In intercropping systems shading conditions significantly impair the seed yield and quality of soybean, and rarely someone investigated the minimum amount of light requirement for soybean growth and development. Therefore, it is an urgent need to determine the threshold light intensity to ensure sustainable soybean production under these systems. An integrated approach combining morphology, physiology, biochemistry and genetic analysis was undertaken to study the light intensity effects on soybean growth and development. A pot experiment was set up in a growth chamber under increasing light intensity treatments of 100 (L₁₀₀), 200 (L₂₀₀), 300 (L₃₀₀), 400 (L₄₀₀), and 500 (L₅₀₀) μmol m⁻² s⁻¹. Compared with L₁₀₀, plant height, hypocotyl length, and abaxial leaf petiole angle were decreased, biomass, root:shoot ratio, and stem diameter were increased, extremum was almost observed in L₄₀₀ and L_500. Leaf petiole movement and leaf hyponasty in each treatment has presented a tendency to decrease the leaf angle from L₅₀₀ to L₁₀₀. In addition, the cytochrome content (Chl a, Chl b, Car), net photosynthetic rate, chlorophyll fluorescence values of F_v/F_m, $F_{\text{v}}{}^{\prime }$/$F_{\text{m}}{}^{\prime }$, ETR, Φ_PSII, and qP were increased as the light intensity increased, and higher values were noted under L₄₀₀. Leaf microstructure and chloroplast ultrastructure positively improved with increasing light intensity, and leaf-thickness, palisade, and spongy tissues-thickness were increased by 105, 90, and 370%, under L₅₀₀ than L₁₀₀. Moreover, the cross-sectional area of chloroplast (C) outer membrane and starch grains (S), and sectional area ratio (S:C) was highest under L₄₀₀ and L₅₀₀, respectively. Compared to L₁₀₀, the content of starch granules increased by 35.5, 122.0, 157.6, and 145.5%, respectively in L₄₀₀. The same trends were observed in the enzyme activity of sucrose-synthase, sucrose phosphate synthase, starch synthase, rubisco, phosphoenol pyruvate carboxykinase, and phosphoenol pyruvate phosphatase. Furthermore, sucrose synthesis-related genes were also up-regulated by increasing light intensity, and the highest seed yield and yield related parameters were recorded in the L₄₀₀. Overall, these results suggested that 400 and 500 μmol m⁻² s⁻¹ is the optimum light intensity which positively changed the leaf orientation and adjusts leaf angle to perpendicular to coming light, consequently, soybean plants grow well under prevailing conditions.

Planting patterns affect nitrogen (N), phosphorus (P), and potassium (K) acquisition and distribution in maize and soybean under intercropping conditions. Here we reveal that strip relay-intercropping increases the N, P, and K uptake and distribution across plant organs (root, straw, and seed) of maize and soybean, accelerates the dry-matter production of intercrop-species, and compensates the slight maize yield loss by considerably increasing the soybean yield. In a two-year experiment, soybean was planted with maize in different planting patterns (SI, 50:50 cm and SII, 40:160 cm) of relay-intercropping, both planting patterns were compared with sole cropping of maize (SM) and soybean (SS). As compared to SI, SII increased the N, P, and K accumulation in each organ of soybean by 20, 32, and 18 (root) %, 71, 61, and 76 (straw) %, and 68, 65, and 62 (seed) %, respectively, whereas decreased the N, P, and K accumulation in each organ of maize by 1, 4, and 8 (root) %, 1, 10, and 3 (straw) %, and 5, 10, and 8 (seed) %, respectively. Overall, in SII, relay-cropped soybean accumulated 91% of total nutrient uptake (TNU) of sole soybean plants, and relay-cropped maize accumulated 94% of TNU of sole maize plants.

