Photosynthetic response to different light intensities and water status of two main Nothofagus species of southern Patagonian forest, Argentina

PERI P.L.; MARTINEZ PASTUR G.; LENCINAS M.V.

Journal of Forest Science

Czech Academy of Agricultural Sciences

Año: 2009 vol. 55 p. 101 - 111

1212-4834

Net photosynthetic rate (A) and stomatal conductance (gs) of seedlings of Nothofagus pumilio and N. antarctica leaves were measured at different light intensity (20, 150, 250, 500, 750, 1000, 1500 and 2200 µmol m-2 s-1 photosynthetic photon flux density, PPFD) and after 60 minutes of shade to determine the lag in the rise of photosynthesis rate from low to high irradiance levels (induction state). Also, A and gs were measured to evaluate the responses to water stress and the tolerance to waterlogging. N. pumilio had higher A values than N. antarctica for all light intensities measured with a maximum value of 16.8 µmol CO2 m-2 s-1 saturated at 1000 µmol m-2 s-1 PPFD. Values of gs for both Nothofagus species also declined as light intensity decreased. The times required for full induction of A were 18 and 27 minutes after the increase of PPFD (full sun) for N. pumilio and N. antarctica, respectively. There was a negative relationship between A and water stress expressed as pre-dawn leaf water potential (ølp) where the reduction in gs was the main factor that reduced A in both species. Tolerance to waterlogging was related with changes in A and gs being N. antarctica was more tolerant. These photosynthetic results of Nothofagus leaves to fluctuating light, water stress and waterlogging could be used to estimate the responses of regeneration to environmental conditions under the dynamic of natural stands, after silviculture practices and for restoration plans.