Visible injury, CO2 assimilation and PSII photochemistry of Eucaliptus plants in response to boron stress

Boron is an essential element required for the normal growth of plants, but in high concentrations it is toxic, causing reduction of leaf area, induction of chlorotic and necrotic lesions in older leaves, delay in development and general inhibition of growth. To gain an insight into the role of photosynthetic mechanisms in the response to boron toxicity, physiological parameters were analyzed in seedlings of Eucaliptus globulus treated with 0.1 (control), 1 and 10 mg l-1 (excess) H3BO3 in nutrient solution during 12 weeks. After 42 days of treatment, plants grown in the excess of boron developed symptoms in the mature leaves, in form of marginal necrosis. At the end of treatment, CO2 assimilation and stomatal conductance decreased (- 71% and - 30%, respectively, compared to control) when plants were supplied with 10 mg l-1 H3BO3; a reduction in growth (- 30% compared to control) and increase of B concentration in roots as a consequence of the treatment have been also observed.