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VPD的概念
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各位大侠： VPD代表饱和蒸汽压差，光合仪测得的VPD和大气VPD一样吗？有什么区别？非常感谢 |
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小木虫: 金币+0.5, 给个红包，谢谢回帖
小木虫: 金币+0.5, 给个红包，谢谢回帖
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Vapor Pressure Deficit (VPD) can be defined as the difference (or deficit) between the pressure exerted by water vapor that could be held in saturated air (100% RH) and the pressure exerted by the water vapor that is actually held in the air being measured. From a plant’s perspective the VPD is the difference between the vapor pressure inside the leaf compared to the vapor pressure of the air. The only problem with leaf-to-air VPD is it’s difficult to determine accurately because you need to know the leaf temperature. The most practical approach that most environmental control companies use to assess VPD is to take measurements of air temperature within the crop canopy. A well positioned sensor measuring the air temperature and humidity close to, or just below, the crop canopy is adequate for providing a good indication of actual leaf conditions. VPD is essentially a combination of temperature and relative humidity in a single value. VPD values run in the opposite way to RH vales, so when RH is high VPD is low. The higher the VPD value, the greater the potential the air has for sucking moisture out of the plant. Computing VPD Saturation Vapor Pressure (es, kPa) =0.6108 * exp(17.27 * T / (T + 237.3)), where T is the air temperature Actual Vapor Pressure (ea, kPa) =RH / 100 * es, where RH is the relative humidity(%) VPD(kPa)=es - ea Vapor pressure inside the leaf(es,lesf, kPa) =0.6108 * exp(17.27 * T / (T + 237.3)), where T is the leaf or canopy temperature leaf-to-air VPD(kPa)=es,leaf - ea |
2楼2013-04-14 08:29:06
3楼2013-04-14 08:57:54
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