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

Abstract

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 (SIF_red and SIF_far-red, respectively) increased nonlinearly with GPP and linearly with absorbed photosynthetically active radiation (APAR). The relatively weak correlation between apparent SIF yield (ΦSIF = SIF/APAR) and light use efficiency implied that both APAR and plant physiology constrained the SIF emission in this wetland. The SIF_red/SIF_far-red ratio showed a significant negative relationship with vegetation greenness indices, and the similar seasonal variation in SIF_red and SIF_far-red indicated that the SIF_red reabsorption effect only weakly influenced the SIF_red–GPP relationship. Episodic temporal reduction in the water table did not distinctly influence SIF and ΦSIF. 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 SIF_red and SIF_far-red to monitor GPP and to predict methane emission in wetlands.