Laboratory of Plant Ecology, Faculty of Bioscience Engineering, Ghent University, Ghent, Belgium.
Plant Cell Environ. 2020 Apr;43(4):981-991. doi: 10.1111/pce.13711. Epub 2020 Jan 23.
A substantial portion of locally respired CO in stems can be assimilated by chloroplast-containing tissues. Woody tissue photosynthesis (P ) therefore plays a major role in the stem carbon balance. To study the impact of P on stem carbon cycling along a gradient of water availability, stem CO efflux (E ), xylem CO concentration ([CO ]), and xylem water potential (Ψ ) were measured in 4-year-old Populus tremula L. trees exposed to drought stress and different regimes of light exclusion of woody tissues. Under well-watered conditions, local P decreased E up to 30%. Axial CO diffusion (D ) induced by distant P caused an additional decrease in E of up to 25% and limited xylem [CO ] build-up. Under drought stress, absolute decreases in E driven by P remained stable, denoting that P was not affected by drought. At the end of the dry period, when transpiration was low, local P and D offset 20% and 10% of stem respiration on a daily basis, respectively. These results highlight (a) the importance of P for an adequate interpretation of E measurements and (b) homeostatic P along a drought stress gradient, which might play a crucial role to fuel stem metabolism when leaf carbon uptake and phloem transport are limited.
大量由茎部本地呼吸产生的 CO 可被含有叶绿体的组织同化。因此，木质部组织光合作用（P）在茎部碳平衡中起着主要作用。为了研究光合作用（P）对水分可利用性梯度下茎部碳循环的影响，我们对 4 年生欧洲山杨（Populus tremula L.）树木的茎部 CO 逸出（E）、木质部 CO 浓度（[CO ]）和木质部水势（Ψ）进行了测量，这些树木经历了干旱胁迫和不同的木质部组织遮光处理。在水分充足的条件下，局部光合作用（P）降低了 E 达 30%。远距离光合作用（P）引起的轴向 CO 扩散（D）导致 E 进一步降低了 25%，并限制了木质部[CO ]的积累。在干旱胁迫下，由光合作用（P）驱动的 E 的绝对减少保持稳定，这表明光合作用（P）不受干旱影响。在干燥期结束时，当蒸腾作用较低时，本地光合作用（P）和 D 分别抵消了茎呼吸的 20%和 10%，每天都有这种情况发生。这些结果突出了（a）光合作用（P）对于充分解释 E 测量的重要性，以及（b）在干旱胁迫梯度上的光合作用（P）的自衡性，这可能在叶片碳吸收和韧皮部运输受到限制时，对为茎部代谢提供燃料起着关键作用。
