A relationship between chlorophyll photosynthetic potential and yield in winter wheat (Triticum aestivum L.) at elevated temperatures

Development of the indices for selection of high-yielding crops and the models, forecasting agrocenosis yields, necessitate the analysis of the relationship between photosynthetic traits and productivity. Chlorophyll photosynthetic potential, characterizing the total amount of chlorophyll in the above-ground parts of plants (or in leaves) per unit of ground surface area during the growing season or a certain period, under optimal weather conditions correlated most closely with the magnitude of yield (T.M. Shadchina et al., 2007; E. Kutasy et al., 2005). Modern global climate change may primarily affect the heat-sensitive crops in particular winter wheat causing disruption in the relationship between photosynthetic traits and productivity. In field experiment, we examined the effects of increased air temperatures during the spring-summer growing season on performance of photosynthetic apparatus in the high-yielding varieties of common winter wheat Smuhlyanka and Pereyaslavka on the different levels of mineral nutrition (without fertilizers and fertilizing in the fall and at different phases of the spring-summer vegetation in doses N 90P 60K 60S 10 and N 120P 90K 90S 20). Investigations were carried out in 2009 and 2011 with elevated air temperatures during the growing season at the experimental agricultural station of the Institute of Plant Physiology and Genetics, National Academy of Sciences of Ukraine (Kyiv region.). It was shown that such weather conditions led to a decrease in chlorophyll content in the leaves, the size of crop surface and the duration of its operation, as well as grain yield. In all cases (both at high level of mineral nutrition and without fertilizers) leaf surface area in 2009 was higher than under the corresponding treatments in 2011 at all studied vegetation phases. Mineral fertilizers increased the leaf area index in both years by average 1.5-2.0 times (in Pereyaslavka at milk-wax ripeness phase it increased almost 5 times if compared to the control). Chlorophyll content in leaves of both varieties depended on year: it was 5.5-6.0 and 3.5-4.5 mg/dm 2, respectively, in 2009 and 2011 if fertilizers were used, and 3.2-4.3 and 2.8 mg/dm 2, respectively, in the control. In most cases, the maximum values of the pigments in the averaged sample of all green leaves from plant were observed in the phase of milk ripeness, probably, due to the complete withering away of leaves of lower layers. Mineral fertilizers increased the amount of chlorophyll in the leaves of both varieties. According to the results of dispersion analysis (F-Fisher test), the greatest influence on changes in the indices of the photosynthetic capacity in our experiments have the conditions of the year, the second most important factor was the level of mineral nutrition. The value of chlorophyll photosynthetic potential was more dependent on a combination of factors variety ½ year conditions and less on the interaction of the factors year conditions ½ mineral nutrition level and variety ½ mineral nutrition level. High and similar correlation coefficient values (0.93 to 0.99) between grain yield and chlorophyll photosynthetic potential were observed for data sets within single year, variety or mineral nutrition treatment, a strong positive dependence revealed for the combined data sets for both years. The data have shown that the close correlation between the leaf chlorophyll photosynthetic potential and yield of winter wheat is retained in the conditions of air high temperature and this dependence can be described by the same regression equation for any varying factors.