The carbon dioxide exchange of Microcoleus- and Scytonema-dominated cryptogamic crusts as related to dehydration was measured in the laboratory with a modified discrete sampling technique and infrared gas analysis. The dehydration curves predicted that carboxylation and dark respiration rates for both crust types would become zero at from 4 to 5% water content (W) (approximately 16-23% soil saturation), with the water contents at which the rates became zero significantly lower in the second treatment cycle than the first. The dehydration curves predicted that net photosynthesis rates would become zero at 6.7-11.2% W (27-44% soil saturation), with the water contents at which the rates became zero significantly higher in the second cycle of treatment than the first.
Keywords: CO2 exchange; Cryptogamic crusts; Microcoleus; Scytonema; dehydration.