Coastal blue carbon systems such as mangroves show the potential to mitigate the climate change crisis. However, the carbon (C) sequestration capacity of natural ecosystems characterized by temporal and spatial variations, which results in the uncertainty for reaching the goal of net-zero carbon emissions by using blue carbon and other natural-based solutions to achieve. Over 60-90% of carbon stored in mangrove ecosystems was allocated in sediments. Natural or artificial disturbances such as droughts or deforestation may accelerate the decomposition of labile organic matter (LOM) by microorganisms, resulting in the decline of long-term C storage in sediments. The refractory organic matters (ROM), which is not easily utilized by microorganisms, are more stable and thus benefit the long-term blue C storage. Therefore, ROM acts as the cornerstone that shape the carbon sequestration of the blue carbon system.

    Based upon the microbial enzyme latching mechanism (ELM), this grant proposal explores the effectiveness of using biochar amendments produced from mangrove litters for soil carbon farming, by increasing the abundance of target microbe population in mangrove sediments. Enzyme activities of the microbe increase the refractory of organic matter, and thus enhance the carbon level and stability in mangrove sediments. Major research goals include: (1) to identify the key microbe population and their functional gene and metabolic pathways that drives the phenol oxidase activities (such as tyrosinase, laccase and peroxidase) by field investigations. (2) to analyze the effect of biochar with different physchemical properties (such as pore size, specific surface area, iodine value and pH value, etc.) on the microbial community, phenol oxidation enzyme activity, and thus the changes in total carbon (TC) content and ROM ratio in the sediment by using the "carbon farming" mesocosm experiments. (3) To test if the ELM established in the 2nd year could work properly in the field mangrove ecosystems to describe the observed responses in the carbon storage and transformation, lateral carbon export and CO2 release under biochar amendment applications.

This project investigates the interaction between the sediment carbon storage in mangrove systems with different root structures between contrasting seasonal rainfall patterns. The developed biochar amendment and the mathematical model of lateral C export can be applied for patents or technology transfer. Research findings contribute to algorithm of coastal blue carbon investigation as well as the knowledge basis for developing the coastal blue carbon trading markets.