Abstract
In maize-soybean intercropping system, soybean plants will be affected by the wide light-fluctuation, which resulted from the shading by maize plants, as the shading of maize the light is not enough for soybean in the early morning and late afternoon, but at noon, the light is strong as the maize shading disappeared. The objective of this study is to evaluate the photosynthetic response of soybean leaf to the wide light-fluctuation. The data of diurnal variation of photosynthetic characters showed that the photosynthetic rate of intercropped soybean was weaker than that of monocropped soybean. The chlorophyll content, ratio of chlorophyll a/b, and AQE (apparent quantum efficiency) were increased and Rd (dark respiration rate) was decreased for the more efficient interception and absorption of light and carbon gain in intercropping. δRo (The efficiency/probability with which an electron from the intersystem electron carriers was transferred to reduce end electron acceptors at the PSI acceptor side) and φRo (the quantum yield for the reduction of the end electron acceptors at the PSI acceptor side) in intercropped soybean leaf were lower compared to those in monocropped one, which showed that the acceptor side of PSI might be inhibited, and also it was the main reason that soybean plants showed a low photosynthetic capacity in intercropping. ψEo (the efficiency/probability with an electron moves further than QA-) in monocropping and intercropping decreased 5.8, and 35.7%, respectively, while φEo (quantum yield for electron transport) decreased 27.7 and 45.3% under the high radiation at noon, which suggested that the acceptor side of PSII was inhibited, while the NPQ became higher. These were beneficial to dissipate excess excitation energy in time, and protect the photosynthetic apparatus against photo-damage. The higher performance index on the absorption basis (PIABS) and lower δRo, φRo, ψEo, and φEo of intercropped soybeans compared to monocropping under high radiation indicated that the electron transfer of intercropped soybean was inhibited more seriously and intercropped soybean adjusted the electron transport between PSII to PSI to adapt the light-fluctuation. Higher NPQ capacity of intercropped soybeans played a key role in keeping the leaf with a better physiological flexibility under the high radiation.
Highlights
Light is one of the most important factors affecting plants growth and development (Li A. et al, 2016), with changes in irradiance having impacts on plant growth, morphology, physiology, etc
Plant leaf grown in shade condition was thinner, had a lower net CO2 assimilation rate (An) (Tateno and Taneda, 2007), CO2 assimilation rate saturated at lower photosynthetic photon flux density (Zhang et al, 2004), and lower amounts of electron transfer carriers than those in unshade condition (Jiang et al, 2011)
The objective of this study is to evaluate the photosynthetic response of soybean leaf to the wide lightfluctuation in intercropping
Summary
Light is one of the most important factors affecting plants growth and development (Li A. et al, 2016), with changes in irradiance having impacts on plant growth, morphology, physiology, etc. Maize-soybean intercropping is one of major planting patterns in China, and has contributed significantly to soybean production and to maintain the yield of maize (Yang et al, 2008; Yan et al, 2010; Li et al, 2014). In this intercropping, soybean grow in the rows between maize, and the light situation of soybean canopy is changed by maize (Awal et al, 2006; Yang et al, 2014). In this study little was known about the effect of high radiation stress on soybean leaf in intercropping
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