Examination of vertical distribution of fine root biomass in a tropical moist forest of the central amazon, Brazil

Abstract

Fine roots are an important component of the carbon flow of forests. Soil properties in tropical forest (terra firme forest) of the Central Amazon differ substantially along topography, and the biomass and vertical distribution of fine roots may also differ accordingly. Information on the vertical distribution of fine roots is essential to obtain unbiased estimates of fine root biomass. Accordingly, we examined fine root biomass and its vertical pattern along the gradient of topography in a typical terra firme forest in this region. The regressions on the cumulative fine root biomass along soil depth (at 5 cm intervals from 0-40 cm in depth) revealed significantly different vertical distribution of fine root biomass among three topographic habitats (lower-slope valley called baixio, mid-slope, and upper-slope plateau). A shallower rooting pattern was observed in the plateau than the other habitats, while fine root biomass was larger in the baixio than the plateau-a difference likely attributable to the soil physical properties than the aboveground stand structures among the sites. More than 74 and 93% of the fine root biomass was estimated to be distributed within the upper 20-and 40-cm soil layers, respectively. Our results suggested that a shallow sampling depth, which is common in fine root research in the Amazon, would be reasonable, though we should examine the consistency of our results in different regions.