『Abstract
　The effects of Weak acids (WA) on the canopy leaching and uptake processes are evaluated by comparing the leached base cations or the absorbed protons while including and excluding WA, e.g. the WA-included method and the WA-excluded method. The seasonal WA throughfall flux is even larger than twice the bulk precipitation flux except summer, which not only partly agrees with the conclusion that the total deposition of WA equals twice the bulk or dry deposition flux in European Intensive Monitoring plots (level II), but also indicates the significant canopy leaching of WA in Shaoshan forest. The seasonal canopy leaching of base cations in association with WA accounts for 6-30％ of the total base cations in throughfall, with an annual mean of 23％, which is slightly higher than the 15％ at the Speulder forest in The Netherlands. The canopy exchange capacity of H⁺ to NH4⁺ is closed to 6.0 while neglecting the WA exchange, which probably supports the assumption that the exchange capacity of H⁺ is six times that of NH4⁺. Simultaneously, we suggest that the WA is competitive to a certain extent with protons to leach base cations of plant tissues during the canopy exchange processes.

Keywords: ammonium; base cations; canopy exchange; proton; subtropical evergreen forest; weak acids 』

1. Introduction
2. Material and methods
　2.1. Study site
　2.2. Sampling design and laboratory analysis
　2.3. Methodology
　　2.3.1. Fluxes calculation
　　2.3.2. WA-included model
　　2.3.3. WA-excluded model
3. Results and discussion
　3.1. Weak acids in bulk precipitation and throughfall
　3.2. Canopy leaching of base cations
　3.3. Canopy exchange of NH4⁺ and H⁺
　3.4. Effects of WA on canopy exchange ratio of H⁺/NH4⁺
4. Uncertainties
5. Conclusions
Acknowledgments
References