Physiological, biochemical, and genome-wide transcriptional analysis reveals that elevated CO2 mitigates the impact of combined heat wave and drought stress in Arabidopsis thaliana at multiple organizational levels

Soil environmental anomalies dominate the responses of net ecosystem productivity to heatwaves in three Mongolian grasslands

Climate change is causing more frequent and intense heatwaves. Therefore, it is important to understand how heatwaves affect the terrestrial carbon cycle, especially in grasslands, which are especially susceptible to climate extremes. This study assessed the impact of naturally occurring, simultaneous short-term heatwaves on CO2 fluxes in three ecosystems on the Mongolia Plateau: meadow steppe (MDW), typical steppe (TPL), and shrub-grassland (SHB). During three heatwaves, net ecosystem productivity (NEP) was reduced by 86 %, 178 %, and 172 % at MDW, TPL, and SHB, respectively. The changes in ecosystem respiration, gross primary production, evapotranspiration, and water use efficiency were divergent, indicating the mechanisms underlying the observed NEP decreases among the sites. The impact of the heatwave in MDW was mitigated by the high soil water content, which enhanced evapotranspiration and subsequent cooling effects. However, at TPL, insufficient soil water led to combined thermal and drought stress and low resilience. At SHB, the ecosystem's low tolerance to an August heatwave was heavily influenced by species phenology, as it coincided with the key phenological growing phase of plants. The potential key mechanism of divergent NEP response to heatwaves lies in the divergent stability and varying importance of environmental factors, combined with the specific sensitivity of NEP to each factor in ecosystems. Furthermore, our findings suggest that anomalies in soil environment, rather than atmospheric anomalies, are the primary determinants of NEP anomalies during heatwaves. This challenges the conventional understanding of heatwaves as a discrete and ephemeral periods of high air temperatures. Instead, heatwaves should be viewed as chronologically variable, compound, and time-sensitive environmental stressors. The ultimate impact of heatwaves on ecosystems is co-determined by a complex interplay of environmental, biological, and heatwave features.

Deciphering the alleviation potential of nitric oxide, for low temperature and chromium stress via maintaining photosynthetic capacity, antioxidant defence, and redox homeostasis in rice (Oryza sativa)

Sodium nitroprusside (SNP) is a potent nitric oxide (NO) donor that enhances plant tolerance to various abiotic stresses. This research aims to assess the effect of SNP application on rice seedlings subjected to individual and combined exposure to two abiotic stresses viz., low-temperature (LT) and chromium (Cr). Exposure to LT, Cr, and LT+Cr caused severe oxidative damage by stimulating greater production and accumulation of reactive oxygen species (ROS) leading to lipid peroxidation and cell membrane instability. The combined LT+CR stress more intensly increased the cellular oxidative stress and excessive Cr uptake that in turn deteriorated the chlorophyll pigments and photosynthesis, as well as effected the level of tetrapyrrole biosynthesis in rice plants. The reduction in rice seedling growth was more obvious under LT+Cr treatment than their individual effects. The exogenous application of SNP diminished the toxic impact of LT and Cr stress. This was attributed to the positive role of SNP in regulating the endogenous NO levels, free amino acids (FAAs) contents, tetrapyrrole biosynthesis and antioxidants. Consequently, SNP-induced NO decreased photorespiration, ROS generation, lipid peroxidation, and electrolyte leakage. Moreover, exogenous SNP diminished the Cr uptake and accumulation by modulating the ionic homeostasis and strengthening the heavy metals detoxification mechanism, thus improving plant height, biomass and photosynthetic indexes. Essentially, SNP boosts plant tolerance to LT and Cr stress by regulating antioxidants, detoxification mechanism, and the plant's physio-biochemical. Hence, applying SNP is an effective method for boosting rice plant resilience and productivity in the face of escalating environmental stresses and pollutants.

The potential of Actinoplanes spp. for alleviating the oxidative stress induced by thallium toxicity in wheat plants

To reduce heavy metal toxicity, like that induced by thallium (TI) in plants, growth-promoting bacteria (GPB) are a widely used to enhance plant tolerance to heavy metals toxicity. In our study, we characterized seven GPB and identified Actinoplanes spp., as the most active strain. This bioactive strain was then applied to alleviate TI phytotoxicity. TI contamination (20 mg/kg soil) induced TI bioaccumulation, reducing wheat growth (biomass accumulation) and photosynthesis rate, by about 55% and 90%, respectively. TI stress also induced oxidative damages as indicated by increased oxidative markers (H2O2 and lipid peroxidation (MDA)). Interestingly, Actinoplanes spp. significantly reduced growth inhibition and oxidative stress by 20% and 70%, respectively. As a defense mechanism to mitigate the TI toxicity, wheat plants showed improved antioxidant and detoxification defense including increased phenolic and tocopherols levels as well as peroxidase (POX), catalase (CAT), superoxide dismutase (SOD), and glutathione reductase (GR) enzymes activities. These defense mechanisms were further induced by Actinoplanes spp. Additionally, Actinoplanes spp. increased the production of heavy metal-binding ligands such as metallothionein, phytochelatins, total glutathione, and glutathione S-transferase activity by 100%, 90%, 120%, and 100%, respectively. This study, therefore, elucidated the physiological and biochemical bases underlying TI-stress mitigation impact of Actinoplanes spp. Overall, Actinoplanes spp. holds promise as a valuable approach for ameliorating TI toxicity in plants. KEYBOARD: Actinobacteria, Bioaccumulation, Detoxification, Membrane damage, Redox regulation.

Drought Has a Greater Negative Effect on the Growth of the C3Chenopodium quinoa Crop Halophyte than Elevated CO2 and/or High Temperature

Plant growth and productivity are predicted to be affected by rising CO2 concentrations, drought and temperature stress. The C3 crop model in a changing climate is Chenopodium quinoa Willd-a protein-rich pseudohalphyte (Amaranthaceae). Morphophysiological, biochemical and molecular genetic studies were performed on quinoa grown at ambient (400 ppm, aCO2) and elevated (800 ppm, eCO2) CO2 concentrations, drought (D) and/or high temperature (eT) treatments. Among the single factors, drought caused the greatest stress response, inducing disturbances in the light and dark photosynthesis reactions (PSII, apparent photosynthesis) and increasing oxidative stress (MDA). Futhermore, compensation mechanisms played an important protective role against eT or eCO2. The disruption of the PSII function was accompanied by the activation of the expression of PGR5, a gene of PSI cyclic electron transport (CET). Wherein under these conditions, the constant Rubisco content was maintained due to an increase in its biosynthesis, which was confirmed by the activation of rbcL gene expression. In addition, the combined stress treatments D+eT and eCO2+D+eT caused the greatest negative effect, as measured by increased oxidative stress, decreased water use efficiency, and the functioning of protective mechanisms, such as photorespiration and the activity of antioxidant enzymes. Furthermore, decreased PSII efficiency and increased non-photochemical quenching (NPQ) were not accompanied by the activation of protective mechanisms involving PSI CET. In summary, results show that the greatest stress experienced by C. quinoa plants was caused by drought and the combined stresses D+eT and eCO2+D+eT. Thus, drought consistently played a decisive role, leading to increased oxidative stress and a decrease in defense mechanism effectiveness.

Interactive Effects of Temperature, Water Regime, and [CO2] on Wheats with Different Heat Susceptibilities

Plants' response to single environmental changes can be highly distinct from the response to multiple changes. The effects of a single environmental factor on wheat growth have been well documented. However, the interactive influences of multiple factors on different wheat genotypes need further investigation. Here, treatments of three important growth factors, namely water regime, temperature, and CO2 concentration ([CO2]), were applied to compare the response of two wheat genotypes with different heat sensitivities. The temperature response curves showed that both genotypes showed more variations at elevated [CO2] (e[CO2]) than ambient [CO2] (a[CO2]) when the plants were treated under different water regimes and temperatures. This corresponded to the results of water use efficiency at the leaf level. At e[CO2], heat-tolerant 'Gladius' showed a higher net photosynthetic rate (Pn), while heat-susceptible 'Paragon' had a lower Pn at reduced water, as compared with full water availability. The temperature optimum for photosynthesis in wheat was increased when the growth temperature was high, while the leaf carbon/nitrogen was increased via a reduced water regime. Generally, water regime, temperature and [CO2] have significant interactive effects on both wheat genotypes. Two wheat genotypes showed different physiological responses to different combinations of environmental factors. Our investigation concerning the interactions of multi-environmental factors on wheat will benefit the future wheat climate-response study.

Appraisal of the Role of Gaseous Signaling Molecules in Thermo-Tolerance Mechanisms in Plants

A significant threat to the ongoing rise in temperature caused by global warming. Plants have many stress-resistance mechanisms, which is responsible for maintaining plant homeostasis. Abiotic stresses largely increase gaseous molecules' synthesis in plants. The study of gaseous signaling molecules has gained attention in recent years. The role of gaseous molecules, such as nitric oxide (NO), hydrogen sulfide (H2S), carbon dioxide (CO2), carbon monoxide (CO), methane (CH4), and ethylene, in plants under temperature high-temperature stress are discussed in the current review. Recent studies revealed the critical function that gaseous molecules play in controlling plant growth and development and their ability to respond to various abiotic stresses. Here, we provide a thorough overview of current advancements that prevent heat stress-related plant damage via gaseous molecules. We also explored and discussed the interaction of gaseous molecules. In addition, we provided an overview of the role played by gaseous molecules in high-temperature stress responses, along with a discussion of the knowledge gaps and how this may affect the development of high-temperature-resistant plant species.

