Nitrate Uptake and Reduction of Aseptically Cultivated Spruce Seedlings,Picea abies(L.) Karst

Spruce (Picea abies (L.) Karst.) seedlings were aseptically cultivated and the effects of different N-nutrition on net uptake and reduction of nitrate were investigated. The characteristics of nitrate uptake were calculated, K_s as 0·2 mol m⁻³ and V_max as 18 μmol g⁻¹ d⁻¹. Low pH, $NH4+$ and Al³⁺ in the medium caused a decrease in nitrate uptake rate. An in vivo assay was set up which allowed the measurement of NRA in both roots and needles of spruce seedlings. The in vivo nitrate reductase activity was repressed by ammonium and stimulated by nitrate. Nitrate reduction was similar to nitrate uptake, negatively affected by low pH and ammonium. Therefore, a limited N-supply to spruce seemed to occur when pH was low in the rhizosphere combined with the presence of Al³⁺ and $NH4+$.