Interactive Effects of Elevated CO2 and N Fertilization on Yield and Quality of Tomato Grown Under Reduced Irrigation Regimes

Elevated concentrations of soil carbon dioxide with partial root-zone drying enhance drought tolerance and agro-physiological characteristics by regulating the expression of genes related to aquaporin and stress response in cucumber plants

Water scarcity and soil carbon dioxide elevation in arid regions are considered the most serious factors affecting crop growth and productivity. This study aimed to investigate the impacts of elevated CO2 levels (eCO2 at rates of 700 and 1000 ppm) on agro-physiological attributes to induce drought tolerance in cucumbers by activating the expression of genes related to aquaporin and stress response, which improved the yield of cucumber under two levels of irrigation water conditions [75% and 100% crop evapotranspiration (ETc)]. Therefore, two field experiments were conducted in a greenhouse with controlled internal climate conditions, at the Mohamed Naguib sector of the national company for protected agriculture, during the winter seasons of 2021-2022 and 2022-2023. The treatments included eCO2 in soil under normal and partial root zoon drying (PRD, 100% ETc Full irrigations, and 75% ETc). All the applied treatments were organized as a randomized complete block design (RCBD) and each treatment was replicated six times. Untreated plants were designed as control treatment (CO2 concentration was 400 ppm). The results of this study showed that elevating CO2 at 700 and 1000 ppm in soil significantly increased plant growth parameters, photosynthesis measurements, and phytohormones [indole acetic acid (IAA) and gibberellic acid (GA3)], under partial root-zone drying (75% ETc) and full irrigation conditions (100% ETc). Under PRD condition, eCO2 at 700 ppm significantly improved plant height (13.68%), number of shoots (19.88%), Leaf greenness index (SPAD value, 16.60%), root length (24.88%), fresh weight (64.77%) and dry weight (61.25%) of cucumber plant, when compared to untreated plants. The pervious treatment also increased photosynthesis rate, stomatal conductance, and intercellular CO2 concentration by 50.65%, 15.30% and 12.18%; respectively, compared to the control treatment. Similar findings were observed in nutrient concentration, carbohydrate content, Proline, total antioxidants in the leaf, and nutrients. In contrast, eCO2 at 700 ppm in the soil reduced the values of transpiration rate (6.33%) and Abscisic acid (ABA, 34.03%) content in cucumber leaves compared to untreated plants under both water levels. Furthermore, the results revealed that the gene transcript levels of the aquaporin-related genes (CsPIP1-2 and CsTIP4) significantly increased compared with a well-watered condition. The transcript levels of CsPIP improved the contribution rate of cell water transportation (intermediated by aquaporin's genes) and root or leaf hydraulic conductivity. The quantitative real-time PCR expression results revealed the upregulation of CsAGO1 stress-response genes in plants exposed to 700 ppm CO2. In conclusion, elevating CO2 at 700 ppm in the soil might be a promising technique to enhance the growth and productivity of cucumber plants in addition to alleviating the adverse effects of drought stresses.

Testing a Simulation Model for the Response of Tomato Fruit Quality Formation to Temperature and Light in Solar Greenhouses

Temperature and light are the key factors affecting the formation of tomato fruit quality in greenhouse cultivation. However, there are few simulation models that examine the relationship between tomato fruit quality formation and temperature and light. In this study, a model was established that investigated the relationships between soluble sugar (SSC), organic acid content (OAC), and SSC/OAC and the cumulative product of thermal effectiveness and photosynthetically active radiation (TEP) during the fruit-ripening period in a solar greenhouse. The root mean square error (RMSE) values were calculated to compare the consistency between the simulated and measured values, and the RMSE values for SSC, OAC, and SSC/OAC were 0.09%, 0.14%, and 0.358, respectively. The combined weights of quality indicators were obtained using the analytic hierarchy process (AHP) and entropy weighting method, ranking as SSC > OAC > SSC/OAC > CI > lycopene > Vc > fruit firmness. The comprehensive fruit quality evaluation value was obtained using the TOPSIS method (Technique for Order Preference by Similarity to an Ideal Solution) and a simulation model between comprehensive tomato fruit quality and TEP was explored. This study could accurately simulate and quantify the accumulation of tomato fruit quality during fruit ripening in response to environmental conditions in a solar greenhouse.

