Seasonal changes in the photosynthetic performance of two evergreen Nothofagus species in south central Chile

the evergreen nothofagus dombeyi and nothofagus nitida are important members of the temperate chilean rainforest. they seldom grow together in nature. nothofagus nitida is more susceptible to excess light and drought than n. dombeyi. we postulate that the different properties of the photosynthetic apparatus under common garden conditions of these species could explain their contrasting habitat preferences. the two species growing in a common garden in south central chile were studied. the optimal photochemical efficiency (fv/fm) of both species remained within normal values (？0.8) with the exception of a decrease in n. dombeyi at midday in summer, suggesting reversible reduction in photochemical efficiency of photosystem ii (psii). during summer the effective photochemical efficiency (fpsii), photochemical quenching (qp), photosynthesis (amax), stomatal conductance (gs) and transpiration rates (e) in n. dombeyi were higher than in n. nitida. the highest increments in photoprotective pigments (zeaxanthin + antheraxanthin and lutein) contents between predawn and midday were obtained in summer in n. dombeyi. in n. nitida a nocturnal retention of dissipative pigments, without a decrease in fv/fm, was found in winter. the results suggest that n. dombeyi showed a better photosynthetic performance than n. nitida under high light, high temperature, and drier conditions. these data support are consistent with the pioneer character of n. dombeyi and the semi-tolerant shade properties and more restricted distribution of n. nitida. these photosynthetic characteristics, along with their freezing and flooding resistance differences, may result from their habitat separation