Department of Plant Sciences, Horticultural Supply Chains Group, Wageningen University, Wageningen, The Netherlands.
Physiol Plant. 2011 Jun;142(2):157-69. doi: 10.1111/j.1399-3054.2011.01456.x. Epub 2011 Mar 11.
Leaves deep in canopies can suddenly be exposed to increased irradiances following e.g. gap formation in forests or pruning in crops. Studies on the acclimation of photosynthesis to increased irradiance have mainly focused on the changes in photosynthetic capacity (A(max)), although actual irradiance often remains below saturating level. We investigated the effect of changes in irradiance on the photosynthesis irradiance response and on nitrogen allocation in fully grown leaves of Cucumis sativus. Leaves that fully developed under low (50 µmol m⁻² s⁻¹) or moderate (200 µmol m⁻² s⁻¹) irradiance were subsequently exposed to, respectively, moderate (LM-leaves) or low (ML-leaves) irradiance or kept at constant irradiance level (LL- and MM-leaves). Acclimation of photosynthesis occurred within 7 days with final A(max) highest in MM-leaves, lowest in LL-leaves and intermediate in ML- and LM-leaves, whereas full acclimation of thylakoid processes underlying photosystem II (PSII) efficiency and non-photochemical quenching occurred in ML- and LM-leaves. Dark respiration correlated with irradiance level, but not with A(max). Light-limited quantum efficiency was similar in all leaves. The increase in photosynthesis at moderate irradiance in LM-leaves was primarily driven by nitrogen import, and nitrogen remained allocated in a similar ratio to Rubisco and bioenergetics, while allocation to light harvesting relatively decreased. A contrary response of nitrogen was associated with the decrease in photosynthesis in ML-leaves. Net assimilation of LM-leaves under moderate irradiance remained lower than in MM-leaves, revealing the importance of photosynthetic acclimation during the leaf developmental phase for crop productivity in scenarios with realistic, moderate fluctuations in irradiance that leaves can be exposed to.
叶片深处在树冠中，如果发生林窗形成或作物修剪等情况，可能会突然暴露在更高的辐射下。关于光合作用对增强辐射的适应能力的研究主要集中在光合能力（A(max)）的变化上，尽管实际辐射通常仍低于饱和水平。我们研究了光照变化对黄瓜完全生长叶片光合作用光照响应和氮分配的影响。在低（50 µmol m⁻² s⁻¹）或中（200 µmol m⁻² s⁻¹）光照下完全发育的叶片随后分别暴露于中（LM-叶片）或低（ML-叶片）光照或保持在恒定光照水平（LL-和 MM-叶片）。光合作用的适应能力在 7 天内发生，最终 MM-叶片的 A(max)最高，LL-叶片最低，ML-和 LM-叶片居中，而 PSII 效率和非光化学猝灭的类囊体过程的完全适应仅在 ML-和 LM-叶片中发生。暗呼吸与光照水平相关，但与 A(max)无关。所有叶片的光限制量子效率相似。LM-叶片在中等光照下光合作用的增加主要是由氮的导入驱动的，氮仍然以相似的比例分配给 Rubisco 和生物能学，而相对减少了对光捕获的分配。氮的相反反应与 ML-叶片中光合作用的下降有关。LM-叶片在中等光照下的净同化率仍低于 MM-叶片，这表明在叶片发育阶段进行光合作用适应对于在现实中具有适度波动的光照条件下的作物生产力非常重要，因为叶片可能会暴露在这种环境中。
