PHYSIOLOGICAL RESPONSES TO WATER STRESS AND NITROGEN MANAGEMENT IN WHEAT (Triticum aestivum L.): EVALUATION OF GAS EXCHANGE, WATER RELATIONS AND WATER USE EFFICIENCY

A field experiment was conducted over 2 years to evaluate the gas exchange, water relations and water use efficiency (WUE) of wheat under different water stress and nitrogen management practices at Crop Physiology Research Area, University of Agriculture, Faisalabad. Pakistan. Four irrigation levels, i.e. one irrigation (Irrigation at tillering stage), two irrigations (Irrigations at tillering and anthesis stages), three irrigations (Irrigations at tillering, anthesis and grain development stages), four irrigations (Irrigations at tillering, stem elongation, anthesis and grain development stages) and four nitrogen levels i.e., 0, 50, 100 and 150 kg N ha were applied in this study. The photosynthetic gas exchange parameters (Net CO2 assimilation rate, transpiration rate and stomatal conductance) are remarkably improved by water application and nitrogen nutrition. The exposure of plants to water and nitrogen stress lead to noticeable decrease in leaf water potential, osmotic potential and relative water content. Relative water content (RWC) of stressed plants dropped from 98 to 75 % with the decrease in number of irrigation and nitrogen nutrition The higher leaf water potential, and relative water contents were associated with higher photosynthetic rate. Water use efficiency (WUE) reduced with increasing number of irrigations and increased with increasing applied nitrogen at all irrigation levels.