Global Change Research Institute of the Czech Academy of Sciences, Bělidla 986/4a, 603 00 Brno, Czech Republic.
Global Change Research Institute of the Czech Academy of Sciences, Bělidla 986/4a, 603 00 Brno, Czech Republic.
Sci Total Environ. 2023 Nov 10;898:166386. doi: 10.1016/j.scitotenv.2023.166386. Epub 2023 Aug 18.
We conducted year-long measurements of the photochemical reflectance index (PRI) and solar-induced fluorescence in the OA oxygen band (SIFA) at a Norway spruce forest and a European beech forest to study relationships of these remote sensing variables to photosynthesis by trees in grown forest stands. Measured PRI and SIFA values were linked to changes in forest gross primary productivity (GPP) and light-use efficiency (LUE). Changes in the shadow fraction (α) within tree crowns influenced PRI and fluorescence signals. In the spruce forest, the quantum yield of SIFA (FYSIFA) decreased around midday together with photosynthesis and GPP. Such decreases in FYSIFA were accompanied by an increase in the α. In the beech forest, we detected an increase in FYSIFA together with a decrease in α in the afternoon hours. The overall sensitivity of PRI to LUE was variable according to the season, presumably influenced by complex changes in photosynthetic pigments. PRI and FYSIFA showed weak correlations with canopy LUE; however, when considered together, the correlation was strengthened (R was 0.63 and 0.34 in spruce and beech forest, respectively). Our model predicting LUE dynamics includes a diurnal minimum of PRI and canopy α to make allowances for seasonal changes in photosynthetic pigments and for diurnal variability of the shadow fraction in forests. The incorporation of these correcting factors allowed us to estimate LUE at R = 0.68 (spruce) and 0.53 (beech). The modeling equations appeared sensitive to the absorbed photosynthetically active radiation (APAR), but less sensitive to the GPP of these forests. Substituting pigments correction with introducing differential PRI (ΔPRI) into the model did not significantly improve the LUE estimation across the season. Our results show that the joint use of PRI and fluorescence improves LUE and GPP estimation accuracy in both daily and seasonal observations.
我们在挪威云杉林和欧洲山毛榉林进行了为期一年的光化学反射指数（PRI）和太阳诱导荧光在 OA 氧带（SIFA）的测量，以研究这些遥感变量与林分中树木光合作用的关系。测量的 PRI 和 SIFA 值与森林总初级生产力（GPP）和光能利用效率（LUE）的变化有关。树冠内阴影分数（α）的变化影响 PRI 和荧光信号。在云杉林中，SIFA 的量子产率（FYSIFA）在中午时分与光合作用和 GPP 一起下降。这种 FYSIFA 的减少伴随着 α 的增加。在山毛榉林中，我们发现下午几小时内 FYSIFA 增加，α 减少。PRI 对 LUE 的整体敏感性随季节而变化，可能受光合色素复杂变化的影响。PRI 和 FYSIFA 与冠层 LUE 的相关性较弱；然而，当一起考虑时，相关性得到加强（云杉林和山毛榉林的 R 分别为 0.63 和 0.34）。我们预测 LUE 动态的模型包括 PRI 和冠层 α 的日最小值，以适应光合色素的季节性变化和森林中阴影分数的日变化。这些校正因子的纳入使我们能够以 R 分别为 0.68（云杉）和 0.53（山毛榉）的精度来估计 LUE。该模型对吸收的光合有效辐射（APAR）敏感，但对这些森林的 GPP 不太敏感。用模型中引入的差分 PRI（ΔPRI）代替色素校正，并没有显著提高整个季节的 LUE 估计精度。我们的结果表明，PRI 和荧光的联合使用提高了日观测和季节观测中 LUE 和 GPP 的估计精度。
