Abstract: Minirhizotron approach was employed to investigate the seasonal variations of fine root production and mortality in Larix gmelinii plantation in 2004-2008. At the same time, air temperature, precipitation, and soil temperature and moisture at 10 cm depth were recorded. The overall aim of this study was to determine the seasonal patterns of fine root production and mortality in the plantation, and their relationships with the four environmental factors. On an annual basis, the fine root length production ranged from 0.20 to 0.78 mm·cm^-2, while the mortality varied from 0.26 to 0.72 mm·cm^-2. The mean fine root production and mortality in 2004-2006 were 0.67 mm·cm^-2 and 0.59 mm·cm^-2, respectively, being greater than the corresponding values (0.37 mm·cm^-2 and 0.39mm·cm^-2) in 2007-2008. During growth season (from May to October), the fine root production in late spring and early summer (June and July) occupied 51%-68% of total, while that in late autumn (October) only occupied 1%-4%. The root mortality in late summer (August) and autumn (September and October) ranged from 59% to 70%, but that in early spring (May) only ranged from 1% to 5%. Correlation analysis indicated that 66% of the variation in fine root production could be explained by air temperature, and only 24% and 27% could be explained by the soil temperature at 10 cm depth and precipitation, respectively. Fine root mortality only showed an exponential positive correlation with the soil temperature at 10 cm depth.

Key words: Larix gmelinii, fine root production, fine root mortality, environmental factor, minirhizotron, δ_D, δ¹⁸O, meteoric water line, excess deuterium (d value), water vapor source, Xiaolangdi Reservoir area, eastern monsoon region.