Photosynthetic plasticity of Nothofagus pumilio seedlings to light intensity and soil moisture

MARTÍNEZ PASTUR, G; LENCINAS, MV; PERI, P; ARENA, M

FOREST ECOLOGY AND MANAGEMENT

ELSEVIER

Lugar: Amsterdam; Año: 2007 vol. 243 p. 274 - 282

0378-1127

Nothofagus seedlings often survive and grow slowly for a long time in the shaded understory. This creates a seedling bank with a potential advantage in reestablishing canopy disturbances. To manage primary forests more effectively, it is important to understand the basis of regeneration ecophysiology, and their plasticity to the changes in environemtal factors. The objective was to evaluate the photosynthesis plasticity of N. pumilio seedlings to light intensity and soil moisture gradients; and to relate them with the silvicultural prescriptions. Six treatments with three light intensities (4%, 26% and 64% of the natural incident irradiance) and two soil moistures (40-60% and 80-100% soil capacity) were assayed under greenhouse controlled conditions. CO2 gas exchanges were measured every month on seedlings growing in each condition. Seedlings grow below their optimum phototsynthetic potential in the shaded treatments (leaf level light-saturated net photosynthesis rate of 5.1 µmol CO2 m-2 s-1), and quickly adapted to the lighted treatments improving their photosynthetic performance (8.3-8.4 µmol CO2 m-2 s-1), as well as in the low soil moisture treatments compared to the higher ones (7.8 µmol CO2 m-2 s-1 and 6.6 µmol CO2 m-2 s-1, respectively). When light (up to 150-200 µmol m-2 s-1) and soil moisture (40-60% soil capacity) levels are favourable, seedling plants could exhibit their maximum photosynthetic capacity. If some of these factors are a limited resource, the plants reduce their photosynthesis, e.g. Nohofagus pumilio seedlings with enough light and high levels of soil moisture, probably decrease their growth and fine roots activity. For this, application of silviculture systems must take in account the changes in both factors (light and soil moisture) for maximize the growth potential in the natural regeneration. These findings must be combined to morphological variables obtained at whole-plant, shoot, crown and leaf levels to determine the optimum growth conditions.