Desiccation tolerance in mosses. II. Differences in the responses of Hedwigia ciliata and Mnium cuspidatum to desiccation and rehydration

The responses of two mosses, Hedwigia ciliata and Mnium cuspidatum, to desiccation and rehydration were studied. Cell and shoot survival were about 30% lower in Mnium than in Hedwigia after the same desiccation and rehydration treatment. Time courses of water loss showed that both species lost water at the same rate and to the same extent, indicating that Hedwigia is desiccation tolerant rather than dehydration resistant. Chlorophyll content decreases in both species after desiccation and rehydration, but in Hedwigia net photosynthesis after desiccation and rehydration was at a rate similar to that in undesiccated plants whereas in Mnium photosynthetic rates were lower after desiccation and rehydration. This decreased photosynthetic rate suggests that chloroplast damage during desiccation and dry storage contributes to Mnium's lessened ability to survive after desiccation and rehydration.