Multiple limiting gradients in peatlands: A call for a new paradigm

Abstract

Peatlands often have readily apparent gradients of plant species distributions, biogeochemistry, and hydrology across several spatial scales. Many inferences have been drawn about lhe colinearity of these gradients, and these assumptions have become ingrained in the terminology that describes and classifies peatlands. We review the literature and present some of our own data that show that many of these inferences are either wrong or correct only under a limited set of ecological conditions. We examine historical classification schemes of peatlands and, in this context, gradients of alkalinity, pH, nutrient availability for plant growth, nutrient mineralization, hydrology, and decomposition. We further suggest a strictly defined set of terms to describe separate gradients of hydrology, alkalinity, and nutrients that limit plant growth in peatlands. Specifically, we make the following suggestions concerning terminology. (1) The suffix "-trophic" should only be used when referring to nutrients that direcdy limit plant growth at natural availabilities (e.g., eutrophic and oligotrophic). (2) Terms such as circnmneutral, moderately acid. and very acidic (or alternatively strong, intermediate, and weak) should be used to describe the pH of peatlands. (3) Ombrogenous and geogenous (or limnogenous, topogenous, and soligenous) should be used to describe the hydrology of peatlands. (4) The terms bog and fen should be defined broadly based on water/soil chemistry and dominant plant species without accompanying assumptions regarding hydrology, topography, ontogeny, nutrient availability, or the presence or absence of nondominant indicator plant species. Better yet, the generic term peatland be used when possible to avoid confusion about conditions that may or may not be present at a particular site.

Relationships among testate amoebae (Protozoa), vegetation and water chemistry in five Sphagnum‐dominated peatlands in Europe

“…Hydrodynamics and hydrochemistry are determinant factors for peatland development (Bridgham et al, 1996). Peatlands are characterized by gradients of nutrients (eutrophic-oligotrophic), hydrology (ombrogenous-geogenous) and acidity.…”

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

“…Depth to the water table, oxygenation, redox potential, pH, and nutrient availability are the most prominent environmental factors varying along the hummock-hollow gradient (Bridgham et al, 1996). Changes in environmental factors are reflected in a different bryophyte and vascular plant species assemblage along the hummock-hollow gradient (Andrus, 1986).…”

Sensitivity to and requirement for iron in Plantago species

“…% under consideration of ligand exchange processes in the nutrient solution seems an adequate means of estimating such indices. It should be stressed that, besides the type of Fe chelate used, experimental C sub and C supra values might be affected by factors such as ontogenetic drift, the concentration of other nutrients, and medium pH (see Bridgham et al (1996) for an extensive discussion).…”