De novo transcriptome profiling reveals the patterns of gene expression in plum fruits with bud mutations

Bud mutation is a common technique for plant breeding and can provide a large number of breeding materials. Through traditional breeding methods, we obtained a plum plant with bud mutations (named "By") from an original plum variety (named "B"). The ripening period of "By" fruit was longer than that of "B" fruit, and its taste was better. In order to understand the characteristics of these plum varieties, we used transcriptome analysis and compared the gene expression patterns in fruits from the two cultivars. Subsequently, we identified the biological processes regulated by the differentially expressed genes (DEGs). Gene ontology (GO) analysis revealed that these DEGs were highly enriched for "single-organism cellular process" and "transferase activity". KEGG analysis demonstrated that the main pathways affected by the bud mutations were plant hormone signal transduction, starch and sucrose metabolism. The IAA, CKX, ARF, and SnRK2 genes were identified as the key regulators of plant hormone signal transduction. Meanwhile, TPP, the beta-glucosidase (EC3.2.1.21) gene, and UGT72E were identified as candidate DEGs affecting secondary metabolite synthesis. The transcriptome sequencing (RNA-seq) data were also validated using RT-qPCR experiments. The transcriptome analysis demonstrated that plant hormones play a significant role in extending the maturity period of plum fruit, with IAA, CKX, ARF, and SnRK2 serving as the key regulators of this process. Further, TPP, beta-glucosidase (EC3.2.1.21), and UGT72E appeared to mediate the synthesis of various soluble secondary metabolites, contributing to the aroma of plum fruits. The expression of BAG6 was upregulated in "B" as the fruit matured, but it was downregulated in "By". This indicated that "B" may have stronger resistance, especially fungal resistance.

Supplementary Information

The online version contains supplementary material available at 10.1007/s12298-024-01472-3.

Transgenerational Seed Exposure to Elevated CO2 Involves Stress Memory Regulation at Metabolic Levels to Confer Drought Resistance in Wheat

Drought is the worst environmental stress constraint that inflicts heavy losses to global food production, such as wheat. The metabolic responses of seeds produced overtransgenerational exposure to e[CO2] to recover drought's effects on wheat are still unexplored. Seeds were produced constantly for four generations (F1 to F4) under ambient CO2 (a[CO2], 400 μmol L-1) and elevated CO2 (e[CO2], 800 μmol L-1) concentrations, and then further regrown under natural CO2 conditions to investigate their effects on the stress memory metabolic processes liable for increasing drought resistance in the next generation (F5). At the anthesis stage, plants were subjected to normal (100% FC, field capacity) and drought stress (60% FC) conditions. Under drought stress, plants of transgenerational e[CO2] exposed seeds showed markedly increased superoxide dismutase (16%), catalase (24%), peroxidase (9%), total antioxidants (14%), and proline (35%) levels that helped the plants to sustain normal growth through scavenging of hydrogen peroxide (11%) and malondialdehyde (26%). The carbohydrate metabolic enzymes such as aldolase (36%), phosphoglucomutase (12%), UDP-glucose pyrophosphorylase (25%), vacuolar invertase (33%), glucose-6-phosphate-dehydrogenase (68%), and cell wall invertase (17%) were decreased significantly; however, transgenerational seeds produced under e[CO2] showed a considerable increase in their activities in drought-stressed wheat plants. Moreover, transgenerational e[CO2] exposed seeds under drought stress caused a marked increase in leaf Ψw (15%), chlorophyll a (19%), chlorophyll b (8%), carotenoids (12%), grain spike (16%), hundred grain weight (19%), and grain yield (10%). Hence, transgenerational seeds exposed to e[CO2] upregulate the drought recovery metabolic processes to improve the grain yield of wheat under drought stress conditions.

