Effects Of Different Ratios Of Red And Blue Light On Photosynthetic Characteristics And Dry Matter Accumulation In Soybean Leaves Under Shade

Light is the main energy source of green plants,and light is also an important signal source during the growth and development of green plants.The change of light environment will directly or indirectly affect the growth,development and adaptation of plants.Under the intercropping pattern of corn and soybean,the shading environment formed by high-crop corn to low-crop soybean is an important factor restricting soybean yield.Under such shading environment,with the decrease of light intensity,the light quality ratio also has obvious changes,especially the change of the ratio of red and blue light.Therefore,it is of great significance to study the effects of different proportions of red and blue matter on photosynthetic characteristics and dry matter accumulation of soybean seedling leaves under shading conditions.The red and blue quality of the three-color culture light box used in this experiment has the characteristics of high purity,convenient adjustment of light to quality ratio and high control of simulated growth environment.In this experiment,two different light intensities and five different light quality environments were set.Plant height,stem diameter and leaf area of soybean plants in V2 stage were measured,leaf anatomical structure and chloroplast ultrastructure were observed,etc.,to explore the effects of different ratios of red and blue light on seedling morphogenesis and photosynthetic structure of soybean plants under shade conditions.The effects of different ratios of red and blue light on the photosynthetic characteristics and dry matter accumulation of soybean seedlings were further explored by measuring the pigment content,photosynthetic characteristics,chlorophyll fluorescence,soluble sugar content,key enzyme activities of sucrose synthesis and 13 C tracer markers of soybean leaves.The main research results are as follows:1.Effects on soybean seedling morphology and dry matter distribution.Under the shading condition,the plant height,first internode length,leaf area and specific leaf area of soybean seedlings decreased by 6.3%,53.3%,9.1% and 50%,respectively,under the treatment of high red light and low blue light(blue light: red light =3:1,HBLRS),and under the control of normal light quality.The stem diameter and leaf dry weight increased by 12.0%and 66.7%,respectively.The dry weight ratio of petiole and stem decreased by 9% and 6%,the dry weight ratio of leaf and root increased by 3.7% and 5.5%,and the plant S:L and P:L significantly decreased by 0.55 and 0.79,respectively.The accumulation of 13 C in leaves,petioles and roots increased by 19.9%,2.1% and 1.8%,respectively,but decreased by 23.9%in stems.2.Effect on leaf structure of soybean plant.Under the shaded condition,the leaf thickness,palisade tissue thickness and spongy tissue thickness of the plant increased by42.2%,58.9% and 41.8% after HBLRS treatment,respectively.The ratio of palisade tissue to spongy tissue thickness in the leaves was 1.55,and the difference was significant.The chloroplast crosscutting area and starch grain crosscutting area of soybean leaves increased by 44.1% and 260.8%,respectively,and the ratio of starch grain crosscutting area to chloroplast crosscutting area was 0.29,and the difference was significant.The number of starch granules and grana lamellae in single chloroplast of soybean leaves increased by 80.0%and 127.7%,respectively,and the number of osmiophilic granules decreased by 19.6%.3.Effects on photosynthetic pigment and photosynthetic parameters of soybean leaves.Chlorophyll a content,chlorophyll b content and chlorophyll a/b value were significantly increased by 42.0%,0.4% and 45.1%,respectively,and carotenoid content was decreased by 52.8% under shade condition and normal light quality environment as control.The net photosynthetic rate(Pn)of soybean leaves decreased by 4.5%,the stomatal conductance(GS),intercellular carbon dioxide concentration(Ci)and transpiration rate(Tr)of soybean leaves increased by 8.2%,15.0% and 0.2%,respectively.However,the maximum photochemical efficiency(Fv/Fm),non-photochemical quenching(NPQ)and photochemical quenching(q P)of leaves remained relatively stable,and the differences were not significant compared with those of natural light treatment under shade condition.4.Effects on soluble sugar and sucrose biosynthesis related enzymes in soybean leaves.Under the shaded condition,the contents of soluble sugar,sucrose and maltose decreased by10.2%,37.6% and 13.6%,respectively,under the normal light condition,and the differences were not significant,while the content of starch increased by 35.8%.The activities of sucrose synthase(SS),sucrose phosphate synthase(SPS)and ribulose 1,5-bisphosphate carboxylase(Rubisco)in soybean seedling leaves were increased by 12.3%,27.0% and 77.3%,respectively.The above results show that: Under shading conditions,HBLRS treatment enhanced lodging resistance by reducing plant height and increasing stem diameter,reduced specific leaf area,and optimized leaf structure and photosynthetic mechanism to enhance shade tolerance of plants.In addition,HBLRS treatment significantly reduced the contents of soluble sugar and sucrose in plant leaves,but promoted the accumulation of starch.As a result,the maltose content of the plant increased,and the activities of sucrose biosynthesis related enzymes in the leaves of the plant increased,so that the photosynthesis mechanism of the soybean plant seedlings maintained efficient and balanced operation.In conclusion,under shading environment,HBLRS treatment can optimize seedling morphology and photosynthetic structure of soybean plant,and achieve a better balance between leaf photosynthetic rate and synthesis and distribution of photochemical products,thus reducing the influence of shading on plant growth and development.