Effect of osmotically induced leaf moisture stress on nodulation and nitrogenase activity ofGlycine max

Abstract

The effect of 2-day cycles of osmotically induced leaf moisture stress followed by partial recovery on the nodulation and nitrogenase activity of 2 soya cultivars was studied. Fourteen days after plant inoculation (mid-growth stage) the total leaf electrochemical water potential (ψwleaf) of control plants ranged from −0.8 to −1.9 bars, whereas the concentrations of osmoticum (polyethylene glycol 4000) induced ψwleaf values ranging from −1.4 (recovery value) to −3.1 bars (low stress), −1.8 to −4.4 bars (mild stress), and −2.2 to −6.2 bars (medium stress). The low stress treatment reduced nodule numbers and their specific activity in both cultivars, without affecting nodule size or the time required for nodule initiation. Nodule initiation was delayed in both cultivars by the mild and medium stress treatments, the former treatment reducing the number and size of the nodules and such nodules exhibited very low specific activity. The medium stress treatment prevented the further development of nodule initials, which remained inactive throughout the experiment. Such results imply an effect of water stress on the infection process and on nodule morphogenesis. The reduction in nodule numbers observed in water stressed plants was not associated with a reduced number of rhizobia in the rhizoplane nor due to an effect on root growth or root hair formation.