Contrasting tree ring Hg records in two conifer species: Multi-site evidence of species-specific radial translocation effects in Scots pine versus European larch

Amsterdam

2021

14 S.

Sonderdruck

40002235

Tree ring records are increasingly being used as a geochemical archive of past atmospheric mercury (Hg) pollution.
However, it is not clearwhether all tree species can be used reliably for this purpose.Wecompared tree-ring Hg records of two coniferous species -widely used Scots pine (Pinus sylvestris) and less frequently used European larch (Larix decidua) at 6 study sites across the Czech Republic. Site-specificmean Hg concentrations in tree-ring segments of larch ranged from 2.1 to 5.2 μg kg−1, whereas pine had higher mean Hg concentrations (3.6–8.3 μg kg−1). Temporal records of Hg concentrations in tree rings of larch and pine differed significantly. Comparisons with previously documented peat Hg records showed that larch tree-ring Hg records more closely agreed with peat archive records. For pines, which had a large, tree-age dependent number of sapwood rings (62 ± 17, 1SD), we found a strong relationship between the year of peak Hg and the number of sapwood tree rings (p = 0.012, r2 = 0.35), as well as between peak Hg year and the sapwood-heartwood boundary year (p < 0.001, r2 = 0.65), rather than with temporal changes in atmospheric Hg levels. The much greater number of pine sapwood tree rings appears to promote radialHg translocation, resulting in the shift ofHg peaks backward in time through the tree-ring record. In contrast, Larch consistently had a low number of sapwood tree rings
(19±6, 1SD), and more closely agreedwith peat Hg records. This study suggests that European larch, a tree species
characterized by a relatively low and consistent number of sapwood tree rings, records changes in atmospheric
Hg concentrations more reliably than does Scots pine, a species with a relatively high and variable number of sapwood tree rings.
Keywords: Tree rings; European larch; Larix decidua; Pinus sylvestris, Mercury Atmospheric Hg; Biogeochemical archives;
Heartwood Sapwood.