Guzmania lingulata (L.) Mez. `Cherry' were grown in coco chips and fertigated with half-strength Hoagland solution containing various concentrations of boric acid. Excessive boron induced changes in growth, relative chlorophyll content, and leaf anatomy were investigated. Plants treated with 5 mg·L–1 or higher boric acid concentration had reduced SPAD-502 readings and Fv/Fm values and increased leaf necrosis in the lower leaves. Boron was distributed unevenly within a leaf, with the maximum concentration in the leaf tip. Increased necrotic length and new leaves with necrosis were evident where average whole leaf boron concentration was higher than 170 μg·g–1 on dry weight basis. More leaf growth and higher transpiration or stomatal conductance were recorded in plants under 40% (average 676 μmol·m–2·s–1PPF at noon) than 76% (average 270 μmol·m–2·s–1PPF at noon) shade. Excessive boron was not found to affect epidermal cells or water storage tissue, but caused browning and shriveling of the chlorenchyma cells.
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