Electron transport rate (ETR), estimated from chlorophyll fluorescence, is a widely-used indicator of photosynthetic activity. However, net photosynthetic CO₂ assimilation rate (A) does not linearly correlate with ETR when the fraction of electron partitioning into photosynthesis and photorespiration changes under fluctuating environmental conditions (CO₂, light, temperature and soil moisture).

Here, we propose a practical approach to estimate A based on ETR with integration of stomatal conductance (g_s) and leaf temperature, taking intercellular CO₂ concentration (C_i)- and temperature-dependent electron partitioning into account.

A estimated with the present approach was in good agreement with A measured under i) various CO₂ concentrations and light intensities in seedlings of Japanese beech and Japanese white birch, and ii) under 400 and 800 μmol mol⁻¹ CO₂ and temperatures of 15–40 °C, and iii) in progress of drought stress after a water withholding in seedlings of Japanese white birch. Furthermore, canopy-level CO₂ uptake could be estimated based on the spectroscopic and flux observations over a Japanese beech stand, under a wide range of environmental conditions.

The present approach is advantageous because it does not require biochemical information, such as the maximum rates of Rubisco carboxylation and electron transport, providing a more forward approach to estimate terrestrial carbon flux through remote sensing approaches.

根据叶绿素荧光估计的电子传输速率（ETR）是光合作用活动的一种广泛使用的指标。然而，当电子分配进入光合作用和光呼吸的比例在变化的环境条件（CO ₂，光，温度和土壤湿度）下发生变化时，净光合作用的CO ₂同化率（A）与ETR线性不相关。

在这里，我们提出了一种基于ETR的A估算方法，其中考虑了细胞间CO ₂浓度（C _i）和依赖温度的电子分配，并结合了气孔导度（g _s）和叶片温度。

本方法的估计值与在以下条件下测得的A高度吻合：i）日本山毛榉和日本白桦树苗中的各种CO ₂浓度和光强度，以及ii）在400和800μmolmol ^-1 CO ₂和温度为15的条件下–40°C，以及iii）在日本白桦树种的水分滞留后，干旱胁迫正在进行。此外，可以基于在各种环境条件下在日本山毛榉林分上的光谱和通量观测结果来估算冠层水平的CO ₂吸收。

本方法是有利的，因为它不需要生化信息，例如Rubisco羧化反应和电子传输的最大速率，从而提供了一种更先进的方法来通过遥感方法估算陆地碳通量。