Stemflow can be an important pathway for the drainage of precipitation and related solutes through tree canopies to forest soils. As stemflow must drain along bark surfaces, the effects of bark structure on stemflow chemical composition is merited. This study examines the relationship between stemflow chemistry and bark surface structure for six species of varying bark morphology (four deciduous broadleaf trees and two evergreen coniferous trees) at a montane and an urban site in Japan. Stemflow from smooth-barked species contained greater concentrations of solutes that appear to be rinsed from the stem surface (i.e., sea salt aerosols); while, rougher-barked tree species contained greater or less concentrations of solutes that appear to be leached (e.g., Ca2+) or taken-up (e.g., inorganic N) by the bark, respectively. Site-specific atmospheric environments also influenced thee bark-stemflow chemistry relationships—where the greater elemental deposition in the urban plot generally resulted in greater stemflow chemistry than observed in the lower-deposition montane plot. Our results therefore suggest that the dynamics of dry deposition wash-off by stemflow, and the exchange of dissolved solutes between stemflow and the bark surface, are influenced by the surface structure of the bark and the site’s atmospheric environment. Therefore, the interactions between bark surface structure and its surrounding atmospheric environment are important factors in the stemflow-related elemental cycling between the tree and precipitation.

A fraction of rainfall drains to the soil surface down tree stems (as “stemflow”), and the resulting stemflow waters can be highly enriched with dissolved nutrients due to prolonged bark contact. To date, stemflow chemistry has been examined mostly in regards to the external morphology of the bark, while its relationship with bark anatomy has received little attention. Arguably, this represents a major knowledge gap, because bark anatomical traits are linked to the storage and transport of soluble (and insoluble) organic materials, and control the proximity of these materials to passing stemflow waters. To initiate this line of investigation, here, we examine bark-water leaching rates for common leachable macronutrient ions (Mg2+, Ca2+, and K+) across six different tree species with varying bark anatomical traits (four deciduous broadleaved and two evergreen coniferous species). These different bark types were subjected to laboratory experiments, including observations of bark anatomy and soaking experiments. Laboratory-derived estimates of leaching rates for Mg2+, Ca2+, and K+ were then analyzed alongside bark anatomical traits. Leaching rates of Mg2+ and Ca2+ appear to be controlled by the thickness of the rhytidome and periderm; while K+ leaching rates appeared to be driven by the presence of cellular structures associated with resource storage (parenchyma) and transfer (sieve cells). Other species-specific results are also identified and discussed. These results suggest that the anatomical features of bark and the concentration of leachable macronutrient ions in stemflow are related, and that these relationships may be important to understand nutrient cycle through the bark. We also conclude that future work on the mechanisms underlying stemflow solute enrichment should consider bark anatomy.