Effects of nitrogen doses on stomatal characteristics, chlorophyll content, and agronomic traits in wheat (<i>Triticum aestivum</i> L.)

It is very important to determine the chlorophyll content (SPAD) and nitrogen (N) requirement in order to increase the seed yield and nutritional quality of wheat. This research was carried out with three N doses (0, 50, 100 kg ha^-1) and nine wheat cultivars (Alpu-2001, Soyer-02, Kate-A1, Bezostaja-1, Altay-2000, Müfitbey, Nacibey, Harmankaya-99 and Sönmez-2001) during 2-years field condition according to factorial randomized complete block design and three replications. In this study, with the increase of N dose (N50), seed yield increased by 13%, plant height by 10.8%, 1,000 seed weight by 10.5% compared to control plants (N0). The increase of N dose from 50 kg ha^-1 to 100 kg gave lower increase rates in the same criteria (11.7%, 11.4%, 10.3%, respectively). However, the spike number per plant, spikelet number in spike, seed number in spike, spike length showed statistically significant differences between N doses and varieties. Boost of N doses caused a significant increase compared to plants without N application. The chlorophyll content and flag leaf area index were determined at three growth times (1^st growth time; early, 2^nd growth time; the middle and end of flowering, 3^rd growth time; with a 10-day interval). Chlorophyll content was significantly (<i>p</i> < 0.01) affected by the N dose, variety and growth time. As N doses increased, chlorophyll content increased, and it was higher at both N doses compared with N0. The chlorophyll content had the highest rates (30.22%) at 1^st growth time and it decreased as the growth period progressed. N doses, varieties and their interactions had significant effects on the flag leaf area index. The highest flag leaf area index (41.9 cm²) was determined from variety Bezostaja-1 and 100 kg ha^-1 N dose treatment. The effect of N dose was found significantly on abaxial and adaxial stomata width-length and epidermal cells. The adaxial and abaxial stomata width were higher than N0 at both N levels. The highest adaxial and abaxial stomata width- length was obtained from 100 kg ha^-1 N dose. As nitrogen concentration increased, both stomatal density and stomatal index increased. The stomatal index varied between 19% and 36%. The lowest stomata density had appeared in the 100 kg ha^-1 N dose and Bezostaja-1 variety. As a result, stomatal characteristics, chlorophyll content, and agronomic traits of wheat were significantly affected by increasing N doses.