Identification of Hub Genes and Physiological Effects of Overexpressing the Photosynthesis-Related Gene Soly720 in Tomato under High-CO2 Conditions

Changes in the atmospheric CO2 concentration influence plant growth and development by affecting the morphological structure and photosynthetic performance. Despite evidence for the macro-effects of elevated CO2 concentrations on plant morphology and yield in tomato, the gene regulatory network and key genes related to cross-regulation have not been reported. To identify the hub genes and metabolic pathways involved in the response of tomato to CO2 enrichment, weighted gene co-expression network analysis was conducted using gene expression profiles obtained by RNA sequencing. The role of the photosynthesis-related gene Soly720 (Solyc01g007720) in CO2-enriched tomato plants was explored. Tomato plants responded to CO2 enrichment primarily through RNA-related pathways and the metabolism of amino acids, fatty acids, and carbohydrates. The hub genes in co-expression networks were associated with plant growth and development, including cellular components and photosynthesis. Compared to wild-type plants, transgenic plants overexpressing the Soly720 gene exhibited 13.4%, 5.5%, 8.9%, and 4.1% increases in plant height, stem diameter, leaf length, and leaf width, respectively, under high-CO2 conditions. The morphological improvements in transgenic plants were accompanied by enhancement of photosynthetic performance in terms of chlorophyll contents, photosynthetic characteristics, and key enzyme activities. This study elucidates the response network of tomato to CO2 enrichment and demonstrates the regulatory role of Soly720 in photosynthesis under high-CO2 conditions.

Root Distribution of Tomato Cultivated in Greenhouse under Different Ventilation and Water Conditions

Mastering root distribution is essential for optimizing the root zone environment and for improving water use efficiency, especially for crops cultivated in greenhouses. Here, we set up two irrigation amount levels based on measurements of the cumulative 20 cm pan evaporation (E_p) (i.e., K_0.9: 0.9 E_p; K_0.5: 0.5 E_p), and three ventilation modes through opening the greenhouse vents at different locations (T_R: open the roof vents only; T_RS: open both the roof and south vents; T_S: open the south vents only) to reveal the effects of the ventilation mode and irrigation amount on the root distribution of greenhouse tomato. Six treatments were designed in blocks with the ventilation mode as the main treatment and the irrigation amount as the vice treatment. On this basis, the normalized root length density (NRLD) model of six treatments was developed by considering air environment, soil water and temperature conditions, root length density (RLD) and yield. The results showed that air speed of the T_RS was significantly higher than T_R and T_S (p < 0.01), and the air temperature and relative humidity under different ventilation showed the rule: T_R > T_S > T_RS. There was a significant third-order polynomial function relationship between NRLD and soil depth, and the coefficient of the cubic term (R₀) had a bivariate quadratic polynomial function relationship with irrigation amount and air speed (determination coefficient, R² = 0.86). Root mean square errors of the simulated and measured value of NRLD under T_R, T_RS and T_S were 0.20, 0.23 and 0.27 in 2020, and 0.31, 0.23 and 0.28 in 2021, respectively, normalized root mean squared errors were 15%, 17%, 20% in 2020, and 23%, 18% and 21% in 2021. The RLD distribution ratio from the ground surface to a one-quarter relative root depth was 74.1%, and 88.0% from the surface to a one-half relative root depth. The results of the yield showed that a better combination of ventilation and irrigation was recommended as T_RS combined with K_0.9.

Feeding the world: impacts of elevated [CO2] on nutrient content of greenhouse grown fruit crops and options for future yield gains

Several long-term studies have provided strong support demonstrating that growing crops under elevated [CO2] can increase photosynthesis and result in an increase in yield, flavour and nutritional content (including but not limited to Vitamins C, E and pro-vitamin A). In the case of tomato, increases in yield by as much as 80% are observed when plants are cultivated at 1000 ppm [CO2], which is consistent with current commercial greenhouse production methods in the tomato fruit industry. These results provide a clear demonstration of the potential for elevating [CO2] for improving yield and quality in greenhouse crops. The major focus of this review is to bring together 50 years of observations evaluating the impact of elevated [CO2] on fruit yield and fruit nutritional quality. In the final section, we consider the need to engineer improvements to photosynthesis and nitrogen assimilation to allow plants to take greater advantage of elevated CO2 growth conditions.

