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Soybean in relay intercropping is initially exposed to a shade environment, followed by exposure to full sunlight after the harvesting of primary crops, e.g., maize. Therefore, soybean's ability to acclimate to this changing light environment determines its growth and yield formation. However, the changes in soybean photosynthesis under such light alternations in relay intercropping are poorly understood. This study compared the photosynthetic acclimation of two soybean varieties with contrasting shade tolerance, i.e., Gongxuan1 (shade-tolerant) and C103 (shade-intolerant). The two soybean genotypes were grown in a greenhouse under full sunlight (HL) and 40% full sunlight (LL) conditions. Subsequently, after the fifth compound leaf expanded, half of the LL plants were transferred to a high-sunlight environment (LL-HL). Morphological traits were measured at 0 and 10 days, while chlorophyll content, gas exchange characteristics and chlorophyll fluorescence were assayed at 0, 2, 4, 7 and 10 days after transfer to an HL environment (LL-HL). Shade-intolerant C103 showed photoinhibition 10 days after transfer, and the net photosynthetic rate (Pn) did not completely recover to that under a high light level. On the day of transfer, the shade-intolerant variety, C103, exhibited a decrease in net photosynthetic rate (Pn), stomatal conductance (Gs) and transpiration rate (E) in the low-light (LL) and low-light-to-high-light (LL-HL) treatments. Additionally, intercellular CO2 concentration (Ci) increased in low light, suggesting that non-stomatal factors were the primary limitations to photosynthesis in C103 following the transfer. In contrast, the shade-tolerant variety, Gongxuan1, displayed a greater increase in Pn 7 days after transfer, with no difference observed between the HL and LL-HL treatments. Ten days after transfer, the shade-tolerant Gongxuan1 exhibited 24.1%, 10.9% and 20.9% higher biomass, leaf area and stem diameter than the intolerant C103. These findings suggest that Gongxuan1 possesses a higher capacity to adapt to variations in light conditions, making it a potential candidate for variety selection in intercropping systems. [ABSTRACT FROM AUTHOR]

Recovery growth is common in relay intercropping systems and is a useful practice to increase total productivity of these systems. A field experiment was conducted during 2014–2016 to investigate the phenotypic and physiological traits related to light interception and utilization changes and cultivars difference of soybean during the recovery growth period. Two cropping patterns (maize–soybean relay strip intercropping (RSI), analogous soybean monoculture (CK)) and two soybean cultivars (shade‐tolerant Nandou12 and shade non‐tolerant Jiuyuehuang) were evaluated. During the co‐growth period, the growth of both two soybean cultivars was suppressed and showed a series of shade avoidance traits. After maize harvest, the LAI and leaflet number of intercropped soybean exhibited rapid growth, the LAI of Nandou12 (3.09) and Jiuyuehuang (1.32) recovered to 79% and 43% of corresponding CK level, respectively. Subsequently, final biomass of Nandou12 (3972.7 kg ha−1) and Jiuyuehuang (2263.3 kg ha−1) recovered 85.7% and 52% of corresponding CK level, respectively. Leaf blade thickness of Nandou12 recovered to the corresponding CK level, while Jiuyuehuang was not. Pn recovered to 84.5% and 82.8% of sole Pn at 80 days after soybean sowing in 2015 and to 72% and 91.2% at 66 days after soybean sowing in 2016 for Nandou12 and Jiuyuehuang, respectively. The above recovery process promoted the recovery of pod formation and grain yield. The yield of Nandou12 (1159.5 kg ha−1) has no significant difference between the CK level (1325.5 kg ha−1) but significantly higher than that of Jiuyuehuang (566.8 kg ha−1). Taken together, some recovery growth did occur in Jiuyuehuang, but it did not completely compensate for the growth reduction that occurred during the co‐growth period. Shade‐tolerant soybean cultivar has more stronger recovery growth ability in LAI, leaflet number, leaf thickness, and photosynthesis after maize harvest, which promoted the recovery growth of aboveground biomass and grain yield. [ABSTRACT FROM AUTHOR]

