## 1 Introduction
[45] quantified the effects of high-temperature stress on canopy photosynthesis and demonstrated that SIF responded sensitively to the physiological down-regulation of GPP based on a high-temperature experiment in a soybean field. [PERSON] et al. [46] explored the relationship between SIF and GPP in a temperate evergreen needleleaf forest during the fall transition, and they found that LUE reached saturation at high air temperatures, whereas the chlorophyll fluorescence yield (\(\phi_{F}\)) did not saturate. In addition, [PERSON] et al. [9] reported that both SIF and GPP in a boreal evergreen needle forest (BoENF) tracked with each other in a consistent, dynamic fashion in response to low temperature. Furthermore, they pointed out that, compared to traditional vegetation-index-based methods, SIF--being directly related to needle physiology--has the unique ability to capture GPP seasonality. It should be pointed out that the photochemistry quantum efficiency of PS II is not significantly affected by temperature at low light intensity, and that the temperature has a direct effect on the kinetics of enzymes involved in carbon reactions [47]. Therefore, different light, moisture, or temperature conditions likely affect the SIF-GPP relationship to some degree [3]. Temperature has large effect on photosynthesis, and the effects of temperature on photosynthetic activities vary with the plant species [35; 48]. The response of photosynthesis to low-growth-temperature conditions depends largely on the original distribution of the species [49]. Plants can be classified as species adapted to cold environmental conditions and species adapted to warm conditions (e.g., tropical or sub-tropical conditions). Some studies have reported that there is a striking difference between those two groups, considering the effect of low temperature on photoinhibition [50; 51]. However, to date, the influence of low temperature on the SIF-GPP relationship for different PFTs has not been well-explored [9; 21; 52]. Launched on 13 October 2017, the TROPOspheric Monitoring Instrument (TROPOMI) on board the Copernicus Sentinel-5 Precursor satellite (S5P) is the first of the atmospheric composition Sentinels, which has relatively fine temporal and spatial resolution [25; 53]. Due to its relatively fine resolution and its ability to take more spatially continuous measurements than other SIF-related satellites, the SIF retrieved from TROPOMI has been widely used to explore the seasonal variations in GPP, enhancing its ability to detect environmental stresses [14; 54]. Tower-based continuous observations also provide reliable data for the study of diurnal and seasonal changes in SIF, as well as its relationship with GPP under various environmental conditions [7; 9; 55; 56; 57]. Therefore, continuous reliable satellite and tower-based data were considered to support our study regarding the effects of temperature on the SIF-GPP relationship for different PFTs. In this study, the influences of low temperature on the SIF-GPP relationship were assessed using both satellite and tower-based observations. We investigated the relationship between the GPP/SIF ratio and temperature for different PFTs in order to address the following specific issues: (1) What are the differences in the SIF-GPP relationship under different growth temperature conditions? (2) How do these relationships vary between PFTs? and (3) What is the potential influence of low temperatures on the GPP/SIF ratio?