Growth and yield responses of potato to mixtures of carbon dioxide and ozone

Elevated ozone decreases the multifunctionality of belowground ecosystems

Elevated tropospheric ozone (O₃ ) affects the allocation of biomass aboveground and belowground and influences terrestrial ecosystem functions. However, how belowground functions respond to elevated O₃ concentrations ([O₃ ]) remains unclear at the global scale. Here, we conducted a detailed synthesis of belowground functioning responses to elevated [O₃ ] by performing a meta-analysis of 2395 paired observations from 222 publications. We found that elevated [O₃ ] significantly reduced the primary productivity of roots by 19.8%, 16.3%, and 26.9% for crops, trees and grasses, respectively. Elevated [O₃ ] strongly decreased the root/shoot ratio by 11.3% for crops and by 4.9% for trees, which indicated that roots were highly sensitive to O₃ . Elevated [O₃ ] impacted carbon and nitrogen cycling in croplands, as evidenced by decreased dissolved organic carbon, microbial biomass carbon, total soil nitrogen, ammonium nitrogen, microbial biomass nitrogen, and nitrification rates in association with increased nitrate nitrogen and denitrification rates. Elevated [O₃ ] significantly decreased fungal phospholipid fatty acids in croplands, which suggested that O₃ altered the microbial community and composition. The responses of belowground functions to elevated [O₃ ] were modified by experimental methods, root environments, and additional global change factors. Therefore, these factors should be considered to avoid the underestimation or overestimation of the impacts of elevated [O₃ ] on belowground functioning. The significant negative relationships between O₃ -treated intensity and the multifunctionality index for croplands, forests, and grasslands implied that elevated [O₃ ] decreases belowground ecosystem multifunctionality.

Responses of a semi-natural grassland community of tropical region to elevated ozone: An assessment of soil dynamics and biomass accumulation

Despite knowing the phytotoxic effects of tropospheric ozone (O₃), which is of global concern, there is no study so far reported about its impacts on grassland community of tropical regions. Therefore, we assessed the responses of a semi-natural grassland community of Indo-Gangetic plains to elevated O₃ exposure (Ambient + 20 ppb) compared to ambient after three years of exposure using open-top chambers. Percent decreases were found in above (26%; p ≤ 0.002) and belowground (30%; p ≤ 0.003) biomass under elevated compared to ambient O₃ exposure. Percent decrements in total organic carbon (TOC; 24%; p ≤ 0.001), total nitrogen (29%; p ≤ 0.001) and available phosphorus (11%; p ≤ 0.002) in the soil were also observed under elevated O₃ exposure. Exposure at elevated O₃ reduced soil microbial biomass and activities of β-glucosidase, amylase, urease and phosphatase, while polyphenol oxidase and peroxidase showed enhancement in their activities, showing negative effects on belowground soil health. Percent reduction in root shoot ratio (10%; p ≤ 0.05) depicts that less C-allocation towards root system led to a reduction in TOC in the soil, which could affect C-sequestration under elevated O₃ condition in the semi-natural grasslands. Elevated O₃ also affected enzymes participating in N and P-cycles, causing reductions in total nitrogen and phosphorus. The study concludes that projected O₃ concentrations have serious implications for aboveground biomass as well as belowground soil health in tropical areas, identified as hotspots of O₃ in the world.

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

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

Elevated tropospheric ozone affects the concentration and allocation of mineral nutrients of two bamboo species

The increase in tropospheric ozone (O₃) affects plant physiology and ecosystem processes, and consequently the cycle of nutrients. While mineral nutrients are critical for plant growth, the effect of elevated tropospheric O₃ concentration on the uptake and allocation of mineral nutrients by plants is not well understood. Using open top chambers (OTCs), we investigated the effect of elevated O₃ on calcium (Ca), magnesium (Mg) and iron (Fe) in mature bamboo species Phyllostachys edulis and Oligostachyum lubricum. Our results showed that elevated O₃ decreased the leaf biomass of P. edulis and O. lubricum by 35.1% and 26.7%, respectively, but had no significant effect on the biomass of branches, stem or root. For P. edulis, elevated O₃ increased the nutrient (Ca, Mg and Fe) concentration and allocation in leaf but reduced the concentration in other organs. In contrast, elevated O₃ increased the nutrient concentration and allocation in the branch of O. lubricum but decreased that of other organs. We also found that that P. edulis and O. lubricum responded differently to elevated O₃ in terms of nutrient (Ca, Mg and Fe) uptake and allocation. This information is critical for nutrient management and adaptation strategies for sustainable growth of P. edulis and O. lubricum under global climate change.