The impact of multifactorial stress combination on plants, crops, and ecosystems: how should we prepare for what comes next?

The complexity of environmental conditions encountered by plants in the field, or in nature, is gradually increasing due to anthropogenic activities that promote global warming, climate change, and increased levels of pollutants. While in the past it seemed sufficient to study how plants acclimate to one or even two different stresses affecting them simultaneously, the complex conditions developing on our planet necessitate a new approach of studying stress in plants: Acclimation to multiple stress conditions occurring concurrently or consecutively (termed, multifactorial stress combination [MFSC]). In an initial study of the plant response to MFSC, conducted with Arabidopsis thaliana seedlings subjected to an MFSC of six different abiotic stresses, it was found that with the increase in the number and complexity of different stresses simultaneously impacting a plant, plant growth and survival declined, even if the effects of each stress involved in such MFSC on the plant was minimal or insignificant. In three recent studies, conducted with different crop plants, MFSC was found to have similar effects on a commercial rice cultivar, a maize hybrid, tomato, and soybean, causing significant reductions in growth, biomass, physiological parameters, and/or yield traits. As the environmental conditions on our planet are gradually worsening, as well as becoming more complex, addressing MFSC and its effects on agriculture and ecosystems worldwide becomes a high priority. In this review, we address the effects of MFSC on plants, crops, agriculture, and different ecosystems worldwide, and highlight potential avenues to enhance the resilience of crops to MFSC.

The complexity of heatwaves impact on terrestrial ecosystem carbon fluxes: Factors, mechanisms and a multi-stage analytical approach

Extreme heatwaves have become more frequent and severe in recent decades, and are expected to significantly influence carbon fluxes at regional scales across global terrestrial ecosystems. Nevertheless, accurate prediction of future heatwave impacts remains challenging due to a lack of a consistent comprehension of intrinsic and extrinsic mechanisms. We approached this knowledge gap by analyzing the complexity factors in heatwave studies, including the methodology for determining heatwave events, divergent responses of individual ecosystem components at multiple ecological and temporal scales, and vegetation status and hydrothermal environment, among other factors. We found that heatwaves essentially are continuously changing compound environmental stress that can unfold into multiple chronological stages, and plant physiology and carbon flux responses differs in each of these stages. This approach offers a holistic perspective, recognizing that the impacts of heatwaves on ecosystems can be better understood when evaluated over time. These stages include instantaneous, post-heatwave, legacy, and cumulative effects, each contributing uniquely to the overall impact on the ecosystem carbon cycle. Next, we investigated the importance of the timing of heatwaves and the possible divergent consequences caused by different annual heatwave patterns. Finally, a conceptual framework is proposed to establish a united foundation for the study and comprehension of the consequences of heatwaves on ecosystem carbon cycle. This instrumental framework will assist in guiding regional assessments of heatwave impacts, shedding light on the underlying mechanisms responsible for the varied responses of terrestrial ecosystems to specific heatwave events, which are imperative for devising efficient adaptation and mitigation approaches.

Suppression of photorespiratory metabolism by low O2 and presence of aminooxyacetic acid induces oxidative stress in Arabidopsis thaliana leaves

Photorespiration, an essential component of plant metabolism, was upregulated under abiotic stress conditions, such as high light or drought. One of the signals for such upregulation was the rise in reactive oxygen species (ROS). Photorespiration was expected to mitigate oxidative stress by reducing ROS levels. However, it was unclear if ROS levels would increase when photorespiration was lowered. Our goal was to examine the redox status in leaves when photorespiratory metabolism was restricted under low O2 (medium flushed with N2 gas) or by adding aminooxyacetic acid (AOA), a photorespiratory inhibitor. We examined the impact of low O2 and AOA in leaves of Arabidopsis thaliana under dark, moderate, or high light. Downregulation of typical photorespiratory enzymes, including catalase (CAT), glycolate oxidase (GO), and phosphoglycolate phosphatase (PGLP) under low O2 or with AOA confirmed the lowering of photorespiratory metabolism. A marked increase in ROS levels (superoxide and H2O2) indicated the induction of oxidative stress. Thus, our results demonstrated for the first time that restricted photorespiratory conditions increased the extent of oxidative stress. We propose that photorespiration is essential to sustain normal ROS levels and optimize metabolism in cellular compartments of Arabidopsis leaves.

Supplementary Information

The online version contains supplementary material available at 10.1007/s12298-023-01388-4.

Soil Contamination with Europium Induces Reduced Oxidative Damage in Hordeum vulgare Grown in a CO2-Enriched Environment

The extensive and uncontrolled utilization of rare earth elements, like europium (Eu), could lead to their accumulation in soils and biota. Herein, we investigated the impact of Eu on the growth, photosynthesis, and redox homeostasis in barley and how that could be affected by the future CO2 climate (eCO2). The plants were exposed to 1.09 mmol Eu3+/kg soil under either ambient CO2 (420 ppm, aCO2) or eCO2 (620 ppm). The soil application of Eu induced its accumulation in the plant shoots and caused significant reductions in biomass- and photosynthesis-related parameters, i.e., chlorophyll content, photochemical efficiency of PSII, Rubisco activity, and photosynthesis rate. Further, Eu induced oxidative stress as indicated by higher levels of H2O2 and lipid peroxidation products, and lower ASC/DHA and GSH/GSSG ratios. Interestingly, the co-application of eCO2 significantly reduced the accumulation of Eu in plant tissues. Elevated CO2 reduced the Eu-induced oxidative damage by supporting the antioxidant defense mechanisms, i.e., ROS-scavenging molecules (carotenoids, flavonoids, and polyphenols), enzymes (CAT and peroxidases), and ASC-GSH recycling enzymes (MDHAR and GR). Further, eCO2 improved the metal detoxification capacity by upregulating GST activity. Overall, these results provide the first comprehensive report for Eu-induced oxidative phytotoxicity and how this could be mitigated by eCO2.

Elevated CO2 differentially attenuates beryllium-induced oxidative stress in oat and alfalfa

Elevated CO2 (eCO2 ) is one of the climate changes that may benefit plant growth under emerging soil contaminants such as heavy metals. In this regard, the morpho-physiological mechanisms underlying the mitigating impact of eCO2 on beryllium (Be) phytotoxicity are poorly known. Hence, we investigated eCO2 and Be interactive effects on the growth and metabolism of two species from different groups: cereal (oat) and legume (alfalfa). Be stress significantly reduced the growth and photosynthetic attributes in both species, but alfalfa was more susceptible to Be toxicity. Be stress induced reactive oxygen species (ROS) accumulation by increasing photorespiration, subsequently resulting in increased lipid and protein oxidation. However, the growth inhibition and oxidative stress induced by Be stress were mitigated by eCO2 . This could be explained, at least partially, by the increase in organic acids (e.g., citric acid) released into the soil, which subsequently reduced Be uptake. Additionally, eCO2 reduced cellular oxidative damage by reducing photorespiration, which was more significant in alfalfa plants. Furthermore, eCO2 improved the redox status and detoxification processes, including phytochelatins, total glutathione and metallothioneins levels, and glutathione-S-transferase activity in both species, but to a greater extend in alfalfa. In this context, eCO2 also stimulated anthocyanin biosynthesis by accumulating its precursors (phenylalanine, coumaric acid, cinnamic acid, and naringenin) and key biosynthetic enzymes (phenylalanine ammonia-lyase, cinnamate hydroxylase, and coumarate:CoA ligase) mainly in alfalfa plants. Overall, this study explored the mechanistic approach by which eCO2 alleviates the harmful effects of Be. Alfalfa was more sensitive to Be stress than oats; however, the alleviating impact of eCO2 on Be stress was more pronounced in alfalfa.

High CO2 facilitates fatty acid biosynthesis and mitigates cellular oxidative stress caused by CAC2 dysfunction in Arabidopsis

Increasing concentration of CO2 has significant impacts on many biological processes in plants, and its impact is closely associated with changes in the ratio of photosynthesis to photorespiration. Studies have reported that high CO2 can promote carbon fixing and alleviate plant oxidative damage in response to environmental stresses. However, the effect of high CO2 on fatty acid (FA) metabolism and cellular redox balance in FA-deficient plants is rarely reported. In this study, we identified a high-CO2 -requiring mutant cac2 through forward genetic screening. CAC2 encodes biotin carboxylase, which is one of the subunits of plastid acetyl-CoA carboxylase and participates in de novo FA biosynthesis. Null mutation of CAC2 is embryonic lethal. A point mutation of CAC2 in cac2 mutants produces severe defects in chloroplast development, plant growth and photosynthetic performance. These morphological and physiological defects were largely absent under high CO2 conditions. Metabolite analyses showed that FA contents in cac2-1 leaves were decreased, while photorespiratory metabolites, such as glycine and glycolate, did not significantly change. Meanwhile, cac2 exhibited higher reactive oxygen species (ROS) levels and mRNA expression of stress-responsive genes than the wild-type, indicating that cac2 plants may suffer oxidative stress under ambient CO2 conditions. Elevated CO2 significantly increased FA contents, especially C18:3-FA, and reduced ROS accumulation in cac2-1 leaves. We propose that stress mitigation by high CO2 in cac2 could be due to increased FA levels by promoting carbon assimilation, and the prevention of over-reduction due to decreased photorespiration.

