Carbon storage of microbes and roots and the flux of CO2 across a moisturegradient

Living root biomass (tree roots less than or equal to 2 mm, tree roots >2 m m, and dwarf shrub roots), dead root biomass, microbial biomass carbon (C-m ic), and soil surface CO2 flux were investigated in a northern boreal mixed forest. Three study sites were established along a 100-m gradient with dif fering moisture and soil texture. The amount of total root biomass did not differ across the moisture gradient. The amount of living root biomass aver aged 1.46 kg.m(-2), and 1.04 kg.m(-2) was found as dead roots. Half of livi ng root biomass was fine roots (diameter less than or equal to 2 mm), and o f this fraction, 75% was fine roots of trees. The total amount of C-mic was lower on the dry site (78.5 g C.m(-2)) compared with the intermediate and mesic sites (95.3 g C.m(-2)). The C-mic to organic C ratio was 1.4% in the L+F+H horizon, and the ratio increased with increasing depth to 4.1% in the C horizon, which indicated that microbes in the deeper soil horizons decom posed recently deposited root litter or exudates. The storage of carbon in fine roots was four times more than that in C-mic. The soil surface CO2 flu x fluctuated seasonally but was similar across the gradient.