Exchanges of major elements in a deciduous forest canopy.

Forest canopy is a complex interface between the atmosphere, the biosphere and the lithosphere, exerting a strong influence on forest durability through element recycling. Leaves are filters of the low atmosphere and can capture dry deposition (DD). Trees have developed strategies, such as resorption (R) during senescence, for nutrient conservation. These strategies seem to depend on the soil type. The chemical composition evolution of leaves is conceptualized as a function of four fluxes: foliar absorption (FA) foliar leaching, (FL), accretion (A), and resorption (R). The objective of this study is to evaluate these five fluxes, i.e., DD, FA, FL, A, and R for different elements (N, P, K, S, Ca, Mg, Mn, and Si) at the experimental forest site in Montiers which includes three plots with contrasting soils and similar climate and stand characteristics. The percentage of resorption was 63% for N, 37% for S, 35% for K and 23% for P, regardless of the soil type. Resorption represents the most efficient recycling mechanism for ecosystems. Accretion during senescence occurs in two elements that are also found as biominerals in leaves: Ca (13–26 kg.ha−1.y−1) and Si (3–6 kg.ha−1.y−1). The effect of soil is limited to leaf concentrations and exchanges, and only for three elements (Mn, Ca and Si) that are not growth-limiting elements in our study site. This study shows that, except for N, taking into account the exchanges between living foliar tissues and leaching solutions is fundamental to accurately estimate the resorption rate. [ABSTRACT FROM AUTHOR]