Abstract: About two third of Nand half of Pin leaves are transferred to trunk, branch and root, but part of Kin bark and wood seems to be excreted into soil during leaf falling season. Owing to the uptake of Ca and Mg being continued and the Si in bark and wood being partly transferred to leaves is much high than that in living leaves. The gross cycling rate of Nduring the season is calculated as 62—67%, mainly from internal cycle. The corresponding figure for Pis 31—36%, with half from internal and another half from external cycle. The gross cycling rate of K, Ca,Mg and Si is about 50% respectively, almost from external cycle.

Key words: Poplar, Nutrient cycling, influencing factor., evapotranspiration, Huaihe Basin, Boreal Ecosystem Productivity Simulator (BEPS)