Effects of Elevated CO2 on the Capacity for Photosynthesis of a Single Leaf and a Whole Plant, and on Growth in a Radish

Low CO2 concentration, a key environmental factor for developing plateau adapted rapeseed

BACKGROUND

Photosynthesis is a fundamental process that underlies the formation of crop yield, wherein light serves as the driving force and carbon dioxide (CO2) as the raw material. These two factors have a direct influence on the progress and efficiency of photosynthesis in crops. Rapeseed is one of the four major oilseed crops worldwide. Plateau rapeseed has now become a research hotspot. However, the lack of high-yielding rapeseed germplasm resources on the plateau and the highly efficient strategy for screening them severely affect the development of rapeseed industry in plateau.

RESULTS

In the rapeseed experimental fields located on the plateau (Lhasa, Tibet), we measured abundant sunlight, characterized by an average daily photosynthetically active radiation (PAR) of 1413 μmol m-2 s-1. In addition, the atmospheric CO2 concentrations range from 300 to 400 ppm, which is only two-thirds of that in the plain (Chengdu, Sichuan). We found that under different measurement conditions of light intensity and CO2 concentration, different rapeseed genotypes showed significant differences in leaf photosynthetic efficiency during the seedling stage. Moreover, the rapeseed materials with high photosynthetic efficiency under low CO2 concentrations rather than high light intensity, exhibited significant advantages in biomass, yield, and oil content when cultivated on the plateau, indicating that the CO2 is the key environmental factor which limited rapeseed production in plateau. Based on photosynthetic efficiency screening under low CO2 concentrations, six rapeseed varieties SC3, SC10, SC25, SC27, SC29 and SC37, shown significantly higher yields in plateau environment compared to local control variety were obtained. In addition, the adaptability of rapeseed to plateau was found to be related to the activities of key Calvin cycle enzymes and the accumulation of photosynthetic products.

CONCLUSIONS

This study established a screening strategy for plateau high-yielding rapeseed materials, obtained six varieties which were suitable for plateau cultivation, explored the mechanism of rapeseed response to the plateau environment, and thus provides a feasible strategy for plateau-adapted rapeseed breeding.

Favorable physiological and morphological effects of molybdenum nanoparticles on tobacco (Nicotiana tabacum L.): root irrigation is superior to foliar spraying

Introduction

Nano fertilizers can provide efficient solutions to the increasing problem of nutrient deficiency caused by low availability. However, the most important prerequisite is to fully understand whether nanomaterials induce phytotoxicity in plants under a variety of different conditions. The mechanisms underlying interactions between molybdenum nanoparticles (Mo NPs) and plants with respect to their uptake and biological effects on crops are still not fully understood.

Methods

In this study, the impacts of Mo NPs over a range of concentrations (0, 25, and 100 μg/mL) on tobacco (Nicotiana tabacum L.) seedling growth were comparatively evaluated under foliar applications and root irrigation.

Results

The results indicated that more significant active biological effects were observed with root irrigation application of Mo NPs than with foliar spraying. The agronomic attributes, water content and sugar content of Mo NPs-exposed seedlings were positively affected, and morphologically, Mo NPs induced root cell lignification and more vascular bundles and vessels in tobacco tissues, especially when applied by means of root irrigation. Moreover, the photosynthetic rate was improved by 131.4% for root exposure to 100 μg/mL Mo NPs, mainly due to the increased chlorophyll content and stomatal conductance. A significant concentration-dependent increase in malonaldehyde (MDA) and defensive enzyme activity for the Mo NPs-treated tobacco seedlings were detected compared to the controls. Significantly improved absorption of Mo by exposed tobacco seedlings was confirmed with inductively coupled plasma mass spectrometry (ICP-MS) in tobacco tissues, regardless of application method. However, the accumulation of Mo in roots increased by 13.94 times, when roots were exposed to 100 mg/L Mo NPs, higher than that under treatment with foliar spray. Additionally, Mo NPs activated the expression of several genes related to photosynthesis and aquaporin processes.

Discussion

The present investigations offer a better understanding of Mo NPs-plant interactions in terrestrial ecosystems and provide a new strategy for the application of Mo NPs as nano fertilizers in crop production.

A high efficiency CO2 concentration interval optimization method for lettuce growth

The decline in carbon fertilization effects has shifted scientific focus toward the efficient and suitable regulation of CO2 concentration ([CO2]) for plant growth. In this study, the rapid A/CO2 response curve (RAC) data of lettuce were analyzed statistically under nine photosynthetic photon flux densities (PPFDs) and four temperatures. An efficient CO2 supplementation interval acquisition method based on the frequency distribution characteristics of RACs was proposed. The characteristic subsections of jumping were obtained depending on the frequency distribution of RACs. The cumulative contribution rate (CCR) of the characteristic subsections were >97 %, which showed the efficiency of the method. Additionally, U-chord curvature theory was used to simultaneously obtain the optimal regulated [CO2] for the same RAC curves, and the results showed that the [CO2] obtained by U-chord length were all within the interval obtained by the method, which proved the rationality of the method. The [CO2] interval supplement improved the daily CO2 exchange rate by 20.27 % and 21.64 % at 150 and 200 μmol·m-2·s-1, and increased the lettuce fresh biomass by 26.78 % at 150 μmol·m-2·s-1. Based on the interval of [CO2] efficient utilization regulation at various temperatures and PPFDs, a genetic algorithm-support vector regression model was built with R2 of the model was >0.84 and the root mean square error was <35.2256 μmol·mol-1. In conclusion, the [CO2] interval obtained by this method has a positive effect on lettuce growth. This work provides a new method for obtaining high-efficiency supplementary concentration of CO2 during the growth of lettuce.

