Dissolved organic carbon and nitrogen in precipitation, throughfall and stemflow fromSchima superba andCunninghamia lanceolata plantations in subtropical China

Abstract

Despite growing attention to the role of dissolved organic carbon (DOC) and dissolved organic nitrogen (DON) in forest nutrient cycling, their monthly concentration dynamics in forest ecosystems, especially in subtropical forests only were little known. The goal of this study is to measure the concentrations and monthly dynamics of DOC and DON in precipitation, throughfall and stemflow for two plantations ofSchima superba (SS) and Chinese fir (Cunninghamia lanceolata, CF) in Jianou, Fujian, China. Samples of precipitation, throughfall and stemflow were collected on a rain event base from January 2002 to December 2002. Upon collection, all water samples were analyzed for DOC, NO3 −−N, NH4 +−N and total dissolved N (TDN). DON was calculated by subtracting NO3 −−N and NH4 +−N from TDN. The results showed that the precipitation had a mean DOC concentration of 1.7 mg·L−1 and DON concentration of 0.13 mg·L−1. The mean DOC and DON concentrations in throughfall were 11.2 and 0.24 mg·L−1 in the SS and 10.3 and 0.19 mg·L−1 in the CF respectively. Stemflow DOC and DON concentrations in the CF (19.1 and 0.66 mg·L−1 respectively) were significantly higher than those in the SS (17.6 and 0.48 mg·L−1 respectively). No clear monthly variation in precipitation DOC concentration was found in our study, while DON concentration in precipitation tended to be higher in summer or autumn. The monthly variations of DON concentrations were very similar in throughfall and stemflow at both forests, showing an increase at the beginning of the rainy season in March. In contrast, monthly changes of the DOC concentrations in throughfall of the SS and CF were different to those in stemflow. Throughfall DOC concentrations were higher from February to April, while relatively higher DOC concentrations in stemflow were found during September–November period.