CO(2) Exchange and Dinitrogen Fixation of Subterranean Clover in Response to Light Level

Small swards of nodulated subterranean clover plants were grown in pots to a common dry weight under controlled conditions. The rooting medium was a porous calcined clay. All mineral nutrients except nitrogen were supplied daily in solution. Pots then were placed in an assimilation chamber for 3 days for the measurement of net CO₂ exchange at light levels ranging from 0.1 to 2.0 millieinsteins per square meter per second. N₂-fixation (acetylene reduction) of each pot was measured subsequently. H₂-evolution and N₂-fixation were measured for similar treatments in separate experiments using smaller pots.