Effects of Nitrogen and Potassium Application Levels on Flag Leaf Photosynthetic Characteristics after Anthesis in Winter Wheat

Grain yield limit is one of the main problems in medium or weak gluten wheat production in middle-lower reaches of the Yangtze River of China.Nitrogen and potassium are key factors affecting leaf photosynthesis,and previous researches have showed that the application of either of the two fertilizers can improve wheat organ construction,therefore,affect grain yield.However,the physiological mechanism of nitrogen and potassium interaction on photosynthetic characteristics in wheat needs to be revealed.In the present study,we used two winter wheat(Triticum aestivum L.) cultivars,'Ningmai 9'(weak gluten) and 'Yangmai 10'(medium gluten) in a field experiment to investigate chlorophyll content(SPAD),net photosynthetic rate(Pn),chlorophyll fluorescence parameters of flag leaves and the relationship among those parameters and nitrogen and potassium fertilization levels.In the experiment,nitrogen was the main plot with 3 levels corresponding to 0,112.5,and 225 kg N ha-1 respectively,and potassium(0,75,and 150 kg K2O ha-1) and cultivar('Ningmai 9' and 'Yangmai 10') were the split plots.The results showed that SPAD and photosynthetic parameters(Pn,Fv /Fm,Fv /Fo,F'v/F'm,and ΦPSⅡ) were increased with N and K supply as compared with CK(no N and K fertilization).Compared with potassium fertilization,the role of nitrogen on SPAD and photosynthetic parameters(Pn,Fv /Fm,Fv /Fo,F'v/F'm,and ΦPSⅡ) was greater.The relationships between chlorophyll fluorescence parameters(Fv /Fm,Fv /Fo,F'v/F'm,and ΦPSⅡ) and Pn were all significant(P 0.01).Photosynthetic parameters except SPAD were higher in 'Yangmai 10' than in 'Ningmai 9'.The results suggested that higher chlorophyll fluorescence parameters(Fv /Fm,Fv /Fo,F'v/F'm,and ΦPSⅡ) affected by reasonable leaf N/K ratio at anthesis were the key physiological basis not only for higher Pn after anthesis,but also for getting almost the same yield of 'Yangmai 10' which needs more energy compared with that in 'Ningmai 9'.