Strategies of desiccation tolerance vary across life phases in the moss Syntrichia caninervis

PREMISE: Desiccation tolerance (DT) is a widespread phenomenon among land plants, and variable ecological strategies for DT are likely to exist. Using Syntrichia caninervis, a dryland moss and model system used in DT studies, we hypothesized that DT is lowest in juvenile (protonemal) tissues, highest in asexual reproductive propagules (gemmae), and intermediate in adults (shoots). We tested the long-standing hypothesis of an inherent constitutive strategy of DT in this species. METHODS: Plants were rapidly dried to levels of equilibrating relative humidity (RHeq) ranging from 0 to 93%. Postrehydration recovery was assessed using chlorophyll fluorescence, regeneration rates, and visual tissue damage. For each life phase, we estimated the minimum rate of drying (RoD(min)) at RHeq = 42% that did not elicit damage 24 h postrehydration. RESULTS: DT strategy varied with life phase, with adult shoots having the lowest RoD(min) (10-25 min), followed by gemmae (3-10 h) and protonema (14-20 h). Adult shoots exhibited no detectable damage 24 h postrehydration following a rapid-dry only at the highest RHeq used (93%), but when dried to lower RHs the response declined to <50% of control fluorescence values. Notably, immediately following rehydration (0 h postrehydration), shoots were damaged below control levels of fluorescence regardless of the RHeq, thus implicating damage. CONCLUSIONS: Life phases of the moss S. caninervis had a range of strategies from near constitutive (adult shoots) to demonstrably inducible (protonema). A new response variable for assessing degree of DT is introduced as the minimum rate of drying from which full recovery occurs.