Abstract Epicuticular wax is thought to enable sorghum [Sorghum bicolor (L.) Moench] plants to cope with drought. Increased reflectivity of solar radiation and reduced conductance of water vapor are mechanisms responsible for aiding plants in water conservation. Increased reflectivity should lead to a decrease in canopy temperature and water use, whereas decreased conductance should lead to an increase in canopy temperature because of a decrease in evaporative cooling. It is not clear how these competing effects exert control over water use in a crop such as sorghum. To better understand the role of epicuticular waxes on the energy balance of sorghum, experiments were conducted to determine the effects of waxes on field-scale energy fluxes using near-isogenic lines of grain sorghum having different levels of epicuticular wax loading. Waxes caused an overall 2% increase in albedo, and about 86% of the reflected energy between 400 and 1100 nm was from near-infrared wavelengths. This is at variance with recent reports that suggest that waxes can substantially increase the reflectivity of sorghum. Instead, our results indicated that the amount of reflected radiant energy due to waxes was small. When water was non-limiting, waxes caused a 22% decrease in canopy conductance compared to a 2% increase in albedo on average. Consequently, at the expense of higher canopy temperatures, waxes caused a 5% reduction in latent heat flux when water was not limiting. Without rain, water became limiting to plants with lower wax load sooner than it did for plants with higher wax load. The high wax load canopy then was on average 0.4 °C cooler, had 24% greater canopy conductance and 13% greater latent heat fluxes compared to the low wax one. Results suggested that the primary mechanism through which waxes affect the energy balance of sorghum is by means of reduced conductance of water vapor.

中文翻译：

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表皮蜡及其对高粱冠层温度和水分利用的影响

摘要 Epicuticular 蜡被认为使高粱 [Sorghum bicolor (L.) Moench] 植物能够应对干旱。太阳辐射反射率的增加和水蒸气传导率的降低是帮助植物节约用水的机制。反射率的增加会导致冠层温度和用水量的降低，而电导率的降低会由于蒸发冷却的减少而导致冠层温度的升高。目前尚不清楚这些竞争效应如何控制高粱等作物的用水量。为了更好地了解表皮蜡对高粱能量平衡的作用，进行了实验以确定蜡对田间规模能量通量的影响，使用具有不同表皮蜡负载水平的谷物高粱的近等基因系。蜡导致反照率总体增加 2%，400 到 1100 nm 之间约 86% 的反射能量来自近红外波长。这与最近的报告不一致，这些报告表明蜡可以显着提高高粱的反射率。相反，我们的结果表明由蜡引起的反射辐射能量很小。当水为非限制性时，蜡导致冠层电导率降低 22%，而反照率平均增加 2%。因此，以较高的冠层温度为代价，当水不受限制时，蜡会导致潜热通量降低 5%。如果没有下雨，与蜡负载较高的植物相比，水对蜡负载较低的植物的限制更快。高蜡载顶篷然后平均冷却 0.4 °C，与低蜡相比，冠层传导率高 24%，潜热通量高 13%。结果表明，蜡影响高粱能量平衡的主要机制是通过降低水蒸气的传导性。