Response of Cucumbers (Cucumis sativus L.) to Waste Wood Fiber Substrates and Additional Nitrogen Fertilization

As the consumption of plant products grown under regulated-climate conditions intensifies, its production also intensifies. Peat substrate as a growing medium is widely used due to its desirable physical, chemical, and biological properties. Peatlands play an important ecological, economic, and cultural role in human well-being, but their resources are decreasing, so wood fiber can be used as a substitute for peat substrate. Cucumbers (Cucumis sativus L.) were cultivated in growing media (Factor A) of peat substrate and wood fiber: (1) peat substrate (PS); (2) wood fiber (WF); (3) WF and PS 50:50 v/v; or (4) WF and PS 25:75 v/v. To evaluate the amount of additional nitrogen, four fertilization rates were used (Factor B): (1) conventional fertilization (CF); (2) N₁₃; (3) N₂₃; or (4) N₃₀. The yield of cucumbers grown in wood fiber depended on the amount of additional nitrogen. When plants were fertilized with the highest rate of additional nitrogen, N₃₀, their yield increased by 22% compared to the yield of cucumbers that were grown in wood fiber using conventional fertilization. Chlorophyll synthesis was the most intense in the leaves of cucumbers grown in wood fiber when the plants were additionally fertilized with N₂₃ and N_30, and in mixtures of wood fiber with peat substrate in ratios of 50:50 and 25:75, fertilized with N₂₃ and N₁₃, respectively. In summary, it can be argued that cucumbers can be grown in wood fiber and in a mixture with peat substrate in a ratio of 50:50, but additional nitrogen is needed to compensate for the amount of nitrogen immobilized in the fiber.

Impact of Climate Change on Dryland Agricultural Systems: A Review of Current Status, Potentials, and Further Work Need

Dryland agricultural system is under threat due to climate extremes and unsustainable management. Understanding of climate change impact is important to design adaptation options for dry land agricultural systems. Thus, the present review was conducted with the objectives to identify gaps and suggest technology-based intervention that can support dry land farming under changing climate. Careful management of the available agricultural resources in the region is a current need, as it will play crucial role in the coming decades to ensure food security, reduce poverty, hunger, and malnutrition. Technology based regional collaborative interventions among Universities, Institutions, Growers, Companies etc. for water conservation, supplemental irrigation, foliar sprays, integrated nutrient management, resilient crops-based cropping systems, artificial intelligence, and precision agriculture (modeling and remote sensing) are needed to support agriculture of the region. Different process-based models have been used in different regions around the world to quantify the impacts of climate change at field, regional, and national scales to design management options for dryland cropping systems. Modeling include water and nutrient management, ideotype designing, modification in tillage practices, application of cover crops, insect, and disease management. However, diversification in the mixed and integrated crop and livestock farming system is needed to have profitable, sustainable business. The main focus in this work is to recommend different agro-adaptation measures to be part of policies for sustainable agricultural production systems in future.

Effects of Elevated CO2 on Photosynthetic Accumulation, Sucrose Metabolism-Related Enzymes, and Genes Identification in Goji Berry (Lycium barbarum L.)