The Impact of Increased CO2 and Drought Stress on the Secondary Metabolites of Cauliflower (Brassica oleracea var. botrytis) and Cabbage (Brassica oleracea var. capitata)

Elevated carbon dioxide and drought are significant stressors in light of climate change. This study explores the interplay between elevated atmospheric CO2, drought stress, and plant physiological responses. Two Brassica oleracea varieties (cauliflowers and cabbage) were utilized as model plants. Our findings indicate that elevated CO2 accelerates assimilation rate decline during drought. The integrity of photosynthetic components influenced electron transport, potentially due to drought-induced nitrate reductase activation changes. While CO2 positively influenced photosynthesis and water-use efficiency during drought, recovery saw decreased stomatal conductance in high-CO2-grown plants. Drought-induced monoterpene emissions varied, influenced by CO2 concentration and species-specific responses. Drought generally increased polyphenols, with an opposing effect under elevated CO2. Flavonoid concentrations fluctuated with drought and CO2 levels, while chlorophyll responses were complex, with high CO2 amplifying drought's effects on chlorophyll content. These findings contribute to a nuanced understanding of CO2-drought interactions and their intricate effects on plant physiology.

Melatonin Role in Plant Growth and Physiology under Abiotic Stress

Phyto-melatonin improves crop yield by mitigating the negative effects of abiotic stresses on plant growth. Numerous studies are currently being conducted to investigate the significant performance of melatonin in crops in regulating agricultural growth and productivity. However, a comprehensive review of the pivotal performance of phyto-melatonin in regulating plant morpho-physiological and biochemical activities under abiotic stresses needs to be clarified. This review focused on the research on morpho-physiological activities, plant growth regulation, redox status, and signal transduction in plants under abiotic stresses. Furthermore, it also highlighted the role of phyto-melatonin in plant defense systems and as biostimulants under abiotic stress conditions. The study revealed that phyto-melatonin enhances some leaf senescence proteins, and that protein further interacts with the plant's photosynthesis activity, macromolecules, and changes in redox and response to abiotic stress. Our goal is to thoroughly evaluate phyto-melatonin performance under abiotic stress, which will help us better understand the mechanism by which phyto-melatonin regulates crop growth and yield.

Future Climate CO2 Reduces the Tungsten Effect in Rye Plants: A Growth and Biochemical Study

Heavy metal pollution is one of the major agronomic challenges. Tungsten (W) exposure leads to its accumulation in plants, which in turn reduces plant growth, inhibits photosynthesis and induces oxidative damage. In addition, the predicted increase in CO2 could boost plant growth under both optimal and heavy metal stress conditions. The aim of the present study was to investigate the effect of W on growth, photosynthetic parameters, oxidative stress and redox status in rye plants under ambient and elevated (eCO2) levels. To this end, rye plants were grown under the following conditions: ambient CO2 (aCO2, 420 ppm), elevated CO2 (eCO2, 720 ppm), W stress (350 mg kg-1 soil) and W+eCO2. W stress induced significant (p < 0.05) decreases in growth and photosynthesis, increases in oxidative damages (lipid peroxidation) and the antioxidant defense system, i.e., ascorbate (ASC), reduced glutathione (GSH), GSH reductase (GR), peroxidase (POX), catalase (CAT), superoxide dismutase (SOD), ASC peroxide (APX) and dehydroascorbate reductase (DHAR). On the other hand, eCO2 decreased W uptake and improved photosynthesis, which sequentially improved plant growth. The obtained results showed that eCO2 can decrease the phytotoxicity risks of W in rye plants. This positive impact of eCO2 on reducing the negative effects of soil W was related to their ability to enhance plant photosynthesis, which in turn provided energy and a carbon source for scavenging the reactive oxygen species (ROS) accumulation caused by soil W stress.

Elevated CO2 Suppresses the Vanadium Stress in Wheat Plants under the Future Climate CO2

Increases in atmospheric CO₂ is known to promote plant growth under heavy metals stress conditions. However, vanadium (V) stress mitigating the impact of eCO₂ as well as the physiological and biochemical bases of this stress mitigation have not been well studied. To this end, this study investigated the growth, photosynthetic parameters, oxidative damages antioxidants, and antioxidants enzymes in wheat plants grown under ambient (420 PPM) and high eCO₂ (720 ppm) levels. Exposing wheat plants to higher V increased its accumulation in plants which consequentially inhibited plant growth and induced oxidative damage. An increase in antioxidant and detoxification defense systems was observed but it was not enough to reduce V stress toxicity. On the other hand, wheat growth was improved as a result of reduced V uptake and toxicity on photosynthesis under eCO₂. To reduce V uptake, wheat accumulated citric acid, and oxalic acid in soil preferentially under both treatments but to more extend under V and eCO₂. Additionally, improved photosynthesis induced high carbon availability that was directed to produce chelating proteins (metallothioneins, phytochelatin) and antioxidants (phenolics, flavonoids, total antioxidant capacity). This study advances our knowledge of the processes behind the variations in the physiological and biochemical responses of the wheat crop under V and eCO₂ conditions.

Elevated CO2 mitigates the impact of drought stress by upregulating glucosinolate metabolism in Arabidopsis thaliana

Elevated CO₂ (eCO₂ ) reduces the impact of drought, but the mechanisms underlying this effect remain unclear. Therefore, we used a multidisciplinary approach to investigate the interaction of drought and eCO₂ in Arabidopsis thaliana leaves. Transcriptome and subsequent metabolite analyses identified a strong induction of the aliphatic glucosinolate (GL) biosynthesis as a main effect of eCO₂ in drought-stressed leaves. Transcriptome results highlighted the upregulation of ABI5 and downregulation of WRKY63 transcription factors (TF), known to enhance and inhibit the expression of genes regulating aliphatic GL biosynthesis (e.g., MYB28 and 29 TFs), respectively. In addition, eCO₂ positively regulated aliphatic GL biosynthesis by MYB28/29 and increasing the accumulation of GL precursors. To test the role of GLs in the stress-mitigating effect of eCO₂ , we investigated the effect of genetic perturbations of the GL biosynthesis. Overexpression of MYB28, 29 and 76 improved drought tolerance by inducing stomatal closure and maintaining plant turgor, whereas loss of cyp79f genes reduced the stress-mitigating effect of eCO₂ and decreased drought tolerance. Overall, the crucial role of GL metabolism in drought stress mitigation by eCO₂ could be a beneficial trait to overcome future climate challenges.

Carbon nanoparticles improve the effect of compost and arbuscular mycorrhizal fungi in drought-stressed corn cultivation

Drought is an important threat worldwide, therefore, it is vital to create workable solutions to mitigate the negative effects of drought stress. To this end, we investigated the interactive effect of compost (Comp), arbuscular mycorrhizal fungi (AMF) and carbon nanoparticles (CNPs) on maize plant crops under drought stress. The combined treatments were more effective at increasing soil fertility and promoting the growth of maize plants under both control and drought stress conditions by 20.1% and 39.4%, respectively. The interactions between treatments, especially the effects of Comp-AMF-CNPs mixture, reduce the activity of photorespiration induced H₂O₂ production that consequently reduces drought-related oxidative damages (lipid peroxidation and protein oxidation). Plants treated with Comp-AMF or Comp-AMF-CNPs showed an increase in their antioxidant defense system. Comp-AMF-CNPs increased enzyme activities by 50.3%, 30.1%, and 71% for ascorbate peroxidase (APX), dehydro-ASC reductase (DHAR), and monodehydro-ASC reductase (MDHAR), respectively. Comp-AMF-CNPs also induced the highest increase in anthocyanins (69.5%) compared to the control treatment. This increase was explained by increased anthocyanin percussor, by 37% and 13% under control and drought, respectively. While the increases in biosynthetic key enzymes, phenylalanine aminolayse (PAL) and chalcone synthase (CHS) were 77% and 5% under control and 69% and 89% under drought, respectively. This work advanced our understanding on how Comp-AMF-CNPs improve growth, physiology, and biochemistry of maize plants under drought stress conditions. Overall, this study suggests the effectiveness of Comp-AMF-CNPs as a promising approach to enhance the growth of maize plants in dry areas.

Effects of elevated CO2 concentration and temperature on the mixed-culture grown wild mustard (Sinapis arvensis L.) response to auxin herbicide

Recently, there has been growing concern over the potential impact of CO₂ concentration and temperature on herbicide efficacy. The aim of the study was to examine the influence of single elevated CO₂ (400 vs. 800 ppm) and elevated CO₂ in combination with temperature (21 °C vs. 25 °C) on the effects of auxin herbicide 4-chloro-2-methylphenoxyacetic acid (MCPA) (0.5-2 × field recommended rate) to wild mustard (Sinapis arvensis L.) grown in mixed-culture with spring barley (Hordeum vulgare L.). MCPA had a detrimental effect on aboveground and belowground biomass, content of chlorophylls, enzymatic and non-enzymatic antioxidants and induced oxidative stress. The significant decline in photosynthetic rate, stomatal conductance and transpiration with MCPA dose was detected. Elevated CO₂ reinforced MCPA efficacy on S. arvensis: sharper decline in biomass, photosynthetic rate and antioxidant enzymes and more pronounced lipid peroxidation were detected. Under elevated CO₂ and temperature, MCPA efficacy to control S. arvensis dropped due to herbicide dilution because of increased root:shoot ratio, higher activity of antioxidants and less pronounced oxidative damage. Reinforced MCPA impact on weeds under elevated CO₂ resulted in higher H. vulgare biomass, while decreased MCPA efficacy under elevated CO₂ and temperature reduced H. vulgare biomass.

