School of the Environment, University of Technology, Sydney, PO Box 123, Broadway, NSW 2007, Australia.
Earth and Environmental Sciences Division, Los Alamos National Laboratory, PO Box 1663, MS J495, Los Alamos, NM 87545, USA.
New Phytol. 2012 Apr;194(2):477-487. doi: 10.1111/j.1469-8137.2012.04058.x. Epub 2012 Feb 1.
Transient lulls in air movement are rarely measured, but can cause leaf temperature to rise rapidly to critical levels. The high heat capacity of thick leaves can damp this rapid change in temperature. However, little is known about the extent to which increased leaf thickness can reduce thermal damage, or how thick leaves would need to be to have biological significance. We evaluated quantitatively the contribution of small increases in leaf thickness to the reduction in thermal damage during critically low wind speeds under desert conditions. We employed a numerical model to investigate the effect of thickness relative to transpiration, absorptance and leaf size on damage avoidance. We used measured traits and thermotolerance thresholds of real leaves to calculate the leaf temperature response to naturally occurring variable low wind speed. Our results demonstrated that an increase in thickness of only fractions of a millimetre can prevent excursions to damaging high temperatures. This damping effect of increased thickness was greatest when other means of reducing leaf temperature (transpiration, reflectance or reduced size) were lacking. For perennial desert flora, we propose that increased leaf thickness is important in decreasing the incidence of extreme heat stress and, in some species, in enhancing long-term survival.
空气流动的短暂停顿很少被测量到，但会导致叶片温度迅速上升到临界水平。厚叶片的高热容量可以减缓这种温度的快速变化。然而，人们对增加叶片厚度在多大程度上可以减少热损伤，或者叶片需要多厚才能具有生物学意义知之甚少。我们定量评估了在沙漠条件下临界低风速下，叶片厚度的微小增加对减少热损伤的贡献。我们采用数值模型研究了厚度相对于蒸腾、吸收率和叶片大小对避免损伤的影响。我们使用实测性状和真实叶片的热耐受阈值来计算叶片对自然发生的低风速变化的温度响应。结果表明，厚度仅增加几毫米就可以防止叶片温度升高到有害的高温。当其他降低叶片温度的方法（蒸腾、反射或减小叶片尺寸）缺乏时，这种增加厚度的阻尼效应最大。对于多年生沙漠植物，我们认为增加叶片厚度对于降低极端热应激的发生率很重要，并且在某些物种中，对于提高长期生存能力也很重要。
