Effects Of Elevated Atmospheric CO2 Research Articles

Effects of elevated CO2 concentration gradients on rice grain quality under two cultivation practices in cold region

AbstractBackground and ObjectivesThe effect of elevated atmospheric CO2 (eCO2) on rice (Oryza sativa L.) grain quality has been widely studied, but mostly under two contrasting levels of CO2 concentration. Our study was conducted in a new version of CO2 Gradient Tunnel (CGT) to study the responses of grain quality of japonica rice cv. Wuyoudao no.4 (WYD4) and Songjing no.9 (SJ9) to five CO2 concentrations (390–600 μmol·mol−1) gradient levels at two cultivation practices: traditional flooding (TF) and non‐flooded plastic film mulching (PM).FindingsThe results showed that the response of SJ9 to eCO2 was more pronounced under TF cultivation. When the CO2 concentration increased to 450 μmol·mol−1, the brown rice ratio and milled rice ratio of SJ9 decreased by 4.2% and 17.7%, respectively. However, when CO2 concentration increased to 600 μmol·mol−1, the brown rice ratio increased by 3.7%. These results reveal that different gradients of eCO2 have different effects on rice quality. Besides that, eCO2 decreased the nutritional quality of SJ9 by decreasing the protein content and amylose content, while eCO2 improved rice appearance and eating quality. Different from SJ9, when CO2 concentration increased to 500–600 μmol·mol–1, the milled rice ratio and head rice ratio of WYD4 increased by 5.9%–7.5% and 16.7%–19.5% under PM cultivation. Furthermore, eCO2 decreased the chalky grain rate or chalkiness by 34.5%–80.5% and 53.1%–77.1%, respectively.ConclusionsUnder PM cultivation, the rice milling quality and appearance quality of WYD4 were promoted by eCO2. Rice nutritional quality was significantly decreased in both cultivation practices. In the comparison of rice quality between the two cultivations, except for rice eating quality, the other grain quality parameters of SJ9 under PM cultivation were better than those under TF cultivation. The opposite was true for WYD4.Significance and NoveltyUnder future production conditions with eCO2, the high‐yielding SJ9 cultivar is more suitable for water‐saving cultivation with mulching film, while the high‐quality WYD4 is suitable for TF cultivation.

Effect of elevated atmospheric CO2 on spectral reflectance of coffee leaves of plants cultivated at face facility

Climate change impacts are stressing many economic sectors worldwide, including agriculture, increasingly hindering efforts to meet human needs. Dioxide carbon is one of the main greenhouse gases and it affects directly the crop production. The objective of this study was to evaluate if established remote sensing indices could detect the effects of elevated atmospheric CO2 on the leaves of coffee (Coffea arabica L.) plantation growing under field conditions. Plots of coffee plants were exposed to ambient air (~390 µmol CO2 mol-1) and elevated CO2 (~550 µmol CO2 mol-1) at the free air CO2 enrichment (FACE) experiment. The statistical design was the completely randomized blocks with six replicates per treatment (ambient CO2 and elevated CO2), with 10m-diameter plots. Coffee leaves were spectrally characterized by reflectance spectra on their adaxial surfaces and seven vegetation indices were calculated from reflectance data: chlorophyll normalized difference index (Chl NDI), normalized difference nitrogen index (NDNI), normalized difference vegetation index (NDVI), photochemical reflectance index (PRI), pigment specific simple ration indices for chlorophyll a (PSSRa) and chlorophyll b (PSSRb), and structural independent pigment index (SIPI). NDNI was a sensitive indicator of the atmospheric CO2 effects on coffee leaves. NDVI, PSSRa and PSSRb were sensitive to estimate the effect of elevated CO2 only under drought conditions. These indices identify the effect of CO2 when a long period with high precipitation deficit stressing the leaves occurred. Chl NDI, PRI and SIPI were not sensitive to atmospheric CO2.

