CARBON AND NITROGEN ECONOMY OF 4 TRITICUM-AESTIVUM CULTIVARS DIFFERING IN RELATIVE GROWTH-RATE AND WATER-USE EFFICIENCY

We investigated physiological and morphological traits underlying vari ation in relative growth rate (RGR) among wheat cultivars, Subsequentl y, we determined whether higher RGR is correlated with higher water de mand and lower plant water use efficiency (WUE(p)). Further, the corre lation between water use efficiency and leaf nitrogen concentration wa s examined, For this purpose we chose four cultivars contrasting in RG R or WUE(p). Gas exchange of shoots and respiration of roots were meas ured on intact plants over a 24 h period, and total carbon and nitroge n concentrations of all plant parts were determined, The highest RGR w as achieved by the cultivars with the highest leaf area ratio. WUE(p) was strongly dependent on photosynthetic water use efficiency and was highest for the cultivars with the highest rate of photosynthesis, whi ch achieved higher rates of photosynthesis per unit leaf nitrogen, We found no evidence for a functional or genetic link between the physiol ogical traits underlying differences in RGR (specific leaf area and le af area ratio) and those causing variation in water use efficiency (ph otosynthetic rate and transpiration rate), These results indicate that , in wheat, it may be possible to select simultaneously for traits ass ociated with a high WUE(p) and a high RGR.