Abstract:In order to understand the relationship between tree structure and its function, the vessel characters of sap wood of eight tree species, Acacia auriculaeformis, Schima superba, Michelia macclurei, Castanopsis hystrix, C. fissa, A. mangium, Eucalyptus citriodora and E. urophylla×E. grandis and their stem sap flux densities in wet and dry season monitored by using Granier's thermal dissipation probe method, were investigated in subtropical south China. The results showed that vessels were of single-type in these tree species except for M. macclurei that had two types of vessels. The vessel length, density and lumen diameter were significantly different among the eight tree species, and obvious relationships among the three vessel characters were observed. The normalized area of sap wood had significant relation with the vessel characters. No significant relation of the maximum sap flow with vessel characters was found, but it existed between the maximum whole tree transpiration rate and the vessel characters in wet season, and so did that of the daily total transpired amount with the vessel characters. Therefore, the vessel in trunk had no influence on sap flow rate, the negative trade-off relation between vessel diameter and sapwood area of trunk could the difference in water transpiration rate of trunk caused by the difference of vessel diameter of the tree species.