Evaluation of carbon storage process into marine sediment based on new optical technology: non-destructive measurement of belowground production and degradation of seagrass

本项目旨在采用陆地生态系统研究中开发的非破坏性光学测量技术，建立一种定量估计海草地下部分产量和退化率的方法。首先，利用室内和室外水族箱进行了鳗草的水产养殖实验，使用光学扫描仪以非破坏性的方式定期监测根茎和根系的生长。结果表明，根系生物量约占总生物量的10%。3%，但整个地下部分占14%，是沉积物中碳的重要汇。其次，在可见光和近红外波段（446- 894 nm）采集了不同年龄海草地下部分的高光谱反射率图像。14-220日龄的生长降低了细根的反射率，主要是在可见光区。死亡的海草部分在整个光谱区都表现出低反射率。通过建立估算模型，利用光谱反射率在12-37%的误差范围内（rRMSE）预测了根龄和碳、氮浓度。综上所述，海草的地下生产具有明显的季节性变化，并对蓝碳储量有贡献。首次证明了利用光谱反射率图像可以无损地确定地下部分的年龄和碳氮平衡。

This project aims to establish a method for quantitatively estimating production and degradation rate of belowground parts of seagrass by adopting non-destructive optical measurement techniques developed in terrestrial ecosystem research. Firstly, an aquaculture experiment of eelgrass was conducted using indoor and outdoor aquaria to periodically monitor growth of rhizomes and roots using an optical scanner in non-destructive manner. It was revealed that the root biomass accounted ca. 3 % of a total biomass of eelgrass, but the whole belowground parts occupied 14% and contributed significantly as a sink of carbon in sediment. Secondarily, hyper spectral reflectance images of different-aged belowground parts of seagrass were captured at visible and near-infrared spectral region (446-894nm). The increase in age from 14-220 days reduced the reflectance of live fine roots mainly at visible spectral region. The dead seagrass parts showed low reflectance at whole spectral region. By developing the estimation model, root age and concentrations of carbon and nitrogen were predicted by the spectral reflectance at the error of 12-37% (rRMSE). In conclusion, it was shown that seagrass belowground production has clear seasonal cycle and contributes to blue carbon storage. It was firstly demonstrated that age of belowground parts, carbon and nitrogen balance can be determined non-destructively using spectral reflectance images.