The pH-lowering ability of Sphagnum magellanicum brid

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The classic explanation of the low pH in bogs attributes this phenomenon to the H+ exchange capacity of Sphagnum. However, recent researchers have challenged this theory, arguing instead that such exchange could not account for the ions measured and that organic acids were a more likely explanation. We have attempted to determine if Sphagnum can exchange sufficient hydrogen to account for the low pH of the bog surface zone. To determine cation exchange capability of Sphagnum magellanicum in relation to the common cations of natural habitats, distilled and deionized water and different concentrations of Mg2+, Ca2+, K+, and Rudolph's Sphagnum nutrient medium were tested. In these experiments Sphagnum changes the pH of a surrounding liquid medium in the pH range of 3 to 7. The cation exchange capacity of Sphagnum magellanicum follows the series K+ < Mg2+ < Ca2+. Rudolph’s medium consists of many compounds that resulted in much less hydrogen being released than from solutions of single compounds. Different parts of plants have different abilities, depending on the cation, for lowering pH, and this ability differs among the cations examined. In our experiments the pH was lowered significantly by Sphagnum in all solutions containing cations, but the pH change was negligible when only distilled or deionized water was used. The lack of any contribution to the H+ concentration and an increase in pH in distilled and deionized water support the theory that the pH lowering in our experiments was a result of cation exchange and not of the contribution of organic acids from the moss. This suggests that for the lowering of pH to occur, cations are necessary in the surrounding medium and that the increase of H+ ions in the medium is due to an exchange withdissolved cations. © 1992 Maney Publishing.

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Journal of Bryology