Leaves absorb red and blue light more efficiently than green light. Within a spatially heterogeneous canopy, both the sieve effect and the detour effect contribute to an increase in the absorption of green light relative to that of red and blue light. Such an increase in the relative absorption of green light tends to be intensified with increasing canopy depth. Consequently, the absorption of green light could be comparable to that of red and blue light when the leaf area index of a canopy is sufficiently high. However, there is no field observational evidence to test this hypothesis. We investigated the spectral composition of downward and upward solar radiation at multiple heights within a temperate larch forest and reconstructed light absorption profiles at three representative wavelengths. With increasing depths from the top of the canopy, absorption of red (680 nm) and green light (550 nm) decreased; but the latter decreased more gradually. Consequently, absorption of green light surpassed that of red light after an equilibrium point (e.g., 19.5 m height above the ground at high sun angles under clear skies) was reached. Absorptance of green light by the canopy (0.5–22 m) was 93.3 %, only slightly lower than that of red (95.0 %) and blue light (460 nm, 93.6 %). Moreover, absorption of green light decreased more gradually and the lower part of the canopy absorbed more green light at low sun angles and under overcast skies, in comparison with those at high sun angles under clear skies. Our results demonstrate that forest canopy can efficiently absorb green light. This finding calls for reconsideration on the role of green light in canopy photosynthesis and photomorphogenesis.

中文翻译：

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单一栽培针叶林树冠对绿光的有效吸收

叶子吸收红光和蓝光比绿光更有效。在空间异质冠层内，筛子效应和绕行效应都有助于增加绿光相对于红光和蓝光的吸收。随着树冠深度的增加，绿光相对吸收的这种增加往往会加剧。因此，当冠层的叶面积指数足够高时，绿光的吸收可以与红光和蓝光的吸收相当。然而，没有现场观察证据来检验这一假设。我们研究了温带落叶松森林内多个高度的向下和向上太阳辐射的光谱组成，并重建了三个代表性波长的光吸收剖面。随着树冠顶部深度的增加，红光（680 nm）和绿光（550 nm）的吸收减少；但后者下降得更为缓慢。因此，在达到平衡点（例如，晴朗天空下高太阳角度下距地面 19.5 m 的高度）后，绿光的吸收超过了红光的吸收。冠层（0.5~22 m）对绿光的吸收率为93.3%，仅略低于红光（95.0%）和蓝光（460 nm，93.6%）。此外，与晴朗天空下的高太阳角相比，在低太阳角和阴天下，绿光的吸收逐渐减少，冠层下部吸收了更多的绿光。我们的结果表明森林冠层可以有效吸收绿光。这一发现需要重新考虑绿光在冠层光合作用和光形态发生中的作用。