Different planting patterns affect the light interception of intercrops under intercropping conditions. Here we revealed that narrow-wide-row relay-intercropping improves the light interception across maize leaves in wide rows (60cm) and narrow rows (40cm), accelerated the biomass production of intercrop-species and compensated the slight maize yield loss by considerably increasing the soybean yield. In a two-year experiment, maize was planted with soybean in different planting patterns (1M1S, 50:50cm and 2M2S, 40:60cm) of relay-intercropping, both planting patterns were compared with sole cropping of maize (M) and soybean (S). As compared to M and 1M1S, 2M2S increased the total light interception of maize leaves in wide rows (WR) by 27% and 23%, 20% and 10%, 16% and 9% which in turn significantly enhanced the photosynthetic rate of WR maize leaves by 7% and 5%, 12% and 9%, and 19% and 4%, at tasseling, grain-filling and maturity stage of maize, respectively. Similarly, the light transmittance at soybean canopy increased by 218%, 160% and 172% at V₂, V₅ and R₁ stage in 2M2S compared with 1M1S. The improved light environment at soybean canopy in 2M2S considerably enhanced the mean biomass accumulation, and allocation to stem and leaves of soybean by 168%, and 131% and 207%, respectively, while it decreased the mean biomass accumulation, and distribution to stem, leaves and seed of maize by 4%, and 4%, 6% and 5%, respectively than 1M1S. Compared to 1M1S, 2M2S also increased the CR values of soybean (by 157%) but decreased the CR values of maize (by 61%). Overall, under 2M2S, relay-cropped maize and soybean produced 94% and 69% of the sole cropping yield, and the 2M2S achieved LER of 1.7 with net income of 1387.7 US $ ha^-1 in 2016 and 1434.4 US $ ha^-1 in 2017. Our findings implied that selection of optimum planting pattern (2M2S) may increase the light interception and influence the light distribution between maize and soybean rows under relay-intercropping conditions which will significantly increase the intercrops productivity. Therefore, more attention should be paid to the light environment when considering the sustainability of maize-soybean relay-intercropping via appropriate planting pattern selection.

Planting arrangements affect radiation use efficiency (RUE) and competitiveness of intercrop species in intercropping systems. Here, we reveal that narrow‐wide‐row planting arrangement in maize‐soybean relay‐intercropping system increases the dry matter and competitiveness of soybean, increased the RUE of maize and soybean, and compensates the yield loss of maize by substantially increasing the yield of soybean. In this field study, maize was planted with soybean in different planting arrangements (P1, 20:180, P2, 40:160; P3, 60:140, and P4, 80:120) of relay intercropping, all the relay‐intercropping treatments were compared with sole crops of maize (SM) and soybean (SS). Results showed that P1 improved the total RUE 3.26 g/MJ (maize RUE + soybean RUE) of maize and soybean in relay‐intercropping system. Compared to P4, treatment P1 increased the soybean competition ratio (CR) values (by 55%) but reduced the maize CR values (by 29%), which in turn significantly improved the yield of soybean by maintaining the maize yield. Generally, in P1, soybean produced 82% of SS yield, and maize produced 88% of SM yield, and it achieved the land equivalent ratio of 1.7. These results suggest that by maintaining the appropriate planting distances between maize and soybean we can improve the competitiveness and yield of intercrop species in relay‐intercropping system.

The BRI1-EMS suppressor 1 (BES1)/brassinazole-resistant 1 (BZR1) transcription factors, key components in the brassinosteroid signaling pathway, play pivotal roles in plant growth and development. However, the function of BES1/BZR1 in crops during stress response remains poorly understood. In the present study, we characterized ZmBES1/BZR1-5 from maize, which was localized to the nucleus and was responsive to abscisic acid (ABA), salt and drought stresses. Heterologous expression of ZmBES1/BZR1-5 in transgenic Arabidopsis resulted in decreased ABA sensitivity, facilitated shoot growth and root development, and enhanced salt and drought tolerance with lower malondialdehyde (MDA) content and relative electrolyte leakage (REL) under osmotic stress. The RNA sequencing (RNA-seq) analysis revealed that 84 common differentially expressed genes (DEGs) were regulated by ZmBES1/BZR1-5 in transgenic Arabidopsis. Subsequently, gene ontology and KEGG pathway enrichment analyses showed that the DEGs were enriched in response to stress, secondary metabolism and metabolic pathways. Furthermore, 30 DEGs were assigned to stress response and possessed 2–15 E-box elements in their promoters, which could be potentially recognized and bound by ZmBES1/BZR1-5. Taken together, our results reveal that the ZmBES1/BZR1-5 transcription factor positively regulates salt and drought tolerance by binding to E-box to induce the expression of downstream stress-related genes. Therefore, our study contributes to the better understanding of BES1/BZR1 function in the stress response of plants.