Physiological and morphological traits associated with nitrogen uptake and use in Moroccan wheats at different moisture regimes

Nitrogen (N) fertilizer recommendations are among the crucial problems to be addressed for the erratic conditions of the arid and semi-arid areas of Morocco. One potential solution to this problem for wheat is the selection of cultivars with improved N use efficiency. However, to be more efficient, selection requires the understanding of the physiological and morphological mechanisms associated with N uptake and use under different soil moisture regimes. To reach this objective, studies were conducted with three bread wheat cultivars. Water regime differences were created by a line source irrigation system in the field, or by withholding water during stem elongation in the controlled environments. Data from the greenhouse and growth chamber studies showed that overall, Merchouch 8 had higher CO{dollar}sb2{dollar} assimilation efficiency (AEI) and CO{dollar}sb2{dollar} exchange rate (CER) and was more adapted to different soil N conditions than the other cultivars. Severe water stress masked the effect of N on dry matter production and shoot N content, and decreased N uptake and influx. The reduction of growth due to water stress was more important under high than low N. Plants that were water stressed during stem elongation increased their N influx during the period of recovery to a higher level than those not stressed. Under water stress, both high and low N tended to stimulate some stomatal closing. However, CER decreased only when N rate was increased.; Field studies showed that grain and biomass yields were affected by water regime x N x cultivar interaction. Merchouch 8 was the most and Saada the least responsive to N rate increase. Nitrogen supply had a negative effect on nitrogen harvest index under the dry regime. The earliest cultivar, Merchouch 8 used more water, but had higher water use efficiency, and produced more grain and biomass when N was provided. Canopy temperature measurement was a better indicator of wheat performance than diffusive resistance. Nitrogen supply tended to increase dry matter production, leaf area index and root length per volume of soil.