Perspectives in Plant Abiotic Stress Signaling

State-of-the-art collections of strategies, approaches, and methods are immediately useful for ongoing characterizations or for novel discoveries in the scientific field of plant abiotic stress signaling. It must however be kept in mind that, in the future, these strategies, approaches, and methods will be facing a number of increasingly complex issues. The development of the necessary confrontation of laboratory-based knowledge on abiotic stress signaling mechanisms with real-life in natura situations of plant-stress interactions involves at least five levels of complexity: (i) plant biodiversity, (ii) the spatio-temporal heterogeneity of stress-related parameters, (iii) the unknowns of future stress-related constraints, (iv) the influence of biotic interactions, (v) the crosstalk between various signaling pathways and their final integration into physiological responses. These complexities are major bottlenecks for assessing the evolutionary, ecological, and agronomical relevance of abiotic stress signaling studies. All of the presently-described strategies, approaches, and methods will have to be gradually complemented with the development of real-time and in natura tools, with systematic application of mathematical modeling to complex interactions and with further research on the impact of stress memory mechanisms on long-term responses.

Rhodospirillum sp. JY3: An innovative tool to mitigate the phytotoxic impact of galaxolide on wheat (Triticum aestivum) and faba bean (Vicia faba) plants

To date, several studies have considered the phytotoxic impact of cosmetics and personal care products on crop plants. Nonetheless, data are scarce about the toxic impact of galaxolide [hexahydro-hexamethyl cyclopentabenzopyran (HHCB)] on the growth, physiology, and biochemistry of plants from different functional groups. To this end, the impact of HHCB on biomass, photosynthetic efficiency, antioxidant production, and detoxification metabolism of grass (wheat) and legume (faba bean) plants has been investigated. On the other hand, plant growth-promoting bacteria (PGPB) can be effectively applied to reduce HHCB phytotoxicity. HHCB significantly reduced the biomass accumulation and the photosynthetic machinery of both crops, but to more extent for wheat. This growth reduction was concomitant with induced oxidative damage and decreased antioxidant defense system. To mitigate HHCB toxicity, a bioactive strain of diazotrophic plant growth-promoting Rhodospirillum sp. JY3 was isolated from heavy metal-contaminated soil in Jazan, Kingdom of Saudi Arabia, and applied to both crops. Overall, Rhodospirillum mitigated HHCB-induced stress by differently modulating the oxidative burst [malondialdehyde (MDA), hydrogen peroxide (H₂O₂), and protein oxidation] in both wheat and faba beans. This alleviation was coincident with improvement in plant biomass and photosynthetic efficiency, particularly in wheat crops. Considering the antioxidant defense system, JY3 augmented the antioxidants in both wheat and faba beans and the detoxification metabolism under HHCB stress conditions. More interestingly, inoculation with JY3 further enhanced the tolerance level of both wheat and faba beans against contamination with HHCB via quenching the lignin metabolism. Overall, this study advanced our understanding of the physiological and biochemical mechanisms underlying HHCB stress and mitigating its impact using Rhodospirillum sp. JY3, which may strikingly reduce the environmental risks on agriculture sustainability.

Elevated CO2 differentially mitigates chromium (VI) toxicity in two rice cultivars by modulating mineral homeostasis and improving redox status

Chromium (Cr) contamination reduces crop productivity worldwide. On the other hand, the expected increase in the future CO₂ levels (eCO₂) would improve plant growth under diverse growth conditions. However, the synergetic effect of eCO₂ has not been investigated at both physiological and biochemical levels in Cr-contaminated soil. This study aims to analyze the mitigating effect of eCO₂ on Cr VI phytotoxicity in two rice cultivars (Giza 181 and Sakha 106). Plants are exposed to different Cr concentrations (0, 200 and 400 mg Cr/kg Soil) at ambient (aCO₂) and eCO₂ (410 and 620 ppm, respectively). Unlike the stress parameters (MDA, H2O2 and protein oxidation), growth and photosynthetic reactions significantly dropped with increasing Cr concentration. However, in eCO₂ conditions, plants were able to mitigate the Cr stress by inducing antioxidants as well as higher concentrations of phytochelatins to detoxify Cr. Notably, the expression levels of the genes involved in mineral nutrition i.e., OsNRAMP1, OsRT1, OsHMA3, OsLCT1 and iron chelate reductase were upregulated in Cr-stressed Giza 181 plants grown under eCO₂. Mainly in Sakha 106, eCO₂ induced ascorbate-glutathione (ASC/GSH)-mediated antioxidative defense system. The present study brings the first ever comprehensive assessment of how future eCO₂ differentially mitigated Cr toxicity in rice.

Protective Responses at the Biochemical and Molecular Level Differ between a Coffea arabica L. Hybrid and Its Parental Genotypes to Supra-Optimal Temperatures and Elevated Air [CO2]

Climate changes with global warming associated with rising atmospheric [CO₂] can strongly impact crop performance, including coffee, which is one of the most world's traded agricultural commodities. Therefore, it is of utmost importance to understand the mechanisms of heat tolerance and the potential role of elevated air CO₂ (eCO₂) in the coffee plant response, particularly regarding the antioxidant and other protective mechanisms, which are crucial for coffee plant acclimation. For that, plants of Coffea arabica cv. Geisha 3, cv. Marsellesa and their hybrid (Geisha 3 × Marsellesa) were grown for 2 years at 25/20 °C (day/night), under 400 (ambient CO₂, aCO₂) or 700 µL (elevated CO₂, eCO₂) CO₂ L^-1, and then gradually submitted to a temperature increase up to 42/30 °C, followed by recovery periods of 4 (Rec4) and 14 days (Rec14). Heat (37/28 °C and/or 42/30 °C) was the major driver of the response of the studied protective molecules and associated genes in all genotypes. That was the case for carotenoids (mostly neoxanthin and lutein), but the maximal (α + β) carotenes pool was found at 37/28 °C only in Marsellesa. All genes (except VDE) encoding for antioxidative enzymes (catalase, CAT; superoxide dismutases, CuSODs; ascorbate peroxidases, APX) or other protective proteins (HSP70, ELIP, Chape20, Chape60) were strongly up-regulated at 37/28 °C, and, especially, at 42/30 °C, in all genotypes, but with maximal transcription in Hybrid plants. Accordingly, heat greatly stimulated the activity of APX and CAT (all genotypes) and glutathione reductase (Geisha3, Hybrid) but not of SOD. Notably, CAT activity increased even at 42/30 °C, concomitantly with a strongly declined APX activity. Therefore, increased thermotolerance might arise through the reinforcement of some ROS-scavenging enzymes and other protective molecules (HSP70, ELIP, Chape20, Chape60). Plants showed low responsiveness to single eCO₂ under unstressed conditions, while heat promoted changes in aCO₂ plants. Only eCO₂ Marsellesa plants showed greater contents of lutein, the pool of the xanthophyll cycle components (V + A + Z), and β-carotene, compared to aCO₂ plants at 42/30 °C. This, together with a lower CAT activity, suggests a lower presence of H₂O₂, likely also associated with the higher photochemical use of energy under eCO₂. An incomplete heat stress recovery seemed evident, especially in aCO₂ plants, as judged by the maintenance of the greater expression of all genes in all genotypes and increased levels of zeaxanthin (Marsellesa and Hybrid) relative to their initial controls. Altogether, heat was the main response driver of the addressed protective molecules and genes, whereas eCO₂ usually attenuated the heat response and promoted a better recovery. Hybrid plants showed stronger gene expression responses, especially at the highest temperature, when compared to their parental genotypes, but altogether, Marsellesa showed a greater acclimation potential. The reinforcement of antioxidative and other protective molecules are, therefore, useful biomarkers to be included in breeding and selection programs to obtain coffee genotypes to thrive under global warming conditions, thus contributing to improved crop sustainability.

Physiological and Antioxidant Response to Different Water Deficit Regimes of Flag Leaves and Ears of Wheat Grown under Combined Elevated CO2 and High Temperature

Triticum aestivum L. cv. Gazul is a spring wheat widely cultivated in Castilla y León (Spain). Potted plants were grown in a scenario emulating the climate change environmental conditions expected by the end of this century, i.e., with elevated CO₂ and high temperature under two water deficit regimes: long (LWD) and terminal (TWD). Changes in biomass and morphology, the content of proline (Pro), ascorbate (AsA) and glutathione (GSH), and enzymatic antioxidant activities were analyzed in flag leaves and ears. Additionally, leaf gas exchange was measured. LWD caused a decrease in biomass and AsA content but an increase in Pro content and catalase and GSH reductase activities in flag leaves, whereas TWD produced no significant changes. Photosynthesis was enhanced under both water deficit regimes. Increase in superoxide dismutase activity and Pro content was only observed in ears under TWD. The lack of a more acute effect of LWD and TWD on both organs was attributed to the ROS relieving effect of elevated CO₂. Gazul acted as a drought tolerant variety with anisohydric behavior. A multifactorial analysis showed better adaptation of ears to water deficit than flag leaves, underlining the importance of this finding for breeding programs to improve grain yield under future climate change.

