Assessment of the relationship between solar-induced fluorescence and environmental parameters for various ecosystems in the south of Western Siberia according to reanalysis and satellite observations

Gross primary production (GPP) is a key characteristic of the global carbon balance. Currently, approaches based on remote sensing data from space are widely used to obtain information on GPP at the regional and global scale. The first group of methods is based on the application of established statistical dependencies between GPP and various indirect plant characteristics, such as vegetation indices. The second approach is based on the use of an energy redistribution model, which allows linking GPP with photo synthetically active radiation (PAR) through empirically selected coefficients. The third approach to estimating GPP from satellite data is based on the use of information on solar-induced fluorescence (SIF, solar-induced fluorescence), which is the plants’ own radiation in the range of 600-800 nm, occurring within a few nanoseconds after the absorption of sunlight by chlorophyll. Despite the fact that fluorescence accounts for only 1-2% of incoming PAR, recording a small signal from the satellite is possible due to the fact that the spectral SIF peaks (680 and 740 nm) are located near the Fraunhofer lines (687 and 760 nm). The advantages of using this approach are its physical justification and sensitivity to plant stress.

Based on numerous previous studies of the GPP-SIF relationship, it has been shown that on a global scale, over long (at least a month) time intervals, a virtually linear relationship is observed between these characteristics. However, on a regional scale of individual ecosystems, the relationship between SIF and GPP can vary significantly depending on environmental conditions, which is especially relevant for regions with high natural heterogeneity - such as the south of Western Siberia.

This paper examines the territory of Western Siberia, including the Altai, Kemerovo, Novosibirsk, Omsk and Tomsk Regions. To identify key environmental parameters that affect their photosynthetic activity, the data from ERA-5 reanalysis and various satellite instruments were used: air temperature at a level of 2 m, temperature of the upper soil layer, amount of precipitation, water vapor pressure deficit, vegetation indices, proportion of PAR absorbed by plants, direct and diffuse PAR fluxes and soil moisture. The monthly values of the above characteristics are considered during the vegetation period of the studied region (May-September) from 2018 to 2024. All information on environmental parameters is reduced to an unified spatial resolution of 0.05°.

To assess the relationship between SIF, reconstructed from the TROPOMI sensor data (Sentinel-5P satellite), and the above characteristics, at this stage of the research, the Pearson correlation coefficients and the level of their statistical significance, as well as the time shifts of the cross-correlation for both the region as a whole and individual administrative regions of the south of Western Siberia, were calculated. Analysis of the results indicated that SIF in the territories under consideration is most closely related to vegetation indices and the proportion of PAR absorbed by plants. It was found that the temperature regime in the studied region is more significant for the photosynthetic activity of ecosystems compared to the humidity parameters.

The work was carried out within the framework of the state assignment of IAO SB RAS.