Nitrogen uptake and use of current bread wheat cultivars in response to higher temperatures

14 current bread wheat cultivars (Triticum aestivum L.) of Çukurova were evaluated for differences in nitrogen uptake and utilization under two temperature regimen, normal temperature (normal sowing time) and high temperature (late sowing time), without water and nutritional limitation under field conditions during the 2005/2006 growing season. High temperature resulted in increases in sterile culms dry weight however decreases of dry weight of other plant parts, including grains. High temperature significantly decreased grains and grain weight of all cultivars. Grain yield of the cultivars under normal temperature conditions changed significantly between 492 g m-2 (Cumhuriyet-75) and 679 g m-2 (Adana-99). Grain yield under high temperature compared to normal temperature decreased in all of the cultivars with an average of 50%. In respect to grain yield response of cultivars to higher temperature, Sagittario was the most sensitive and Balattila the most tolerant cultivar. Grain yield decreases were resulted more in grain number losses than in grain weight decreases. All of the investigated traits related to the N uptake and distribution showed significant cultivar differences in both regimes. In spite of substantial tissue N concentration rises under high temperature, N uptake reduced significantly due to dry weight decreases of most of the organs especially of grains. Significant variations were observed among cultivars in percentage reductions. Differences in N uptake among cultivars were also related more to the variation to dry matter than that of N concentration variation. Key words: Bread wheat, yield, nitrogen uptake, nitrogen harvest index, high temperature