Differential responses of Abies fabri and Rhododendron calophytum at two sites with contrasting pollution deposition and available calcium in southwestern China

The correlation between forest decline and calcium (Ca) depletion under long-term acid deposition remains elusive in China due to the high level of Ca deposition. We compared two species (Abies fabri and Rhododendron calophytum) for their growth pattern and base elements concentration in both polluted (Mt. Emei) and unpolluted (Mt. Gongga) sites in Sichuan, southwestern China. A. fabri grown at Mt. Emei had poorer crown condition, slower radial growth rate, and lower seedling density under long-term acid deposition, which correlated closely with the reduced Ca concentration in foliage and tree-ring, in comparison with those at Mt. Gongga. In contrast, R. calophytum showed a stable Ca level and thus displayed normal growth between the two sites. The differential capability of these two species to acclimate to poor Ca environment is one of the keys to understanding the long-term ecological effect of changing atmospheric acid and Ca deposition in the subalpine forest in southwestern China.