Canopy settings shape elemental composition of the epiphytic lichen Lobaria pulmonaria in unmanaged conifer forests

Abstract

• Ecologically significant canopy leachates should be explored in undisturbed forests. • We used lichens to assess leachates from cottonwood/aspen and hybrid spruce canopy. • Standardized lichen transplants accumulated elements for 1 year in tree dripzones. • Base cations, soil pH and conifer bark pH was highest in cottonwood/aspen dripzones. • Lichen transplants are ecologically relevant indicators of throughfall chemistry. The importance of forest canopy settings for the elemental chemistry of epiphytic lichens in undisturbed forests is poorly understood despite its impact on epiphytes, understory vegetation and microbial soil communities. Here, we examine the elemental composition in standardized thalli of the cephalolichen Lobaria pulmonaria transplanted to the lower branches of Picea glauca x engelmannii in inland British Columbia. Transplants were attached to nets (avoiding direct contact with tree bark) exposed to natural canopy throughfall in three categories of natural forest stands: 1) within dripzones of Populus species in mixed stands always supporting L. pulmonaria ; 2) outside Populus dripzones, yet with L. pulmonaria and 3) outside Populus dripzones and without L. pulmonaria , which is the most common canopy setting. After one year, and with the exception of Fe and Al, the elemental content in lichen transplants changed within and between forest categories. Lichen transplants within Populus dripzones had more base cations (Ca, Mg, K) and less Mn than in the two categories outside dripzones. In Picea canopies outside Populus dripzones , lichen transplants had higher Ca, Na, Mo and lower C, S and Cu in trees with L. pulmonaria than without. The pH of Picea branches and soil within the rooting zone of trees with transplants were both approximately ten times more acidic outside Populus dripzones than within them. However, bark pH did not differ between the two categories of stands outside Populus dripzones. Based on our findings we conclude that canopy setting shapes the elemental composition of epiphytic lichen transplants, suggesting that such transplants might be used to monitor spatial variation in throughfall elements from forest canopies in unmanaged stands. We also conclude that elemental concentrations, Ca in particular, is a better predictor than bark pH for the occurrence of L. pulmonaria on Picea .