Salinity, waterlogging, and elevated [CO2] interact to induce complex responses in cultivated and wild tomato

The effects of individual climatic factors on crops are well documented, whereas the interaction of such factors in combination has received less attention. The frequency of salinity and waterlogging stress is increasing with climate change, accompanied by elevated CO2 concentration (e[CO2]). This study explored how these three variables interacted and affected two tomato genotypes. Cultivated and wild tomato (Solanum lycopersicum and Solanum pimpinellifolium) were grown at ambient [CO2] and e[CO2], and subjected to salinity, waterlogging, and combined stress. Leaf photosynthesis, chlorophyll fluorescence, quenching analysis, pigment, and plant growth were analyzed. The response of tomatoes depended on both genotype and stress type. In cultivated tomato, photosynthesis was inhibited by salinity and combined stress, whereas in wild tomato, both salinity and waterlogging stress, alone and in combination, decreased photosynthesis. e[CO2] increased photosynthesis and biomass of cultivated tomato under salinity and combined stress compared with ambient [CO2]. Differences between tomato genotypes in response to individual and combined stress were observed in key photosynthetic and growth parameters. Hierarchical clustering and principal component analysis revealed genetic variations of tomatoes responding to the three climatic factors. Understanding the interacting effects of salinity and waterlogging with e[CO2] in tomato will facilitate improvement of crop resilience to climate change.

Increasing atmospheric CO2 differentially supports arsenite stress mitigating impact of arbuscular mycorrhizal fungi in wheat and soybean plants

Arbuscular mycorrhizal fungi (AMF) are beneficial for the plant growth under heavy metal stress. Such beneficial effect is improved by elevated CO2 (eCO2). However, the mechanisms by which eCO2 improves AMF symbiotic associations under arsenite (AsIII) toxicity are hardly studied. Herein, we compared these regulatory mechanisms in species from two agronomical important plant families - grasses (wheat) and legumes (soybean). AsIII decreased plant growth (i.e., 53.75 and 60.29% of wheat and soybean, respectively) and photosynthesis. It also increased photorespiration and oxidative injury in both species, but soybean was more sensitive to oxidative stress as indicated by higher H2O2 accumulation and oxidation of protein and lipid. eCO2 significantly improved AMF colonization by increasing auxin levels, which induced high carotenoid cleavage dioxygenase (CCDs) activity, particularly in soybean roots. The improved sugar metabolism in plant shoots by co-application of eCO2 and AsIII allocated more sugars to roots sequentially. Sugar accumulation in plant roots is further induced by AMF, resulting in more C skeletons to produce organic acids, which are effectively exudated into the soil to reduce AsIII uptake. Exposure to eCO2 reduced oxidative damage and this mitigation was stronger in soybean. This could be attributed to a greater reduction in photorespiration as well as a stronger antioxidant and detoxification defence systems. The grass/legume-specificity was supported by principal component analysis, which revealed that soybean was more affected by AsIII stress and more responsive to AMF and eCO2. This study provided a mechanistic understanding of the impact of AMF, eCO2 and their interaction on As-stressed grass and legume plants, allowing better practical strategies to mitigate AsIII phytotoxicity.

Can biochemical traits bridge the gap between genomics and plant performance? A study in rice under drought

The possibility of introducing metabolic/biochemical phenotyping to complement genomics-based predictions in breeding pipelines has been considered for years. Here we examine to what extent and under what environmental conditions metabolic/biochemical traits can effectively contribute to understanding and predicting plant performance. In this study, multivariable statistical models based on flag leaf central metabolism and oxidative stress status were used to predict grain yield (GY) performance for 271 indica rice (Oryza sativa) accessions grown in the field under well-watered and reproductive stage drought conditions. The resulting models displayed significantly higher predictability than multivariable models based on genomic data for the prediction of GY under drought (Q2 = 0.54-0.56 versus 0.35) and for stress-induced GY loss (Q2 = 0.59-0.64 versus 0.03-0.06). Models based on the combined datasets showed predictabilities similar to metabolic/biochemical-based models alone. In contrast to genetic markers, models with enzyme activities and metabolite values also quantitatively integrated the effect of physiological differences such as plant height on GY. The models highlighted antioxidant enzymes of the ascorbate-glutathione cycle and a lipid oxidation stress marker as important predictors of rice GY stability under drought at the reproductive stage, and these stress-related variables were more predictive than leaf central metabolites. These findings provide evidence that metabolic/biochemical traits can integrate dynamic cellular and physiological responses to the environment and can help bridge the gap between the genome and the phenome of crops as predictors of GY performance under drought.

Selection of Newly Identified Growth-Promoting Archaea Haloferax Species With a Potential Action on Cobalt Resistance in Maize Plants

Soil contamination with cobalt (Co) negatively impacts plant growth and production. To combat Co toxicity, plant growth-promoting microorganisms for improving plant growth are effectively applied. To this end, unclassified haloarchaeal species strain NRS_31 (OL912833), belonging to Haloferax genus, was isolated, identified for the first time, and applied to mitigate the Co phytotoxic effects on maize plants. This study found that high Co levels in soil lead to Co accumulation in maize leaves. Co accumulation in the leaves inhibited maize growth and photosynthetic efficiency, inducing oxidative damage in the tissue. Interestingly, pre-inoculation with haloarchaeal species significantly reduced Co uptake and mitigated the Co toxicity. Induced photosynthesis improved sugar metabolism, allocating more carbon to defend against Co stress. Concomitantly, the biosynthetic key enzymes involved in sucrose (sucrose-P-synthase and invertases) and proline (pyrroline-5- carboxylate synthetase (P5CS), pyrroline-5-carboxylate reductase (P5CR)) biosynthesis significantly increased to maintain plant osmotic potential. In addition to their osmoregulation potential, soluble sugars and proline can contribute to maintaining ROS hemostasis. Maize leaves managed their oxidative homeostasis by increasing the production of antioxidant metabolites (such as phenolics and tocopherols) and increasing the activity of ROS-scavenging enzymes (such as POX, CAT, SOD, and enzymes involved in the AsA/GSH cycle). Inside the plant tissue, to overcome heavy Co toxicity, maize plants increased the synthesis of heavy metal-binding ligands (metallothionein, phytochelatins) and the metal detoxifying enzymes (glutathione S transferase). Overall, the improved ROS homeostasis, osmoregulation, and Co detoxification systems were the basis underlying Co oxidative stress, mitigating haloarchaeal treatment's impact.

Enhancement of Bioactive Constituents in Fresh Cauliflower By-Products in Challenging Climate Conditions

In order to mitigate the detrimental impact that climate change is having on plants, the study of new practices that allow for the reduction of such effects has become imperative. In addition, the revaluation of the promotion of healthy plant by-products has also markedly increased in importance in recent years. In this work, the modifications in biomass and some antioxidant compounds of cauliflower by-products treated with putrescine under extreme temperatures in two different CO₂ scenarios (the control (400 ppm) and a high concentration of CO₂ (1000 ppm)) were studied. Additionally, the compositions of inner and outer leaves were also compared. According to results found in this work, cauliflower grown under elevated CO₂ and treated with putrescine (2.5 mM) prior to heat stress showed the highest biomass accumulation (20%) compared to the control. Moreover, in the outer leaves from cauliflower grown under elevated CO₂ and treated with putrescine prior to high temperature exposure, the highest biosynthesis of sugars (20%) was recorded. Although cauliflower by-products turned out to be rich in polyamines (208.6 nmoles g⁻¹ fresh weight (FW) and 124.3 nmoles g⁻¹ FW for outer and inner leaves, respectively) and phenolic compounds (1070.2 mg gallic acid equivalents ( (GAE) 100 g⁻¹ FW in outer leaves and 772.0 mg GAE 100 g⁻¹ FW in inner leaves), it was the outer leaves that after applying the new strategy showed the greatest increase in polyamines (68%) and phenolic compounds (39%), obtaining here the highest increase in antioxidant activity (3%). Thus, they should no longer be regarded as mere by-products and should be used for pharmaceutical or nutraceutical purposes. The novel strategy presented in this work may allow us to take advantage of both the continued increase in CO₂ and heat waves that are becoming more frequent.

Mechanistic Insights of Plant Growth Promoting Bacteria Mediated Drought and Salt Stress Tolerance in Plants for Sustainable Agriculture

Climate change has devastating effects on plant growth and yield. During ontogenesis, plants are subjected to a variety of abiotic stresses, including drought and salinity, affecting the crop loss (20-50%) and making them vulnerable in terms of survival. These stresses lead to the excessive production of reactive oxygen species (ROS) that damage nucleic acid, proteins, and lipids. Plant growth-promoting bacteria (PGPB) have remarkable capabilities in combating drought and salinity stress and improving plant growth, which enhances the crop productivity and contributes to food security. PGPB inoculation under abiotic stresses promotes plant growth through several modes of actions, such as the production of phytohormones, 1-aminocyclopropane-1-carboxylic acid deaminase, exopolysaccharide, siderophore, hydrogen cyanide, extracellular polymeric substances, volatile organic compounds, modulate antioxidants defense machinery, and abscisic acid, thereby preventing oxidative stress. These bacteria also provide osmotic balance; maintain ion homeostasis; and induce drought and salt-responsive genes, metabolic reprogramming, provide transcriptional changes in ion transporter genes, etc. Therefore, in this review, we summarize the effects of PGPB on drought and salinity stress to mitigate its detrimental effects. Furthermore, we also discuss the mechanistic insights of PGPB towards drought and salinity stress tolerance for sustainable agriculture.