Effect of Elevated CO2 and Temperature on Phosphorus Harvest Index of Wheat (Triticum aestivum L.) at Various Levels of Phosphorus Fertilization

The possible alteration in plant growth, productivity and phosphorus (P) demand of wheat under rising atmospheric CO2 and temperature is expected to influence the partitioning of P to different plant parts of wheat. A phytotron experiment was conducted to study the effects of elevated atmospheric CO2 (650 µmol mol-1) and elevated temperature (ambient + 3 °C) on phosphorus harvest index of wheat at various levels (control, 100% and 200% of recommended P) of P fertilization. While there was a slight increase (5.6%) in P harvest index of wheat under elevated CO2, the reverse trend (12.7% decline) was observed under elevated temperature with no consistent effect at various levels of P fertilization. Interestingly, there was a moderate decline (7.7%) in P harvest index of wheat under combined elevation of CO2 and temperature as compared to their ambient combination. The results suggest that temperature could be the dominant factor as compared to the atmospheric CO2 in deciding the overall impact of projected increase in atmospheric CO2 and temperature on P harvest index of wheat. As there is logically possible relationship between P harvest index of wheat and various physical and nutritional qualities of wheat grains such as grain Zn and Fe content and their bio-availability, grain protein content, seedling vigour, etc., the decline in wheat’s P harvest index under projected levels of CO2 and temperature in our study underscores the need of undertaking elaborate experimentations to investigate the probable effects of climate change on quality parameters associated with P harvest index of wheat.

High-resolution dynamics of available N in a grassland ecosystem under a multiple climate manipulation experiment

Nitrogen (N) is the most important limiting nutrient for plants and soil microorganisms in almost all ecosystems. Global environmental changes significantly affect the terrestrial N cycle but implications for plant available N in-situ remain unclear. Here, we investigated the simultaneous effect of elevated atmospheric CO2, an increase in temperature and a drying-rewetting event on diffusive N fluxes in soil of a managed permanent grassland at the multifactor climate manipulation experimental site ClimGrass (Austria) using microdialysis. Rewetting caused a significant, but short-lived increase in diffusive NH4+ and NO3− fluxes, which subsequently dropped until the end of the experiment. Harvesting induced a significant increase in diffusive NH4+ fluxes in the drying-rewetting treatments. However, elevated CO2 and soil warming had little effect on diffusive N fluxes. Our study suggests that more frequent soil drying-rewetting cycles associated with increased extreme weather events are uppermost among the climate change drivers affecting soil N availability.

Preference of carbon absorption determines the competitive ability of algae along atmospheric CO2 concentration.

Although many studies have focused on the effects of elevated atmospheric CO2 on algal growth, few of them have demonstrated how CO2 interacts with carbon absorption capacity to determine the algal competition at the population level. We conducted a pairwise competition experiment of Phormidium sp., Scenedesmus quadricauda, Chlorella vulgaris and Synedra ulna. The results showed that when the CO2 concentration increased from 400 to 760 ppm, the competitiveness of S. quadricauda increased, the competitiveness of Phormidium sp. and C. vulgaris decreased, and the competitiveness of S. ulna was always the lowest. We constructed a model to explore whether interspecific differences in affinity and flux rate for CO2 and HCO3 − could explain changes in competitiveness between algae species along the gradient of atmospheric CO2 concentration. Affinity and flux rates are the capture capacity and transport capacity of substrate respectively, and are inversely proportional to each other. The simulation results showed that, when the atmospheric CO2 concentration was low, species with high affinity for both CO2 and HCO3 − (HCHH) had the highest competitiveness, followed by the species with high affinity for CO2 and low affinity for HCO3 − (HCLH), the species with low affinity for CO2 and high affinity for HCO3 − (LCHH) and the species with low affinity for both CO2 and HCO3 − (LCLH); when the CO2 concentration was high, the species were ranked according to the competitive ability: LCHH > LCLH > HCHH > HCLH. Thus, low resource concentration is beneficial to the growth and reproduction of algae with high affinity. With the increase in atmospheric CO2 concentration, the competitive advantage changed from HCHH species to LCHH species. These results indicate the important species types contributing to water bloom under the background of increasing global atmospheric CO2, highlighting the importance of carbon absorption characteristics in understanding, predicting and regulating population dynamics and community composition of algae.

