CO2 exchange, photosynthetic pigment composition, and cell ultrastructure of Sphagnum mosses during dehydration and subsequent rehydration

Sphagnum mosses of three different species (S. capillifolium, S. magellanicum, and S. fallax) were allowed to dry in a controlled environment. The three species lost water at different rates, but after 11 days of exposure to drying atmosphere all were dry and unable to photosynthesize. The chlorophyllose cells of all three species showed signs of alteration, mainly membrane shrinkage. Upon rehydration, concentrations of photosynthetic pigments (chlorophyll a to a greater extent than chlorophyll b) declined in tissues of S. magellanicum and especially in S. fallax. Sphagnum capillifolium and S. magellanicum resumed photosynthesis, although slowly, whereas S. fallax did not achieve a net carbon gain (most of its chlorophyllose cells were irreversibly damaged) after 7 days of rewetting. In the field, prolonged drought may alter the interspecific equilibria among coexisting Sphagnum species possessing different degrees of desiccation-tolerance and especially different water-holding abilities.