Regulatory Effects of Elevated Carbon Dioxide on Growth and Biochemical Responses to Ozone Stress in Chinese Pine (Pinus tabulaeformis Carr.)

This study examined whether carbon dioxide (CO₂) might alleviate ozone (O₃) injury to the dominant coniferous forest species of northern China, Pinus tabulaeformis Carr. After 90 days O₃ exposure, biomass and net photosynthetic rate (Pn) decreased significantly by 24.44 % and 42.89 % compared with the control. A significant increase in malondialdehyde (MDA) was shown, suggesting cell membrane damage and oxidative stress. However, the positive responses of biomass dry weight, antioxidative enzymes and soluble sugar contents under elevated CO₂ alone and the combination of elevated CO₂ and O₃ were observed, indicating that CO₂ could ameliorate O₃-induced injury. The study provided increasing evidence that moderately elevated CO₂ levels may have a beneficial effect on the forest ecosystem to respond to global climate change.

Hidden shift of the ionome of plants exposed to elevated CO₂depletes minerals at the base of human nutrition

Mineral malnutrition stemming from undiversified plant-based diets is a top global challenge. In C3 plants (e.g., rice, wheat), elevated concentrations of atmospheric carbon dioxide (eCO2) reduce protein and nitrogen concentrations, and can increase the total non-structural carbohydrates (TNC; mainly starch, sugars). However, contradictory findings have obscured the effect of eCO2 on the ionome-the mineral and trace-element composition-of plants. Consequently, CO2-induced shifts in plant quality have been ignored in the estimation of the impact of global change on humans. This study shows that eCO2 reduces the overall mineral concentrations (-8%, 95% confidence interval: -9.1 to -6.9, p<0.00001) and increases TNC:minerals > carbon:minerals in C3 plants. The meta-analysis of 7761 observations, including 2264 observations at state of the art FACE centers, covers 130 species/cultivars. The attained statistical power reveals that the shift is systemic and global. Its potential to exacerbate the prevalence of 'hidden hunger' and obesity is discussed.DOI: http://dx.doi.org/10.7554/eLife.02245.001.

Hidden shift of the ionome of plants exposed to elevated CO₂depletes minerals at the base of human nutrition

Mineral malnutrition stemming from undiversified plant-based diets is a top global challenge. In C3 plants (e.g., rice, wheat), elevated concentrations of atmospheric carbon dioxide (eCO2) reduce protein and nitrogen concentrations, and can increase the total non-structural carbohydrates (TNC; mainly starch, sugars). However, contradictory findings have obscured the effect of eCO2 on the ionome-the mineral and trace-element composition-of plants. Consequently, CO2-induced shifts in plant quality have been ignored in the estimation of the impact of global change on humans. This study shows that eCO2 reduces the overall mineral concentrations (-8%, 95% confidence interval: -9.1 to -6.9, p<0.00001) and increases TNC:minerals > carbon:minerals in C3 plants. The meta-analysis of 7761 observations, including 2264 observations at state of the art FACE centers, covers 130 species/cultivars. The attained statistical power reveals that the shift is systemic and global. Its potential to exacerbate the prevalence of 'hidden hunger' and obesity is discussed.DOI: http://dx.doi.org/10.7554/eLife.02245.001.

