Cushion size, surface roughness, and the control of water balance and carbon flux in the cushion mossLeucobryum glaucum(Leucobryaceae)

Abstract

We explored the size dependence of water balance and carbon flux in the cushion moss Leucobryum glaucum (Leucobryaceae). Conductance to water vapor (g(a)) was modeled empirically using 4-24 cm diameter cushions (N = 14) evaluated across wind speeds from 0.7 to 4.3 m/s in a wind tunnel. Model parameters included wind speed (u), kinematic viscosity (v), cushion diameter (L(d)), and surface roughness (L(r)). The model g(a) = -9.62(u/v)(1.21) · L(d)(-0.35) · L(r-in)(-1.85) (where L(r-in) represents a dimensionless form of L(r); R(2) = 0.88) indicates negative relationships between g(a) and both L(d) and L(r). These predictions were evaluated during a 5-d field experiment where water loss and net carbon exchange (estimated by ΔF/F(m)') were monitored. In the field (N = 18, 4-34 cm diameter cushions), L(r), but not L(d), controlled rates of evaporation due to additional turbulence that reduced size dependence of cushions along the forest floor. However, the duration of positive net carbon gain varied from 1.4 to 4.4 d and was significantly longer in larger diameter cushions. Thus, under field conditions, size-dependent changes in surface-area-to-volume relationships influence the duration of net carbon gain more than differences in water flux and lead to a strong size dependence of water balance and carbon flux.

Dehydration protection provided by a maternal cuticle improves offspring fitness in the moss Funaria hygrometrica

“…In mosses, the undifferentiated apical region experiences higher levels of dehydration as it is elevated during seta elongation, escaping the buffering effects of the boundry layer that surrounds the leafy gametophyte (Rice and Schneider, 2004). The protective abilities of the maternal calyptra allow sporangium differentiation to be delayed and may have enabled the evolution of taller sporophyte offspring with permanent seta.…”

Measurement and modelling of bryophyte evaporation in a boreal forest chronosequence

“…In poorly drained areas, moss growth and differential growth rates create and reinforce the hummock-hollow microtopography characteristic of these areas (Yabe and Uemura, 2001;Benscoter et al, 2005). Microtopography affects not only calculated fluxes-by 5-10% here, and sometimes much larger (30-40%) values (Vitt, 2007)-but also species distribution (Andrus et al, 1983) and small-scale water balance and carbon fluxes, due to turbulence effects on the local environment (Rice and Schneider, 2004) and small-scale variations in the water table (Roy et al, 1999). The correction values reported here are consistent with those previously measured in Ontario, Canada (Rochefort et al, 1990).…”

“…Kellner (2001) reported surface resistance (r s ) values of 160 š 70 s m 1 for a Swedish Sphagnum bog, consistent with the results here ( Figure 3). It is interesting that S. fuscum has a dense, tightly woven canopy to retard water loss (Rice and Schneider, 2004), but in the laboratory, this moss evaporated at the same rate as hollow and feather mosses. This result is surprising, as differential evaporative rates have been previously observed (e.g.…”

“…Water loss in bryophytes is controlled by canopy structural properties (Proctor, 1980(Proctor, , 1982Zotz et al, 2000;Rice and Schneider, 2004), as opposed to vascular plants, in which leaf stomata regulate water fluxes. As a poikilohydric plant, a bryophyte-more specifically the water vapour partial pressure of the plant body-is always in equilibrium with ambient humidity (Green and Lange, 1994); this lack of active control over plant water status implies fundamentally different ecosystemlevel dynamics as well (Longton, 1992;Turetsky, 2003).…”

Estimation of stand-level leaf area for boreal bryophytes

“…These few studies have generally measured the leaf area of individual samples (Proctor 2000;Rice and Schneider 2004;Williams and Flanagan 1998;Zotz et al 2000), although DeLucia et al (2003) estimated stand-level bryophyte LAI in a New Zealand forest. In most vascular plant systems, LAI strongly inXuences energy, water and carbon dioxide exchange between terrestrial ecosystems and the atmosphere and is tightly coupled with photosynthesis, litterfall, microclimate and productivity (Gower et al 1999).…”