Survival and growth of seedlings of 12 Chilean rainforest trees in two light environments: Gas exchange and biomass distribution correlates

Mortality, growth, gas exchange and biomass distribution were measured in the seedlings of 12 Chilean temperate rainforest angiosperm trees in two contrasting artificial light environments (150 and 12 mumoles m(-2) s(-1)), in order to explore life history diversity in this forest type, and examine the physiological and/or morphological traits associated with interspecific variation in seedling performance. Gas exchange traits were measured only in the high-light treatment (150 mumoles m(-2) s(-1)), owing to the very small size of leaves in the low-light treatment. Relative growth rates (RGR) in high light were strongly correlated with photosynthetic capacity (P < 0.0001). Mortality rates in low light had a strong positive correlation with light compensation point (P = 0.007) and photosynthetic capacity (P = 0.004). Furthermore, high-light RGR was strongly positively correlated with low-light mortality (P = 0.001). Biomass distribution traits showed little relationship with mortality or growth within either light level, except for a marginally significant positive correlation (P = 0.04) between leaf area ratio and mortality in low light. In view of the large interspecific differences in final size, the weak relationships between biomass distribution parameters and plant performance could be partially attributable to ontogenetic drift in these traits. Among taxa with high mortality rates in low light, short-lived species (e.g. Aristotelia chilensis) had lower light compensation points, had greater phenotypic plasticity and grew much faster in both light environments than did longer-lived species (Nothofagus dombeyi , Weinmannia trichosperma, Eucryphia cordifolia). Results support the view that survival of first-year seedlings in low light is not enhanced by morphological traits that maximize growth potential (e.g. high leaf area ratio), and that leaf-level gas exchange traits have an important role as determinants of interspecific variation in seedling performance. However, the limited range of interspecific variation observed in light compensation points indicates that other traits apart from those that we measured (e.g. carbon storage) must also be involved in seedling shade tolerance differences. The weak relationship between longevity and shade tolerance level among our 12 species suggests that it may not be feasible to ordinate life histories of Chilean temperate rainforest trees on a single axis of trait variation.