Impact of Elevated CO2 and Temperature on Growth, Development and Nutrient Uptake of Tomato

Elevated carbon dioxide (EC) can increase the growth and development of different C3 fruit crops, which may further increase the nutrient demand by the accumulated biomass. In this context, the current investigation was conceptualized to evaluate the growth performance and nutrient uptake by tomato plants under elevated CO2 (EC700 and EC550 ppm) and temperature (+2 °C) in comparison to ambient conditions. Significant improvement in the growth indicating parameters like leaf area, leaf area index, leaf area duration and crop growth rate were measured at EC700 and EC550 at different stages of crop growth. Further, broader and thicker leaves of plants under EC700 and EC550 have intercepted higher radiation by almost 11% more than open field plants. Conversely, elevated temperature (+2 °C) had negative influence on crop growth and intercepted almost 7% lower radiation over plants under ambient conditions. Interestingly, earliness of phenophases viz., branch initiation (3.0 days), flower initiation (4.14 days), fruit initiation (4.07 days) and fruit maturation (7.60 days) were observed at EC700 + 2 °C, but it was statistically on par with EC700 and EC550 + 2 °C. Irrespective of the plant parts and growth stages, plants under EC700 and EC550 have showed significantly higher nutrient uptake due to higher root biomass. At EC700, the tune of increase in total nitrogen, phosphorus and potassium uptake was almost 134%, 126% and 135%, respectively compared to open field crop. This indicates higher nutrient demand by the crop under elevated CO2 levels because of higher dry matter accumulation and radiation interception. Thus, nutrient application is needed to be monitored at different growth stages as per the crop needs.

Transcriptome Reveals the Rice Response to Elevated Free Air CO2 Concentration and TiO2 Nanoparticles

Increasing CO₂ levels are speculated to change the effects of engineered nanomaterials in soil and on plant growth. How plants will respond to a combination of elevated CO₂ and nanomaterials stress has rarely been investigated, and the underlying mechanism remains largely unknown. Here, we conducted a field experiment to investigate the rice (Oryza sativa L. cv. IIyou) response to TiO₂ nanoparticles (nano-TiO₂, 0 and 200 mg kg^-1) using a free-air CO₂ enrichment system with different CO₂ levels (ambient ∼370 μmol mol^-1 and elevated ∼570 μmol mol^-1). The results showed that elevated CO₂ or nano-TiO₂ alone did not significantly affect rice chlorophyll content and antioxidant enzyme activities. However, in the presence of nano-TiO₂, elevated CO₂ significantly enhanced the rice height, shoot biomass, and panicle biomass (by 9.4%, 12.8%, and 15.8%, respectively). Furthermore, the Kyoto Encyclopedia of Genes and Genomes pathway enrichment analysis revealed that genes involved in photosynthesis were up-regulated while most genes associated with secondary metabolite biosynthesis were down-regulated in combination-treated rice. This indicated that elevated CO₂ and nano-TiO₂ might stimulate rice growth by adjusting resource allocation between photosynthesis and metabolism. This study provides novel insights into rice responses to increasing contamination under climate change.

Heritable Changes in Physiological Gas Exchange Traits in Response to Long-Term, Moderate Free-Air Carbon Dioxide Enrichment

Atmospheric carbon dioxide ([CO₂]) concentrations significantly alter developmental plant traits with potentially far-reaching consequences for ecosystem function and productivity. However, contemporary evolutionary responses among extant plant species that coincide with modern, anthropogenically driven [CO₂] rise have rarely been demonstrated among field-grown plant populations. Here we present findings from a long-term, free-air carbon dioxide enrichment (FACE) study in a seminatural European grassland ecosystem in which we observe a differential capacity among plant species to acclimate intrinsic water-use efficiencies (WUEs) in response to prolonged multigenerational exposure to elevated [CO₂] concentrations. In a reciprocal swap trial, using controlled environment growth chambers, we germinated seeds from six of the most dominant plant species at the FACE site [Arrhenatherum elatius (L.), Trisetum flavescens (L.), Holcus lanatus (L.), Geranium pratense (L.), Sanguisorba officinalis (L.), and Plantago lanceolata (L.)]. We found that long-term exposure to elevated [CO₂] strongly influenced the dynamic control of WUE_i in the first filial generations (F₁) of all species as well as an unequal ability to adapt to changes in the [CO₂] of the growth environment among those species. Furthermore, despite trait-environment relationships of this nature often being considered evidence for local adaptation in plants, we demonstrate that the ability to increase WUE_i does not necessarily translate to an ecological advantage in diverse species mixtures.

