Role of morphological structure and layering ofSphagnumandTomenthypnummosses on moss productivity and evaporation rates

Abstract

Price, J. S. 2015. Role of morphological structure and layering of Sphagnum and Tomenthypnum mosses on moss productivity and evaporation rates. Can. J. Soil Sci. 95: 109Á124. Morphological structures of peatland mosses control moss water relations and the rate of water loss by drainage and evaporation, thus influencing their physiological functions. While many of these mechanisms are understood for Sphagnum mosses, there is a limited understanding of how these processes operate in Tomenthypnum nitens, a dominant brown moss species in northern rich fens. This study contrasts how different hydrophysical characteristics of Tomenthypnum and Sphagnum species affect capillary water flow that supports evaporation and productivity. Laboratory investigations indicate that volumetric water content (u), gross ecosystem productivity, and evaporation decreased with water ). Despite lower u and a smaller fraction of pores between 66 and 661 mm to retain water within the Tomenthypnum structure (10%) compared with Sphagnum (27%), both mosses had similar fractions of water conducting pore spaces and were able to maintain capillary rise throughout the experiment. While there was a larger difference in the bulk density and porosity of the Tomenthypnum moss compared with its underlying peat than there was in the Sphagnum profile, a layer of partially decomposed moss of intermediate properties was sufficient to provide a connection between the moss and peat under low water table conditions. In trying to characterize the soil-water pressure (c) in near-surface mosses of Tomenthypnum based on measurements of vapour pressure, we found disequilibrium conditions that severely underestimated c (i.e., very large negative pressures). It is this disequilibrium that drives evaporation and draws up capillary water to the moss surface for peatlandÁatmosphere carbon and water transfers.Key words: Peatlands, bryophytes, water retention, hydraulic conductivity, theoretical pore-size distribution, water vapour Goetz, J. D. et Price, J. S. 2015. Influence de la morphologie et de la superposition des couches de mousses de type Sphagnum et Tomenthypnum sur la productivite´de la plante et le taux d'e´vaporation. Can. J. Soil Sci. 95: 109Á124. Dans les tourbie`res, la morphologie des mousses controˆle les relations entre l'eau et la plante, ainsi que la vitesse a`laquelle l'eau disparaıˆt par drainage et e´vaporation, ce qui exerce une influence sur les fonctions physiologiques de la mousse. Quoique beaucoup de ces me´canismes soient bien connus chez les mousses du genre Sphagnum, nos connaissances sont plus limite´es sur ces processus chez Tomenthypnum nitens, une mousse brune qui domine dans les riches marais du nord. Cette e´tude illustre combien les caracte´ristiques hydrophysiques diffe´rentes des espe`ces des genres Tomenthypnum et Sphagnum modifient l'e´coulement capillaire de l'eau, dont de´pendent l'e´vaporation et la productivite´. Les e´tudes en laboratoire indiquent que la masse volumique de l'eau (u), la productivite´brute de l'e´cosyste`me...

A pore-size classification for peat bogs derived from unsaturated hydraulic properties

“…5, left panel) show an increased water holding capacity with increasing depth across a wide pressure head range, from saturation up to pF = 3.2 (a pressure head of −1500 cm). This finding is supported by literature data for conditions near water saturation (Price et al, 2008;Price and Whittington, 2010;McCarter and Price, 2012;Goetz and Price;. Concurrently, the HCCs show a pronounced decrease in the saturated conductivity and systematically higher unsaturated conductivities with increasing depth (Fig.…”

“…complete wettability is assumed during monotonic drying (Goetz and Price, 2015). The PSD function, f (h), was defined as the change in capillary saturation with log pressure head (Durner, 1994):…”

The effect of compression on Sphagnum hydrophysical properties: Implications for increasing hydrological connectivity in restored cutover peatlands

“…Higher ϕ vw at the same pore diameter indicates a greater abundance of pores less than or equal to the given pore diameter (Goetz & Price, 2015;McCarter & Price, 2014). Higher ϕ vw at the same pore diameter indicates a greater abundance of pores less than or equal to the given pore diameter (Goetz & Price, 2015;McCarter & Price, 2014).…”

“…Unsaturated hydraulic conductivity is, in turn, a function of the volumetric moisture content (VMC) of the moss (θ) that is governed by the pore network within the moss matrix. In natural peatlands, a gradual gradient of living mosses to dead and decomposed mosses is observed, creating a gradation of larger pores at the surface, to smaller pores below (Boelter, 1968;Goetz & Price, 2015;McCarter & Price, 2014;Rezanezhad et al, 2010;Weber, Iden, & Durner, 2017a). In natural peatlands, a gradual gradient of living mosses to dead and decomposed mosses is observed, creating a gradation of larger pores at the surface, to smaller pores below (Boelter, 1968;Goetz & Price, 2015;McCarter & Price, 2014;Rezanezhad et al, 2010;Weber, Iden, & Durner, 2017a).…”

“…In natural peatlands, a gradual gradient of living mosses to dead and decomposed mosses is observed, creating a gradation of larger pores at the surface, to smaller pores below (Boelter, 1968;Goetz & Price, 2015;McCarter & Price, 2014;Rezanezhad et al, 2010;Weber, Iden, & Durner, 2017a). Water retention capacity is higher within these smaller pores at a given pressure head (Goetz & Price, 2015;McCarter & Price, 2015). Water retention capacity is higher within these smaller pores at a given pressure head (Goetz & Price, 2015;McCarter & Price, 2015).…”