The response to water stress was studied on white clover grown hydroponically. Two varieties (Crau and Huia) were both subjected to a moderate and a more-severe stress, induced by polyethylene glycol (10 and 20% respectively), in the presence of a nutrient solution poor in potassium (K] = 0.005 mM), or abundantly supplied (K2 = 5 raM). Dawn water potential and nitrogen fixation (acetylene reduction activity) decreased with the increasing stress. Conversely, the stomatal resistance increased when osmoticum was added. Crau had a lower stomatal resistance to the deficit, than did Huia. In relation with the K supply, treatment K2~ confirmed the superiority of Crau. Crau also showed greater nodule mass and number than Huia. The data show relationships between dawn water potential, stomatal resistance and nitrogen fixation activity.

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