Effects of elevated atmospheric CO2 and its interaction with temperature and nitrogen on yield of barley (Hordeum vulgare L.): a meta-analysis

AimsThe general aim of this meta-analysis is to synthesize and summarize the mean response of barley yield variables to elevated CO2 (eCO2) and how temperature and nitrogen (N) affect the CO2-induced yield responses of barley.MethodsA meta-analysis procedure was used to analyze five yield variables of barley extracted from 22 studies to determine the effect size and the magnitude concerning eCO2 and its interaction with temperature and N.ResultsCO2 enrichment increased aboveground biomass (23.8%), grain number (24.8%), and grain yield (27.4%). The magnitude of the responses to eCO2 was affected by genotype, temperature, nitrogen, and CO2 exposure methods. Genotype “Anakin” shows the highest CO2 response of aboveground biomass (47.1%), while “Bambina” had the highest grain number (58.4%). Grain yield response was observed to be higher for genotypes “Alexis” (38.1%) and “Atem” (33.7%) under eCO2. The increase of aboveground biomass and grain yield was higher when plants were grown under eCO2 in combination with higher N (151–200 kg ha−1). The interaction between eCO2 and three different temperature levels was analyzed to identify the impacts on barley yield components. The results revealed that the CO2-induced increase in grain number and grain yield was higher in combination with a temperature level of 21–25 °C as compared to lower levels (< 15 and 16–20 ℃). The response of barley yield to eCO2 was higher in growth chambers than in other CO2 exposure methods. Moreover, a higher response of aboveground biomass and grain yield to eCO2 was observed for pot-grown plants compared to field-grown.ConclusionsOverall, results suggest that the maximal barley production under eCO2 will be obtained in combination with high N fertilizer and temperature levels (21–25 °C).

Effects of Elevated Atmospheric Carbon Dioxide on the Vineyard System of Vitis vinifera: A Review

Global atmospheric carbon dioxide concentrations will continue increasing throughout the next century, with profound effects on agriculture. The literature concerning the effects of climate change on viticulture has largely focused on the isolated effects of variables such as temperature and soil water deficit. Likewise, the research on the effects of elevated atmospheric CO₂ on grapevines is stunted at the categorical level, chiefly because of the difficulty of experimentally controlling the gaseous environment in situ for the years necessary to replicate the vineyard system in a future climate condition. Despite numerous studies on the short-term influence of environmental and cultural factors on grapevine development at elevated CO₂, the long-term effects remain poorly understood. The lack of field based elevated CO₂ experiments in the United States is an added challenge to predicting viticultural changes, particularly in California. This review focuses on the systemic effect of atmospheric CO₂ on <i>Vitis vinifera</i>, synthesizing physiological, phenological, and plant-pest interactions. Major findings from this synthesis inform of a predicted increase in pest pressure, advanced phenological timing, transient increase in water use efficiency for grapevine, and changes in grape berry chemistry. While water use efficiency is highly desirable, the prediction for current winegrape growing regions is a transient increase in water use efficiency subsequently limited by a lack of available soil water. Grapevine is influenced by the negative synergistic effects of heat, drought, and elevated CO₂, which will alter cultural practices including harvest and pest and disease control, with downstream effects on winemaking. Several options for adaptation are discussed including leaf removal, planting alternative varieties, and selective breeding of new varieties.