Elevated CO2 concentration promotes photosynthesis of grape (Vitis vinifera L. cv. 'Pinot noir') plantlet in vitro by regulating RbcS and Rca revealed by proteomic and transcriptomic profiles

BACKGROUND

Plant photosynthesis can be improved by elevated CO₂ concentration (eCO₂). In vitro growth under CO₂ enriched environment can lead to greater biomass accumulation than the conventional in micropropagation. However, little is know about how eCO₂ promotes transformation of grape plantlets in vitro from heterotrophic to autotrophic. In addition, how photosynthesis-related genes and their proteins are expressed under eCO₂ and the mechanisms of how eCO₂ regulates RbcS, Rca and their proteins have not been reported.

RESULTS

Grape (Vitis vinifera L. cv. 'Pinot Noir') plantlets in vitro were cultured with 2% sucrose designated as control (CK), with eCO₂ (1000 μmol·mol^- 1) as C0, with both 2% sucrose and eCO₂ as Cs. Here, transcriptomic and proteomic profiles associated with photosynthesis and growth in leaves of V. vinifera at different CO₂ concentration were analyzed. A total of 1814 genes (465 up-regulated and 1349 down-regulated) and 172 proteins (80 up-regulated and 97 down-regulated) were significantly differentially expressed in eCO₂ compared to CK. Photosynthesis-antenna, photosynthesis and metabolism pathways were enriched based on GO and KEGG. Simultaneously, 9, 6 and 48 proteins were involved in the three pathways, respectively. The leaf area, plantlet height, qP, ΦPSII and ETR increased under eCO₂, whereas Fv/Fm and NPQ decreased. Changes of these physiological indexes are related to the function of DEPs. After combined analysis of proteomic and transcriptomic, the results make clear that eCO₂ have different effects on gene transcription and translation. RbcS was not correlated with its mRNA level, suggesting that the change in the amount of RbcS is regulated at their transcript levels by eCO₂. However, Rca was negatively correlated with its mRNA level, it is suggested that the change in the amount of its corresponding protein is regulated at their translation levels by eCO₂.

CONCLUSIONS

Transcriptomic, proteomic and physiological analysis were used to evaluate eCO2 effects on photosynthesis. The eCO₂ triggered the RbcS and Rca up-regulated, thus promoting photosynthesis and then advancing transformation of grape plantlets from heterotrophic to autotrophic. This research will helpful to understand the influence of eCO₂ on plant growth and promote reveal the mechanism of plant transformation from heterotrophic to autotrophic.

The radish genome and comprehensive gene expression profile of tuberous root formation and development

Understanding the processes that regulate plant sink formation and development at the molecular level will contribute to the areas of crop breeding, food production and plant evolutionary studies. We report the annotation and analysis of the draft genome sequence of the radish Raphanus sativus var. hortensis (long and thick root radish) and transcriptome analysis during root development. Based on the hybrid assembly approach of next-generation sequencing, a total of 383 Mb (N50 scaffold: 138.17 kb) of sequences of the radish genome was constructed containing 54,357 genes. Syntenic and phylogenetic analyses indicated that divergence between Raphanus and Brassica coincide with the time of whole genome triplication (WGT), suggesting that WGT triggered diversification of Brassiceae crop plants. Further transcriptome analysis showed that the gene functions and pathways related to carbohydrate metabolism were prominently activated in thickening roots, particularly in cell proliferating tissues. Notably, the expression levels of sucrose synthase 1 (SUS1) were correlated with root thickening rates. We also identified the genes involved in pungency synthesis and their transcription factors.

Yield, chemical composition and nutritional quality responses of carrot, radish and turnip to elevated atmospheric carbon dioxide

BACKGROUND

Future concentration of carbon dioxide in the atmosphere is very important due to its apparent economic and environmental impact in terms of climate change. However, a compressive assessment of its effect on the nutritional and chemical characteristics of food crops has yet to be established. In the present study the impact of elevated atmospheric CO2 on the yield, chemical composition and nutritional quality of three root vegetables, carrot (Daucus carota L. cv. T-1-111), radish (Raphanus sativus L. cv. Mino) and turnip (Brassica rapa L. cv. Grabe) has been investigated.

RESULTS

The yield of carrot, radish and turnip increased by 69, 139 and 72%, respectively, when grown under elevated CO2 conditions. Among the proximate composition, protein, vitamin C and fat contents decreased significantly for all the vegetables while sugar and fibre contents were increased. Response of the vegetables to elevated CO2 , in terms of elemental composition, was different with a significant decrease in many important minerals. Elevated CO2 decreased the amount of majority of the fatty acids and amino acids in these vegetables.

CONCLUSIONS

It was observed that elevated CO2 increased the yield of root vegetables but many important nutritional parameters including protein, vitamin C, minerals, essential fatty acids and amino acids were decreased.