Contributions of the Radiative, Structural, and Physiological Components of SIF to the SIF-GPP Relationship in a Subtropical Evergreen Mixed Forest.

Solar-induced chlorophyll fluorescence (SIF) is a promising new proxy for global carbon cycle monitoring. Although many studies consider SIF to be linearly correlated with gross primary production (GPP), the relationship between SIF and GPP is jointly influenced by instantaneous radiation, canopy structure, and plant physiological factors, and their complex interactions lead to intricate SIF-GPP dynamics. Current research on SIF and GPP in subtropical evergreen mixed forests remains limited, primarily due to the lack of observational data from forest flux sites. Based on observations from the Dabie Mountain subtropical evergreen forest flux station from 2023 to 2024, we investigated the relative contributions of the radiative, structural, and physiological components of SIF to the SIF-GPP relationship at different temporal scales. The results revealed that: (1) At both seasonal and diurnal scales, SIF effectively tracks the changes in GPP; (2) The radiative component of SIF dominates the SIF-GPP linear relationship, with canopy structural variations driving its seasonal-scale dynamics while physiological response mechanisms reduce the correlation at hourly scales; and (3) During the growing season, as the time scale increased from half-hourly to daily, the SIF-GPP correlation strengthened (R² rising from 0.36 to 0.44), while the radiative component contribution decreased slightly and the physiological component contribution weakened. Understanding the influences of these different factors on the SIF-GPP relationship can contribute to the development of more accurate models for GPP estimation using SIF. [ABSTRACT FROM AUTHOR]