This Article Full Text (PDF) Alert me when this article is cited Alert me if a correction is posted Services Email this article to a friend Similar articles in this journal Similar articles in Web of Science Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via CrossRef Citing Articles via Web of Science (15) Citing Articles via Google Scholar Google Scholar Articles by Sasakawa, H. Articles by Larue, T. A. Search for Related Content PubMed PubMed Citation Articles by Sasakawa, H. Articles by Larue, T. A. Agricola Articles by Sasakawa, H. Articles by Larue, T. A.

Articles

Root Respiration Associated with Nitrate Assimilation by Cowpea ¹

Boyce Thompson Institute, Ithaca, New York 14853

Nitrate uptake by roots of cowpea (Vigna unguiculata) was measured using ¹⁵NO₃^–, and the energy cost to the root was estimated by respirometry. Roots of 8-day-old cowpea seedlings respired 0.6 to 0.8 milligram CO₂ per plant per hour for growth and maintenance. Adding 10 millimolar NO₃^– to the root medium increased respiration by 20 to 30% during the following 6 hours. This increase was not observed if the shoots were in the dark. Removal of NO₃^– from the root medium slowed the increase of root respiration. The ratios of additional respiration to the total nitrogen uptake and reduced nitrogen content in roots were 0.4 gram C per gram N and 2.3 grams C per gram N, respectively. The latter value is close to theoretical estimates of nitrate assimilation, and is similar to estimates of 1 to 4 grams C per gram N for the respiratory cost of symbiotic N₂ fixation.

¹ Supported by grant 05-0560 from the United Nations Development Program to the International Institute for Tropical Agriculture.