Robe W E, Griffiths H
Department of Biology, The University, NE1 7RU, Newcastle upon Tyne, UK.
Windermere Laboratory, Institute of Freshwater Ecology, The Ferry House, Far Sawrey, LA22 OLP, Ambleside, Cumbria, UK.
Oecologia. 1990 Nov;85(1):128-136. doi: 10.1007/BF00317353.
The submersed aquatic macrophyte Littorella uniflora was grown under 50 and 300 μmol m s photosynthetically active radiation (PAR) (low and high PAR regimes) but identical sediment CO supply (1.0 mol m). The interactions between plant morphology, whole plant CO and O exchange, CAM activity, [CO] and [O] have been investigated in comparison with in vitro CO and PAR response characteristics (using 1 mm leaf sections). In terms of morphology, high-PAR-grown plants were smaller and leaves contained less chlorophyll, although root growth was proportionally larger. Gas exchange fluxes over roots and shoots of intact plants were similar in direction under the two PAR regimes, with the majority of CO uptake via the roots. Photosynthetic O evolution from intact plants was greater in high-PAR-grown L. uniflora (2.18 compared with 1.49 μmol Og fresh weight h for the low PAR regime). Although net daytime CO uptake was similar for both PAR regimes (0.79 and 0.75 μmol g fwt h), net dark CO uptake was at a higher rate (0.92 compared with 0.52 μmol CO g fwt h), and dark fixation (as malic acid) was threefold greater in high PAR plants (ΔH 117 compared with 42 μmol H g fwt). Comparison of dark CO uptake with dark fixation suggested that much of the CO fixed at night and regenerated during the day may be respiratory in origin (60% low PAR plants, 71% high PAR plants). Regeneration of CO from CAM could account for 62% of daytime CO supply in low PAR plants and 81% in high PAR plants. [CO] values (ranging from 0.42 to 1.03 mol m) were close to or above the concentration required to saturate photosynthesis in vitro (0.5 mol m) under both PAR regimes, and combined with the low [O] (2.6-4.3 mol m) should have suppressed photorespiration. However, PAR inside leaves would have been well below the in vitro light saturation requirement (850-1000 μmol m s for both treatments). Thus PAR rather than CO supply appeared to limit photosynthesis even in high PAR grown plants, and CAM appears to have an important role in the regulation of CO supply for photosynthesis in response to variation in light regime.
沉水水生植物单花水麦冬在光合有效辐射（PAR）为50和300 μmol m² s²（低PAR和高PAR条件）下生长，但沉积物CO供应相同（1.0 mol m²）。与体外CO和PAR响应特征（使用1毫米叶片切片）相比，研究了植物形态、整株植物CO和O交换、景天酸代谢（CAM）活性、[CO₂]和[O₂]之间的相互作用。在形态方面，高PAR条件下生长的植物较小，叶片叶绿素含量较低，尽管根系生长相对较大。在两种PAR条件下，完整植株根和地上部分的气体交换通量方向相似，大部分CO通过根系吸收。高PAR条件下生长的单花水麦冬完整植株的光合O释放量更大（低PAR条件下为1.49 μmol O₂ g鲜重 h，高PAR条件下为2.18 μmol O₂ g鲜重 h）。尽管两种PAR条件下白天的净CO吸收量相似（分别为0.79和0.75 μmol CO₂ g干重 h），但夜间的净CO吸收速率更高（分别为0.92和0.52 μmol CO₂ g干重 h），并且高PAR植株中暗固定（以苹果酸形式）是低PAR植株的三倍（分别为117和42 μmol H⁺ g干重）。夜间CO吸收与暗固定的比较表明，夜间固定并在白天再生的大部分CO可能源于呼吸作用（低PAR植株为60%，高PAR植株为71%）。CAM再生的CO₂在低PAR植株中可占白天CO₂供应的62%，在高PAR植株中可占81%。在两种PAR条件下，[CO₂]值（范围为0.42至1.03 mol m³）接近或高于体外光合作用饱和所需浓度（0.5 mol m³），并且与低[O₂]（2.6 - 4.3 mol m³）相结合应能抑制光呼吸。然而，叶片内部的PAR远低于体外光饱和要求（两种处理均为850 - 1000 μmol m² s²）。因此，即使在高PAR条件下生长的植物中，PAR而非CO₂供应似乎限制了光合作用，并且CAM在响应光照条件变化调节光合作用的CO₂供应方面似乎具有重要作用。
