Impacts of CO2 elevation on the physiology and seed quality of soybean

Modified speed breeding approach reduced breeding cycle to less than half in vegetable soybean [Glycine max (L.) Merr.]

Vegetable soybean [Glycine max (L.) Merr.] is gaining popularity because of its high nutritive values and health benefits; however, its productivity is scarce. Recognizing the need to accelerate breeding progress, a modified approach of 'speed breeding' was used in 16 vegetable soybean genotypes to reduce the breeding periods. The genotypes were exposed to cycles of 10 h light (30 °C) and 14 h dark (25 °C) with CO2 (550 ppm) and without CO2 supplementation under the light intensity of 220 µmol m-2 s-1 at the canopy level and 70-80% relative humidity. To reduce the time further, physiologically matured pods were harvested once they changed their color from green to greenish yellow and dried in the oven for 7 days at 25 ± 2 °C with RH 10-20%. The genotypes showed variable responses towards days to flowering coupled with an increase in the number of pods, number of seeds and seed weight per plant, and 100 seed weight during a short breeding period under CO2 supplement. A couple of genotypes behaved indifferently under normal and elevated CO2 levels. The fresh oven-dried seeds displayed 73.33-100% germination, while that in the seeds stored at 4 °C for 10 months was 80-100%. Thus, the modified speed breeding technique could effectively reduce the breeding period without affecting the germination of the seeds. With this approach, we could save 6-34 days in a genotype dependent way which would at least give 4-4.5 generations of soybean per year instead of the usual 1-2 generations. Further, the reduction in maturity duration was more in longer duration genotypes than the shorter duration ones. This represents the country's initial report of rapid breeding in vegetable soybean and offers ample opportunity for rapid generation advancement in this crop.

Supplementary Information

The online version contains supplementary material available at 10.1007/s12298-024-01503-z.

Protein plant factories: production and resource use efficiency of soybean proteins in vertical farming

BACKGROUND

Controlled environment agriculture, particularly vertical farms (VF), also called plant factories, is often claimed as a solution for global food security due to its ability to produce crops unaffected by weather or pests. In principle, essential macronutrients of the human diet, like protein, could technically be produced in VF. This aspect becomes relevant in the era of protein transition, marked by an increasing consumer interest in plant-based protein and environmental challenges faced by conventional farming. However, the real question is: what does the cultivation of protein crops in VF imply in terms of resource use? To address this, a study was conducted using a VF experiment focusing on two soybean cultivars.

RESULTS

With a variable plant density to optimize area use, and because of the ability to have more crop cycles per year, protein yield per square metre of crop was about eight times higher than in the open field. Assuming soy as the only protein source in the diet, the resources needed to get total yearly protein requirement of a reference adult would be 20 m2 of crop area, 2.4 m3 of water and 16 MWh of electricity, versus 164 m2, 111 m3 and 0.009 MWh in the field.

CONCLUSIONS

The study's results inform the debate on protein production and the efficiency of VF compared to conventional methods. With current electricity prices, it is unlikely to justify production of simple protein crops in VF or promote it as a solution to meet global protein needs. © 2024 The Authors. Journal of The Science of Food and Agriculture published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.

Gene editing to improve legume-rhizobia symbiosis in a changing climate

In the last three years, several gene editing techniques have been developed for both model and crop legumes. CRISPR-Cas9-based tools, in particular, are outpacing other comparable gene editing technologies used in legume hosts and their microbial symbionts to understand the molecular basis of symbiotic nitrogen-fixation. Gene editing has helped identify new gene functions, validate genetic screens, resolve gene redundancy, examine the role of tandemly duplicated genes, and investigate symbiotic signaling networks in non-model plants. In this review, we discuss the advances made in understanding the legume-rhizobia symbiosis through the use of gene editing and highlight studies conducted under varying environmental conditions. We reason that future climate-hardy legumes must be able to better integrate environmental signals with nitrogen fixation by fine-tuning long distance signaling, continuing to select efficient rhizobial partners, and adjusting their molecular circuitry to function optimally under variable light and nutrient availability and rising atmospheric carbon dioxide.

