Vertical distribution of fine root biomass of emergent Nothofagus dombeyi and its canopy associates in a Chilean temperate rainforest

In south-central Chile, basal area and wood volume development of Nothofagus spp. in some forests has been shown to be independent of that of associated tree species. Although this has been attributed to the emergent habit of Nothofagus, here we explore the possible role of belowground resource partitioning. We measured fine root biomass and vertical distribution of emergent Nothofagus dombeyi and its canopy associates in an old-growth rain forest, to test for evidence of vertical partitioning of belowground resources. Fine roots were sampled to a depth of 80 cm in three plots. Total fine root biomass averaged 4685 g m^-1, N. dombeyi contributing about 22% of this figure. Roots were concentrated mainly in the upper horizons, with 69% of the total occurring at <30 cm. However, fine root biomass of N. dombeyi declined significantly more steeply with depth than that of its associates did, the average contribution of N. dombeyi to total fine root biomass decreasing from 29% in the uppermost 10 cm, to little more than 1% at 70–80 cm. The observed differences in rooting depth could be linked to differences in mycorrhizal syndromes: ectomycorrhizal Nothofagus might be expected to be more shallow-rooted than the VAM and non-mycorrhizal canopy species, because of the reportedly greater ability of ectomycorrhizal species to assimilate organic nitrogen from the litter layer. A degree of belowground resource use complementarity may therefore minimize competition between N. dombeyi and its associates, and could thus contribute to the additive basal area and productivity observed in these forests.