Agronomical and physiological response of geranium to salinity and boron toxicity

High salinity and boron often occur together in irrigation water in arid climates. A greenhouse experiment was conducted to evaluate: 1) the effects of high salinity and boron on growth, water relations, gas exchange, photochemical performance and ion uptake in geranium of the Mediterranean area (Pelargonium x hortorum L.H. Bailey); and 2) the interaction of both factors. Potted plants were irrigated in a factorial combination of boron (1 and 10 mg/L) and NaCl (2 and 9 dS/m). Toxicity by boron reduced aerial part dry weight and caused edge burn in the mature leaves, while salinity decreased the aerial growth and caused little visible damage to leaf blades. At high salinity levels, boron excess was less detrimental, both visually and quantitatively, than at low salinity levels. A strong accumulation of boron, chloride and/or sodium in the leaves was the determining factor of damage to this species. At the two concentrations of boron studied, increased salinity reduced the leaf boron content. High salinity induced plant growth reduction, principally due to a smaller leaf area available for photosynthesis rather than due to a restriction in net assimilation rates, while both aspects participated under boron toxicity. The photochemical apparatus of geranium was not damaged by excess boron or high salinity (non-burned part). Overall, the interaction of salinity with boron had an antagonistic effect; however, an additive effect was observed when we studied, leaf sodium, leaf chloride and evapotranspiration.