Cation‐exchange properties and adaptation to soil acidity in bryophytes

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Abstract
Summary: Cation‐exchange processes of plant tissue are often hypothesized to affect ion uptake. Fixation of cations on exchange sites could either withdraw cations from further uptake, or concentrate them for the absorption sites. For a number of bryophyte taxa (Atrichum undulatum(Hedw.) P. Beauv.,Homalothecium sericeum(Hedw.) B.S.&G.,Leucobryum glaucum(Hedw.) Angstr.,Mnium hornumHedw.,Plagiomnium undulatum(Hedw.) T. Kop.,Polytrichum formosumHedw.), these contrasting hypotheses were tested by studying cation‐exchange properties and soil preference of populations with respect to soil acidity and soil exchangeable cations (Al, H, Fe, Mn, Ca, Mg, K). Acidiphilous and acidicline taxa (preference for soils with pH < 5) with relatively lower cation‐exchange capacities tolerate high exchangeable aluminium levels and low calcium levels. Neutrocline taxa (preference for soils with pH > 5) with higher cation‐exchange capacity avoid aluminium in the substrate and thrive on calcium‐rich substrates. Cation‐exchange properties therefore do not protect mosses against potentially toxic cations such as aluminium through a sequestration mechanism. However cation exchange sites may increase the availability of cations. High cation‐exchange capacity was indeed shown to favour fixation of aluminium over calcium ions and hence a low capacity is a prerequisite for taxa adapted to acid soils.