Physiological and Transcriptome Responses to Elevated CO2 Concentration in Populus

Global climate change is heavily affected by an increase in CO2. As one of several efforts to cope with this, research on poplar, a representative, fast growing, and model organism in plants, is actively underway. The effects of elevated atmospheric CO2 on the metabolism, growth, and transcriptome of poplar were investigated to predict productivity in an environment where CO2 concentrations are increasing. Poplar trees were grown at ambient (400 ppm) or elevated CO2 concentrations (1.4× ambient, 560 ppm, and 1.8× ambient, 720 ppm) for 16 weeks in open-top chambers (OTCs). We analyzed the differences in the transcriptomes of Populusalba × Populus glandulosa clone “Clivus” and Populus euramericana clone “I-476” using high-throughput sequencing techniques and elucidated the functions of the differentially expressed genes (DEGs) using various functional annotation methods. About 272,355 contigs and 207,063 unigenes were obtained from transcriptome assembly with the Trinity assembly package. Common DEGs were identified which were consistently regulated in both the elevated CO2 concentrations. In Clivus 29, common DEGs were found, and most of these correspond to cell wall proteins, especially hydroxyproline-rich glycoproteins (HRGP), or related to fatty acid metabolism. Concomitantly, in I-476, 25 were identified, and they were related to heat shock protein (HSP) chaperone family, photosynthesis, nitrogen metabolism, and carbon metabolism. In addition, carbohydrate contents, including starch and total soluble sugar, were significantly increased in response to elevated CO2. These data should be useful for future gene discovery, molecular studies, and tree improvement strategies for the upcoming increased-CO2 environments.

Effect of enriched CO2 atmosphere on morphological and chemical characteristics of Alternanthera philoxeroides

Carbon dioxide (CO2) is one of the vital resources for plants and its concentrations in the atmosphere have been on the increase globally from the 18th century, and continue to rise at approximately 0.4% per year. Atmospheric CO2 enrichment could possibly modify growth and chemical profiles of plants, as well as plant–insect interactions. The present study investigated the effects of elevated atmospheric CO2 on stem diameters, above-ground biomass and secondary metabolite components of both terrestrial and aquatic forms of Alternanthera philoxeroides. Stem fragments of the weed were grown in six Open Top Chambers (OTCs): three chambers of ambient (~400 ppm) and three chambers of elevated (~1000 ppm) CO2 levels to simulate the current and future CO2 levels, respectively, based on prediction by IPCC (2013). Total dry weights of leaves and stems, as well as stem diameters were measured to evaluate growth and biomass accumulation in A. philoxeroides. Furthermore, chemical analyses were performed on leaf tissues of plants grown under both elevated and ambient atmospheric CO2 treatments to determine the concentration of secondary metabolites (phenolic acids and flavonoids). Results of the analyses revealed that CO2 enrichment significantly increased stem diameters and enhanced above-ground biomass accumulation in both aquatic and terrestrial environments. Enriched CO2 atmosphere treatments increased concentration of secondary metabolites in leaf tissues, with leaves of plants grown under elevated CO2 exhibiting remarkably higher concentrations of phenolic acids and flavonoids. Total flavonoid content increased by 51.02% in aquatic plants and by 99.03% in terrestrial plants. Total phenolic content increased by 29.57% in aquatic plant leaves while in terrestrial plant leaves the increase was by 61.11%. Above-ground biomass accumulation and increase in stem diameters could enhance competitive ability of the species and its ability to invade and colonize new habitats in response to a future CO2-enriched atmosphere.

Elevated CO2 modulates carbon assimilation and leaf water use efficiency of Nicotiana tabacum L. (tobacco) under patchy soil nutrient deficiency

Effect of elevated atmospheric CO2 (e[CO2]) on plant growth and physiology depends on soil nutrient availability. The objective of this study was to evaluate the effect of e[CO2] impact on tobacco (Nicotiana tabacum L.) growth and physiology, and to test if patchy root-zone nutrient supply could modulate the e[CO2] effects on tobacco crops. In this study, we investigated how partial root-zone nutrient deficiency (PRN) affect carbon assimilation, biomass accumulation and partitioning, and water use efficiency (WUE) of tobacco grown under e[CO2]. A split-pot experiment was conducted with tobacco plants grown in a sandy loam soil with two fertilizer levels [0 and 113-68-258 (N-P2O5-K2O) mg kg−1 soil] and three fertilization regimes (PRN, full root-zone fertilization – CRN, and no fertilization – CK) and two CO2 environments (400 μmol L−1 and 800 μmol L−1). Compared with ambient [CO2] (a[CO2]), e[CO2] increased the leaf photosynthetic rate (Pn) and reduced the transpiration rate (Tr) and stomatal conductance (gs), resulting in an increased WUE. Besides, e[CO2] enhanced tobacco leaf biomass and partitioning towards roots compared with a[CO2]. Improved growth under e[CO2] compared with a[CO2] was more pronounced under PRN than under CRN. Root hydraulic conductance was significantly greater under PRN as compared with other fertilization regimes particularly under e[CO2]. Root exudates of glucose and sucrose were significantly improved by the interaction of [CO2] and patchy fertilization regime, especially after 7 days exposure to different CO2 growth conditions. The soil pH was unaffected by CO2 growth environment but was significantly lowered in the fertilized side under PRN as compared to other fertilization regimes. Collectively, our results offer novel information about the modulation of e[CO2] on the physiology and growth of tobacco plants under patchy soil nutrient deficiency.