Mildew severely reduces soybean yield and quality, and pods are the first line of defence against pathogens. Maize‐soybean intercropping (MSI) reduces mildew incidence on soybean pods; however, the mechanism remains unclear. Changing light (CL) from maize shading is the most important environmental feature in MSI. We hypothesized that CL affects isoflavone accumulation in soybean pods, affecting their disease resistance. In the present study, shading treatments were applied to soybean plants during different developmental stages according to various CL environments under MSI. Chlorophyll fluorescence imaging (CFI) and classical evaluation methods confirmed that CL, especially vegetative stage shading (VS), enhanced pod resistance to mildew. Further metabolomic analyses and exogenous jasmonic acid (JA) and biosynthesis inhibitor experiments revealed the important relationship between JA and isoflavone biosynthesis, which had a synergistic effect on the enhanced resistance of CL‐treated pods to mildew. VS promoted the biosynthesis and accumulation of constitutive isoflavones upstream of the isoflavone pathway, such as aglycones and glycosides, in soybean pods. When mildew infects pods, endogenous JA signalling stimulated the biosynthesis of downstream inducible malonyl isoflavone (MIF) and glyceollin to improve pod resistance. Changing light from maize shading is the most important environmental feature in maize‐soybean intercropping, which reduces mildew incidence on soybean (Glycine max L. Merr.) pods.Weak to bright light conditions promotes constitutive isoflavone biosynthesis in soybean pods, and provides sufficient precursors for downstream inducible malonylated isoflavones and glyceolin to improve pod resistance.JA signalling and isoflavone have a synergistic effect on the enhanced resistance of changing light treated pods to mildew. [ABSTRACT FROM AUTHOR]

Leaf anatomy and the stomatal development of developing leaves of plants have been shown to be regulated by the same light environment as that of mature leaves, but no report has yet been written on whether such a long-distance signal from mature leaves regulates the total leaf area of newly emerged leaves. To explore this question, we created an investigation in which we collected data on the leaf area, leaf mass per area (LMA), leaf anatomy, cell size, cell number, gas exchange and soluble sugar content of leaves from three soybean varieties grown under full sunlight (NS), shaded mature leaves (MS) or whole plants grown in shade (WS). Our results show that MS or WS cause a marked decline both in leaf area and LMA in newly developing leaves. Leaf anatomy also showed characteristics of shade leaves with decreased leaf thickness, palisade tissue thickness, sponge tissue thickness, cell size and cell numbers. In addition, in the MS and WS treatments, newly developed leaves exhibited lower net photosynthetic rate (Pn), stomatal conductance (Gs) and transpiration rate (E), but higher carbon dioxide (CO2) concentration in the intercellular space (Ci) than plants grown in full sunlight. Moreover, soluble sugar content was significantly decreased in newly developed leaves in MS and WS treatments. These results clearly indicate that (1) leaf area, leaf anatomical structure, and photosynthetic function of newly developing leaves are regulated by a systemic irradiance signal from mature leaves; (2) decreased cell size and cell number are the major cause of smaller and thinner leaves in shade; and (3) sugars could possibly act as candidate signal substances to regulate leaf area systemically. [ABSTRACT FROM AUTHOR]

Multi-species intercropping is a sustainable agricultural practice worldwide used to utilize resources more efficiently. In intercropping systems, short crops often grow under vegetative shade of tall crops. Soybean, one important legume, is often planted in intercropping. However, little is known about the mechanisms of shade inhibition effect on leaf size in soybean leaves at the transcriptome level. We analyzed the transcriptome of shaded soybean leaves via RNA-Seq technology. We found that transcription 1085 genes in mature leaves and 1847 genes in young leaves were significantly affected by shade. Gene ontology analyses showed that expression of genes enriched in polysaccharide metabolism was down-regulated, but genes enriched in auxin stimulus were up-regulated in mature leaves; and genes enriched in cell cycling, DNA-replication were down-regulated in young leaves. These results suggest that the inhibition of higher auxin content and shortage of sugar supply on cell division and cell expansion contribute to smaller and thinner leaf morphology, which highlights potential research targets such as auxin and sugar regulation on leaves for crop adaptation to shade in intercropping. [ABSTRACT FROM AUTHOR]

