###### Abstract  
Northern hemisphere evergreen needleleaf forest (ENF) contributes a significant fraction of global water exchange but regional transpiration (T) observation in ENF ecosystems is still challenging. Traditional remote sensing techniques and terrestrial biosphere models reproduce the transpiration seasonality with difficulty, and with large uncertainties. Solar-induced chlorophyll fluorescence (SIF) emission from vegetation correlates to photosynthesis at multiple spatial and temporal scales. However, how SIF links to transpiration of evergreen forest during seasonal transition is unclear. Here, we explored the relationship between canopy SIF and T retrieved from ground observation towers in ENF. We also examined the role of meteorological and soil factors on the relationship between SIF and T. A slow decrease of SIF and T with a fast reduction in photosynthetically active radiation (PAR), air temperature, vapor pressure deficit (VPD), soil temperature and soil water content (SWC) were found in the ENF during the fall transition. The correlation between SIF and T at hourly and daily scales varied significantly among different months (_Pearson correlation coefficient_ = 0.29-0.68, \(p\) < 0.01). SIF and T were significantly linearly correlated at hourly (R\({}^{2}\) = 0.53, \(p\) < 0.001) and daily (R\({}^{2}\) = 0.67, \(p\) < 0.001) timescales in the October. Air temperature and PAR were the major moderating factors for the relationship between SIF and T in the fall transition. Soil water content (SWC) influenced the SIF-T relationship at an hourly scale. Soil temperature and VPD's effect on the SIF-T relationship was evident at a daily scale. This study can help extend the possibility of constraining ecosystem T by SIF at an unprecedented spatiotemporal resolution during season transitions.  
2022130 December 202130 December 20216 January 20  
monthly time scales [12; 13; 14]. However, stomatal conductance and SIF respond to environmental changes at an instantaneous time scale. Therefore, mean daily or weekly SIF and T provide little information about how environmental conditions mediate the dynamic relationship between SIF and T [10; 15]. Analysis of the SIF-T relationships in grassland, broadleaf forest and wheat has shed light on the effects of environmental condition changes on water fluxes and has helped quantify water balance at hourly and daily scales [16; 17; 18]. To improve estimates of T, SIF and its link to T at higher temporal resolution requires refining in ENF. The impacts of meteorological and soil factors on the SIF-T relationship in the seasonal transition of evergreen forest ecosystems require further investigation [19].  
Using canopy SIF observations and T separated by synchronous half-hour eddy flux ET of ENF, we (i) investigated the dynamics of T, SIF, meteorological and soil factors in the fall transition, (ii) quantified the SIF and T correlation at hourly and daily scales during the fall transition, and (iii) investigated the effects of meteorological and soil factors on the canopy SIF-T relationship. Our results will extend the possibility of constraining ecosystem T by SIF during seasonal transitions and prompt more precise T estimations at an unprecedented spatiotemporal resolution.