Growth, yield and quality attributes of a tropical potato variety (Solanum tuberosum L. cv Kufri chandramukhi) under ambient and elevated carbon dioxide and ozone and their interactions

The present study was designed to study the growth and yield responses of a tropical potato variety (Solanum tuberosum L. cv. Kufri chandramukhi) to different levels of carbon dioxide (382 and 570ppm) and ozone (50 and 70ppb) in combinations using open top chambers (OTCs). Plants were exposed to three ozone levels in combination with ambient CO2 and two ozone levels at elevated CO2. Significant increments in leaf area and total biomass were observed under elevated CO2 in combination with ambient O3 (ECO2+AO3) and elevated O3 (ECO2+EO3), compared to the plants grown under ambient concentrations (ACO2+AO3). Yield measured as fresh weight of potato also increased significantly under ECO2+AO3 and ECO2+EO3. Yield, however, reduced under ambient (ACO2+AO3) and elevated ozone (ACO2+EO3) compared to ACO2 (filtered chamber). Number, fresh and dry weights of tubers of size 35-50mm and>50mm used for direct consumption and industrial purposes, respectively increased maximally under ECO2+AO3. Ambient as well as elevated levels of O3 negatively affected the growth parameters and yield mainly due to reductions in number and weight of tubers of sizes >35mm. The quality of potato tubers was also modified under different treatments. Starch content increased and K, Zn and Fe concentrations decreased under ECO2+AO3 and ECO2+EO3 compared to ACO2+AO3. Starch content reduced under ACO2+AO3 and ACO2+EO3 treatments compared to ACO2. These results clearly suggest that elevated CO2 has provided complete protection to ambient O3 as the potato yield was higher under ECO2+AO3 compared to ACO2. However, ambient CO2 is not enough to protect the plants under ambient O3 levels. Elevated CO2 also provided protection against elevated O3 by improving the yield. Quality of tubers is modified by both CO2 and O3, which have serious implications on human health at present and in future.

Tropospheric ozone and plants: absorption, responses, and consequences

Ozone is now considered to be the second most important gaseous pollutant in our environment. The phytotoxic potential of O₃ was first observed on grape foliage by B.L. Richards and coworkers in 1958 (Richards et al. 1958). To date, unsustainable resource utilization has turned this secondary pollutant into a major component of global climate change and a prime threat to agricultural production. The projected levels to which O₃ will increase are critically alarming and have become a major issue of concern for agriculturalists, biologists, environmentalists and others plants are soft targets for O₃. Ozone enters plants through stomata, where it disolves in the apoplastic fluid. O₃ has several potential effects on plants: direct reaction with cell membranes; conversion into ROS and H₂O₂ (which alters cellular function by causing cell death); induction of premature senescence; and induction of and up- or down-regulation of responsive components such as genes , proteins and metabolites. In this review we attempt to present an overview picture of plant O₃ interactions. We summarize the vast number of available reports on plant responses to O₃ at the morphological, physiological, cellular, biochemical levels, and address effects on crop yield, and on genes, proteins and metabolites. it is now clear that the machinery of photosynthesis, thereby decreasing the economic yield of most plants and inducing a common morphological symptom, called the "foliar injury". The "foliar injury" symptoms can be authentically utilized for biomonitoring of O₃ under natural conditions. Elevated O₃ stress has been convincingly demonstrated to trigger an antioxidative defense system in plants. The past several years have seen the development and application of high-throughput omics technologies (transcriptomics, proteomics, and metabolomics) that are capable of identifying and prolifiling the O₃-responsive components in model and nonmodel plants. Such studies have been carried out ans have generated an inventory of O₃-Responsive components--a great resource to the scientific community. Recently, it has been shown that certain organic chemicals ans elevated CO₂ levels are effective in ameliorating O₃-generated stress. Both targeted and highthroughput approaches have advanced our knowledge concerning what O₃-triggerred signaling and metabolic pathways exist in plants. Moreover, recently generated information, and several biomarkers for O₃, may, in the future, be exploited to better screen and develop O₃-tolerant plants.

