Comparative Foliar Atmospheric Mercury Accumulation across Functional Types in Temperate Trees

Abstract

Vegetation assimilation of atmospheric gaseous elemental mercury (GEM) represents the largest dry deposition pathway in global terrestrial ecosystems. This study investigated Hg accumulation mechanisms in deciduous broadleaves and evergreen needles, focusing on how ecophysiological strategies─reflected by δ¹³C, δ¹⁸O, leaf mass per area, and leaf dry matter content-mediated Hg accumulation. Results showed that deciduous leaves exhibited higher total Hg (THg) concentrations and accumulation rates (THg_rate), which were 85.3 ± 17.7 and 110.0 ± 0.3% higher than those in evergreen needles. The two tree types exhibited distinct ecophysiological strategies: deciduous broadleaves, with higher stomatal conductance and photosynthetic rates, rapidly adjust stomata to changes in meteorological and pollutant factors, playing a key role in controlling THg_rate. In contrast, evergreen needles featured stable stomatal control, highlighting the direct positive effect of GEM on their THg_rate. Precipitation and wind speed negatively influenced foliar THg_rate. Correlations between PM_2.5, NO₂, and THg_rate in evergreen needles suggested synergistic patterns between atmospheric Hg and pollutants. This study underscores distinct GEM accumulation mechanisms across tree functional types and emphasizes the importance of species-specific foliar ecophysiological strategies. An empirical model linking THg_rate with ecophysiological, meteorological, and atmospheric pollution factors was provided, contributing to the refinement of foliar Hg accumulation models.