Goji berry (Lycium barbarum L.) exposure to elevated CO₂ (eCO₂) for long periods reduces their sugar and secondary metabolite contents. However, sugar accumulation in fruit depends on photosynthesis and photoassimilate partitioning. This study aimed to explore photosynthesis, sugar content, and sucrose metabolism-related enzyme activities in goji berry leaves and fruits under ambient and eCO₂ levels, and identify the genes encoding L. barbarum acid invertase (LBAI), L. barbarum sucrose synthase (LBSS), L. barbarum sucrose phosphate synthase (LBSPS), and L. barbarum neutral invertase (LBNI), based on transcriptome profiling. Further, the characterization of four identified genes was analyzed including subcellular localization and expression patterns. In plants grown under eCO₂ for 90 or 120 days, the expression of the above-mentioned genes changed significantly as the photosynthetic rate increased. In addition, leaf and fruit sugar contents decreased, and the activities of four sucrose metabolism-related enzymes increased in leaves, while acid and neutral invertase increased in fruits. Protein sequence analysis demonstrated that LBAI and LBNI contain a conservative structure domain belonging to the glycosyl hydrolases (Glyco_hydro) family, and both LBSS and LBSPS belonging to the sucrose synthase (Sucrose_synth) and glycosyltransferase (Glycos_transf) family. Subcellular localization analysis showed that LBAI, LBNI, and LBSS were all located in the nucleus, plasma membrane, and cytoplasm, while LBSPS was located in the plasma membrane. The expressions of LBAI, LBSPS, and LBNI were high in the stems, whereas LBSS was predominantly expressed in the fruits. Our findings provide fundamental data on photosynthesis and sugar accumulation trends in goji berries under eCO₂ exposure.

Response and Modeling of Hybrid Maize Seed Vigor to Water Deficit at Different Growth Stages

Research is imperative to predict seed vigor of hybrid maize production under water deficit in arid areas. Field experiments were conducted in 2018 and 2019 in arid areas of northwestern China to investigate the effects of different irrigation strategies at various growth stages with drip irrigation under film mulching on grain yield, kernel weight, seed protein content, and seed vigor of hybrid maize (Zea mays L.). Water deficit at vegetative, flowering, and grain-filling stages was considered and a total of 16 irrigation treatments was applied. A total of 12 indices of germination percentage, germination index (GI), shoot length (SL), and root length (RL) under different germination conditions (standard germination and accelerated aging); electrical conductivity (EC) of the leachate; and activities of peroxidase, catalase, and superoxide dismutase in seeds were measured and analyzed using the combinational evaluation method (CEM). Furthermore, five water production functions (Blank, Stewart, Rao, Jensen, and Minhas) were used to predict seed vigor evaluated by CEM under water deficit. The results showed that leachate EC was higher under water deficit than that under sufficient irrigation. The SL, RL, and GI of different germination conditions increased under water deficit at the flowering stage. The Rao model was considered the best fitted model to predict the vigor of hybrid maize seeds under water deficit, and an appropriate water deficit at the flowering stage is recommended to ensure high seed vigor of hybrid maize production with drip irrigation under film mulching. Our findings would be useful for reducing crop water use while ensuring seed vigor for hybrid maize production in arid areas.

The Alleviation of Photosynthetic Damage in Tomato under Drought and Cold Stress by High CO2 and Melatonin

The atmospheric CO₂ concentration (a[CO₂]) is increasing at an unprecedented pace. Exogenous melatonin plays positive roles in the response of plants to abiotic stresses, including drought and cold. The effect of elevated CO₂ concentration (e[CO₂]) accompanied by exogenous melatonin on plants under drought and cold stresses remains unknown. Here, tomato plants were grown under a[CO₂] and e[CO₂], with half of the plants pre-treated with melatonin. The plants were subsequently treated with drought stress followed by cold stress. The results showed that a decreased net photosynthetic rate (P_N) was aggravated by a prolonged water deficit. The P_N was partially restored after recovery from drought but stayed low under a successive cold stress. Starch content was downregulated by drought but upregulated by cold. The e[CO₂] enhanced P_N of the plants under non-stressed conditions, and moderate drought and recovery but not severe drought. Stomatal conductance (g_s) and the transpiration rate (E) was less inhibited by drought under e[CO₂] than under a[CO₂]. Tomato grown under e[CO₂] had better leaf cooling than under a[CO₂] when subjected to drought. Moreover, melatonin enhanced P_N during recovery from drought and cold stress, and enhanced biomass accumulation in tomato under e[CO₂]. The chlorophyll a content in plants treated with melatonin was higher than in non-treated plants under e[CO₂] during cold stress. Our findings will improve the knowledge on plant responses to abiotic stresses in a future [CO₂]-rich environment accompanied by exogenous melatonin.

