Water-relations parameters of some bryophytes evaluated by thermocouple psychrometry

Abstract

Water-relations parameters are presented for four mosses, and for four leafy and four thalloid liverworts. Osmotic potentials of mosses and leafy liverworts at full turgor mostly lie in the range −1.0 to −1.5 MPa; multistratose thalloid liverworts generally give values in the range −0.5 to −1.0 MPa. These figures are less negative than older measurements based on plasmolysis, which more nearly reflect osmotic potential at turgor loss. Full-turgor water content can generally be estimated with fair accuracy from the graph of water content against water potential; careful blotting of saturated material may give acceptable approximate values for many purposes. Mosses and leafy liverworts of well-drained habitats generally have full-turgor water contents in the range 100-300% dry weight; values for thalloid liverworts may be much higher. Full-turgor water content (as % d.w.) varies seasonally, being high in new growth, and falling progressively through the growing season. The bulk modulus of elasticity (εB) is low (implying highly extensible cell walls) in most thalloid liverworts, and in such desiccation-tolerant mosses as Syntrichia ruraliformis and Racomitrium lanuginosum, but reaches values of 12-20 or more in some leafy liverworts with more rigid cells. Variation in water-relations parameters shows less relation to habitat than might be expected, probably because even in dry habitats bryophytes are fully hydrated for most of the time they are metabolically active, and only suffer water stress transiently as they dry out.