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Samples of the moss Tortula ruralis were desiccated either rapidly or slowly to different tissue water contents to determine the limits of desiccation tolerance. Experimental samples were rehydrated rapidly by contact with wet filter paper, and gas exchange, chlorophyll content, electrolyte efflux, and linear growth rate were compared with those of control samples. Drying to 0.30–0.089 g H2O∙g dry weight−1 did not significantly affect the moss. Slow drying to 0.058–0.008 g H2O∙g dry weight−1 caused temporary increases in dark respiration and electrolyte leakage, and a slight inhibition of growth. Rapid drying of the same water contents caused visible injury, reduced total chlorophyll and the ratio of chlorophyll a:b, greatly enhanced electrolyte efflux, and severely inhibited gross photosynthesis and linear growth. The damaging effects of rapid drying could be eliminated either by partial desiccation for 1–3 h before rapid drying, or by placing the dry moss in a 100% relative humidity (RH) atmosphere for 1–5 h before rehydration.Tortula ruralis demonstrated greater drought tolerance than many other bryophytes, algae, seeds, and desert angiosperms, and is clearly capable of surviving any drought which might occur in its natural habitat.

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