Effect of Excess and Limited Soil Moisture on Nitrogen Fixation of Several Leguminous Crops

摘要

Greenhouse experiments were conducted to examine the effects of flooding and drought on the leaf and nodule water status, stomatal conductance, root respiration and nitrogen fixation of cowpea (Vigna unuiculata), alfalfa (Medicago sativa), soybean (Glycine max), bean (Phaseolus vulgaris), Aeschynomene americana, and Desmodium heterocarpon. Soybeans, cowpeas, and Aeschynomene exhibited a tolerance to flooding and the capacity to fix nitrogen in flooded plants remained about the same as the well-watered controls, whereas flooded Desmodium, bean, and alfalfa showed marked reductions in nitrogenase activity with a concommitant decline in plant water status and root respiration. Drought stress resulted in reductions in leaf and nodule water potentials, stomatal conductance, and root respiration as gravimetric soil water content decreased below 1% in the sandy soil medium. In general, nitrogenase activity declined along with other physiological processes, however, there was an indication that nitrogen fixation was more severely inhibited by drought.