Plant Biology Graduate Course, Department of Plant Biology, Institute of Biology, Monteiro Lobato Street, 255, University of Campinas - UNICAMP, PO Box 6109, Campinas, SP 13083-970, Brazil.
Institute for Physical Geography, Goethe University, Altenhöferallee 1, Frankfurt am Main 60438, Germany.
Tree Physiol. 2020 Jun 30;40(7):856-868. doi: 10.1093/treephys/tpaa034.
Gas inside wood plays an important role in plant functioning, but there has been no study examining the adaptive nature of gas inside wood across plants differing in biomechanical demands. Using a comparative approach, we measured gas volumetric content, xylem's anatomical traits and wood density of 15 tree and 16 liana species, to test whether gas content varies between these plant types strongly differing in their biomechanical demands. We asked (i) whether trees and lianas differ in gas content and (ii) how anatomical traits and wood density are related to gas content. Lianas had significantly less gas content in their branches compared with tree species. In tree species, gas content scaled positively with fiber, vessel and xylem cross-sectional area and fiber and vessel diameter, and negatively with dry-mass density. When pooling trees and lianas together, fiber cross-sectional area was the strongest predictor of gas content, with higher xylem cross-sectional area of fiber associated with higher gas content. In addition, we showed, through a simple analytical model, that gas inside wood increases the minimum branch diameter needed to prevent rupture, and this effect was stronger on trees compared with lianas. Our results support the view that gas inside wood plays an important role in the evolution of biomechanical functioning in different plant forms. Gas inside wood may also play an important role in physiological activities such as water transport, storage, photosynthesis and respiration, but it is still unknown whether these roles are or are not secondary to the mechanical support.
木材内的气体在植物功能中起着重要作用，但目前还没有研究考察过不同力学需求的植物之间木材内气体的适应性本质。本研究采用比较的方法，测量了 15 种树木和 16 种藤本植物的气体体积含量、木质部解剖特征和木材密度，以检验气体含量是否因力学需求差异极大的植物类型而有很大差异。我们提出了以下两个问题：（i）树木和藤本植物的气体含量是否存在差异；（ii）解剖特征和木材密度与气体含量有何关系。与树木物种相比，藤本植物的树枝内气体含量明显较少。在树木物种中，气体含量与纤维、导管和木质部横截面积以及纤维和导管直径呈正相关，与干物质密度呈负相关。当将树木和藤本植物合并时，纤维横截面积是预测气体含量的最强指标，与较高的木质部纤维横截面积相关的气体含量也较高。此外，我们通过一个简单的分析模型表明，木材内的气体增加了防止破裂所需的最小树枝直径，并且这种效应在树木中比在藤本植物中更强。我们的结果支持这样一种观点，即木材内的气体在不同植物形态的力学功能进化中起着重要作用。木材内的气体在水分运输、储存、光合作用和呼吸等生理活动中也可能发挥重要作用，但目前尚不清楚这些作用是否次于机械支撑。
