Research Group of Plant and Vegetation Ecology, Department of Biology, Universiteit Antwerpen (Campus Drie Eiken), Universiteitsplein 1, Wilrijk, B-2610, Belgium.
Glob Chang Biol. 2012 Sep;18(9):2860-8. doi: 10.1111/j.1365-2486.2012.02734.x. Epub 2012 Jun 12.
Here we investigate the extent to which infrared heating used to warm plant canopies in climate manipulation experiments increases transpiration. Concerns regarding the impact of the infrared heater technique on the water balance have been raised before, but a quantification is lacking. We calculate transpiration rates under infrared heaters and compare these with air warming at constant relative humidity. As infrared heating primarily warms the leaves and not the air, this method increases both the gradient and the conductance for water vapour. Stomatal conductance is determined both independently of vapour pressure differences and as a function thereof, while boundary layer conductance is calculated using several approaches. We argue that none of these approaches is fully accurate, and opt to present results as an interval in which the actual water loss is likely to be found. For typical conditions in a temperate climate, our results suggest a 12-15% increase in transpiration under infrared heaters for a 1 °C warming. This effect decreases when stomatal conductance is allowed to vary with the vapour pressure difference. Importantly, the artefact is less of a concern when simulating heat waves. The higher atmospheric water demand underneath the heaters reflects naturally occurring increases of potential evapotranspiration during heat waves resulting from atmospheric feedback. While air warming encompasses no increases in transpiration, this fully depends on the ability to keep humidity constant, which in the case of greenhouses requires the presence of an air humidification system. As various artefacts have been associated with chamber experiments, we argue that manipulating climate in the field should be prioritized, while striving to limit confounding factors. The excess water loss underneath infrared heaters reported upon here could be compensated by increasing irrigation or applying newly developed techniques for increasing air humidity in the field.
在这里，我们研究了在气候操纵实验中用于加热植物冠层的红外加热在多大程度上增加了蒸腾作用。以前曾有人担心红外加热器技术对水平衡的影响，但缺乏量化。我们计算了在红外加热器下的蒸腾速率，并将其与在恒定相对湿度下的空气加热进行了比较。由于红外加热主要加热叶片而不是空气，因此这种方法增加了水蒸气的梯度和导度。气孔导度是独立于蒸气压差和作为其函数来确定的，而边界层导度则使用几种方法来计算。我们认为这些方法都不完全准确，因此选择以可能的实际水分损失所在的区间来呈现结果。对于温带气候的典型条件，我们的结果表明，在红外加热器下，1°C 的升温会导致蒸腾作用增加 12-15%。当允许气孔导度随蒸气压差变化时，这种效应会减小。重要的是，在模拟热浪时，这种人为因素的影响较小。加热器下方的大气水分需求增加反映了由于大气反馈导致热浪期间潜在蒸散量的自然增加。虽然空气加热不会增加蒸腾作用，但这完全取决于保持湿度恒定的能力，而在温室中，这需要存在空气加湿系统。由于与室验相关的各种人为因素，我们认为应该优先在野外操纵气候，同时努力限制混杂因素。这里报道的红外加热器下的过量水分损失可以通过增加灌溉或应用新开发的现场增加空气湿度的技术来补偿。
