Temporal and depth-related patterns of fine root dynamics in northern hardwood forests

1 The dynamics of fine (< 2.0 mm) roots growing in two northern hardwood forests were quantified to a depth of 1 m in 10-cm increments, We hypothesized that patterns of root production and mortality would be broadly synchronous at all depths, but that deep roots would be comparatively less dynamic than shallow roots, 2 Our data showed that shallow roots were responsible for the majority of total annual fine root production and mortality. Nearly half of all roots growing and dying in the I-m profile occurred in the upper 20 cm of the soil, while roots located at depths of 75 cm or more accounted for only 11% of annual production and 4% of annual mortality. 3 Fine root production prior to, or coincident with, canopy expansion was significant at all depths. The relative importance of early fine root growth generally increased with depth, with between 50 and 80% of annual production occurring prior to mid-June at depths exceeding 50 cm. Episodic deep root production during the growing season appeared to be related to periods of high water demand. 4 Patterns of fine root mortality were more variable among depths. Mortality was distributed rather evenly throughout the year near the soil surface, but mid-season mortality was generally low at depths greater than 50 cm.