Chronic ozone exposure impairs the mineral nutrition of date palm (Phoenix dactylifera) seedlings

Chronic ozone (O-3) exposure in the atmosphere preferentially disturbs metabolic processes in the roots rather than the shoot as a consequence of reduced photosynthesis and carbohydrate allocation from the leaves to the roots. The aim of the present study was to elucidate if mineral nutrition is also impaired by chronic O3 exposure. For this purpose, date palm (Phoenix dactylifera) plants were fumigated with ambient, 1.5 x ambient and 2 x ambient O-3 in a free air con-trolled exposure (FACE) system for one growing season and concentrations of major nutrients were analyzed in leaves and roots. In addition, concentrations of C and N and their partitioning between different metabolic C and N pools were determined in both organs. The results showed that calcium (Ca), magnesium (Mg), iron (Fe), zinc (Zn), sodium (Na) and potassium (K) acquisition by roots was diminished by O-3 exposure of the shoot. For Ca, Mg, Fe and Zn reduced uptake by the roots was combined with reduced allocation to the shoot, resulting in a decline of foliar concentrations; for Na and K, allocation to the shoot was maintained at the expense of the roots. Thus, elevated O3 impaired both mineral uptake by the roots and partitioning of minerals between roots and shoots, but in an element specific way. Thereby, elevated O-3 affected roots and shoots differently already after one growing season. However, considerable changes in total C and N concentrations and their partitioning between different metabolic pools upon chronic O-3 ex-posure were not observed in either leaves or roots, except for reduced foliar lignin concentrations at 2 x ambient O-3. Significant differences in these parameters were shown between leaves and roots independent of O(3 )application. The physiological consequences of the effects of chronic O-3 exposure on mineral acquisition and partitioning between leaves and roots are discussed.