Effects Of Interaction Between Shading And Phosphate Fertilizer On Growth And Grain Quality Of Tartary Buckwheat Starch

Tartary buckwheat has high nutritional value and is a kind of medical-food homologous crop with great development and utilization value.But in recent years,due to industrial development and climate change,the amount of solar radiation reaching the ground has decreased significantly.In the main producing areas of Tartary buckwheat,the lack of rainfall occurred frequently during its growth period,and the weak light stress caused by the reduction of solar radiation and sunshine duration has become an important factor limiting the further improvement of Tartary buckwheat yield and quality.Therefore,the growth and development characteristics of Tartary buckwheat under weak light environment were analyzed,the effects of phosphate fertilizer on the growth and development of Tartary buckwheat under weak light stress were explored,and the correlation between the application of phosphate fertilizer under weak light environment and the utilization of weak light provided theoretical basis for the rational application of phosphate fertilizer under weak light environment.The experiments were conducted in Shaanxi Yulin Comprehensive Experiment and Demonstration Station of Small grains from 2020 to 2021.The split plot design was adopted.The main plot was shaded with three shading gradients of no shading（S0）,40%shading（S1）and 80%shading（S2）,and the sub-plot was phosphate fertilizer treatment.Three phosphate fertilizer levels were set as 0（P0）,35kg/hm²（P1）and70kg/hm²（P2）,and shading treatment was conducted from the beginning of budding stage to the end of maturity stage.The effects of shading and phosphate fertilizer and their interaction on dry matter accumulation,yield and related components of Tartary buckwheat were studied.The chlorophyll content,photosynthetic gas exchange parameters,chlorophyll fluorescence parameters and chemical properties of Tartary buckwheat starch were analyzed.The main conclusions were as follows:（1）Compared with the normal light environment,Tartary buckwheat under shade increased significantly stem diameter and effective branch number of main stem,decreased significantly dry matter accumulation,grain weight per plant and yield and the greater the shade degree,the greater the decrease.The yield of Tartary buckwheat under mild shade and severe shade decreased by 32.58%and 70.56%,respectively.Under the same shading environment,suitable p fertilizer could improve the agronomic traits of Tartary buckwheat,and significantly increase the stem diameter and effective branch number of main stem.At the same time,application of P fertilizer also helped to increase grain weight per plant,1000-grain weight and yield of Tartary buckwheat under shading environment,and the appropriate amount of P fertilizer under shading environment was 35kg/hm²（P1）.Compared with that without P fertilizer（P0）,the1000-grain weight and yield of Tartary buckwheat under P1 treatment increased by1.17%-2.05%and 19.70%-22.4%,respectively.In addition,grain weight per plant,1000-grain weight and yield of Tartary buckwheat were significantly positively correlated with node number and effective branch number of main stem.（2）Shading significantly inhibited photosynthesis of Tartary buckwheat leaves,and p fertilizer application significantly increased photosynthetic capacity of Tartary buckwheat under shading environment.Chlorophyll content has certain adaptive response to shading environment.Compared with the normal illumination,buckwheat leaf chlorophyll a and chlorophyll b under shade environment have increased,chlorophyll a/b decreased,the capture and use of weak light ability improved.But the growth period buckwheat leaf net photosynthetic rate and the maximal photochemical efficiency,actual photochemical efficiency and light chemical quenching coefficient decreased significantly,The concentration of intercellular CO₂ and non-photochemical quenching coefficient increased significantly,and the photochemical activity of PSⅡreaction center in Tartary buckwheat leaves decreased and photosynthesis was inhibited under shading condition.In the shaded environment,p fertilizer increased the total chlorophyll content,and the net photosynthetic rate and chlorophyll fluorescence parameters Fv/Fm,ΦPSⅡand q P of Tartary buckwheat leaves increased by 12.2%-27.7%,1.37%-2.50%,1.28%-5.85%and 0.92%-2.92%,respectively,compared with that without P fertilizer.Application of p fertilizer increased the activity of photosystemⅱreaction center in Tartary buckwheat leaves,increased the proportion of light energy used for photochemical reaction and electron transfer,and improved the efficiency of light energy capture and utilization in Tartary buckwheat leaves under shading environment.（3）Flavonoids and amylose contents of Tartary buckwheat decreased significantly,while protein content increased under shading environment.Shade and phosphate fertilizer did not affect buckwheat starch grain morphology and crystal structure,but promoted the buckwheat starch granule size distribution,shade increased significantly the proportion of small starch granules in the buckwheat,reduce the proportion of the large starch granules.Under shade environment,applying the right amount of phosphate fertilizer can improve the volume average particle size of buckwheat starch.Shading and phosphate fertilizer significantly increased the relative crystallinity and the starch order of Tartary buckwheat starch.Under the same p fertilizer level,the damage value and regeneration value of Tartary buckwheat starch were significantly increased by shading,which reduced the thermal stability of Tartary buckwheat starch and made it easier to regenerate,while the combination ability of Tartary buckwheat starch with water and swelling ability were improved by applying P fertilizer under shading environment,and the anti-aging ability of Tartary buckwheat starch was improved.