'Omics' approaches in developing combined drought and heat tolerance in food crops

Global climate change will significantly increase the intensity and frequency of hot, dry days. The simultaneous occurrence of drought and heat stress is also likely to increase, influencing various agronomic characteristics, such as biomass and other growth traits, phenology, and yield-contributing traits, of various crops. At the same time, vital physiological traits will be seriously disrupted, including leaf water content, canopy temperature depression, membrane stability, photosynthesis, and related attributes such as chlorophyll content, stomatal conductance, and chlorophyll fluorescence. Several metabolic processes contributing to general growth and development will be restricted, along with the production of reactive oxygen species (ROS) that negatively affect cellular homeostasis. Plants have adaptive defense strategies, such as ROS-scavenging mechanisms, osmolyte production, secondary metabolite modulation, and different phytohormones, which can help distinguish tolerant crop genotypes. Understanding plant responses to combined drought/heat stress at various organizational levels is vital for developing stress-resilient crops. Elucidating the genomic, proteomic, and metabolic responses of various crops, particularly tolerant genotypes, to identify tolerance mechanisms will markedly enhance the continuing efforts to introduce combined drought/heat stress tolerance. Besides agronomic management, genetic engineering and molecular breeding approaches have great potential in this direction.

Influence of Drought Stress and Post-Drought Rewatering on Phytoremediation Effect of Arabidopsis thaliana

Globally, plants face large amounts of environmental stresses, which can inhibit their growth rate and element uptake capacity. Droughts are a critical limitation to plant growth in arid and semi-arid areas. Effects of drought stress and post-drought rewatering on the compensatory growth and Cd phytoremediation efficiency of Arabidopsis thaliana were estimated using slight and moderate drought conditions. Results showed compensatory growth can be induced by post-drought rewatering, as manifested by the increased dry weight and photosynthetic efficiency of the species under drought stress (particularly slight stress) as compared to those of the control. Slight stress increased concentrations of Cd in roots and leaves of A. thaliana by elevating its transpiration rate, whereas moderate stress induced the opposite effect. When the species was subjected to slight stress, Cd concentrations in plant tissues surpassed those in the control after rewatering, indicating that post-drought rewatering can compensate for the detrimental impacts caused by slight drought in A. thaliana. At the end of the experiment, slight and moderate drought stresses increased the Cd extraction ability of the species by 48.9% and 12.7%, respectively, compared to the control. This study demonstrates compensatory effects of post-drought rewatering on the Cd phytoextraction capacity of A. thaliana and suggests that suitable water deficit irrigation practices can enhance soil remediation efficiency and simultaneously save water in the field.

Elevated CO2 Differentially Mitigated Oxidative Stress Induced by Indium Oxide Nanoparticles in Young and Old Leaves of C3 and C4 Crops

Soil contamination with indium (In) oxide nanoparticles (In2O3-NPs) threatens plant growth and development. However, their toxicity in plants under ambient (aCO2) and elevated (eCO2) conditions is scarcely studied. To this end, this study was conducted to investigate In2O3-NPs toxicity in the young and old leaves of C3 (barley) and C4 (maize) plants and to understand the mechanisms underlying the stress mitigating impact of eCO2. Treatment of C3 and C4 plants with In2O3-NPs significantly reduced growth and photosynthesis, induced oxidative damage (H2O2, lipid peroxidation), and impaired P and Fe homeostasis, particularly in the young leaves of C4 plants. On the other hand, this phytotoxic hazard was mitigated by eCO2 which improved both C3 and C4 growth, decreased In accumulation and increased phosphorus (P) and iron (Fe) uptake, particularly in the young leaves of C4 plants. Moreover, the improved photosynthesis by eCO2 accordingly enhanced carbon availability under the challenge of In2O3-NPs that were directed to the elevated production of metabolites involved in antioxidant and detoxification systems. Our physiological and biochemical analyses implicated the role of the antioxidant defenses, including superoxide dismutase (SOD) in stress mitigation under eCO2. This was validated by studying the effect of In2O3-stress on a transgenic maize line (TG) constitutively overexpressing the AtFeSOD gene and its wild type (WT). Although it did not alter In accumulation, the TG plants showed improved growth and photosynthesis and reduced oxidative damage. Overall, this work demonstrated that C3 was more sensitive to In2O3-NPs stress; however, C4 plants were more responsive to eCO2. Moreover, it demonstrated the role of SOD in determining the hazardous effect of In2O3-NPs.

Effect of light combination on the characteristics of dissolved organic matter and chemical forms of Cd in the rhizosphere of Arabidopsis thaliana involved in phytoremediation

Light, one of the most important natural resources for plant species, significantly influences the biomass yield and nutrient uptake capacity in plants. Light sources with different spectra combinations can impact the bioavailability, toxicity, and solubility of heavy metals in soils by altering the concentrations and fractionations of soil dissolved organic matter (DOM). A series of light irradiation treatments were performed to evaluate the influence of red, yellow, and blue lights on the characteristics of DOM in the rhizosphere soils of Arabidopsis thaliana. The results showed that monochromatic red light significantly raised the levels of DOM and proportions of hydrophilic fractionations in the rhizosphere of A. thaliana relative to the control, while monochromatic blue light had the opposite effect. Moreover, the proportions of hydrophobic acid, which can mobilize Cd effectively, also raised with increasing doses of red light, which stimulated Cd mobilization. The application of yellow light not only increased the levels of hydrophobic acid in monochromatic red light treatment but also decreased the proportion of hydrophobic fractions in monochromatic blue light treatment, partially weakening the negative impacts of pure blue light on soil Cd activation. Moreover, DOM from the combined red, yellow, and blue lights resulted in a significantly stronger Cd extraction efficiency than the other light irradiation treatments, consequently enhancing the Cd phytoextraction efficiency of A. thaliana. The findings of this study demonstrated that a suitable light combination could enhance the phytoremediation effect of A. thaliana by activating soil Cd, and this method can be extrapolated to the real field, where light irradiation can be easily applied and modulated.

Potential use of a novel actinobacterial species to ameliorate tungsten nanoparticles induced oxidative damage in cereal crops

Tungsten nanoparticles (WNPs) could induce hazard impact on plant growth and development; however, no study investigated their phytotoxicity. On the other hand, plant growth-promoting bacteria (PGPB) can effectively reduce WNPs toxicity. To this end, Nocardiopsis sp. was isolated and employed to mitigate the phytotoxic effect of WNPs on three crops (wheat, barley, and oat). Soil contamination with WPNs induced the W accumulation in all tested crops, inhibited both growth and photosynthesis and induced oxidative damage. On the other hand, pre-inoculation with Nocardiopsis sp. significantly reduced W level in treated plants. Concomitantly, Nocardiopsis sp. strikingly mitigated the inhibitory effect of WNPs by augmenting both growth and reactive oxygen species (ROS) homeostasis. To cope with heavy metal stress, all the tested species orchestrated their antioxidant homeostasis through enhancing the production of antioxidant metabolites (e.g., phenolics, flavonoids and tocopherols) and elevated the activities of ROS-scavenging enzymes (e.g., APX, POX, CAT, as well as the enzymes involved in AsA/GSH cycle). Moreover, pre-inoculation with Nocardiopsis sp. improved the detoxification metabolism by enhancing the accumulation of phytochelatins (PCs), metallothionein (MTC) and glutathione-S-transferase (GST) in grasses grown in WNPs-contaminated soils. Overall, restrained ROS homeostasis and improved WNPs detoxification systems were the bases underlie the WNPs stress mitigating impact of Nocardiopsis sp treatment.

Developing climate-resilient crops: improving plant tolerance to stress combination

Global warming and climate change are driving an alarming increase in the frequency and intensity of different abiotic stresses, such as droughts, heat waves, cold snaps, and flooding, negatively affecting crop yields and causing food shortages. Climate change is also altering the composition and behavior of different insect and pathogen populations adding to yield losses worldwide. Additional constraints to agriculture are caused by the increasing amounts of human-generated pollutants, as well as the negative impact of climate change on soil microbiomes. Although in the laboratory, we are trained to study the impact of individual stress conditions on plants, in the field many stresses, pollutants, and pests could simultaneously or sequentially affect plants, causing conditions of stress combination. Because climate change is expected to increase the frequency and intensity of such stress combination events (e.g., heat waves combined with drought, flooding, or other abiotic stresses, pollutants, and/or pathogens), a concentrated effort is needed to study how stress combination is affecting crops. This need is particularly critical, as many studies have shown that the response of plants to stress combination is unique and cannot be predicted from simply studying each of the different stresses that are part of the stress combination. Strategies to enhance crop tolerance to a particular stress may therefore fail to enhance tolerance to this specific stress, when combined with other factors. Here we review recent studies of stress combinations in different plants and propose new approaches and avenues for the development of stress combination- and climate change-resilient crops.

Harnessing Endophytic Fungi for Enhancing Growth, Tolerance and Quality of Rose-Scented Geranium (Pelargonium graveolens (L'Hér) Thunb.) Plants under Cadmium Stress: A Biochemical Study

Heavy metal contamination in soil is increasing rapidly due to increasing anthropogenic activities. Despite the importance of rose-scented geranium as a medicinal plant, little attention was paid to enhancing its productivity in heavy metal-polluted soil. In this regard, endophytes improve plant resistance to heavy metal toxicity and enhance its tissue quality. Here, the impact of the three endophytic fungi Talaromyces versatilis (E6651), Emericella nidulans (E6658), and Aspergillus niger (E6657) on geranium growth, tolerance, and tissue quality under cadmium (Cd) stress was investigated. In contrast to E. nidulans, T. versatilis and A. niger enhanced geranium growth and the stimulatory effect was more pronounced under Cd-stress. The three endophytes significantly alleviated Cd accumulation and increased mineral content in geranium leaves. In addition, endophytic fungi successfully alleviated Cd-induced membrane damage and reinforced the antioxidant defenses in geranium leaves. Inoculation with endophytes stimulated all the antioxidant enzymes under Cd-stress, and the response was more obvious in the case of T. versatilis and A. niger. To reduce the toxicity of tissue-Cd levels, T. versatilis and A. niger upregulated the detoxification mechanisms; glutathione-S-transferase, phytochelatin, and metallothionein levels. Moreover, endophytic fungi improved the medicinal value and quality of geranium by increasing total antioxidant capacity (TAC), phenolic compound biosynthesis (phenylalanine ammonia-lyase), and vitamin content as well as the quantity and quality of essential oil, particularly under Cd-stress conditions. The variation in the mechanisms modulated by the different endophytic fungi was supported by Principal Component Analysis (PCA). Overall, this study provided fundamental insights into endophytes' impact as a feasible strategy to mitigate the phytotoxicity hazards of Cd-stress in geranium and enhance its quality, based on the growth and biochemical investigations.

