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)