The effects of temperature and moisture on CO2 uptake and total resistance to water loss in the antarctic foliose lichen Umbilicaria antarctica

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Abstract
Maximum net photosynthesis of field-fresh thalli, illuminated at 200 .mu.mol photons m-2 s-1 (PAR), was attained at 13 .degree.C and 1.cntdot.10 g g-1 water content. Small but significant rates of photosynthesis were measured at -5.cntdot.5 .degree.C. Depression of net photosynthesis at high thallus water contents is explained in terms of thallus anatomy. Calculation of evaporative resistance of the thallus by a new method showed a moisture-dependent response pattern, and was in agreement with direct observations made on other foliose species.