Relating tree ring chemistry of Pinus densiflora to precipitation acidity in an industrial area of South Korea

To test the possible use of tree ring chemical properties as proxies for precipitation acidity ([H⁺]), we investigated the relationships between tree ring chemistry (δ¹³C, δ¹⁵N, Ca-to-Al ratio, and N concentration) of Pinus densiflora and precipitation [H⁺] between 1992 and 2005 in an industrial area in the southwest region of South Korea. Statistical analyses showed that all tree ring chemistry parameters were significantly correlated with precipitation [H⁺]. Tree ring δ¹³C was negatively correlated with precipitation acidity (r∈=∈-0.67, P∈<∈0.01), reflecting the photosynthetic fixation of ¹³C-depleted CO₂ from fossil fuel combustion that would be the primary source of precipitation acidity. A positive correlation of N concentration (r∈=∈0.89, P∈<∈0.001) and a negative correlation of δ¹⁵N (r∈=∈-0.63, P∈<∈0.05) in tree rings with precipitation acidity most likely reflected the influence of ¹⁵N-depleted N compounds deposited via precipitation. The Ca-to-Al ratio was negatively (r∈=∈-0.58, P∈<∈0.05) correlated with precipitation acidity, indicating that soil acidification caused the loss of Ca from the soil and solubilization of Al resulting from acid precipitation. Such relationships suggest that δ¹³C, δ¹⁵N, N concentration, and Ca-to-Al ratio in tree rings can be reliably used to evaluate the impact of acid precipitation on the studied P. densiflora stands.