Biomass production and nitrogen utilization byAlnus incanawhen grown on N2or NH4+made available at the same rate

摘要

A single clone ofAlnus incana(L.) Moench was grown in a controlled-environment chamber. The plants were either inoculated withFrankiaand fixed atmospheric nitrogen or were left uninoculated but received ammonium at the same rate as the first group fixed their nitrogen. Nitrogen fixation was calculated from frequenct measurements of acetylene reduction and hydrogen evolution. The diurnal variation of acetylene reduction was also taken into account. The relative efficiency of nitrogenase could be used in the calculations of fixed nitrogen since theFrankiaused did not show any detectable hydrogenase activity. Alders fixing nitrogen developed more biomass, longer shoots, larger leaf areas and contained more nitrogen than alders receiving ammonium. In one experiment, almost all ammonium given to the non-nodulated alders was taken up and 15 of the nitrogen taken up was excreted. In the other experiment, 34 of the ammonium was left in the nutrient solution and 8 of the nitrogen taken up was excreted. Alders inoculated withFrankiadid not excrete any detectable amount of nitrogen. It seems that the energy demand for nitrogen fixation is not so high that biomass production in alders is retarded. The symbiotic system ofA. incanaandFrankiaseems to be more efficient in utilizing its nitrogen than non-symbioticA. incanareceiving ammonium.