Vapour-pressure deficit the plant may dry out and die. For this reason the ideal range for VPD in a greenhouse is from 0.45 kPa to 1.25 kPa, ideally sitting at around 0.85 kPa. As a general rule, most plants grow well at VPDs of between 0.8 and 0.95 kPa. In ecology, it is the difference between the actual water vapour pressure and the saturation water vapour pressure at a particular temperature. Unlike relative humidity, vapour-pressure deficit has a simple nearly straight-line relationship to the rate of evapotranspiration and other measures of evaporation. To compute the VPD, we need the ambient (greenhouse) air
Tendency of the rate of profit to fall unequal exchange theory to the modern Marxian theory of competition, and tested it out in the case of the trade between Greece and Germany. One of the first ecological Marxists, Elmar Altvater, argued that "[t]he costs of clean air and clean water belong to the capital outlays and therefore increase the amount of constant capital fixed in the production process with the effect of an increasing organic composition of capital. Hence, the profit rate will fall (of course ceteris paribus)." However, not everyone agrees with that idea. Firstly, it all depends who has to pay for the cost, and what