FLOODING, MINERAL-NUTRITION AND GAS-EXCHANGE OF MANGO TREES

Two-year-old cultivar 'Peach' mango trees (Mangifera indica L.) were grown in containers with (+ Fe) or without (- Fe) chelated iron in limestone soil for 7 months and exposed to one of three flooding regimes: non-flooded (control) and 10 or 20 days of flooding. Prior to the imposition of flooding, and about 80 days later, total leaf chlorophyll content (Chl) and foliar concentrations of N, P, K, Ca, Mg, Fe, Mn, Cu and Zn were determined. Initially, Chl and foliar Fe and Mn concentrations were higher, but foliar K, Ca and Mg concentrations were lower, in the + Fe trees than in the - Fe trees. After the imposition of flooding treatments, significant interactions were observed between iron fertilization and flooding treatments with regard to Chl and certain foliar nutrient concentrations. Therefore, the effect of flooding on mineral nutrition was analysed separately for each iron fertilization regime. For + Fe trees, Chl was unaffected by flooding treatment, but for - Fe trees Chl increased with increased flooding duration. For both iron fertilization regimes, foliar Mn increased with flooding and tended to be greatest with increased flooding duration. For both iron fertilization regimes, there was no effect of flooding on foliar N, Fe or Zn concentrations, and no clear effect of flooding on foliar Cu concentration. For + Fe trees, foliar P concentration was reduced in trees flooded for 20 days, but there was no effect of flooding on foliar P concentration in - Fe trees. Flooding resulted in reductions in foliar K concentration in - Fe trees, but not in + Fe trees. For both iron fertilization regimes, flooding resulted in a reduction in foliar Ca concentration. For + Fe trees, flooding for 20 days resulted in increased foliar Mg concentration, but there was no effect of flooding on foliar Mg in - Fe trees. Prior to flooding, net CO2 assimilation (A) was greater for + Fe trees than for - Fe trees.