Ecophysiological and edaphic studies in a Chilean mixed evergreen-deciduous Nothofagus forest.

摘要

This investigation has the following objectives: (1) to determine the age and size structure of five Nothofagus forest stands in central Chile, (2) to examine nutrient dynamics in soils and litter from those stands, and (3) to determine changes in photosynthesis rates and nitrogen use efficiency (NUE) with leaf age in evergreen and deciduous Nothofagus seedlings.; I first examined the size and age structure of five stands within a contiguous Nothofagus forest. The stands were (1) a pure stand of N. pumilio, a high elevation deciduous species, (2) a pure stand of N. dombeyi, a mid-elevation evergreen, (3) a pure stand of N. obliqua, a mid-elevation deciduous species, (4) a 2-species mixed N. dombeyi-N. obliqua stand, and (5) a 3-species mixed stand comprised of all three species. In these stands I measured dbh and used tree ring analysis to determine periodic basal area incremental growth rates (PBAI) for each species within each stand. Stand were uneven aged with median ages in the following order: pure N. dombeyi > pure N. pumilio > pure N. obliqua = 2-species mixed.; I also determined soil N mineralization, nitrification plant available P, organic C, and pH in each of these five stands. The N. obliqua stand had consistently higher soil nitrification rates and pH than pure stands of the other two species. Soils from pure deciduous stands had more plant available P than those of the pure evergreen stand.; Leaf litter from the three Nothofagus species released N and P at different rates. Evergreen N. dombeyi litter released N and P slower than litter from either deciduous species.; Photosynthesis rates and foliar N declined with leaf age in seedlings of both N. obliqua and N. dombeyi. Photosynthesis rates and NUE did not differ between the species.; These results suggest that the evergreen, N. dombeyi is adapted to nutrient poor soils, and in the relatively slow nutrient release from its leaf litter. I further suggest from these results that the first year of an evergreen N. dombeyi leaf is as efficient in its N use and C gain as is a deciduous N. obliqua.