Abstract: 【Objective】In the maize-soybean intercropping system, the shading by the taller maize crop modifies the light environment experienced by the lower soybean crop in terms of both light intensity and light quality, while these changes were affected by the intercropping configuration and crop architecture. The objective of this study was to provide a theoretical basis of physiological response for light intensity and light quality. 【Method】 The variety of soybean Nandou 12 used as test material, the experiment was conducted in controlled growth chamber by pot method. In this experiment, four treatments were set up, including A1 (normal light + far red light), A2 (weak light + far red light), A3 (weak light), and CK (normal illumination). The morphological and physiological parameters of soybean seedlings were determined. 【Result】When soybean growth under the normal light and the low ratio of red to far red light, compared with CK, the soybean plant height, biomass and net photosynthetic rate of A1 treatment were increased. On the contrary, the root length, root surface area, root volume, carotenoid content and the actual photochemical quantum efficiency of A1 treatment were decreased significantly, but the photochemical quenching coefficient was not significantly different (P>0.05). Compared with A3 treatment, the A2 treatment soybean plant height decreased, stem diameter increased, biomass increased by 9.8%, and chlorophyll a and total chlorophyll content decreased. The chlorophyll b content decreased by 6.48%, the net photosynthetic rate, maximum photochemical quantum yield, non-photochemical quenching, effective photochemical quantum yield of A2 treatment increased significantly, but the root characteristics was not significantly different (P>0.05). Under the invariant light quality and reduced light intensity, compared with A2 treatment, the plant height of A1 treatment soybean decreased significantly, root length, root surface area and root volume increased significantly, biomass increased by 62.87%. The leaf biomass of A1 treatment accounted for 54.96% of the whole plant, while the stem biomass accounted for 52.08%, the chlorophyll a, b, carotenoids and total chlorophyll content increased, the net photosynthetic rate increased by 16.22% and the chlorophyll fluorescence parameters of A2 treatment were not difference (P>0.05). Compared with CK, the A3 treatment soybean plant height increased significantly, while stem diameter, root length, root surface area and root volume decreased significantly. Meanwhile, the biomass decreased significantly by 61.09%, but the biomass of stem was increased significantly under A3 treatment. The A3 treatment accumulation of chlorophyll a, chlorophyll b and carotenoid increased by 29.41%, 4.17% and 41.51%, respectively, the net photosynthetic rate and actual photochemical quantum efficiency decreased significantly (P<0.05). 【Conclusion】 The results showed that light intensity directly influences the soybean morphogenesis and biomass accumulation. The low ratio of red to far red light could promote the photosynthetic rate and the substance accumulation of soybean.

Key words: soybean, light intensity, light quality, morphological characteristics, photosynthetic characteristics