Exchange of Proton and Major Elements in Two-Layer Canopies Under Acid Rain in a Subtropical Evergreen Forest in Central-South China

Canopy exchanges of H⁺ and N (NH₄⁺‐N, NO₃^?‐N) and other major ions were evaluated and quantified in two‐layer canopies based on throughfall measurements in Shaoshan Forest during the period 2000–2002, central‐south China. The collected annual rainfall, throughfall, and sub‐throughfall were 1401,1191, and 1 084 mm/year, respectively. Fifteen percent and 8% of rainfall (or 9% of throughfall) were intercepted by the top canopy and sub‐canopy layers, respectively. The foliar leaching of base cations from the top canopy was significantly higher than that from the sub‐canopy, and the latter accounted for 25% of the former. The uptake of H⁺ and NH₄⁺ was significantly higher in the top canopy than in the sub‐canopy, indicating that the canopy buffering capacity in the top canopy was stronger than the sub‐canopy; Mg²⁺ can be absorbed from water flux on the sub‐canopy foliar surfaces to compensate for the Mg deficit in the forest soil during the growing season. (Managing editor: Ya‐Qin Han)