Assessing the role of foliar habit on nutrient losses in a sub-Antarctic forest

Biogeochemical cycles drive global biodiversity and plant productivity. In terrestrial ecosystems, nutrient losses through plants' litter are a critical component of these biogeochemical cycles. In forests, nutrient losses are thought to be higher in deciduous angiosperm species than in evergreen conifers. However, this premise of nutrient loss differentiation between contrasting leaf habits has not been evaluated in co-occurring deciduous and evergreen broadleaved tree species. We conducted a high-frequency monitoring study of nutrient losses in congeneric and sympatric broadleaved tree species with contrasting leaf habits. We collected litter periodically for three years from 979 co-occurring trees of the deciduous Nothofagus pumilio and Nothofagus antarctica and the evergreen Nothofagus dombeyi in a sub-Antarctic forest of southern Chile. We estimated and compared foliar habits' litterfall biomass (senescent and green leaves and fruits), nutrient return through litterfall's nitrogen (N) and phosphorus (P) contents, and synchronization between litterfall mass and nutrient concentrations for each species. Annual litter biomass was higher in the two deciduous species (on average 2.01 t ha^-1) than in the evergreen species (1.63 t ha^-1), with senescent leaves representing >90% of litter in the three species. Litter N and P concentrations were significantly lower in the evergreen species. Thus, deciduous species had significantly higher N (15.82 kg ha^-1) and P (1.55 kg ha^-1) annual returns than the evergreen species (N: 8.20 kg ha^-1, P: 0.83 kg ha^-1) through litter of senescent leaves. A synchronization between maximum litterfall production and minimum litter concentrations for N but not for P was found in both leaf habits, although more consistently for deciduous than for the evergreen. Nutrient losses through litter were higher in deciduous than in evergreen Nothofagus species, demonstrating a nutrient loss differentiation between contrasting leaf habits of co-occurring broadleaved tree species. This study deepens our understanding of plant nutrient strategies associated with leaf habit and underscores the importance of diverse mechanisms of nutrient loss when evaluating forest nutrient dynamics.