Jacobsen Anna L, Ewers Frank W, Pratt R Brandon, Paddock William A, Davis Stephen D
Department of Plant Biology, Michigan State University, East Lansing, 48824-1312, USA.
Plant Physiol. 2005 Sep;139(1):546-56. doi: 10.1104/pp.104.058404. Epub 2005 Aug 12.
Possible mechanical and hydraulic costs to increased cavitation resistance were examined among six co-occurring species of chaparral shrubs in southern California. We measured cavitation resistance (xylem pressure at 50% loss of hydraulic conductivity), seasonal low pressure potential (P(min)), xylem conductive efficiency (specific conductivity), mechanical strength of stems (modulus of elasticity and modulus of rupture), and xylem density. At the cellular level, we measured vessel and fiber wall thickness and lumen diameter, transverse fiber wall and total lumen area, and estimated vessel implosion resistance using (t/b)(h)(2), where t is the thickness of adjoining vessel walls and b is the vessel lumen diameter. Increased cavitation resistance was correlated with increased mechanical strength (r(2) = 0.74 and 0.76 for modulus of elasticity and modulus of rupture, respectively), xylem density (r(2) = 0.88), and P(min) (r(2) = 0.96). In contrast, cavitation resistance and P(min) were not correlated with decreased specific conductivity, suggesting no tradeoff between these traits. At the cellular level, increased cavitation resistance was correlated with increased (t/b)(h)(2) (r(2) = 0.95), increased transverse fiber wall area (r(2) = 0.89), and decreased fiber lumen area (r(2) = 0.76). To our knowledge, the correlation between cavitation resistance and fiber wall area has not been shown previously and suggests a mechanical role for fibers in cavitation resistance. Fiber efficacy in prevention of vessel implosion, defined as inward bending or collapse of vessels, is discussed.
在南加州的六种共生灌丛物种中，研究了提高抗气穴能力可能产生的机械和水力成本。我们测量了抗气穴能力（水力传导率损失50%时的木质部压力）、季节性低压潜力（P(min)）、木质部传导效率（比导率）、茎的机械强度（弹性模量和断裂模量）以及木质部密度。在细胞水平上，我们测量了导管和纤维壁厚度、管腔直径、横向纤维壁和总管腔面积，并使用(t/b)(h)(2)估算导管抗内爆能力，其中t是相邻导管壁的厚度，b是导管管腔直径。抗气穴能力的提高与机械强度的增加（弹性模量和断裂模量的r(2)分别为0.74和0.76）、木质部密度（r(2) = 0.88）和P(min)（r(2) = 0.96）相关。相比之下，抗气穴能力和P(min)与比导率的降低无关，表明这些性状之间不存在权衡。在细胞水平上，抗气穴能力增强与(t/b)(h)(2)增加（r(2) = 0.95）、横向纤维壁面积增加（r(2) = 0.89）和纤维管腔面积减小（r(2) = 0.76）相关。据我们所知，抗气穴能力与纤维壁面积之间的相关性此前尚未见报道，这表明纤维在抗气穴能力中具有机械作用。文中讨论了纤维在防止导管向内弯曲或塌陷（即导管内爆）方面的功效。
