Biomass accumulation and allocation in seedlings of three Nothofagus species at the edges of a light gradient in canopy gaps of a Subantarctic forest.

摘要

Models of optimal partitioning and shade-tolerance propose that a proportional high aerial biomass contributes to plant persistence in light-limited environments. In this context, biomass accumulation and allocation in 4-year saplings of Nothofagus dombeyi, N. nervosa [N. alpina] and N. obliqua, growing at the edges of an irradiance gradient in canopy gaps of a Subantarctic forest, in Northern Patagonia [Argentina], was compared. Within the gap, relative mean light transmittance for summer was 5% in the northern periphery and 36% in the centre. Total saplings biomass (B) increased with light availability. N. nervosa tend to exhibit the higher B under the reduced sunlight of the northern periphery, probably due to its less light-demanding character. Although N. dombeyi in the adult stage is a fast-growing species, saplings accumulated less biomass than those of N. nervosa and N. obliqua, probably influenced by its comparatively lower seed nutrient content. Conversely, leaf biomass (H) was equivalent in all species. For each species, leaf mass fraction (H/B) was similar in both light conditions. This pattern is not consistent with the prediction based on optimal resource partitioning: plants invested less in the organ that would cause the strongest growth limitation at low irradiance. N. dombeyi allocated more assimilates to leaves compared to N. nervosa and N. obliqua, despite its extremely light-demanding character. Such a result does not comply with the hypothesis of a proportionally high leaf mass in species adapted to shade. This research may improve the understanding of an ecosystem encompassing trees with divergent light responses, and dependent on spatial and temporarily heterogeneous gaps for regeneration.