Measuring mangrove root exudation with sealed cuvettes

Mangroves store substantial carbon, particularly below ground. The release of organic compounds by living roots, known as root exudation, might represent a major contribution to the carbon budgets of mangrove ecosystems. Root exudates influence soil organic matter dynamics, for example, by stimulating the breakdown of stabilized organic carbon. However, traditional sampling tools for measuring root exudation, such as the standard terrestrial cuvette method, fail under the tidal flooding and saline sediment conditions of coastal wetlands. Consequently, below-ground processes in mangrove ecosystems remain understudied and the pathways of photosynthetic carbon transfer to the soils are poorly understood.

The sealed-cuvette method can compare root exudation across species, ecological zones, and seasons and improves understanding of coastal wetland carbon budgets. When combined with fine-root biomass, the measured exudation can be scaled to estimate ecosystem-level carbon fluxes. For example, measurements in Can Gio, Vietnam suggest that exudation represents ~10% of mangrove gross primary productivity. The approach can also be adapted for other wetland ecosystems, such as saltmarshes, and to characterize specific exudate compounds in the cuvette solution to provide insight on rhizospheric processes.