Carbon Balance for Two Sphagnum Mosses: Water Balance Resolves a Physiological Paradox

Abstract

Sphagnum fallax is generally found closer to the water table than S. nemoreum along the hummock—hollow gradient of an Adirondack bog. However, at low water contents S. fallax unexpectedly fixes carbon at higher rates than S. nemoreum, as we have previously reported. We here compare water and carbon balances for these species to resolve this puzzling contrast. S. nemoreum maintains a more favorable water balance by virtue of its greater water—holding capacity, lower rates of water loss from moist plants, and apparently more effective capillary conduction of water. The consequence is a significantly higher tissue water content in the field compared to adjacent patches of S. fallax for a wide range of dates and heights above the water table. We developed a simulation model, PEATMOSS, to evaluate the relative importance of contrasting physiological relationships and water balances of the two species. The model integrates physiological and field data to estimate 24—h carbon balance for these mosses in adjacent patches at two heights above the water table under different conditions. PEATMOSS estimated a greater carbon gain for S. fallax at the low site, where it is a clear dominant over S. nemoreum, and a markedly more favorable carbon balance for S. nemoreum at the hummock site, where S. nemoreum is common but S. fallax is infrequent. Morphological features of S. nemoreum which effect its more favorable water balance apparently confer an advantage over S. fallax when water availability is limited.

Substrate‐derived CO2 is important in the development of Sphagnum spp.

“…A vertical growth strategy is of great advantage for S. magellanicum as in wet conditions Sphagna from wet habitats (for instance Sphagnum fallax or Sphagnum cuspidatum) generally have a more efficient CO 2 uptake than species from drier habitats (Titus & Wagner, 1984;Andrus, 1986;Rice & Schuepp, 1995). By increasing their vertical growth sufficiently, hummock and lawn species can avoid competition with species from wetter habitats by creating their own microenvironment.…”

“…By increasing their vertical growth sufficiently, hummock and lawn species can avoid competition with species from wetter habitats by creating their own microenvironment. The species from wet habitats are less competitive in the drier habitats that are created by the hummock and lawn species (Andrus et al, 1983;Titus & Wagner, 1984;Andrus, 1986;Rydin, 1993;Grosvernier et al, 1997).…”

“…The pendant branches of the Sphagnum mosses provide a capillary structure that enables efficient external transport of water and thus of dissolved CO 2 to the capitula (Hayward & Clymo, 1982). The driving force behind this transport is evaporation (Titus & Wagner, 1984). Furthermore, Rydin & Clymo (1989) demonstrated that Sphagnum possesses an efficient acropetal carbon transport system within the central parenchyma of the stems.…”

A Decade of Plant Species Changes on a Mire in the Italian Alps: Vegetation-Controlled or Climate-Driven Mechanisms?

“…Relatively wetter conditions in recent years may explain this shift of Sphagnum species that are competitive dominants in wetter microhabitats. Indeed, Sphagnum species in the Cuspidata Section possess a competitive advantage in wet conditions (Hayward and Clymo, 1983;Brock and Bregman, 1989;Rydin, 1993;Gerdol, 1995), with S. fallax growing faster than S. capillifolium under greater water availability (Titus and Wagner, 1984;Grosvernier et al, 1997).…”

Effects of simulated nitrogen deposition and a stable isotopic assessment for the neotropical epiphytic orchid Laelia speciosa

“…Epiphytic vascular plants are another potentially apt group for bioindication of nitrogen deposition. Unlike bryophytes, many vascular epiphytes are physiologically active year round thus increasing their exposure to atmospheric pollution (Titus and Wagner, 1984;Benzing, 1990, Hietz et al, 2002Silvera et al, 2009;Zotz and Bader 2009). Moreover, because some species of epiphytic orchids annually produce pseudobulbs, a water and carbon storage organ that persist over time, it is likely that a history of nitrogen deposition can be reconstructed from these longevous organs (Dressler, 1981;Ng and Hew, 2000).…”