Carbohydrate storage, survival, and growth of two evergreen Nothofagus species in two contrasting light environments

A number of traits have been attributed important roles in tolerance of shade by plants. Some explanations emphasize traits enhancing net carbon gain; others emphasize energy conservation traits such as storage of non-structural carbohydrates (NSC). To date, cross-species studies have provided mixed support for the role of NSC storage in low-light survival. We examined NSC status, survival, biomass, and growth of large seedlings of two evergreen species of differing shade tolerance (Nothofagus nitida and N. dombeyi) grown in deep shade and 50% light for two growing seasons. We expected to find higher NSC concentration in the more shade-tolerant N. nitida and since allocation to storage involves sacrificing growth, higher growth rate in the shade-intolerant N. dombeyi. NSC concentration of both species was > twofold higher in 50% light than in deep shade, and in roots and stems did not differ significantly between species in either environment. NSC contents per plant were also similar between dead and living plants in deep shade. N. dombeyi outgrew N. nitida in 50% light, while this pattern was reversed in deep shade. Survival in deep shade was not correlated with NSC concentration. Leaf mass fraction was similar between species in 50% light, but lower in N. dombeyi in deep shade. Results provide little evidence of a link between carbohydrate storage and low-light survival in Nothofagus species, and support the view that understorey survival is primarily a function of net carbon gain. Patterns of variation in NSC concentration of the temperate species we studied are likely dominated by more important influences than adaptation to shade, such as limitation of growth or adaptation to cold stress.