Department of Horticulture, Michigan State University, East Lansing, Michigan, United States of America.
PLoS One. 2024 Nov 15;19(11):e0313084. doi: 10.1371/journal.pone.0313084. eCollection 2024.
Despite being outside of the traditionally defined photosynthetically active radiation (PAR) waveband (400-700 nm), far-red (FR; 700-799 nm) light can increase photosynthesis and induce shade-avoidance responses, which increases light interception and thus, whole-plant growth. However, it is unclear how the promotion of growth from FR light depends on PAR wavebands and specifically how the substitution of red light (600-699 nm) with green light (500-599 nm) influences the efficacy of FR light on increasing shoot biomass accumulation. To determine this, we grew red- and green-leaf lettuce (Lactuca sativa) at a fixed total photon flux density (PFD) with 12 different fractions of red, green, and FR light and the same PFD of blue (400-499 nm) light. We postulated that decreasing the red:FR by substituting FR light for green light, red light, or both would increase shoot fresh mass (FM) until a fraction beyond which growth (but not leaf area) would begin to decrease. Indeed, the substitution of red with FR light increased the leaf area of both cultivars, but FM was greatest under an FR fraction [FR/(R+FR)] of approximately 0.25. Under the greatest FR PFD, FM was similar to lettuce grown without FR light, despite having greater leaf surface area for light interception. Green light had less of an effect on leaf expansion and FM than FR light, and plant diameter and leaf area of red-leaf 'Rouxai' were the greatest when green light fully replaced red light at the highest FR PFD. We conclude that under a modest light intensity and blue PFD, a spectrum that includes up to 25% of far-red photons can increase leaf area and biomass accumulation. While leaf area may continue to increase at higher far-red fractions, fresh mass does not, and plant quality begins to deteriorate.
尽管远红光（FR；700-799nm）不在传统定义的光合有效辐射（PAR）波段（400-700nm）内，但它可以增加光合作用并诱导避荫反应，从而增加光的捕获，进而增加整个植物的生长。然而，目前尚不清楚 FR 光促进生长的机制取决于 PAR 波段，特别是用绿光（500-599nm）替代红光（600-699nm）如何影响 FR 光增加茎生物量积累的效果。为了确定这一点，我们在固定的总光子通量密度（PFD）下，用 12 种不同比例的红、绿和 FR 光以及相同的蓝（400-499nm）光生长红色和绿色生菜（Lactuca sativa）。我们假设，通过用 FR 光替代红、绿光或两者的组合来减少红：FR 比例，会增加茎的鲜重（FM），直到超过某一比例后生长（但不是叶面积）开始减少。事实上，用 FR 光替代红光增加了两个品种的叶面积，但在 FR 比例（FR/（R+FR））约为 0.25 时，FM 最大。在最大 FR PFD 下，FM 与没有 FR 光的生菜相似，尽管有更大的叶片表面积用于光捕获。绿光对叶片扩展和 FM 的影响小于 FR 光，当绿光在最高 FR PFD 下完全替代红光时，红生菜‘Rouxai’的植株直径和叶面积最大。我们的结论是，在适度的光强度和蓝 PFD 下，包含高达 25%远红光光子的光谱可以增加叶面积和生物量积累。虽然叶面积可能会在更高的远红光比例下继续增加，但鲜重不会增加，植物品质开始恶化。
