Organic matter composition regulates residual potential of organic carbon of the seagrass Zostera marina L. during its decomposition process in seawater

Although the seagrass Zostera marina L. (Z. marina) is expected to significantly contribute to environmental carbon dynamics, the residual potential of organic carbon (Corg) in this plant during its decomposition process in seawater remains insufficiently understood. In this study, the factors regulating this potential were examined by evaluating Z. marina decomposition in seawater and conducting a multiple regression analysis on data from the experiment as well as the original plant organic matter composition. The residual ratio during the decomposition experiment (RDEC) of carbon in Z. marina for 111 days ranged from 0.30 to 0.84 (n = 16), and the variation resulted from differences in the sampling season of this plant. Regression analysis was conducted to explain the RDEC of carbon using the RDEC of nitrogen, concentrations of carbon, nitrogen, HCl-extractable Corg and nitrogen, contributions of carbohydrate (CCAR) of total and non-structural fractions and lipid (CLIP) to carbon concentration. The RDEC of carbon was most adequately fitted using a multiple regression including three parameters, carbon concentration, CLIP, and CCAR of total carbohydrate with a significant determination coefficient. The former two parameters (carbon concentration and CLIP) have negative coefficients, indicating that these parameters correspond to bacterially available Corg in Z. marina in the regression analysis. The latter parameter (CCAR of total carbohydrate) shows a positive coefficient that indicates recalcitrant Corg in the regression. Parameters related to nitrogen were not included in the regression formula, although this element is reportedly an important parameter regulating the environmental decomposition rate of Corg. Finally, we suggested that total carbon, carbohydrate, and lipid are especially important factors to regulate the environmental residual potential of Z. marina Corg among organic components of this plant.