• We implemented the light interception model for strip intercropping into APSIM-Classic. • A quasi-Bayesian optimisation approach was used to derive parameter by constraining the model to LAI, biomass and yield. • Key model parameters were changed with row configuration, indicating a need to improve modelling physiology of intercrops. • A potential application is to optimize row configurations in strip intercropping across climates. Intercropping of two or more crop species increases the efficiency of resource use and often produces a greater yield per unit land area. The relative efficiency of intercropping depends on row configuration, but there is a shortage of modelling-based evaluation of alternative intercropping options due to the inadequacy of standard process-based crop models to simulate resource capture, growth and yield formation when the canopy is spatially structured in strips. We implemented a light interception model for strip crops into the APSIM Classic model and combined it with a quasi-Bayesian approach to derive the model parameters to simulate crop growth and grain yield in maize-soybean strip intercropping. We used 4 years of field data for 5 different row configurations to derive key model parameters for simulation of light interception, LAI dynamics, biomass growth and grain yield of maize and soybean intercrops. Key model parameters (e.g. RUE, k etc.) were found to change with row-spacing and configuration, posing challenges to simulate different configurations with a single parameter set. The potential ranges of these key parameters were derived by constraining the model to observed data. The model can be potentially used to evaluate impact of planting configurations on productivity of strip intercropping systems, but the variability of key model parameters among configuration treatments calls for further in-depth research to improve modelling physiology of strip intercrops. [ABSTRACT FROM AUTHOR]

• Observed phenology, LAI, biomass & yield of 72 soybean cultivars are presented. • APSIM captured LAI & biomass dynamics of multiple cultivars across different years. • APSIM improvement need to include simulation of grain setting & its impact on yield. • We provided the first data set in APSIM for modelling soybean genotypes in China. This paper combines the analysis of soybean growth data with modelling to quantify cultivar differences and to evaluate the ability of the APSIM-Soybean model for simulation of soybean biomass and grain yield. Crop data include main developmental stages, leaf area index (LAI), above ground biomass, grain yield and grain number of 72 soybean cultivars in China. We derived the parameters controlling soybean flowering and maturity time in the lack of data from contrasting environments, then tested APSIM to simulate LAI, biomass and grain yield. Our results show that once phenology is correctly simulated, APSIM was able to capture the LAI and biomass growth dynamics of multiple cultivars and across different years. Our data showed a strong correlation of grain yield with grain number, but not with grain size. Future model improvement could include the simulation of grain setting (grain number and grain filling rate) and their difference between cultivars so that yield difference can be simulated. Further scenario modelling demonstrated that APSIM also captured the genotype by environment interactions as they impact on yield. The derived parameters for 72 soybean cultivars provide the first data set in APSIM for improved modelling of soybean genotypes in China and beyond, adding to the current APSIM validation database of soybean. This also formed the basis for future modelling of intercropping systems with soybean, e.g. maize/soybean intercropping. [ABSTRACT FROM AUTHOR]

BACKGROUND RESULTS CONCLUSION Relay intercropping of maize and soybean can improve land productivity. However, the mechanism behind N2O emissions in this practice remains unclear. A two‐factor randomized block field trial was conducted to reveal the mechanism of N2O emissions in a full additive maize–soybean relay intercropping. Factor A was three cropping systems – that is, monoculture maize (Zea mays L.), monoculture soybean (Glycine max L. Merr.) and maize–soybean relay intercropping. Factor B was different N supply, containing no N, reduced N and conventional N. Differences in N2O emissions, soil properties, rhizosphere bacterial communities and yield advantage were evaluated.The land equivalent ratio was 1.55–2.44, and the cumulative N2O emission (CEN2O$$ \mathrm{C}{\mathrm{E}}_{{\mathrm{N}}_2\mathrm{O}} $$) was notably lower by 60.2% in intercropping than in monoculture, respectively. Reduced N declined CEN2O$$ \mathrm{C}{\mathrm{E}}_{{\mathrm{N}}_2\mathrm{O}} $$ without penalty on the yield advantages. The relay intercropping shifted soil properties – for example, soil organic matter, total N, NH4+$$ {\mathrm{NH}}_4^{+} $$ and protease activity – and improved the soil microorganism community – for example, Proteobacteria and Acidobacteria. Intercropping reduced CEN2O$$ \mathrm{C}{\mathrm{E}}_{{\mathrm{N}}_2\mathrm{O}} $$ by directly suppressing nirS‐ and amoA‐regulated N2O generation during soil N cycling, or nirS‐ and amoA‐mediated soil properties shifted to reduce CEN2O$$ \mathrm{C}{\mathrm{E}}_{{\mathrm{N}}_2\mathrm{O}} $$ indirectly. Reduced N directly reduced CEN2O$$ \mathrm{C}{\mathrm{E}}_{{\mathrm{N}}_2\mathrm{O}} $$ by decreasing soil N content and reducing soil microorganism activities to alleviate N2O produced in soil N cycling.Conducting a full additive maize–soybean relay intercropping with reduced nitrogen supply provides a way to alleviate N2O emissions without the penalty on the yield advantage by changing rhizosphere bacterial communities and soil N cycling. © 2024 Society of Chemical Industry. [ABSTRACT FROM AUTHOR]

