Solar-Induced Chlorophyll Fluorescence as a Potential Proxy for Gross Primary Production and Methane Emission in a Cool-Temperate Bog in Northern Japan

Wetlands play an essential role in the global greenhouse gas budget via carbon dioxide sequestration as well as methane emission. In recent decades, solar-induced chlorophyll fluorescence (SIF) has been recognized as a remotely sensed proxy of gross primary productivity (GPP), which generates substrates for methane production. To examine the suitability of SIF for estimation of these two fluxes, we conducted ground tower-based SIF observation with an ultrafine-resolution spectroradiometer in conjunction with eddy covariance measurement in a cool-temperate bog. The daily SIF retrieved in the red (687 nm) and far-red (760 nm) bands (SIFred and SIFfar-red, respectively) increased nonlinearly with GPP and linearly with absorbed photosynthetically active radiation (APAR). The relatively weak correlation between apparent SIF yield (Phi SIF = SIF/APAR) and light use efficiency implied that both APAR and plant physiology constrained the SIF emission in this wetland. The SIFred/SIFfar-red ratio showed a significant negative relationship with vegetation greenness indices, and the similar seasonal variation in SIFred and SIFfar-red indicated that the SIFred reabsorption effect only weakly influenced the SIFred-GPP relationship. Episodic temporal reduction in the water table did not distinctly influence SIF and Phi SIF. Estimation of the methane emission rate was subtly improved by incorporating SIF, which was substituted for GPP as the methanogenesis substrate, in a multivariable regression analysis together with two environmental factors: soil temperature and water table depth. This study illustrates the potential of both SIFred and SIFfar-red to monitor GPP and to predict methane emission in wetlands. Wetlands play a crucial role in the carbon cycle on Earth, involving both storing carbon and releasing methane. A small energy emission from plants, known as solar-induced chlorophyll fluorescence (SIF), is a recent discovery that serves as a signal for plant productivity. It's a useful tool for tracking plant productivity. This study was conducted in a cool-temperate bog, and we found that daily SIF measurements increased differently with plant growth and sunlight absorption. This suggests that both sunlight and plant health affect SIF in wetlands. The study also showed that SIF measurements could be useful for monitoring plant growth and predicting methane emissions in wetlands. To make these predictions better, we combined SIF with information about the environment, like soil temperature and water depth. Overall, this research highlights the potential of using SIF measurements to keep an eye on plant growth and predict methane emissions in wetlands. Chlorophyll fluorescence in the 687 and 760 nm bands (SIFred and SIFfar-red) has promise as a photosynthesis proxy in temperate bogs The simple canopy structure of the wetland plant community contributed to a weak reabsorption effect of SIFred Methane prediction improved subtly with incorporation of solar-induced chlorophyll fluorescence and environmental factors in a multivariable regression model