Responses of Mosses, Especially Hedwigia Ciliata and Mnium Cuspidatum, to Desiccation and Rehydration.

Experiments were performed to determine the mechanisms by which mosses survive dry conditions. Moss samples were desiccated over silica gel and rehydrated on filter paper soaked with distilled water. Desiccation damage was measured by analyzing cell and shoot survival after rehydration. Photosynthetic measurements were made with an open flow IRGA system. Photosynthetic pigments were extracted in 80% acetone and concentrations were calculated by conventional methods. The effects of desiccation and rehydration on 10 local moss species were examined; 4 species were desiccation-sensitive, 3 species were drought-evaders, surviving by producing new growth from severely damaged shoots, 2 species were desiccation-resistant and were not affected by the treatment. Drought-evasion was correlated with fluctuating water levels in the habitat; desiccation-resistance occurred in species from dry habitats. High variance in cell damage within the same clump of moss led to development of a st and ardized method of sampling cell damage; the technique involves counting a minimum of 10 cells in 6 locations on each leaf and 6 leaves on each of 10 shoots for each treatment. The results of this method correlate well with shoot survival (r = 0.98). Detailed experiments were performed on 2 species, Hedwigia ciliata and Mnium cuspidatum. Studies on cell survival, shoot survival, and time courses for desiccation and rehydration indicate that both species lose water at the same rate and to the same extent, that Hedwigia is desiccation-tolerant and that Mnium is desiccation-sensitive. Chlorophyll content decreases in Mnium after desiccation and rehydration, with preferential damage to chlorophyll a. Hedwigia appears to lose chlorophyll after desiccation and rehydration also, but the pigment composition of plants does not change, suggesting that Hedwigia has adaptations which protect the chlorophyll a from desiccation damage. Possible models for the mechanism of desiccation damage in Mnium and desiccation-tolerance in Hedwigia are presented.PhDBotanyUniversity of Michiganhttp://deepblue.lib.umich.edu/bitstream/2027.42/160046/1/8412258.pd