Combined effect of inorganic carbon and different nitrogen sources in the growth media on biomass production and nitrogen uptake in young willow and birch plants

The combined effects of inorganic carbon in the nutrient solution and different nitrogen sources on biomass production were studied in young plants of birch (Betula pendula Roth.) and willow (Salix sp., clone no. DK 6351) grown in hydroponic culture media for 35 (birch) and 37 (willow) days. The plants were randomly assigned to six different treatments, in which three different nitrogen sources (ammonium, nitrate or both ions in a combination of 1:1) were used with or without bicarbonate. In all treatments, inorganic carbon increased the biomass production of birch by ca 10% compared with the controls. In willow, when nitrate was the source of nitrogen, the biomass production was ca. 50% greater with bicarbonate than without bicarbonate. When ammonium was the nitrogen source, the effect of inorganic carbon on growth of willow was smaller, and the dry mass production was only 19% greater than that of the controls. When ammonium and nitrate were given as 1: 1 combination, growth of willow was 19% less with bicarbonate than without bicarbonate. In willows, the large increase in biomass production obtained with the combination of bicarbonate and nitrate was associated with a great loss of inorganic carbon from the roots and decreased exudation of organic compounds.