Gas Exchange in Paphiopedilum

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Abstract
Net photosynthesis and stomatal conductance were measured in attached leaves of Paphiopedilum insigne. At 20°C and a vapor-pressure deficit of 0.5 kilopascal, both net photosynthesis and stomatal conductance were light-saturated below 0.2 millimole per square meter per second, a response typical of shade plants. The absolute values of photosynthetic rate and conductance however were remarkably low, presumably reflecting an adaptation to the low-light, limited-nutrient habitat characteristic of these orchids. The leaves also showed a vapor-pressure deficit response, with net photosynthesis and conductance varying over a 2-fold range between 0.3 and 1.6 kilopascals.