Cobalt and nickel accumulation in Nyssa (tupelo) species and its significance for New Zealand agriculture

Ninety-seven leaf samples taken from three cobalt-accumulating species of N yssa (tupelo) growing at various localities in New Zealand were analysed fo r Co and Ni to examine the range of Co and Ni concentrations found in New Z ealand specimens, as well as to determine whether their Co content was a me asure of the Co status of the soils. A further aim was to establish whether leaves could be used as a feed supplement to sheep and cattle in order to avoid Co deficiency in farm animals. Maximum Co and Ni concentrations were 95 and 32 mu g g(-1) (dry mass) in leaves of N. sylvatica with geometric me ans of 7.1 and 4.0 mu g g(-1), respectively. Comparable values were obtaine d for N. aquatica and N, sinensis. Bioaccumulation coefficients (BAC, i.e., plant/soil Co or Ni quotients) were 4-6 times higher for Co than for Ni an d showed a disproportionately high uptake of Co compared with Ni. BAC value s increased exponentially with decreasing Co concentrations in the soil, th us highlighting the possibility of using Nyssa to recover Co from soils imp overished in this element. It was calculated that leaf fall from three Nyss a trees, when used as a feed supplement, may provide sufficient Co to allev iate Co deficiency for up to 10 sheep, though this procedure will require f urther study before being recommended unequivocally.