欧亚国际

综述

与叶片相比，木质组织中的光合作用对水分缺乏的敏感性较低，因此，木质组织光合作用（Pwt）可能是缓解干旱胁迫的关键碳源。为了评估木质组织光合作用（Pwt）对树木耐旱性的影响，对4米高干旱胁迫下的杨树（Populus tremula）的木质组织进行了全株遮光处理，以抑制木质组织光合作用（Pwt）。

监测木质部水势（ψ木质部）、树液流（FH2O）、叶片净光合作用（Pn，l）、茎直径变化（DD）、茎内声发射（AEs）和非结构性碳水化合物浓度（NSC），以全面评估整个树木水平上的水和碳关系。

在水分充足的条件下，木质组织光合作用（Pwt）保持了较高的ψ木质部水平，降低了FH2O，对[NSC]没有影响。干旱条件下，不受光照影响的树木的ψ木质部、FH2O和Pn、l迅速下降，与枝条木质部淀粉浓度降低一致。此外，DD、FH2O和AEs的亚日模式密切相关，这表明体内AEs不仅可以告知栓塞事件，还可以告知干细胞水池的电容性释放和补充。

结果表明了Pwt在干旱条件下维持木质部水力完整性和维持NSC池以限制木质部张力增加方面的重要性。

Woody tissue photosynthesis delays drought stress in Populus tremula trees and maintains starch reserves in branch xylem tissues

Summary

Photosynthesis in woody tissues (Pwt) is less sensitive to water shortage than in leaves,hence, Pwt might be a crucial carbon source to alleviate drought stress. To evalsuate the impact of Pwt on tree drought tolerance, woody tissues of 4-m-tall drought-stressed Populus tremula trees were subjected to a light-exclusion treatment across the entire plant to inhibit Pwt.

Xylem water potential (Ψxylem), sap flow (FH2O), leaf net photosynthesis (Pn,l), stem diameter variations (DD), in vivo acoustic emissions in stems (AEs) and nonstructural carbohydrate concentrations ([NSC]) were monitored to comprehensively assess water and carbon relations at whole-tree level.

Under well-watered conditions, Pwt kept Ψxylem at a higher level, lowered FH2O and had no effect on [NSC]. Under drought, Ψxylem, FH2O and Pn,l in light-excluded trees rapidly decreased in concert with reductions in branch xylem starch concentration. Moreover, sub-daily patterns of DD, FH2O and AEs were strongly related, suggesting that in vivo AEs may inform not only about embolism events, but also about capacitive release and replenishment of stem water pools.

Results highlight the importance of Pwt in maintaining xylem hydraulic integrity under drought conditions and in sustaining NSC pools to potentially limit increases in xylem tension.

Fig. 1 Midday xylem water potential (Ψxylem) (a), cumulative daily sap flow (FH2O) (b), mean daily pattern of FH2O (c), cumulative daily leaf photosynthesis (Pn,l) (d), mean daily pattern of Pn,l (e), stem diameter variation (DD) (f) and mean daily pattern of DD (g) in aspen trees. Trees were subjected to a wellwatered regime (WET) and a combination of well-watered and light-exclusion of woody tissues (WETLE). Asterisks indicate statistical differences between treatments (P < 0.05) and error bars and bands represent SE.

Fig. 2 Midday xylem water potential (Ψxylem) (a), cumulative daily sap flow (FH2O) (b), mean daily pattern of FH2O (c), cumulative daily leaf photosynthesis (Pn,l) (d), mean daily pattern of Pn,l (e), stem maximum daily shrinkage (MDS) (f) and mean daily pattern of stem diameter variation (DD) (g) in aspen trees.Trees were subjected to a well-watered regime (WET), drought stress (DRY) and a combination of drought stress and light-exclusion of woody tissues (DRYLE). Asterisks indicate statistical differences (P < 0.05) among treatments and error bars and bands represent SE. Vertical dashed line indicates the start of severe drought