and sub-samplings were taken on Days 0, 7, 15, 30, 60, 120, and 180. Microbial DNA was extracted from leaf samples using a DNeasy PowerSoil kit (Qiagen, Germany). The V4 region of the 16S ribosomal RNA (16S rRNA) genes was amplified using PCR and sequenced by Illumina Miseq platform. In addition, decay rate and elemental analyses of eelgrass leaf detritus were calculated for each microcosm container at every subsampling. The results showed that the fast-growing microbes (i.e., Alphaproteobacteria, Gammaproteobacteria, and Flavobacteriia) rapidly adhered to the eelgrass leaf surface and proliferated in the first two weeks but gradually decreased the relative abundance as the months moved on. On the other hand, the slow-growing microbes (i.e., Cytophagia, Anaerolineae, Thaumarchaeota, and Actinobacteria) became predominant over the eelgrass surface late in the culture experiment (120, 180 days). The fast-growing groups of Gammaproteobacteria and Flavobacteriia appear to be closely related to the initial decomposition of eelgrass, especially the rapid decomposition of leaf-derived biopolymers. In addition, microbial community shifts were significantly correlated with leaf biomass, carbon and nitrogen contents, and C/N ratios.