The differential tolerance of C3 and C4 cereals to aluminum toxicity is faded under future CO2 climate

Industrial activities have led to a gradual and global increase in soil aluminum (Al) and atmospheric CO₂ concentrations. Al bioavailability strongly depends on the soil pH, which in turn is affected by atmospheric CO₂ levels. In spite of the concurrent impact which Al and elevated CO₂ (eCO₂) could have on plants, their interaction and how it might affect the growth of economically important crop species has not been investigated. Here, we have investigated the combined impact of soil Al and eCO₂ exposure on key C3 (wheat, oat) and C4 (maize, sorghum) crops, at the physiological and biochemical level. Compared to C3 plants, C4 plants accumulated less Al by stimulating soil Al retention through exudation of root organic acids. Consequently, Al-exposed C4 plants maintained photosynthetic performance and anti-oxidative capacity. Exposure to eCO₂ reduced the stress responses of C3 and C4 crops to Al exposure. Elevated CO₂ decreased Al accumulation and oxidative damage in all cereals, and ameliorated C3 plant growth. This was reflected on the biochemical level, where eCO₂ inhibited ROS production and restored RuBisCo activity in C3 crops only. Overall, our data suggest that, compared to C3 crops, C4 cereals are more tolerant to soil Al exposure under current ambient CO₂ (aCO₂) levels whereas future eCO₂ levels might stimulate Al tolerance in C3 crops.

Mechanisms of elevated CO2-induced thermotolerance in plants: the role of phytohormones

Rising atmospheric CO₂ is a key driver of climate change, intensifying drastic changes in meteorological parameters. Plants can sense and respond to changes in environmental parameters including atmospheric CO₂ and temperatures. High temperatures beyond the physiological threshold can significantly affect plant growth and development and thus attenuate crop productivity. However, elevated atmospheric CO₂ can mitigate the deleterious effects of heat stress on plants. Despite a large body of literature supporting the positive impact of elevated CO₂ on thermotolerance, the underlying biological mechanisms and precise molecular pathways that lead to enhanced tolerance to heat stress remain largely unclear. Under heat stress, elevated CO₂-induced expression of respiratory burst oxidase homologs (RBOHs) and reactive oxygen species (ROS) signaling play a critical role in stomatal movement, which optimizes gas exchange to enhance photosynthesis and water use efficiency. Notably, elevated CO₂ also fortifies antioxidant defense and redox homeostasis to alleviate heat-induced oxidative damage. Both hormone-dependent and independent pathways have been shown to mediate high CO₂-induced thermotolerance. The activation of heat-shock factors and subsequent expression of heat-shock proteins are thought to be the essential mechanism downstream of hormone and ROS signaling. Here we review the role of phytohormones in plant response to high atmospheric CO₂ and temperatures. We also discuss the potential mechanisms of elevated CO₂-induced thermotolerance by focusing on several key phytohormones such as ethylene. Finally, we address some limitations of our current understanding and the need for further research to unveil the yet-unknown crosstalk between plant hormones in mediating high CO₂-induced thermotolerance in plants.

Amelioration of plant responses to drought under elevated CO2 by rejuvenating photosynthesis and nitrogen use efficiency: implications for future climate-resilient crops

The contemporary global agriculture is beset with serious threats from diverse eco-environmental conditions causing decreases in crop yields by ~ 15%. These yield losses might increase further due to climate change scenarios leading to increased food prices triggering social unrest and famines. Urbanization and industrialization are often associated with rapid increases in greenhouse gases (GHGs) especially atmospheric CO₂ concentration [(CO₂)]. Increase in atmospheric [CO₂] significantly improved crop photosynthesis and productivity initially which vary with plant species, genotype, [CO₂] exposure time and biotic as well as abiotic stress factors. Numerous attempts have been made using different plant species to unravel the physiological, cellular and molecular effects of elevated [CO₂] as well as drought. This review focuses on plant responses to elevated [CO₂] and drought individually as well as in combination with special reference to physiology of photosynthesis including its acclimation. Furthermore, the functional role of nitrogen use efficiency (NUE) and its relation to photosynthetic acclimation and crop productivity under elevated [CO₂] and drought are reviewed. In addition, we also discussed different strategies to ameliorate the limitations of ribulose-1,5-bisphosphate (RuBP) carboxylation and RuBP regeneration. Further, improved stomatal and mesophyll conductance and NUE for enhanced crop productivity under fast changing global climate conditions through biotechnological approaches are also discussed here. We conclude that multiple gene editing approaches for key events in photosynthetic processes would serve as the best strategy to generate resilient crop plants with improved productivity under fast changing climate.

Water Deficit Modulates the CO2 Fertilization Effect on Plant Gas Exchange and Leaf-Level Water Use Efficiency: A Meta-Analysis

Elevated atmospheric CO2 concentrations ([eCO2]) and soil water deficits significantly influence gas exchange in plant leaves, affecting the carbon-water cycle in terrestrial ecosystems. However, it remains unclear how the soil water deficit modulates the plant CO2 fertilization effect, especially for gas exchange and leaf-level water use efficiency (WUE). Here, we synthesized a comprehensive dataset including 554 observations from 54 individual studies and quantified the responses for leaf gas exchange induced by e[CO2] under water deficit. Moreover, we investigated the contribution of plant net photosynthesis rate (P n ) and transpiration rates (T r) toward WUE in water deficit conditions and e[CO2] using graphical vector analysis (GVA). In summary, e[CO2] significantly increased P n and WUE by 11.9 and 29.3% under well-watered conditions, respectively, whereas the interaction of water deficit and e[CO2] slightly decreased P n by 8.3%. Plants grown under light in an open environment were stimulated to a greater degree compared with plants grown under a lamp in a closed environment. Meanwhile, water deficit reduced P n by 40.5 and 37.8%, while increasing WUE by 24.5 and 21.5% under ambient CO2 concentration (a[CO2]) and e[CO2], respectively. The e[CO2]-induced stimulation of WUE was attributed to the common effect of P n and T r, whereas a water deficit induced increase in WUE was linked to the decrease in T r. These results suggested that water deficit lowered the stimulation of e[CO2] induced in plants. Therefore, fumigation conditions that closely mimic field conditions and multi-factorial experiments such as water availability are needed to predict the response of plants to future climate change.

Establishment of actinobacteria-Satureja hortensis interactions under future climate CO2-enhanced crop productivity in drought environments of Saudi Arabia

Drought is a significant global constraint on agricultural production and food security. As a promising approach to improve plant growth and yield under challenging conditions, plant growth-promoting actinobacteria has attracted much interest. Further, elevated levels of atmospheric CO2 (eCO2) may promote the plant-actinobacteria interactions which could be effective to improve the plant growth for food production. Herein, we have investigated the impact of actinobacteria and/or CO2 on biomass production, photosynthesis, macronutrients, levels of organic acids, amino acids, and essential oils as well as antioxidant activities of Satureja hortensis under water-deficit conditions. Among different actinobacterial isolates evaluated for development of secondary metabolites and biological activities, Ac9 was highly capable of producing flavonoids, and it also showed high antioxidant and microbial activities. It markedly induced the plant growth, photosynthesis, and global metabolic improvement, under water-deficit conditions. Interestingly, treatment with Ac9 in combination with eCO2 substantially minimized drought stress-induced biomass and photosynthesis reductions in Satureja hortensis. Improved photosynthesis by Ac9 and/or eCO2 induced the primary and secondary metabolisms in drought-stressed plants. The levels of the majority of the detected organic acids, essential oil, and amino acids were further improved as a result of the synergistic action of Ac9 and eCO2, as compared to the individual treatments. Furthermore, Ac9 or eCO2 significantly improved the antioxidant activities in stressed plants; however, much more positive impact was obtained by their synchronous application. Thus, the current study suggests that actinobacterial treatment induces global metabolic changes in water-stressed Satureja hortensis, the effects that have been much more strengthened under eCO2.