Interactive effects of elevated CO2 concentration and combined heat and drought stress on tomato photosynthesis

BACKGROUND

Extreme weather events are predicted to increase, such as combined heat and drought. The CO₂ concentration ([CO₂]) is predicted to approximately double by 2100. We aim to explore how tomato physiology, especially photosynthesis, is affected by combined heat and drought under elevated [CO₂] (e [CO₂]).

RESULTS

Two genotypes, 'OuBei' ('OB', Solanum lycopersicum) and 'LA2093' (S. pimpinellifolium) were grown at a [CO₂] (atmospheric [CO₂], 400 ppm) and e [CO₂] (800 ppm), respectively. The 27-days-old seedlings were treated at 1) a [CO₂], 2) a [CO₂] + combined stress, 3) e [CO₂] and 4) e [CO₂] + combined stress, followed by recovery. The P_N (net photosynthetic rate) increased at e [CO₂] as compared with a [CO₂] and combined stress inhibited the P_N. Combined stress decreased the F_v/F_m (maximum quantum efficiency of photosystem II) of 'OB' at e [CO₂] and that of 'LA2093' in regardless of [CO₂]. Genotypic difference was observed in the e [CO₂] effect on the gas exchange, carbohydrate accumulation, pigment content and dry matter accumulation.

CONCLUSIONS

Short-term combined stress caused reversible damage on tomato while the e [CO₂] alleviated the damage on photosynthesis. However, the e [CO₂] cannot be always assumed have positive effects on plant growth during stress due to increased water consumption. This study provided insights into the physiological effects of e [CO₂] on tomato growth under combined stress and contributed to tomato breeding and management under climate change.

The Optimization of Nitrogen Fertilization Regulates Crop Performance and Quality of Processing Tomato (Solanum lycopersicum L. cv. Heinz 3402)

In this study, we evaluated the effect of various fertilization regimes on processing tomato (Solanum lycopersicum L. cv. Heinz 3402) yield and quality by applying the following treatments: (i) control (C), (ii) conventional fertilizer (21-0-0, N-P-K) (CF), (iii) slow release nitrogen fertilizer 46-0-0 (SR), (iv) conventional fertilizer (21-0-0, N-P-K) + Zeolite (CFZ), and v) composted sheep manure (M). The results of the study showed that the SR and CFZ treatments resulted in the highest fruit yield per hectare compared to the rest of the fertilizer and the control treatments. Fruit firmness was higher for the treatments C, M and SR, while color parameters (chroma and hue angle) were higher for the C and M treatments, respectively. Moreover, the total soluble solids content (TSS; °Brix) was higher when manure (M) was applied. In terms of chemical composition, the total and individual tocopherols and sugars were the highest for the M and C treatments, respectively, whereas the oxalic, malic and total organic acid contents were the highest for the CFZ treatment. Moreover, the tested treatments showed a varied response in different antioxidant assays, although the M treatment exhibited a high antioxidant capacity in most of the assays, except for the β-carotene/linoleate assay. The carotenoid and chlorophyll contents were the highest for the control treatment. The main detected fatty acid was linoleic acid, followed by palmitic, oleic and α-linolenic acid, while the CFZ treatment had the highest content of polyunsaturated fatty acids (PUFA) due to its high content of linoleic acid. In conclusion, although the application of fertilizers increased yield, the quality parameters and chemical composition showed a varied response to the fertilization regime, especially the TSS content and juice pH and electric conductivity (EC), which are significant for the marketability of the final product.

