ANNOUNCEMENTS
Solar induced chlorophyll fluorescence (SIF) refers to emission by plants whilst they photosynthesise; which is driven by excitation of electrons to higher energy levels and their subsequent return to the ground level after absorbing the photosynthetically active radiation (PAR). SIF, being a narrow radiation band, is detected by several satellites including Global Ozone Monitoring Experiment-2 (GOME-2), Orbiting Carbon Observatory-2 (OCO-2) and Greenhouse Gases Observing Satellite (GOSAT). Gross primary productivity (GPP) quantifies the photosynthetic carbon uptake of plants, which can be estimated using eddy covariance technique. By exploring the linkage between SIF and GPP, the potential of SIF to act as a proxy of photosynthesis can be figured out. In addition, a look at absorbed photosynthetically active radiation (APAR), bulk canopy maximum carboxylation rate at 25 ºC (Vcmax25) and meteorological variables, along with the visualisation of SIF can help in bolstering this hypothesis. APAR refers to the portion of sunlight that is captured and used by plants for photosynthesis. Vcmax25 refers to the maximum rate at which photosynthesis can occur in a canopy of plants under optimal conditions and at a temperature of 25ºC. In the work undertaken here, we have utilised EC flux tower GPP measurements at two vegetations in India, namely the broadleaf deciduous forest in the Kaziranga National Park (KNP) in Assam and a coniferous evergreen forest in the Kosi-Katarmal watershed (KKM) in Uttarakhand. Our findings show linear relationships to exist between SIF and GPP at both these sites. Despite significant discord among the various SIF datasets, the promising replication of the photosynthesis pattern by the sensors points to the high possibility of using these to track photosynthesis. However, there remains a caveat to explore the functional relationships to better decipher these. Overall, we see expected linear relationships between SIF and GPP are maintained during coarser temporal resolutions but at finer scales, it does not, probably owing to the underlying microclimatic variations within the study region.
Keywords: Solar induced chlorophyll fluorescence (SIF), Photosynthesis, Gross primary productivity (GPP), Climate change, Carbon cycle, Forest ecosystems.
