Effects of shading and light recovery on soybean morphology and photosynthetic characteristics in soybean-maize intercropping system

Light environment directly affects crop growth, resulting in yield change. Three soybean varieties were used to investigate the characteristics of morphology and photosynthetic physiology under shading and light recovery conditions to explore response of soybean to light environment change. Relay strip intercropping with maize and monoculture planting patterns of soybean were investigated in term of light environment. Morphological characteristics, net photosynthetic rate, leaf anatomical structure and chlorophyll content of soybean were analyzed in the study. The results indicated that stem diameter, biomass, leaf thickness (including palisade and spongy tissues), chlorophyll a content, chlorophyll a/b and net photosynthetic rate of soybean decreased significantly at V5 stage (symbiotic period of maize and soybean) in relay intercropping compared with monoculture systems. The results of plant height, chlorophyll b content and thickness ratio between palisade and spongy tissue were the reverse for intercropping. In addition, the fractions of stem, leaf and stripe biomass accounted for 58%, 37% and 6%, respectively, of total above-ground biomass under relay intercropping, and 36%, 50% and 14% under mono-cropping. The results revealed that dry matter production center was transformed from leaves to stems under shading condition. When shading was removed after maize harvest, the differences among plant height, stem diameter, leaf area and biomass accumulation of above-ground biomass of soybean decreased at seed-filling stage of soybean (R6) between relay intercropping and monoculture treatments. The fractions of stem, leaf and stipe of total biomass were 41%, 49% and 10%, respectively. The thickness of leaf, palisade tissue and spongy tissue increased by 117%, 99% and 81%, respectively, compared with those at V5 stage (symbiotic period of maize and soybean). There was no significant difference in photosynthetic pigments between relay intercropping and monoculture after light recovery in relay intercropping. Photosynthetic rate of intercropped soybean significantly decreased, compared with that of mono-cropping. The yields of the three soybean varieties had significant difference in relay strip intercropping. Relay strip intercropping decreased per-plant yields of soybean varieties of ‘Jianyangjiuyuehuang’, ‘Jiangpuheidou’ and ‘Yongshengheidou’ by 33%, 64% and 40%, respectively, compared with soybean monoculture. It was therefore concluded that soybean was adaptable to changes in light environment due to plasticity in morphology and photosynthetic physiology. There were, however, differences in plasticity between different varieties.