McCulloh Katherine A, Johnson Daniel M, Petitmermet Joshua, McNellis Brandon, Meinzer Frederick C, Lachenbruch Barbara
Department of Botany, University of Wisconsin-Madison, Madison, WI 53706, USA
Department of Forest, Rangeland and Fire Sciences, University of Idaho, Moscow, ID 83843, USA.
Tree Physiol. 2015 Jul;35(7):723-31. doi: 10.1093/treephys/tpv035. Epub 2015 May 13.
The physiological mechanisms underlying the short maximum height of shrubs are not understood. One possible explanation is that differences in the hydraulic architecture of shrubs compared with co-occurring taller trees prevent the shrubs from growing taller. To explore this hypothesis, we examined various hydraulic parameters, including vessel lumen diameter, hydraulic conductivity and vulnerability to drought-induced embolism, of three co-occurring species that differed in their maximum potential height. We examined one species of shrub, one short-statured tree and one taller tree. We worked with individuals that were approximately the same age and height, which was near the maximum for the shrub species. A number of variables correlated with the maximum potential height of the species. For example, vessel diameter and vulnerability to embolism both increased while wood density declined with maximum potential height. The difference between the pressure causing 50% reduction in hydraulic conductance in the leaves and the midday leaf water potential (the leaf's hydraulic safety margin) was much larger in the shrub than the other two species. In general, trends were consistent with understory shrubs having a more conservative life history strategy than co-occurring taller species.
灌木最大高度较低的生理机制尚不清楚。一种可能的解释是，与同时生长的较高树木相比，灌木的水力结构差异使其无法长得更高。为了探究这一假设，我们研究了三种最大潜在高度不同的共生物种的各种水力参数，包括导管腔直径、水力传导率和对干旱诱导栓塞的脆弱性。我们研究了一种灌木、一种矮树和一种较高的树。我们研究的个体年龄和高度大致相同，接近灌木物种的最大高度。许多变量与物种的最大潜在高度相关。例如，导管直径和对栓塞的脆弱性都随着最大潜在高度的增加而增加，而木材密度则下降。导致叶片水力传导率降低50%的压力与中午叶片水势（叶片的水力安全边际）之间的差异，灌木比其他两个物种大得多。总体而言，这些趋势与林下灌木比同时生长的较高物种具有更保守的生活史策略一致。
