Abstract: Fine root turnover has close relations with soil nutrient availability. However, owing to the differences in test objects and in the methodology for assessing fine root behaviors, some contradictory results could be obtained. In this paper, sequential soil core, in-growth core, and decomposition method were employed to study the effects of nitrogen fertilization on the fine root (diameter<1 mm) biomass production and turnover of Manchurian ash (Fraxinus mandshurica) plantation, and four calculation methods were used to determine the fine root’s standing biomass and turnover rate. The results showed that under nitrogen fertilization, the fine root’s standing biomass decreased, but its mean annual production (93.105 g·m^-2·a^-1) in 0-30 cm soil layer in 2003 and 2004 was similar to the control (93.505 g·m^-2·a^-1). The fine root’s mean turnover rate was higher under nitrogen fertilization (0.917 times·a^-1) than under the control (0.710 times·a^-1). Fine root production decreased significantly with soil depth, but its turnover rate was generally in adverse. Greater differences were observed in estimating the fine root production and turnover rate by the four calculation methods, with the highest values by sequential coring approach with compartmental-flow calculation, followed by in-growth-core, minimum maximum and adding increments method calculations.

Key words: Fate of apex buds, Box-counting dimension, Branching type, Branching pattern