Factors influencing the difference in dissolved ion inputs to the forest floor between deciduous and coniferous stands: comparison under high and low atmospheric deposition conditions

It is necessary to clear the relationship between physical and vegetation factors on the processes governing dissolved ion inputs to the forest floor to estimate correctly the values of atmospheric input to the forest. This study identified the factors influencing the differences in dissolved ion inputs to the forest floor between coniferous evergreen and broad-leaved deciduous species by analyzing the phenological variations of dry deposition and canopy exchange calculated by the canopy budget model under a high-deposition site near the city of Tokyo and a low-deposition site 84 km further away. At low-deposition site, vegetation factors such as capture efficiency did not explain the differences in Na⁺ or Cl^- dry deposition. Leaf physiological characteristics influenced the differences in the Mg²⁺ and Ca²⁺ canopy leaching values, and phenology, leaf wettability, and diffusion processes from water film into leaves influenced the differences in NH₄⁺ and NO₃^- input processes between tree types. At the high-deposition site, differences in the dry deposition of Na⁺, SO₄^2-, Cl^-, Mg²⁺, Ca²⁺, NH₄⁺, and NO₃^- between tree types were influenced by differences in capture efficiency between coniferous and broad-leaved canopies in the leafed period and by the absence of leaves in deciduous species after leaf fall. These results indicated that atmospheric deposition affected the capture efficiency of coniferous trees for dry deposition and enhanced the difference of dissolved ion inputs to the forest floor between coniferous and deciduous species.