The combined effects of elevated atmospheric CO2 and cadmium exposure on flavonoids in the leaves of Robinia pseudoacacia L. seedlings

Flavonoids participate in several plant processes such as growth and physiological protection in adverse environments. In this study, we investigated the combined effects of eCO2 and cadmium (Cd)-contaminated soils on the total flavonoid and monomer contents in the leaves of Robinia pseudoacacia L. seedlings. Elevated CO2, Cd, and eCO2+ Cd increased the total flavonoids in the leaves relative to the control, and eCO2 mostly increased (p < 0.05) the total flavonoid content under Cd exposure. Elevated CO2 increased (p < 0.05) robinin, rutin, and acacetin contents in the leaves of 45-day seedlings and decreased (p < 0.05) the content of robinin and acacetin at 90 and 135 d under Cd exposure except for robinin at day 45 under Cd1 and acacetin on day 135 under Cd1. Quercetin content decreased (p < 0.05) under the combined conditions relative to Cd alone. Kaempferol in the leaves was only detected under eCO2 on day 135. The responses of total chlorophyll, total soluble sugars, starch, C, N, S, and the C/N ratio in the leaves to eCO2 significantly affected the synthesis of total flavonoids and monomers under Cd exposure. Overall, rutin was more sensitive to eCO2+ Cd than the other flavonoids. Cadmium, CO2, and time had significant interactive effects on the synthesis of flavonoids in the leaves of R. pseudoacacia L. seedlings. Elevated CO2 may improve the protection and defense system of seedlings grown in Cd-contaminated soils by promoting the synthesis of total flavonoids, although robinin, rutin, quercetin, and acacetin yields may reduce with time. Additionally, increased Cd in the leaves suggested that eCO2 could improve the phytoremediation of Cd-contaminated soils.

Effects of elevated atmospheric CO2 on rhizosphere microbial community of Pinus densiflora (Korean red pine)

The concentration of atmospheric CO2 is increasing largely owing to human activities. Although it is well established that elevated CO2 (eCO2) stimulates plant growth and primary productivity, the effect of eCO2 on soil microbial communities remains poorly understood. In this study, we aimed to examine the effects of eCO2 on the taxonomical diversity, composition, and structure of rhizosphere microbial communities of Korean red pine (Pinus densiflora) through next-generation sequencing (NGS) of 16S rRNA genes. Three bacterial phyla, Proteobacteria, Acidobacteria, and Actinobacteria, were found to be dominant in all samples. Species richness estimates (Chao1 and ACE) and diversity indices (Shannon and Simpson) for the three sampling chambers were the highest from the eCO2 (approximately 1.4× ambient, ≈ 560 ppm). These findings suggested that elevated atmospheric CO2 affected the bacterial community composition in the rhizosphere of Korean red pine (Pinus densiflora).

