Plant uptake of dual-labeled organic N biased by inorganic C uptake: Results of a triple labeling study

Direct plant uptake of organic nitrogen (N) is often studied using the dual-labeling approach ((15)N + (13)C or (15)N + (14)C). However, the method might be hampered by uptake of labeled inorganic carbon (C) produced by mineralization of labeled organic compounds. Here we report the results from a triple labeling experiment ((15)N + (13)C + (14)C) investigating whether root uptake of labeled inorganic C can bias the results obtained in studies of organic N uptake using dual-labeled amino acids ((15)N, (13)C). In a rhizosphere tube experiment we investigated (13)C and (14)C uptake by maize either supplied with labeled glycine or CO(3)(2-), but found no differences in uptake rates between these C-sources. The uptake of inorganic C to the shoot tissue was higher for maize grown in full light compared to shading, which indicates a passive uptake of inorganic C with water. We conclude that uptake of inorganic C produced by mineralization of amino acids can significantly bias the interpretations of organic N uptake studies using dual-labeling. (C) 2009 Elsevier Ltd. All rights reserved.