Effects of different nitrogen application rates on chlorophyll content and fluorescence characteristics of spring wheat under high temperature after anthesis

ObjectiveIn the present study, effects of different nitrogen application rates on chlorophyll fluorescence characteristics of spring wheat under high temperature after anthesis were investigated , in order to provide guidance for analysis for inner mechanism of nitrogen nutrition regulation of high temperature harm to spring wheat. MethodNingchun 4 and Ningchun 47 were used as plant materials. Three nitrogen application rates, 120 kg/ha(N1), 240 kg/ha (N2) and 300 kg/ha(N3), were set and no nitrogen application was treated as control(CK). High temperature treatment during 18-22 d after anthesis on wheat was conducted. Chlorophyll content and fluorescence parameters were measured 7 , 14, 23, 28 and 33 d after anthesis. ResultUnder high temperature stress(23-33 d after anthesis), SPAD values, maxi-mum fluorescence(Fm) and variable fluorescence(Fv) in leaves of Ningchun 4 and Ningchun 47 under three nitrogen app-lication rates increased, but original fluorescence(Fo) declined, which rose Fv/Fo and Fv/Fm and decreased Fo/Fm. The variation ranges of wheats in N1 and N2 treatment were larger than the one in N3 treatment compared with CK. Ab-sorption flux per RC (ABS/RC) , trapped energy flux per RC (TR0/RC) and dissipated energy flux per RC (DI0/RC) in N1 and N2 treatments were significantly higher than those of CK during 23-28 d after anthesis (P<0.05,the same below), and significantly lower than those of CK on day 33 after anthesis. Electron transport flux per RC (ET0/RC) was expressed as N2>N1>N3>CK during 23-33 d after anthesis. ConclusionAppropriate application of nitrogen fertilizer can alleviate the damages to structure and function of spring wheat photosynthetic organ caused by high temperature , and improve pho-tosynthetic performance.