Tomato Fruit Development and Metabolism

Tomato (Solanum lycopersicum L.) belongs to the Solanaceae family and is the second most important fruit or vegetable crop next to potato (Solanum tuberosum L.). It is cultivated for fresh fruit and processed products. Tomatoes contain many health-promoting compounds including vitamins, carotenoids, and phenolic compounds. In addition to its economic and nutritional importance, tomatoes have become the model for the study of fleshy fruit development. Tomato is a climacteric fruit and dramatic metabolic changes occur during its fruit development. In this review, we provide an overview of our current understanding of tomato fruit metabolism. We begin by detailing the genetic and hormonal control of fruit development and ripening, after which we document the primary metabolism of tomato fruits, with a special focus on sugar, organic acid, and amino acid metabolism. Links between primary and secondary metabolic pathways are further highlighted by the importance of pigments, flavonoids, and volatiles for tomato fruit quality. Finally, as tomato plants are sensitive to several abiotic stresses, we briefly summarize the effects of adverse environmental conditions on tomato fruit metabolism and quality.

De novo characterization of the Goji berry (Lycium barbarium L.) fruit transcriptome and analysis of candidate genes involved in sugar metabolism under different CO2 concentrations

Goji berry (Lycium barbarum L.) is one of the important economic crops due to its exceptional nutritional value and medicinal benefits. Although reduced sugar levels in goji berry exposed to long-term elevated carbon dioxide (CO2) have been documented, the underlying molecular mechanisms remain unknown. The objective of this study was to explore the transcriptome of goji berry fruit under ambient and elevated CO2 concentrations and further to screen the differentially expressed genes (DEGs) for functions related to sugar metabolism. Fruit samples from goji berry exposed to ambient (400 μmol mol-1) and elevated (700 μmol mol-1) levels of CO2 for 120 days were analyzed for total sugar, carotenoid and flavone analysis. In this study, a reduction in total sugar and carotenoid levels in the fruits grown under elevated CO2 levels were observed. Fruit samples were also used to construct cDNA libraries using a HiSeqTM2500 platform. Consequently, 81,100 unigenes were assembled, of which 35,111 (43.3%) were annotated using various databases. Through DEGs analysis, it was found that 55 genes were upregulated and 18 were down-regulated in response to elevated CO2 treatment. Genes involved in the sugar metabolism and the related pathways were identified by Gene Ontology and Kyoto encyclopedia of genes and genomes (KEGG) pathway enrichment analysis. Furthermore, three genes, LBGAE (Lycium barbarum UDP-glucuronate 4-epimerase), LBGALA (Lycium barbarum alpha-galactosidase) and LBMS (Lycium barbarum malate synthase), associated with sugar metabolism were identified and discussed with respect to the reduction in the total sugar levels along with the enzymes acid invertase (AI), sucrose synthase (SS) and sucrose phosphate synthase (SPS) of the sucrose metabolism. This study can provide gene sources for elucidating the molecular mechanisms of sugar metabolism in the fruit of goji berry under elevated CO2.

Effects of Elevated CO2 on Nutritional Quality of Vegetables: A Review

Elevated atmospheric CO2 (eCO2) enhances the yield of vegetables and could also affect their nutritional quality. We conducted a meta-analysis using 57 articles consisting of 1,015 observations and found that eCO2 increased the concentrations of fructose, glucose, total soluble sugar, total antioxidant capacity, total phenols, total flavonoids, ascorbic acid, and calcium in the edible part of vegetables by 14.2%, 13.2%, 17.5%, 59.0%, 8.9%, 45.5%, 9.5%, and 8.2%, respectively, but decreased the concentrations of protein, nitrate, magnesium, iron, and zinc by 9.5%, 18.0%, 9.2%, 16.0%, and 9.4%. The concentrations of titratable acidity, total chlorophyll, carotenoids, lycopene, anthocyanins, phosphorus, potassium, sulfur, copper, and manganese were not affected by eCO2. Furthermore, we propose several approaches to improving vegetable quality based on the interaction of eCO2 with various factors, including species, cultivars, CO2 levels, growth stages, light, O3 stress, nutrient, and salinity. Finally, we present a summary of the eCO2 impact on the quality of three widely cultivated crops, namely, lettuce, tomato, and potato.