Heterogeneous drought stress (HED) is prevalent in drought-resistant practices such as deficit irrigation, root zone irrigation and strip intercropping. The mechanisms and improvement of crop drought resistance under HED are not fully understood. This study used double-root grafted Nandou 12 (ND12) soybean seedlings to simulate HED treatment under controlled conditions. Seedlings were transplanted into root cups with waterproof partitions to establish different soil moisture treatments: sufficient irrigation (SI) with 80 % soil moisture on both sides, HED with 80 % on one side and 40 % on the other, and homogeneous drought stress (HOD) with 60 % on both sides. The results indicated that soybean plants treated with HED exhibited healthier growth compared to those treated with HOD. Photosynthesis rate (Pn), stomatal conductance (cond.), transpiration rate (Tr), and relative water content (RWC) decreased by 10.24 %, 43.90 %, 152.66 %, and 8.69 % in HED-treated plants, respectively, but dry biomass increased by 3.38 %. Conversely, HOD conditions led to a significant decline in these parameters. Metabolomic and transcriptomic analyses revealed significant changes in the biosynthesis and signaling pathways of key phytohormones and metabolites, including abscisic acid (ABA), gibberellin (GA), jasmonic acid (JA), isoflavones, starch, and sugars. In HED-treated plants, GmNCED downregulation resulted in 54.22 % less ABA than HOD. GA levels increased under HED with upregulation of GmGA3OX1 and GmGA3OX2. JA content in HED-treated roots was 90.90 % higher than in HOD-treated roots. Isoflavones concentration including genistein (73.01 %), genistin (63.63 %), malonylgenistin (20.58 %), malonylgenistin (65 %), diadzin (38.15 %), and malonyldiadzin (47.61 %) levels, were significantly higher in HED-treated plants. Antioxidant enzyme activities indicated a 20 % increase in peroxidase (POD) activity under HED, while malondialdehyde (MDA) content was 27 % higher in HOD-treated plants, indicating greater oxidative stress. Chlorophyll content remained stable, and starch concentration increased by 33.33 % in HED-treated plants compared to HOD-treated plants. HED enhances phytohormonal responses and metabolic adjustments in soybean plants, boosting photosynthetic efficiency, antioxidant capabilities, growth, and drought resilience. This regulatory mechanism balances growth promotion and drought resistance, highlighting HED potential in improving crop resilience. • Heterogeneous drought stress (HED) promotes healthier growth in soybeans compared to homogeneous drought stress (HOD). • HED alters key phytohormones and metabolites. • HED boosts photosynthesis and drought resilience. [ABSTRACT FROM AUTHOR]

Relay intercropping soybean [ Glycine max (L.) Merr.] with cereal provides an approach to increase land productivity and improve N fixation. To explore the physiological mechanisms underlying the N fixation, leaf and nodule traits, biomass and N accumulations, nodule sucrose content, paraffin section and transmission electron microscope observations, and nodule antioxidant capacity were compared in sole and relay intercropped soybean with N levels. The growth of relay intercropped soybean was suppressed during the coexistence duration, and N addition promotes leaf growth and suppressed nodule development. After maize harvest, a boosted recovery of intercropped soybean than sole cropping notably enhanced sucrose by 20.4% allocated to the nodule. Sufficient sucrose partition delayed nodule senescence by increasing antioxidant capacity in intercropped soybeans contrast in the sole cropping. The delayed nodule senescence of intercropped soybean continuously provides ureides to the aboveground. The ureide-N in total N of intercropped soybean was 37.3% notably higher than sole cropping at the R5 stage. Finally, the adverse effects of shade on soybean growth and N fixation during the coexistence duration were compensated through the recovery growth, which benefits obtaining yield advantage of the intercropped soybean. • A boosting recovery growth increasing nodule sucrose partition in relay intercropping. • A higher sucrose partition to nodules delayed nodule senescence. • The delayed nodule senescence improves shoot ureides accumulation in relay intercropping. [ABSTRACT FROM AUTHOR]

