Element concentrations in the boreal forest moss Hylocomium splendens: variation related to gradients in vegetation and local environmental factors

Abstract

This study aims at assessing the suitability of Hylocomium splendens as a biomonitor for heavy metal deposition and contributing to the understanding of mineral nutrient uptake mechanisms in forest floor bryophytes. Concentrations of Ca, Mg, K, Cd, Cu and Pb were determined in Hylocomium splendens segment samples collected at 196 permanent vegetation plots from eleven monitoring areas, where the vegetation-environment relationships had previously been thoroughly studied. Element concentrations in Hylocomium splendens were related to environmentally interpreted vegetational gradients, cover of understorey vascular plants, and local environmental conditions, including element concentrations in humus, soil moisture and tree impact, by means of correlation analyses performed separately for each area. A combined test was performed for each Hylocomium splendens variable over all eleven areas, showing that concentrations of Ca, Cd and Mg in Hylocomium splendens were strongly correlated with the main vegetational gradient and with pH and concentrations of Ca and total N in humus, indicating considerable uptake of nutrients by Hylocomium splendens from water that has been in contact with humus. These relationships were less strong in the climatically most humid areas. Concentrations of all elements were more or less strongly correlated with one or more variables reflecting tree influence (tree density as measured by basal area and two crown influence indices) reflecting that throughfall precipitation, modified by leaching from the canopy, partly accounts for input of elements, especially for K, Cd and Mg. Only concentrations of Pb, Cd and Cu were significantly correlated, negatively, with vascular plant cover, indicating that supply of elements by leaching from understorey vascular plant foliage is negligible. The concentration of Cu in Hylocomium splendens was only weakly correlated, and the concentration of Pb unrelated to vegetational gradients and most environmental conditions. The results indicate that atmospheric deposition accounts for most of the input of Pb, confirming the suitability of Hylocomium splendens as a biomonitor for this element. For elements such as Cd local environmental conditions should be carefully considered, even when data from regional moss surveys are to be interpreted.