Effects Of Reduced Solar Irradiance On The Physio-biological Characteristics And Yield Of Winter Wheat

The solar irradiance and its environmental impacts are growing concerns worldwide. In the recent years, the aerosol loading, atmospheric turbidity and haze day over china area increase considerably, resulting in decrease in the surface shortwave radiation and the reduction in Yangtze delta is more obvious. On this study, the reduced solar irradiance on the growth, photosynthetic characteristics, biomass production and yield of winter wheat were investigated via field experiments and model simulation. Further more, the dry matter accumulation and distribution characteristics of this cultivar were elucidated by means of CERES-Wheat model. Results are as follows:(1) Under reduced solar irradiance condition, the contents of chlorophyll (Chla, Chlb, Chl(a+b)), carotenoid and xanthophyll in winter wheat leaves increase significantly, which can improve the plant's ability for light absorption and utilization. Irradiance of 60%-20% incident solar light significantly decreased the net photosynthetic rate(Pn), stomata conductance(Gs), transpiration rate(Tr), water use efficience(WUE) and stomatal limitation(Ls), but increased the intercellular CO2 concentration(Ci), and the sensitivity to light of the above parameters was also restrained. Photoinhibition or photo-damage to the PSII didn't occur when the plants were subjected to 60%-20% incident solar irradiance, thus the maximum quantum yield of PSII(Fv/Fm) and the initial fluorescence(Fo) increased substantially. The effective quantum yield of PSII(Yield), maximum photosynthesis(Pm) and photochemical quenching(qP) were restricted under reduced solar irradiance condition, while the non-photochemical quenching(NPQ) increased significantly, demonstrating that more excess of light energy in PSII was dissipated through heat dissipation. The contents of peroxidase(POD), superoxide dismutase (SOD), malonaldehyde(MDA) and electrolyte leakage(EC) increased pronouncedly in response to 60%-20%incident solar irradiance treatments, thus the plants could effectively eliminate the attack of active oxygen species (AOS) to cell membrane, preventing peroxidation damage caused by reduced solar light. The solar irradiance intensity lower than 60% incident solar light significantly decreased the contents of soluble sugar and soluble protein, while increased the total free amino acid content in leaves of winter wheat.(2)Under long term negative effects of 60%-20% incident solar light, the plant height(PH), leaf area(LA), leaf mass ratio(LMR),leaf mass fraction(LMF),leaf area ratio(LAR) and leaf area-root mass ratio(LARMR) of winter wheat increased significantly, on the contrary, the leaf mass per unit area(LMA), root mass ratio(RMR), stem mass ratio(SMR) and root crown ratio(RCR) presented a trend of increase. This strategy of biomass distribution could enhance the ability of light capture and light use efficiency to a certain extern, but could not off set the negative impact of insurfficient light, thus the total biomass(TB), net simulation rate(NAR) and relative growth rate(RGR) decreased substantially.(3) The revised WheatGrow(WG) model has good preferment on predicting photosynthesis and biomass assimilation of winter wheat. Solar irradiance of 60% and 40% incident solar light could respectively resulted in significant reduction of 23% and 31% in photosynthetic rate of winter wheat,35% and 41% for total biomass and 34.08% and 47.91% in grain yield. When the solar irradiance decreased to 20% and 15% incident solar light, thepho to synthetic rate declined by 46% and 48%, total biomass decreased by 56% and 57%, and reduction of grain yield was 88.31% and 87.40%, respectively.(4) The CERES-Wheat has certain of ability to assess the biomass accumulation of winter wheat, but can not well simulate the distribution of biomass among organs under reduced solar irradiance condition..When solar irradiance decreased to 60%-15% of incident solar light, the total biomass decreased by 37.61%-71.69%, and the root, stem and leaf biomass declined by 46.49%-57.30%,21.7%-76.76% and 51.8%-66.2%,respectively.