Nitrogen and Carbon Utilization inAlnus incanaFixing N2or Supplied with NO3-at the Same Rate

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Abstract
The purpose of this study was (i) to evaluate biomass production and nitrogen utilization in grey alder and (ii) to investigate carbon utilization in alders fixing nitrogen or supplied with nitrate. Two experiments were made, each using two groups of alders (Alnus incana (L.) Moench) growing in a climate chamber. In each experiment one group was inoculated with a local source of Frankia. The other group was not inoculated but received nitrate in the same amount as the first group fixed nitrogen. Therefore, the rate of nitrate application increased during the experimental period. Biomass production, growth, nitrogen content and nitrogen utilization were determined in one experiment. Growth, nitrate reductase activity, net photosynthesis and root respiration were measured in the second experiment. In experiment one there was no significant difference in biomass production between the two groups of plants. Of the nitrate given 99% was taken up and 1% of this uptake was excreted in an organic form. In the second experiment the plant development was similar in nodulated and non-nodulated alders during the period studied. Nitrate reductase activity was found in both root- and shoot-tips of the non-nodulated alders. At both days 24 and 30, the amount of carbon respired compared to the amount of carbon assimilated was similar for the nodulated alders as for the non-nodulated alders. As nitrogen fixation increased, photosynthesis also increased. Thus, there was an inter-relationship between net photosynthesis and nitrogen fixation.