[A-CG41] Coastal Ecosystems -2. Coral reefs, seagrass and macroalgal beds, and mangroves

[ACG41-P09] Evaluation of the effect of differences in nitrogen loading on the chemical composition and decomposition characteristics of eelgrass(Zostera marina).

*Toru Miyata¹, Yu Umezawa¹, Takunari Ida¹, Yoshiki Horikawa¹, Makoto Watanabe¹, Shigeki Wada², Masahiro Nakaoka³, Tomohiro Kuwae⁴ (1.Tokyo University of Agriculture and Technology, 2.University of Tsukuba, 3.Hokkaido University, 4.Port and Airport Research Institute)

Keywords:Blue carbon, Nitrogen load, Refractory organic carbon, Eelgrass(Zostera marina)

Nitrogen is one of the elements that can limit the primary production of plants, therefore nitrogen supply potentially affects coastal primary production. On the other hand, it is known that some secondary metabolites such as phenolic compounds that are not directly involved in growth and catabolism such as photosynthesis, respiration, and assimilation act as protective compounds against predators and pathogens. Some report that the abundance of these substances varies with the supply of nitrogen. Thus, differences in nitrogen supply may contribute not only to the growth of these plants, but also to the biodegradation properties of the plant.

In this study, we focused on the eelgrass (Zostera marina) widely distributed in the coastal area of Japan, and examined the followings, potential effects of the nitrogen supply in the coastal area on the function as “blue carbon”.

1) Possibility of measuring nitrogen content in eelgrass leaf using portable nitrogen meter

The measured values of multiple portable nitrogen meters for land herbs were compared with the chlorophyll content and actual nitrogen content of the eelgrass Z. marina. Conditions that enable us to effectively estimate the nitrogen content of eelgrass are discussed.


2) Relationship between nitrogen content and the amount of structural and repellent substances in the eelgrass leaves

The amount of structural substances and repellent substances of eelgrass plants were evaluated using chemical (KOH, NaClO₂, and NaOH) treatments and Folin-ciocalteu method, respectively, and compared with the nitrogen content.


3)Evaluation of the decomposition characteristics of eelgrass in the different environmental conditions

Effects of nitrogen load on the decomposition characteristics of eelgrass were evaluated by monitoring in the different environmental conditions.