| Abstract: | The impact of nitrogen(N)deposition on dissolved organic carbon(DOC)fractions in throughfall is not well understood.We performed a laboratory experiment and compared DOC leaching from canopy leaves after dipping leaves in pure water(control)and NH_4 NO_3 solution(N-treatment)for 18 h.Net changes of DOC,NH_4~+,NO_3~-,SO_4~(2-),K~+,Mg~(2+),Ca~(2+) and H+ contents after dipping leaves were determined by comparing solutions with and without leaves.We recorded no differences of DOC leaching between control and N-treatment,implying that N deposition had minor impacts on canopy DOC production.This confirmed that previous experiments testing the effects of N addition on DOC dynamics without considering the effects of the canopy reaction successfully described the real situation.We also confirmed the previously-reported canopy exchange process in spite of a high background N deposition at our study site.N-treatment significantly increased base cation leaching,especially K~+,and the increase was positively correlated with foliar NH_4~+ retention.Net leaching of H~+ and SO_4~(2-) was not affected by the N-treatment. |
