Element concentrations in the boreal forest moss, Hylocomium splendens: variation due to segment size, branching patterns and pigmentation

Abstract

Concentrations of K, Mg, Ca, Cu, and Pb and dry weight were determined and branching patterns recorded for each of 353 mature annual Hylocomium splendens segments from a southern Norwegian boreal spruce forest-Concentrations of K, Ca, and Pb were negatively correlated with segment dry weight. This is interpreted as being due to luxury consumption of K in small segments, while a higher number of ion exchange sites per unit dry weight in small segments is considered to be the main reason for size-dependent variation in Ca and Pb concentrations. K, Mg, Ca, and Cu levels were lower in segments that ramify than in terminating segments, while the converse was true for Pb. When a new growing point is present to act as a sink for nutrients, extracellularly bound Mg is likely to be actively taken up to replace the Mg lost from the cytoplasm by translocation. Reduced competition from Mg for the exchange sites probably accounts for higher Pb concentrations in ramifying segments. Implications of the dependence of element concentrations on dry weight (growth rate) and branching patterns for biomonitoring by the moss method are briefly discussed. Segments possessing a characteristic bleaching syndrome showed reduced K and Mg levels compared to normal green shoots. A combination of several factors that favour ion leakage and chlorophyll degradation is likely to promote development of such pale segments. The role of acid precipitation in this respect is discussed.