Do moss sporophytes maintain water balance? New insights from sporophyte water relations and the wild maturation cycle in Funaria hygrometrica Hedw.

ABSTRACT Introduction The water relations of Funaria hygrometrica Hedw. sporophytes have never been investigated, although unchanged morphology through periods of drought suggests that they may be homoiohydric. Knowledge of the sporophyte maturation cycle is also incomplete and based on glasshouse plants. Methods We followed sporophyte development in wild populations of Funaria, recording fresh weights of every phenophase. Rates of water loss under laboratory conditions from sporophytes of different ages were recorded, and the ontogeny of the intercellular spaces and the maturational deposition of extra wall materials and waxes were investigated by cryo-SEM. Key results The sporophyte maturation cycle in wild Funaria lasted from December until July (> 200 days), nearly three times that recorded in glasshouses. Fresh weights of green capsules increased until after sporogenesis. Mature brown capsules were highly dehydrated. Prevailing weather conditions or addition of water had no effect on weights. Low rates of water loss, comparable with those from vascular plant leaves, decreased throughout sporophyte maturation under laboratory conditions. These data indicate that Funaria sporophytes mirror homoiohydric vascular plants. Deposition of additional wall materials around the stomatal apertures prevents closure soon after their opening towards the end of post-meiosis capsule expansion. Conclusions With phenophases similar to those of perennial species, Funaria may not be as much a fugitive species as previously assumed. The very brief window in nascent stomata ontogeny when reversible aperture changes might be possible indicates that the likely principal role of Funaria stomata is facilitation of capsule dehydration and not active regulation of gaseous exchange.