Response to light of shade-grown beech seedlings subjected to different watering regimes

The morphological and physiological responses (net photosynthesis,
stomatal conductance, leaf chlorophyll concentration and leaf
orientation) of shade-grown beech seedlings after transfer to a
high-light regime were studied in well-watered plants and in plants
subjected to water stress. Immediately after exposure to high
irradiance, shade-grown seedlings displayed a lower photosynthetic rate,
a higher leaf chlorophyll concentration and a more horizontal leaf
orientation than light-acclimated plants (control plants). The
chlorophyll concentration of shade-grown plants gradually declined
throughout the period of exposure to high irradiance reaching the amount
observed in control plants. Rates of photosynthesis of shade-grown
plants began to recover after 8 days of exposure to high irradiance and
recovery was nearly complete after 30 days. Leaf orientation of
shade-grown plants also changed rapidly during the first 8 days of
exposure to high irradiance and by the end of the experiment, there were
no significant differences between shade-grown and control plants. Water
stress caused significant declines in net photosynthesis and leaf
conductance in both shade-grown and control plants. Net photosynthesis
did not recover completely in the shade-grown water-stressed plants
during the 30-day exposure to high irradiance. Reversible leaf
paraheliotropism and chlorophyll bleaching were observed in response to
soil drying followed by rewatering.