Influence of nitrogen supply on uptake and translocation of strontium and calcium in wheat seedlings

Supplying nitrate to N-depleted wheat seedlings (Triticum vulgare cv. Knox) stimulated the uptake and translocation of both 83Sr and 45Ca. Since the increase in 45Ca accumulation was greater, the 85Sr/45Ca ratio in the plant tissue was decreased. Nitrate had relatively little influence on the amount of the divalent cations and 85Sr/45Ca ratio in the exchangeable fraction on the root surfaces, whereas it greatly increased the uptake into root tissue and translocation to shoots. The increase in percent transported to shoots occurred largely in the period of most rapid nitrate uptake. A split root study indicated that nitrate was ineffective when it was supplied to a different portion of the root system than that exposed to 85Sr and 45Ca. Nevertheless, ammonium and urea also increased the translocation of the two cations, indicating that the effects of nitrate could not entirely be ascribed to a direct effect of the nitrate anion.