Seasonal changes in biomass and vertical distribution of mycorrhizal and fibrous-textured conifer fine roots in 23- and 180-year-old subalpine Abiesamabilis stands

Abstract

Seasonal changes in biomass and vertical distribution of fibrous, mycorrhizal, and total conifer fine roots (≤ 2 mm) were examined in 23- and 180-year-old Pacific silver fir (Abiesamabilis (Dougl.) Forbes) ecosystems. In both stands, > 80% of fine roots was located in the upper 15 cm of the soil profile, in the forest floor (O1 and O2) and A horizon. During periods of active root growth in the young stand, significantly higher conifer root biomass occurred in the A horizon (370 to 690 g/m2) than the forest floor (200 to 350 g/m2). At all sampling times, a significantly higher biomass of conifer fine roots was located in the forest floor (550 to 1090 g/m2) than the A horizon (290 to 640 g/m2) in the old stand. In both stands, mycorrhizal roots comprised 10 to 15% of the total weight of conifer fine roots during peak root growth, 2 to 6% when roots were not growing, and 21 to 29% during the winter and early spring when roots were growing. Up to 69% of the biomass of fibrous and mycorrhizal roots was located in the forest floor in both stands.