Screening three cultivars of Vigna mungo L. against ozone by application of ethylenediurea (EDU)

Three Indian black gram cultivars (Vigna mungo L. cv. Barkha, Shekhar and TU-94-2) were grown at a tropical suburban site in Varanasi, India to evaluate the varietal differences in response to ambient O(3) under field conditions using ethylenediurea (EDU). EDU (400 ppm) was given as soil drench at 10-day intervals during the growth period of the cultivars. O(3) monitoring data clearly showed high concentrations with a mean value ranging between 41.3 and 59.9 ppb. EDU treatment caused significant increases in various growth parameters and total biomass accumulation in Barkha and Shekhar. EDU caused retention of more biomass in leaves during vegetative period and translocated more photosynthates towards reproductive parts, which resulted into yield enhancement. Weight of seeds plant(-1) was higher by 36.4% and 35.6% in Barkha and Shekhar, respectively, treated with EDU compared to non-EDU-treated plants. However, TU-94-2 did not exhibit any significant difference in weight of seeds plant(-1). Starch, total sugar, amino acids and K contents increased in seeds of EDU-treated plants leading to improvement in quality response index (QRI) of seeds. EDU helped in identifying the cultivar susceptibility to O(3) stress and therefore is very useful as a monitoring tool to assess the impact of ambient O(3) on plants under natural field conditions particularly in areas experiencing moderate concentrations of O(3).

Effects of ozone on growth, yield and leaf gas exchange rates of four Bangladeshi cultivars of rice (Oryza sativa L.)

To assess the effects of tropospheric O3 on rice cultivated in Bangladesh, four Bangladeshi cultivars (BR11, BR14, BR28 and BR29) of rice (Oryza sativa L.) were exposed daily to charcoal-filtered air or O3 at 60 and 100 nl l(-1) (10:00-17:00) from 1 July to 28 November 2008. The whole-plant dry mass and grain yield per plant of the four cultivars were significantly reduced by the exposure to O3. The exposure to O3 significantly reduced net photosynthetic rate of the 12th and flag leaves of the four cultivars. The sensitivity to O3 of growth, yield and leaf gas exchange rates was not significantly different among the four cultivars. The present study suggests that the sensitivity to O3 of yield of the four Bangladeshi rice cultivars is greater than that of American rice cultivars and is similar to that of Japanese rice cultivars and that O3 may detrimentally affect rice production in Bangladesh.

The role of ozone flux and antioxidants in the suppression of ozone injury by elevated CO2 in soybean

The projected rise in atmospheric CO2 concentration is expected to increase growth and yield of many agricultural crops. The magnitude of this stimulus will partly depend on interactions with other components of the atmosphere such as tropospheric O3. Elevated CO2 concentrations often lessen the deleterious effects of O3, but the mechanisms responsible for this response have received little direct examination. Previous studies have indicated that protection against O3 injury by elevated CO2 can be attributed to reduced O3 uptake, while other studies suggest that CO2 effects on anti-oxidant metabolism might also be involved. The aim of this experiment was to test further the roles of O3 flux and antioxidant metabolism in the suppression of O3 injury by elevated CO2. In a two-year experiment, soybean [Glycine max (L.) Merr.] was exposed from emergence to maturity to charcoal-filtered air or charcoal-filtered air plus a range of O3 concentrations in combination with ambient or approximately twice-ambient CO2 concentrations in open-top field chambers. Experimental manipulation of O3 concentrations and estimates of plant O3 uptake indicated that equivalent O3 fluxes that suppressed net photosynthesis, growth, and yield at ambient concentrations of CO2 were generally much less detrimental to plants treated concurrently with elevated CO2. These responses appeared unrelated to treatment effects on superoxide dismutase, glutathione reductase, and peroxidase activities and glutathione concentration. Total ascorbic acid concentration increased by 28-72% in lower canopy leaves in response to elevated CO2 and O3 but not in upper canopy leaves. Increasing concentrations of atmospheric CO2 will likely ameliorate O3 damage to many crops due to reduced O3 uptake, increased carbon assimilation, and possibly as yet undetermined additional factors. The results of this study further suggest that elevated CO2 may increase the threshold O3 flux for biomass and yield loss in soybean.