Effect of inorganic carbon and different nitrogen sources on the uptake of mineral nutrients in small willow and birch plants

The combined effect of inorganic carbon and different nitrogen sources on the uptake of K, Mg, Ca, P, Fe, Mn, B, and Zn was studied in small birch (Betula pendula Roth) and willow (Salix sp., clone no. DK 6351) plants grown in hydroponic culture solution for 35 (birch) and 37 (willow) days. The plants were assigned randomly to eight treatments, in which four different nitrogen treatments (3 mmol/L NH4+-N, 3 mmol/L NO3- -N, and 3 mmol/L and 0.5 mmol/L combinations of NH4+-N + NO3--N, 1:1) were used without or with bicarbonate (0.74 mmol/L). Birch and willow plants grown with bicarbonate had different responses to the uptake of mineral nutrients, but both of the plants the effect of bicarbonate depended markedly on the source of nitrogen. The main consequence of the supply of bicarbonate was the increase in the uptake of K and Mg in plants grown in NO3--containing nutrient solution compared with the control plants. This increase in the uptake of K and Mg may be due to (i) the formation of organic acid as a result of bicarbonate metabolism in roots and/or to (ii) the increased demand for these nutrients after increased nitrogen uptake and higher biomass production in the NO3--N + HCO3- treatment than in the other treatments.