Plant growth, leaf water potential, nitrogenase activity and nodule anatomy in Leucaena leucocephala as affected by water stress and nitrogen availability

Abstract

The effects of water stress and nitrogen availability on leaf water potential, nitrogenase activity, and growth was studied in a pot experiment with Leucaena leucocephala seedlings. Water stress was imposed on fertilized and unfertilized plants after inoculation with Rhizobium. Non-inoculated seedlings were used as control plants. Water stress lowered leaf water potential in all seedlings after 14 days of treatment. In inoculated seedlings, fertilized plants were more sensitive to water stress than unfertilized plants, as shown by a higher leaf water potential in plants of the latter treatment. Uninoculated and fertilized seedlings were most affected by water stress. This indicates that Rhizobium might increase stress tolerance in unfertilized seedlings at moderate water stress levels. The combined effects of water stress and applied fertilizers resulted in cessation of nitrogen fixation. Nitrogen fixation came to a complete stop after 22 days of water stress in fertilized seedlings. The different treatments were accompanied by anatomical changes of nodule structure. It is hypothesised that the leaf water potential may be used as an indicator to predict changes in nitrogen fixation in legume tree/shrub species during periods of water stress.