ASSOCIATION OF WATER-USE EFFICIENCY AND NITROGEN USE EFFICIENCY WITH PHOTOSYNTHETIC CHARACTERISTICS OF 2 WHEAT CULTIVARS

We examined if higher plant water use efficiency is related to a highe r investment of nitrogen in components of the photosynthetic apparatus and if this is associated with a less efficient use of nitrogen for p hotosynthesis or for growth, We also assessed the influence of a reduc ed supply of water and nitrogen on these relationships, For this purpo se we used two Triticum aestivum cultivars, differing in whole plant w ater use efficiency, Differences in leaf water use efficiency (A/E) be tween cultivars or treatments were associated with differences in Rubi sco activity or rate of electron transport and, in general, with diffe rences in plant water use efficiency, They were not invariably related to a low photosynthetic nitrogen use efficiency (PNUE), A high A/E wa s associated with a low PNUE, e.g, when we compared cultivars at high irradiance. In this case, a high A/E and a high leaf nitrogen concentr ation were associated with a low stomatal conductance and an equal rat e of photosynthesis, A high A/E was not associated with a low PNUE whe n differences in A/E were mainly caused by higher rates of photosynthe sis associated with higher nitrogen concentrations, e,g, when we compa red cultivars at low irradiance and high water and nitrogen supply. An increase in the proportion of total leaf nitrogen associated with the photosynthetic apparatus at low soil-nitrogen increased PNUE, without affecting A/E in the opposite way, We conclude that whole plant nitro gen use efficiency was low for the cultivars with a high plant water u se efficiency.