Far-red photons (701-750 nm) are abundant in sunlight but are considered inactive for photosynthesis and are thus excluded from the definition of photosynthetically active radiation (PAR; 400-700 nm). Several recent studies have shown that far-red photons synergistically interact with shorter wavelength photons to increase leaf photochemical efficiency. The value of far-red photons in canopy photosynthesis has not been studied. Here, we report the effects of far-red photons on single leaf and canopy photosynthesis in 14 diverse crop species. Adding far-red photons (up to 40%) to a background of shorter wavelength photons caused an increase in canopy photosynthesis equal to adding 400-700 nm photons. Far-red alone minimally increased photosynthesis. This indicates that far-red photons are equally efficient at driving canopy photosynthesis when acting synergistically with traditionally defined photosynthetic photons. Measurements made using LEDs with peak wavelength of 711, 723, or 746 nm showed that the magnitude of the effect was less at longer wavelengths. The consistent response among diverse species indicates that the mechanism is common in higher plants. These results suggest that far-red photons (701-750 nm) should be included in the definition of PAR.

中文翻译：

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远红光子具有与传统光合光子相同的效率：重新定义光合有效辐射的含义。

远红光子（701-750 nm）在阳光下充足，但被认为对光合作用无效，因此被排除在光合有效辐射（PAR; 400-700 nm）的定义之外。最近的一些研究表明，远红光子与较短波长的光子协同作用，以提高叶片的光化学效率。尚未研究远红光子在冠层光合作用中的价值。在这里，我们报告了远红外光子对14种不同农作物物种的单叶和冠层光合作用的影响。在较短波长光子的背景中添加远红光子（最多40％）会导致冠层光合作用的增加，等同于添加400-700 nm光子。单独的远红色光合作用最少。这表明当与传统定义的光合光子协同作用时，远红光子在驱动冠层光合作用方面同样有效。使用峰值波长为711、723或746 nm的LED进行的测量表明，在更长的波长处，影响的大小较小。不同物种之间的一致反应表明该机制在高等植物中很常见。这些结果表明，PAR的定义中应包括远红光子（701-750 nm）。