| Wheat is the main food crop in China,and increasing planting density can effectively increase yield.However,in a high-density environment,individuals compete for limited resources,and the competition becomes more serious,resulting in dysplasia of individuals and deterioration of population structure,which is easy to lead to lodging and serious yield reduction.In recent years,due to human activities,the solar radiation is reduced,resulting in insufficient light,crop shading effect,poor quality of stalk,which seriously affects the yield of wheat.Therefore,two wheat SN16（lodging sensitive type）and SN23（lodging resistant type）with different lodging resistance properties were selected as test materials in this experiment,and 50%shading treatment（S1）was set up from jointing stage to maturity stage,and natural light was used as control（S0）.Three planting density treatments were set:1.2million ha-1（D1）,2.7 million ha-1（D2）,and 4.2 million ha-1（D3）.In order to improve lodging resistance of wheat,silicon spraying treatment was set at the jointing stage of wheat:400 mg L-1（C1）,with no spraying as control（C0）.The effects of silica fertilizer spraying on photosynthetic characteristics,stem morphological characteristics,mechanical characteristics,dry matter accumulation and lignin metabolism of winter wheat under weak light stress were studied.The mechanism of silicon spraying on wheat resistance and yield increase was clarified,and theoretical guidance was provided for the resistance and yield increase of wheat in extreme shade weather.The main research results are as follows:1.The grain weight and grain number per spike of wheat decreased with the increase of grain density.The low light treatment from jointing stage to maturity stage of wheat reduced the photosynthetic rate,dry matter accumulation and grain transfer volume due to insufficient light,resulting in yield reduction.The number of spikes,grain number per spike and 1000-grain weight of wheat could be increased by Si application,and the yield of SN16 and SN23could be increased by 14.09%and 12.92%,respectively,under S1 treatment.2.Under low light stress,the intercepted effective photosynthetic radiation in wheat canopy decreased and the photosynthetic rate of wheat decreased.Compared with S0,the net photosynthetic rate of SN16 and SN23 under S1 condition decreased by 25.67%and 29.11%,respectively.SPAD value and photosynthetic interception amount of flag leaves were increased by Si spraying,net photosynthetic rate（Pn）and stomatal conductance（Gs）were increased,and intercellular carbon dioxide concentration（Ci）was decreased.Under low light stress,the net photosynthetic rate of SN16 and SN23 under C1 treatment increased by 6.61%and 6.84%,respectively,compared with C0 treatment.3.With the increase of planting density,wheat stem quality deteriorates,plant height,center of gravity height and basal internode length increase,stem thickness and wall thickness of basal internode decrease,and the enrichment decreases,which leads to the decrease of wheat bending resistance and the increase of lodging risk.The effects of low light and high density on wheat were basically the same.The application of silicon increased stem thickness,wall thickness and stem bending resistance of wheat,and improved lodging resistance.Compared with C0,the bending strength of SN16 and SN23 treated by C1 increased by16.65%and 11.53%,respectively.4.Low light stress and densification were not conducive to the accumulation of lignin in wheat stem.Low light and high-density treatments resulted in a decrease in lignin content and the proportion of S and G monomers,while increasing the proportion of H monomers.Silicon spraying promoted the accumulation of lignin in stems.Under the treatment of C1,the total lignin in SN16 and SN23 increased by 10.82%and 12.87%,respectively,and the content of G and S of lignin monomer increased,while the proportion of H decreased. |
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