Shade avoidance syndrome (SAS) is an important measure of how plants respond to shade. Shade conditions are characterized by low light density and low red-to-far-red light (R/FR) ratio. However, low light intensity and low R/FR ratio play considerable and diverse roles in SAS. In the present study, soybean plants were grown in the presence and absence of additional FR at two light levels to investigate the different effects on soybean plants. Compared with normal light intensity, net photosynthetic rate significantly decreased in low light, but increased in low R/FR ratio. Chlorophyll a fluorescence transient curves showed that the absorption of light flux increased under low light intensity and low R/FR ratio, whereas the number of photo reaction centers decreased under low light intensity. In addition, the content of porphyrins and chlorophyll metabolites (magnesium protoporphyrin IX, protochlorophyllide, and chlorophyll a and b) was significantly enhanced by low light intensity and the relative gene expression levels of protoporphyrin IX magnesium chelatase , chlorophyll a oxygenase and protochlorophyllide oxidoreductases involved in the porphyrin pathway were significantly increased. The inhibitory effects of low light on the photosynthetic rate and biomass of soybean plants were alleviated by a low R/FR ratio. A low R/FR ratio optimized light capture and achieved efficient light energy utilization under low light intensity by fine-tuning the chlorophyll level and the relative gene expression level of critical chlorophyll biosynthesis-related enzymes. • Far-red light can improve the net photosynthetic rate of soybean under low light intensity. • Low R/FR ratio optimizes light energy capture and distribution under low light intensity. • Low R/FR ratio can be fine-tuned for accumulation of chlorophyll under low light intensity by decreasing the relative expression of CHL and POR. [ABSTRACT FROM AUTHOR]

Maize–soybean strip intercropping can effectively alleviate arable land competition, improve land output, and be conducive to the sustainable development. The key to achieve these advantages is to stabilize the maize yield. Suitable narrow row spacing could maximize the benefit of maize–soybean strip intercropping, and an increasing bandwidth with suitable narrow row spacing is beneficial to the mechanized production of soybean. In practice, to ensure the maize yield in additive maize strip intercropping, maize plant spacing decreases and intraspecific competition intensifies as the bandwidth increases. However, interspecific interactions have been the primary focus of studies because of the better rhizosphere nitrogen fixation ability of soybean and the activation of maize rhizosphere nutrients. Therefore, it is particularly urgent to identify the trade-offs between intraspecific competition and interspecific interactions in maize and the regulatory effects on maize yield. Field experiments were conducted from 2017 to 2020 to analyze the results of interindividual competition in maize and interactions with soybeans under different bandwidths. It was found that maize biomass and yield at the maturity stage decreased by 8.0% and 6.4%; 20.5% and 19.4%; and 28.7% and 44.1% from 2 m to 2.8 m, respectively, but the biomass proportion in ears showed no significant difference. Intraspecific competition of maize was weakened by special promotion in intercropping, but stable yield was achieved only at 2 m. In response to suitable competition, maize roots can flourish only on the basis of ensuring aboveground biomass. The results revealed that the primary negative determinant of maize yield was intraspecific aboveground competition and strengthening intraspecific competition reduced biomass accumulation without altering the allocation ratio to the ear. We concluded that maize yield was guaranteed at 2 m due to the special strip planting design compensated for the enhanced intraspecific competition of maize aboveground parts in the additive maize–soybean strip intercropping system. • Lower intraspecific competition was a driver of maize yield under different bandwidths. • The aboveground part of maize contributed more to the yield advantage than the underground part. • Decrease in biomass, not the proportion of partitioning to the ear, affected the maize yield. [ABSTRACT FROM AUTHOR]