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.

KEYWORDS:

• Cryo-scanning electron microscopy
• homoiohydry
• intercellular spaces
• Physcomitrium
• poikilohydry
• stomata

Acknowledgements

We thank Zophia Ludlinska (Nanovision Centre, Queen Mary University of London), for skilled technical assistance using the cryo-SEM.

Disclosure statement

No potential conflicts of interest were reported by the authors.

Supplemental material

Supplemental material for this article can be accessed here: https://doi.org/10.1080/03736687.2022.2154736 in July 2017, in relation to London rainfall.

Additional information

Notes on contributors

Jeffrey G. Duckett

Jeffrey G. Duckett is a research associate at the Natural History Museum, London. Current research includes bryophyte stomata, morphological consequences of poikilohydry, urban bryophyte distributions, and post-fire successions.

Silvia Pressel

Silvia Pressel is a senior research lead and Merit Researcher, Science Group, at the Natural History Museum, London. Current research foci in her laboratory include bryophyte diversity and biogeography on South Atlantic Oceanic Islands, bryophyte ex situ conservation, the evolution and diversity of mycorrhizal associations in land plants, and stomatal development and function in bryophytes.