Effect of the Interaction between Elevated Carbon Dioxide and Iron Limitation on Proteomic Profiling of Soybean

Elevated atmospheric CO2 (eCO2) and iron (Fe) availability are important factors affecting plant growth that may impact the proteomic profile of crop plants. In this study, soybean plants treated under Fe-limited (0.5 mM) and Fe-sufficient (20 mM) conditions were grown at ambient (400 μmol mol−1) and eCO2 (800 μmol mol−1) in hydroponic solutions. Elevated CO2 increased biomass from 2.14 to 3.14 g plant−1 and from 1.18 to 2.91 g plant−1 under Fe-sufficient and Fe-limited conditions, respectively, but did not affect leaf photosynthesis. Sugar concentration increased from 10.92 to 26.17 μmol g FW−1 in roots of Fe-sufficient plants and from 8.75 to 19.89 μmol g FW−1 of Fe-limited plants after exposure to eCO2. In leaves, sugar concentration increased from 33.62 to 52.22 μmol g FW−1 and from 34.80 to 46.70 μmol g FW−1 in Fe-sufficient and Fe-limited conditions, respectively, under eCO2. However, Fe-limitation decreases photosynthesis and biomass. Pathway enrichment analysis showed that cell wall organization, glutathione metabolism, photosynthesis, stress-related proteins, and biosynthesis of secondary compounds changed in root tissues to cope with Fe-stress. Moreover, under eCO2, at sufficient or limited Fe supply, it was shown an increase in the abundance of proteins involved in glycolysis, starch and sucrose metabolism, biosynthesis of plant hormones gibberellins, and decreased levels of protein biosynthesis. Our results revealed that proteins and metabolic pathways related to Fe-limitation changed the effects of eCO2 and negatively impacted soybean production.

Crops' response to the emergent air pollutants

Consequences of air pollutants on physiology, biology, yield and quality in the crops are evident. Crop and soil management can play significant roles in attenuating the impacts of air pollutants. With rapid urbanization and industrialization, air pollution has emerged as a serious threat to quality crop production. Assessing the effect of the elevated level of pollutants on the performance of the crops is crucial. Compared to the soil and water pollutants, the air pollutants spread more rapidly to the extensive area. This paper has reviewed and highlighted the major findings of the previous research works on the morphological, physiological and biochemical changes in some important crops and fruits exposed to the increasing levels of air pollutants. The crop, soil and environmental factors governing the effect of air pollutants have been discussed. The majority of the observations suggest that the air pollutants alter the physiology and biochemical in the plants, i.e., while some pollutants are beneficial to the growth and yields and modify physiological and morphological processes, most of them appeared to be detrimental to the crop yields and their quality. A better understanding of the mechanisms of the uptake of air pollutants and crop responses is quite important for devising the measures ‒ at both policy and program levels ‒ to minimize their possible negative impacts on crops. Further research directions in this field have also been presented.

Flax and Sorghum: Multi-Element Contents and Nutritional Values within 210 Varieties and Potential Selection for Future Climates to Sustain Food Security

The Dietary Guidelines for Americans recommends giving priority to nutrient-dense foods while decreasing energy-dense foods. Although both flax (Linum usitatissimum) and sorghum (Sorghum bicolor) are rich in various essential minerals, their ionomes have yet to be investigated. Furthermore, previous studies have shown that elevated CO₂ levels could reduce key nutrients in crops. In this study, we analyzed 102 flax and 108 sorghum varieties to investigate their ionomic variations (N, P, K, Ca, Mg, S, B, Zn, Mn, Fe, Cu, and Mo), elemental level interactions, and nutritional value. The results showed substantial genetic variations and elemental correlations in flax and sorghum. While a serving size of 28 g of flax delivers 37% daily value (DV) of Cu, 31% of Mn, 28% of Mg, and 19% of Zn, sorghum delivers 24% of Mn, 16% of Cu, 11% of Mg, and 10% of Zn of the recommended daily value (DV). We identified a set of promising flax and sorghum varieties with superior seed mineral composition that could complement breeding programs for improving the nutritional quality of flax and sorghum. Overall, we demonstrate additional minerals data and their corresponding health and food security benefits within flax and sorghum that could be considered by consumers and breeding programs to facilitate improving seed nutritional content and to help mitigate human malnutrition as well as the effects of rising CO₂ stress.

Genotypic variation in the response of soybean to elevated CO2

The impact of elevated CO2 (eCO2) on soybean productivity is essential to the global food supply because it is the world's leading source of vegetable proteins. This study aimed to understand the yield responses and nutritional impact under free-air CO2 enrichment (FACE) conditions of soybean genotypes. Here we report that grain yield increased by 46.9% and no reduction in harvest index was observed among soybean genotypes. Elevated CO2 improved the photosynthetic carbon assimilation rate, leaf area, plant height, and aboveground biomass at vegetative and pod filling stages. Besides the positive effects on yield parameters, eCO2 differentially affected the overall grain quality. The levels of calcium (Ca), phosphorous (P), potassium (K), magnesium (Mg), manganese (Mn), iron (Fe), boron (B), and zinc (Zn) grain minerals decreased by 22.9, 9.0, 4.9, 10.1, 21.3, 28.1, 18.5, and 25.9% under eCO2 conditions, respectively. Soluble sugars and starch increased by 9.1 and 16.0%, respectively, phytic acid accumulation increased by 8.1%, but grain protein content significantly decreased by 5.6% across soybean genotypes. Furthermore, the antioxidant activity decreased by 36.9%, but the total phenolic content was not affected by eCO2 conditions. Genotypes, such as Winsconsin Black, Primorskaja, and L-117, were considered the most responsive to eCO2 in terms of yield enhancement and less affected in the nutritional quality. Our results confirm the existence of genetic variability in soybean responses to eCO2, and differences between genotypes in yield improvement and decreased sensitivity to eCO2 in terms of grain quality loss could be included in future soybean selection to enable adaptation to climate change.