Elevated carbon dioxide offers promise for wheat adaptation to heat stress by adjusting carbohydrate metabolism

Carbohydrate metabolism in plants is influenced by thermodynamics. The amount of carbon dioxide (CO₂) in the atmosphere is expected to rise in the future. As a result, understanding the effects of higher CO₂ on carbohydrate metabolism and heat stress tolerance is necessary for anticipating plant responses to global warming and elevated CO₂. In this study, five wheat cultivars were exposed to heat stress (40 °C) at the onset of anthesis for three continuous days. These cultivars were grown at two levels of CO₂ i.e. ambient CO₂ level (a[CO₂], 380 mmol L^-1) and elevated CO₂ level (e[CO₂], 780 mmol L^-1), to determine the interactive effect of elevated CO₂ and heat stress on carbohydrate metabolism and antioxidant enzyme activity in wheat. Heat stress reduced the photosynthetic rate (Pn) and grain yield in all five cultivars, but cultivars grown in e[CO₂] sustained Pn and grain yield in contrast to cultivars grown in a[CO₂]. Heat stress reduced the activity of ADP-glucose pyrophosphorylase, UDP-glucose pyrophosphorylase, invertases, Glutathione reductase (GR), Peroxidase (POX), and Superoxide dismutase (SOD) at a[CO₂] but increased at e[CO₂]. The concentration of sucrose, glucose, and fructose mainly increased in tolerant cultivars under heat stress at e[CO₂]. This study confirms the interaction between the heat stress and e[CO2] to mitigate the effect of heat stress on wheat and suggests to have in-depth knowledge and precise understanding of carbohydrate metabolism in heat stressed plants in order to prevent the negative effects of high temperatures on productivity and other physiological attributes.

SUPPLEMENTARY INFORMATION

The online version contains supplementary material available at 10.1007/s12298-021-01080-5.

An actinomycete strain of Nocardiopsis lucentensis reduces arsenic toxicity in barley and maize

Accumulation of arsenic in plant tissues poses a substantial threat to global crop yields. The use of plant growth-promoting bacterial strains to mitigate heavy metal toxicity has been illustrated before. However, its potential to reduce plant arsenic uptake and toxicity has not been investigated to date. Here, we describe the identification and characterization of a Nocardiopsis lucentensis strain isolated from heavy metal contaminated soil. Inoculation with this bioactive actinomycete strain decreased arsenic root and shoot bioaccumulation in both C3 and C4 crop species namely barley and maize. Upon arsenate treatment, N. lucentensis S5 stimulated root citric acid production and the plant's innate detoxification capacity in a species-specific manner. In addition, this specific strain promoted biomass gain, despite substantial tissue arsenic levels. Detoxification (metallothionein, phytochelatin, glutathione-S-transferase levels) was upregulated in arsenate-exposed shoot and roots, and this response was further enhanced upon S5 supplementation, particularly in barley and maize roots. Compared to barley, maize plants were more tolerant to arsenate-induced oxidative stress (less H₂O₂ and lipid peroxidation levels). However, barley plants invested more in antioxidative capacity induction (ascorbate-glutathione turnover) to mitigate arsenic oxidative stress, which was strongly enhanced by S5. We quantify and mechanistically discuss the physiological and biochemical basis of N. lucentensis-mediated plant biomass recovery on arsenate polluted soils. Our findings substantiate the potential applicability of a bactoremediation strategy to mitigate arsenic-induced yield loss in crops.

Future climate CO2 can harness ROS homeostasis and improve cell wall fortification to alleviate the hazardous effect of Phelipanche infection in pea seedlings

Parasitic weeds such as Phelipanche aegyptiaca pose one of the most significant environmental constraints to cropping systems worldwide. The influence of P. aegyptiaca upon host plants is well studied, nevertheless, how future climate CO2 (eCO2) can affect P. aegyptiaca parasite-host interactions is not yet investigated. Considering the protective effect of eCO2, we studied its ability to mitigate the severity of P. aegyptiaca infection in pea plants (Pisum sativum). Our results revealed that Phelipanche infection strikingly reduced pea growth and photosynthesis. Moreover, infection with Phelipanche greatly burst the oxidative damage in pea plants by elevating photorespiration and NADPH oxidase activity. Contradictory, eCO2 extremely quenched the severity of P. aegyptiaca infection by diminishing the number and biomass of P. aegyptiaca tubercles. Additionally, eCO2 considerably mitigated the physiological and biochemical alterations exerted by Phelipanche upon pea seedlings. Within the physiological range, eCO2 augmented photosynthesis, that consequentially affected carbohydrate metabolism. Moreover, eCO2 highly mitigated the infection menace via quenching ROS overaccumulation which, sequentially reduced oxidative damage in infected pea plants. More interestingly, eCO2 improved cell wall fortification by enhancing lignin accumulation that considers the first line of defense against parasite penetration. Overall, this study concluded that pea plants grown in an atmosphere enriched with CO2 can efficiently cope with P. aegyptiaca infection via reducing Phelipanche tubercles, modulating ROS homeostasis, and enhancing cell wall fortification.

Soil arsenic toxicity differentially impacts C3 (barley) and C4 (maize) crops under future climate atmospheric CO2

Soil arsenic (As) contamination limits global agricultural productivity. Anthropogenic emissions are causing atmospheric CO₂ levels to rise. Elevated CO₂ (eCO₂) boosts plant growth both under optimal and suboptimal growth conditions. However, the crop-specific interaction between eCO₂ and soil arsenic exposure has not been investigated at the whole plant, physiological and biochemical level. Here, we tested the effects of eCO₂ (620 ppm) and soil As exposure (mild and severe treatments, 25 and 100 mg As/Kg soil) on growth, photosynthesis and redox homeostasis in barley (C3) and maize (C4). Compared to maize, barley was more susceptible to soil As exposure at ambient CO₂ levels. Barley plants accumulated more As, particularly in roots. As accumulation inhibited plant growth and induced oxidative damage in a species-specific manner. As-exposed barley experienced severe oxidative stress as illustrated by high H₂O₂ and protein oxidation levels. Interestingly, eCO₂ differentially mitigated As-induced stress in barley and maize. In barley, eCO₂ exposure reduced photorespiration, H₂O₂ production, and lipid/protein oxidation. In maize eCO₂ exposure led to an upregulation of the ascorbate-glutathione (ASC/GSH)-mediated antioxidative defense system. Combined, this work highlights how ambient and future eCO₂ levels differentially affect the growth, physiology and biochemistry of barley and maize crops exposed to soil As pollution.

Elevated CO2 modulates the effect of heat stress responses in Triticum aestivum by differential expression of isoflavone reductase-like (IRL) gene

Two wheat genotypes forming high and low biomass (HB and LB), exhibiting differential expression of an isoflavone reductase-like (IRL) gene, and resulting in contrasting grain yield under heat stress field conditions, were analyzed in detail for their responses under controlled heat and elevated CO2 conditions. Significant differences in IRL expression between the two lines were hypothesized to be the basis of their differential performance under the tested conditions and their stress tolerance potential. By a holistic approach integrating advanced cell physiological phenotyping of the antioxidative and phytohormone system in spikes and leaves with measurements of ecophysiological and agronomic traits, the genetic differences of the genotypes in IRL expression were assessed. In response to heat and elevated CO2, the two genotypes showed opposite regulation of IRL expression, which was associated with cytokinin concentration, total flavonoid contents, activity of superoxide dismutase, antioxidant capacity and photosynthetic rate in leaves and cytokinin concentration and ascorbate peroxidase activity in spikes. Our study showed that IRL expression is associated with wheat yield performance under heat stress at anthesis, mediated by diverse physiological mechanisms. Hence, based on our results, the IRL gene is a promising candidate for developing genetic markers for breeding heat-tolerant wheat.

Dissecting the molecular responses of lentil to individual and combined drought and heat stresses by comparative transcriptomic analysis

Lentil cultivation could be challenged by combined heat and drought stress in semi-arid regions. We used RNA-seq approach to profile transcriptome changes of Lens culinaris exposed to individual and combined heat and drought stresses. It was determined that most of the differentially expressed genes observed in response to combined stress, could not be identified by analysis of transcriptome exposed to corresponding individual stresses. Interestingly, this study results revealed that the expression of ribosome generation and protein biosynthesis and starch degradation pathways related genes were uniquely up-regulated under the combined stress. Although multiple genes related to antioxidant activity were up-regulated in response to all stresses, variation in types and expression levels of these genes under the combined stress were higher than that of individual stresses. Using this comparative approach, for the first time, we reported up-regulation of several TF, CDPK, CYP, and antioxidant genes in response to combined stress in plants.

Interactive effects of mercuric oxide nanoparticles and future climate CO2 on maize plant

So far, the phytotoxic hazards of nano-sized mercuric oxide (HgO-NPs) are not investigated. Herein, the phytotoxicity of fully characterized HgO-NPs (100 mg/kg soil), prepared by coprecipitation method, on maize grown under ambient (aCO₂, 410 ppm) and elevated CO₂ (eCO₂, 620 ppm) was investigated. Regardless of CO₂ concentration, HgO-NPs treatment increased Hg levels in maize organs. HgO-NPs induced severe oxidative stress in aCO₂ grown plants as indicated by reduced growth and photosynthesis and accumulation of reactive oxygen species (ROS), through photorespiration and nicotinamide adenine dinucleotide phosphate (NADPH) oxidase activities, and lipid and protein oxidation products. Although HgO-NPs increased molecular (polyphenols, flavonoids, tocopherols) and enzymatic (superoxide dismutase, catalase, peroxidase, ascorbate peroxidase, glutathione peroxidase) antioxidants in shoots of aCO₂ plants, but this failed to fight the eruption of increased ROS. On contrary, eCO₂ treatment mitigated the HgO-NPs impact by promoting photosynthesis and reducing the Hg-induced ROS production. Moreover, eCO₂ promoted ROS detoxification via molecular antioxidants overproduction, enhanced superoxide dismutase, catalase and peroxidases activities, and modulation of reduced ascorbate/oxidized ascorbate and reduced glutathione/oxidized glutathione homeostasis. The combined HgO-NPs + eCO₂ treatment also enhanced the glutathione-S-transferase activity. This study suggests that HgO-NPs cause severe phytotoxic hazards and this effect will be less detrimental under future CO₂ climate.