Hydrogen evolution from root nodules ofTrifolium repensandMedicago sativaplants grown under elevated atmospheric CO2

Abstract

Abstract Nitrogenase activity and hydrogen (H2) evolution from nodules of Trifolium repens L. and Medicago sativa L. were measured on plants grown under 700 or 350 μl/1 atmospheric CO2 and day/night temperatures of 18/13°C or 28/23°C. Assays were done after 39, 47, and 54 days' exposure to the treatments. In Trifolium, nitrogenase activity/plant was stimulated by elevated CO2 and higher temperatures but in Medicago only temperature had an effect. Hydrogen emission/plant was greater in Trifolium plants grown at 700 °l/1 CO2 than in plants at 350 °l/1 CO2, but in Medicago, H2 emission rates did not respond to elevated CO2. Elevated CO2 reduced nodule relative efficiency (RE) in 39-day-old Trifolium plants growing at 18/13°C, but not under other conditions. It is concluded that predicted future CO2 concentration will lead to a greater contribution from legume nitrogen (N) fixation to global H2 sources. The magnitude of the increase will be influenced by the legume species involved and temperature.