Delineating the mechanisms of elevated CO2 mediated growth, stress tolerance and phytohormonal regulation in plants

Global climate change has drastically affected natural ecosystems and crop productivity. Among several factors of global climate change, CO₂ is considered to be the dynamic parameter that will regulate the responses of all biological system on earth in the coming decade. A number of experimental studies in the past have demonstrated the positive effects of elevated CO₂ on photosynthesis, growth and biomass, biochemical and physiological processes such as increased C:N ratio, secondary metabolite production, as well as phytohormone concentrations. On the other hand, elevated CO₂ imparts an adverse effect on the nutritional quality of crop plants and seed quality. Investigations have also revealed effects of elevated CO₂ both at cellular and molecular level altering expression of various genes involved in various metabolic processes and stress signaling pathways. Elevated CO₂ is known to have mitigating effect on plants in presence of abiotic stresses such as drought, salinity, temperature etc., while contrasting effects in the presence of different biotic agents i.e. phytopathogens, insects and herbivores. However, a well-defined crosstalk is incited by elevated CO₂ both under abiotic and biotic stresses in terms of phytohormones concentration and secondary metabolites production. With this background, the present review attempts to shed light on the major effects of elevated CO₂ on plant growth, physiological and molecular responses and will highlight the interactive effects of elevated CO₂ with other abiotic and biotic factors. The article will also provide deep insights into the phytohormones modulation under elevated CO₂.

Implications of rising atmospheric carbon dioxide concentration on seed quality

Regeneration of plants through seed is governed by the ability and rate to germinate, which largely depends on the climatic variables prevailing during pre-harvest (mother plant growth) and post-harvest (processing and storage) stages. Atmospheric carbon dioxide concentration [CO₂] is increasing rapidly and is expected to surpass 550 ppm within this century. Elevated CO₂ (e[CO₂]) is reported to influence the mother plant at morphological, phenological, physiological and biochemical levels across the species. Such changes are expected to alter the quality components of the progeny seeds, which has received very little research attention. This review discusses about the possible implications of e[CO₂] on quality attributes of seed affecting its planting value with much emphasis on seed weight, germination, vigour and its biochemical constituents. Research indicates that the effect of e[CO₂] on seed weight is variable and influenced by the availability of nutrients particularly nitrogen. Likewise, seed germination shows a divergent effect, whereas seed vigour that indicates the strength of a seed usually is compromised under e[CO₂]. It generally alters the balance between tissue carbon and nitrogen content, thus impairs the normal C:N ratio in progeny seed, which eventually impacts the next generation crop. For mitigation, while global breeding efforts focused on elite but narrow gene pool across the crop species shredded some of the ecologically important seed traits, such as thick and dark seed coat in legumes, such traits must be considered in designing breeding programs as they provide resilience to various stresses. We have suggested additional potential mitigation strategies and areas for future research.

Interactive Impact of Arbuscular Mycorrhizal Fungi and Elevated CO2 on Growth and Functional Food Value of Thymus vulgare

Arbuscular mycorrhizal fungi (AMF) and elevated CO₂ (eCO₂) have been effectively integrated to the agricultural procedures as an ecofriendly approach to support the production and quality of plants. However, less attention has been given to the synchronous application of AMF and eCO₂ and how that could affect the global plant metabolism. This study was conducted to investigate the effects of AMF and eCO₂, individually or in combination, on growth, photosynthesis, metabolism and the functional food value of Thymus vulgare. Results revealed that both AMF and eCO₂ treatments improved the photosynthesis and biomass production, however much more positive impact was obtained by their synchronous application. Moreover, the levels of the majority of the detected sugars, organic acids, amino acids, unsaturated fatty acids, volatile compounds, phenolic acids and flavonoids were further improved as a result of the synergistic action of AMF and eCO₂, as compared to the individual treatments. Overall, this study clearly shows that co-application of AMF and eCO₂ induces a synergistic biofertilization impact and enhances the functional food value of T. vulgare by affecting its global metabolism.