Element microdistribution in the bark of Abies balsamea and Picea rubens and its impact on epiphytic lichen abundance on Whiteface Mountain, New York

Abstract

Epiphytic lichen cover and total element concentrations of bark were studied in a montane Abies balsamea-Picea rubens forest on Whiteface Mountain in upstate New York. Epiphytic lichen abundance was much higher on A. balsamea compared to P. rubens. The bark of A. balsamea was characterized by high total concentrations of Mn. Mn is known to limit epiphytic lichen abundance on Picea abies in the Harz Mountains, Germany, where total Mn concentrations in bark are much lower. The rich lichen cover on A. balsamea included a well-developed population of Hypogymnia physodes. This species has been experimentally proven to be sensitive to Mn in previous studies. Total Mn concentrations in the bark of P. rubens on Whiteface Mountain were in the same range as in the bark of P. abies in Germany. X-ray microanalysis showed that A. balsamea immobilized most Mn in crystals in spongy cork and in sclerotic phelloid cells of the outer bark. This immobilization explains the high lichen abundance on A. balsamea despite the high total Mn concentrations. Immobilization of Mn in the bark may also be a cause for the generally high epiphytic lichen abundance on Abies species other than A. balsamea. No Mn deposits were observed in P. rubens. The cover of several lichen species including H. physodes decreased with increasing (total) Mn/Fe ratio in the P. rubens bark. These correlations match with previous experimental findings showing an alleviation of Mn toxicity in H. physodes by Fe.