Abstract: The accumulation of abiotic heavy metal elements may adversely affect plant growth. However, whether forest leaves resorb these heavy metals during senescence is not fully understood. We analyzed the changes of chromium (Cr), cadmium (Cd), and plumbum (Pb) contents in mature and senescent leaves during the growing season (from April to October) to elucidate resorption or accumulation efficiency of heavy metals in four types of mid-subtropical forests. The results showed obvious leaf resorption of Cr, Cd and Pb in four types of forests, although the resorption efficiency significantly varied across forest types, elements, and sampling months. The Castanopsis carlesii natural forest displayed Cr resorption in April and from July to October with the highest resorption rate of 67.8% in April, and Cd resorption in April and June, but Pb resorption only in October, while the elements showed accumulation in senescent leaves in other months. In contrast, the C. carlesii secondary forest displayed Cr resorption in April (the highest resorption rate of 62.5%), May, and October; it also showed Cd and Pb resorption in April and October, but the elements exhibited accumulation in senescent leaves in other months. Cr was accumulated in senescent leaves throughout the growing season in C. carlesii plantation, although Cd was resorbed in August and September, and Pb was resorbed in April, from July to August and October. Moreover, Cunning hamia lanceolata plantation showed Cr resorption in April and October, and Pb resorption in October, but Cd was accumulated in senescent leaves throughout the growing season. The resorptions of Cr and Cd were significantly higher in natural and secondary forests than those in plantations, while Pb showed an opposite pattern. In addition, the dynamics of Cr and Pb in mature and senescent leaves were significantly positively correlated with precipitation and negatively with temperature in four types of forests, whereas the changes of Cd were negatively correlated with the Cr and Pb. These results indicated that the natural and secondary forests are more efficient in avoiding Pb toxicity than plantations, which provides a new insight for forest establishment and sustainable management.

Key words: heavy metal, plantation forest, natural forest, resorption efficiency, mature leaf, senescent leaf.