RESPONSE TO SOIL MOISTURE SUPPLY IN THREE LEGUMINOUS SPECIES

Abstract

Detached nodules of Medicago lupulina, Lotus corniculatus and Trifolium repens were able to reduce acetylene for a period of 8 h in moist conditions, but the rate fell after 2 h when water stress was applied. Under moist conditions, nodules of Medicago lupulina and Trifolium repens , when measured while attached to or detached from the host plant, possessed the most rapid rate of N 2 (C 2 H 2 )‐fixation. Nodules of Lotus corniculatus showed by far the slowest rates. Relatively mild drought had less effect on N 2 (C 2 H 2 )‐fixation of L. corniculatus than the other two species. This legume also suffered fewer fatalities, maintained a relatively high shoot turgidity and shedded fewer root nodules during periods of desiccation. Under similar drought conditions, the N 2 (C 2 H 2 )‐fixation rate of Medicago lupulina nodules was drastically reduced and about half of the root nodules were lost. However, only half the plants died. The same severity of desiccation caused similar reductions of N 2 (C 2 H 2 )‐fixation in Trifolium repens as well as a very high fatality rate and massive loss of nodules. Severe and prolonged desiccation greatly affected N 2 (C 2 H 2 )‐fixation in all three species.