Sphagnum under pressure: towards an ecohydrological approach to examining Sphagnum productivity

Abstract The genus Sphagnum is the key peat‐forming bryophyte in boreal ecosystems. Relying entirely on passive capillary action for water transport, soil moisture is often the limiting factor in Sphagnum production, and hence peat accumulation. While several hydrological models of peat physics and peatland water movement exist, these models do not readily interface with observations and models of peatland carbon accumulation. A conflict of approaches exists, where hydrological studies primarily utilize variables such as hydraulic head, while ecological models of Sphagnum growth adopt the coarse hydrological variables of water table (WT), volumetric water content (VWC) or gravimetric water content (WC). This review examines the potential of soil pressure head as a measurement to link the hydrological and ecological functioning of Sphagnum in peatlands. The non‐vascular structure of Sphagnum mosses and the reliance on external capillary transport of water in the mosses make them an ideal candidate for this approach. The main advantage of pressure head is the ability to mechanistically link plot‐scale hydrology to cellular‐scale water requirements and carbon exchange. Measurement of pressure head may improve photosynthetic process representation in the next generation of peatland models. Copyright © 2008 John Wiley & Sons, Ltd.