Sugars from woody tissue photosynthesis reduce xylem vulnerability to cavitation

Corresponding author: Niels J. F. De Baerdemaeker

Reassimilation (重新同化) of internal CO2 via woody tissue photosynthesis has a substantial effect on tree carbon income and wood production. However, little is known about its role in xylem vulnerability to cavitation (木质部空穴化) and its implications in drought-driven tree mortality (死亡).

Young trees of Populus nigra (黑杨) were subjected to light exclusion at the branch and stem levels. After 40 d, measurements of xylem water potential (水势), diameter variation and acoustic emission (AE; 声发射) were performed in detached (分离的) branches to obtain acoustic vulnerability curves (脆弱性曲线) to cavitation following bench-top dehydration (台式脱水).

Acoustic vulnerability curves and derived AE50 values (i.e. water potential at which 50% of cavitation-related acoustic emissions occur) differed significantly between light-excluded and control branches (AE50,light-excluded = −1.00 ± 0.13 MPa; AE50,control = −1.45 ± 0.09 MPa; P = 0.007) denoting higher vulnerability to cavitation in light-excluded trees.

通过木质部对植株体内的CO2进行重新同化在树木碳吸收和木材产量方面扮演着重要角色。然而，目前其对于木质部空穴化及干旱驱使的林木死亡的影响还了解不多。本文对黑杨的枝条和茎干进行为期40天的遮光处理，然后对离体的枝条进行木质部水势、直径变异以及声发射的测量，用以获得木质部空穴化后的声音脆弱性曲线。遮光处理与对照的声音脆弱性曲线以及衍生的AE50值（即在50%空穴化声发射时的水势值）呈显著差异，这表明遮光处理下林木更易发生木质部的空穴化。木质部组织的光合作用代表了林木中非结构性的碳水化合物（NSC）另外一种来源，而NSC通过糖介导的机制赋予林木避免木质部的空穴化的能力。栓塞修复和木质部结构的改变并不足以解释观测到的现象，因为处理组相对于对照组在总的AE积累量和基础的木材密度上并未发生变化。本文研究表明木质组织同化可能在压力条件下起稳定纳米气泡作用的木质部表面活性剂的合成上具有重要作用。

通讯：Niels J. F. De Baeqrdemaeker (http://www.plantecology.ugent.be/people/)

doi: 10.1111/nph.14787