Fine root biomass in a tropical moist forest in the upper Negro River basin, Brazilian Amazon

Limited information on fine roots is hindering understanding of the geographical-scale variations in belowground carbon stock across the Amazon Basin. Fine root biomass (< 2 mm in diameter) was studied in the upper Negro River basin of Brazil, where no previous study on fine roots had been reported. Two plots (20x125 m), each of which included 3 subplots (20x20 m), were set in a tropical moist forest at Sao Gabriel da Cachoeira, north-western Brazil. The diameter of the trees (dbh > 10 cm) within each subplot was measured, and fine roots were sampled by coring soils from depths of 0-5, 5-10 and 10-20 cm at 12 points in each subplot. The fine root, coarse root, and aboveground biomass in the study forest were estimated as 7.03 +/- 0.65 (95 % CI), 32.6 +/- 15.0 and 253.6 +/- 152.7 Mg ha-1, respectively. Most of the spatial variance in fine root biomass was accounted among and within the subplot spatial scale of less than 20x20 m. The fine root biomass of the study site exceeded the values reported for some tropical forests in the central and eastern Amazon, which suggested regional differences in the fine root biomass in Amazonian forests.