Shade-Tolerant Soybean Reduces Yield Loss by Regulating Its Canopy Structure and Stem Characteristics in the Maize-Soybean Strip Intercropping System.

Bin Cheng,Irshan Ahmad,Ranjin Liu,Shuzhong Jing,Wenyan Wang,Liang Yu,Weiguo Liu,Wenyu Yang,Shengjun Jiang,Chunyan Liu,Li Wang,Weibing Wang,Tao Zhou,Ali Raza,Mei Xu,Renwei Yu

doi:10.3389/fpls.2022.848893

Abstract

The shading of maize is an important factor, which leads to lodging and yield loss of soybean in the maize–soybean strip intercropping system, especially in areas with low solar radiation. This study was designed to explore how shade-tolerant soybean reduces yield loss by regulating its canopy structure and stem characteristics in the maize–soybean strip intercropping system. The soybean cultivars Tianlong No.1 (TL-1, representative of shade-tolerant plants) and Chuandou-16 (CD-16, representative of shade-intolerant plants) were grown in monocropping and intercropping systems from 2020 to 2021 in Chongzhou, Sichuan, China. Regardless of shade-intolerant or shade-tolerant soybean, the canopy and stem of soybean in strip intercropping were weaker than those of the corresponding monoculture. But compared with shade-intolerant soybean, the shade-tolerant soybean slightly changed its spatial structure of canopy and stem morphology and physiology in maize–soybean strip intercropping system, especially in the later growth stages. On the one hand, the canopy of shade-tolerant soybean showed relatively high transmission coefficient (TC) and relatively low leaf area index (LAI) and mean leaf angle (MLA). On the other hand, the stem of shade-tolerant soybean was obviously stronger than that of shade-intolerant soybean in terms of external morphology, internal structure, and physiological characteristics. Additionally, compared with shade-intolerant soybean, shade-tolerant soybean showed higher APnWP (the average net photosynthetic rate of the whole plant) and seed yield in the strip intercropping. The results showed that shade-tolerant soybean increased light energy capture and photosynthesis in the different canopy levels to promote the morphological and physiological development of the stem and ultimately reduce the yield loss of the strip intercropping system. However, the molecular mechanism of low radiation regulating soybean canopy structure (LAI, TC, and MLA) needs further in-depth research to provide theoretical guidance for cultivating plants with ideal canopy shape that can adapt to changing light environment in intercropping system.

Highlights

Intercropping of maize (Zea mays L.) and soybean (Glycine max L.) has been practiced on a large scale in the world, especially in China (Du et al, 2018; Iqbal et al, 2019)
The shade-tolerant soybean Tianlong No 1 (TL-1) had high shading-tolerance coefficient (STC) of canopy structure (STCLAI = 0.799, STCTC = 0.839, and STCMLA = 0.949) (Figures 10A–C), which was conducive to maintaining the relative stability of spatial structure of the canopy in low-light environment
Our results demonstrated that compared with shade-intolerant soybean, the shade-tolerant soybean (CSTC = 0.713) slightly changed its spatial structure of canopy and stem morphology and physiology in maize–soybean strip intercropping system, especially in the middle and later growth stages

Summary

Introduction

Intercropping of maize (Zea mays L.) and soybean (Glycine max L.) has been practiced on a large scale in the world, especially in China (Du et al, 2018; Iqbal et al, 2019). Soybean plants suffer severe shading stress from maize during the intergrowth in maize–soybean intercropping systems (Zhou et al, 2019a,b; Hussain et al, 2020b), which reduces the red-to-far-red ratio of light inside the soybean canopy (Yang et al, 2014, 2020; Fan et al, 2018). These plants in this shaded environment show strong shade avoidance responses, which include reduced stem thickness, longer stem length, and petiole length and lower photosynthetic capacity and biomass (Yang et al, 2014; Liu et al, 2016; Fan et al, 2018). The phenotypes and physiology of soybean cultivars with a different shade tolerance have corresponding shade-avoiding strategies and plasticity under shade stress

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Discussion

Conclusion