大气CO2浓度升高对春玉米土壤呼吸的影响

为探讨春玉米不同生育期土壤呼吸速率对大气CO₂浓度升高的响应，以黄土高原旱作春玉米为研究对象，通过改进的开顶式气室（OTC）模拟大气CO₂浓度升高的环境，在田间条件下设置自然大气CO₂浓度（CK）、OTC对照（OTC，CO₂浓度同CK）与CO₂浓度升高（OTC+CO₂，OTC系统自动控制CO₂浓度700 μmol/mol）3种处理。研究了旱区覆膜高产栽培春玉米播前（V0）、六叶期（V6）、九叶期（V9）、吐丝期（R1）、乳熟期（R3）、蜡熟期（R5）及完熟期（R6）土壤呼吸速率对大气CO₂浓度升高的响应特征，以及大气CO₂浓度升高对土壤呼吸速率的温度与水分效应的影响。研究发现，OTC+CO₂处理土壤呼吸速率，与CK相比，在R3和R5期分别增加43%、104%（P<0.05），与OTC相比，R3和R5期分别提升了63%、109%（P<0.05）；OTC处理与CK相比，在整个生育期对土壤呼吸影响不显著；3种处理条件下，土壤温度和水分随生育期变化趋势基本一致，土壤呼吸速率与土壤温度和水分分别呈指数相关和抛物线型相关；结果表明：大气CO₂浓度升高对土壤呼吸的影响因生育期而异，土壤温度和土壤水分是影响旱地农田土壤呼吸的重要因素，CO₂浓度升高会使土壤呼吸温度效应值（Q₁₀）降低，土壤呼吸对土壤水分响应的阈值提高。;Understanding the effects of elevated atmospheric CO₂ on soil respiration is crucial for predicting the greenhouse gas emission in the future. A field experiment was conducted to study the effects of elevated CO₂ on soil respiration of spring maize under three atmospheric conditions (treatments):natural atmospheric conditions with the current CO₂ concentration (marked as CK), open-top chamber (OTC) system with the current atmospheric CO₂ concentration (as the contrast, marked as OTC), and OTC system with elevated CO₂ concentration of 700 μmol/mol (marked as OTC+CO₂). Soil respiration, soil temperature and moisture were measured at the main growth stages of spring maize including pre-sowing (V0), jointing stage (V6), ninth-leaf stage (V9), silking stage (R1), milk stage (R3), dent stage (R5), and physiological maturity stage (R6). The results showed that, compared with CK, OTC+CO₂ enhanced soil respiration rates by 43% and 104% (P<0.05), respectively, at the R3 and R5 stage. Compared with OTC, OTC+CO₂ increased soil respiration rates by 63% and 109% (P<0.05) at the R3 and R5 stage, respectively. There was no significant difference in soil respiration between OTC and CK during the whole growth period of spring maize. The changing dynamics of soil temperature with growth period for the three treatments were consistent, also soil moisture changing dynamics with growth period under the three atmospheric conditions were similar. Soil respiration showed an exponential and parabolic correlation with the soil temperature and soil moisture, respectively. In conclusion, the effects of elevated CO₂ on soil respiration varied with growth stage. Soil temperature and soil moisture were the main factors affecting soil respiration, the elevated CO₂ decreased the temperature effect value (Q₁₀), and increased the threshold value of soil respiration to soil moisture.

The effects of elevated atmospheric CO2 concentration on the biological control of invasive aquatic weeds

Abstract There has been a rapid increase in atmospheric CO2 concentration, from pre-industrial values of 280 ppm to more than 400 ppm currently, and this is expected to double by the end of the 21st century. Studies have shown that plants grown at elevated CO2 concentrations have increased growth rates and invest more in carbon-based defences. This has important implications for the management of invasive alien plants, especially using biological control which is mostly dependent on herbivorous insects. The aim of this study was to investigate the effects of elevated atmospheric CO2 on the biological control of four invasive aquatic weeds (Azolla filiculoides, Salvinia molesta, Pistia stratiotes and Myriophyllum aquaticum). These species are currently under successful control by their respective biological control agents (Stenopelmus rufinasus, Cyrtobagous salviniae, Neohydronomus affinis, and Lysathia sp.) in South Africa. The plant species were grown in a two factorial design experiment, where atmospheric CO2 concentrations were set at ambient (400 ppm) or elevated (800 ppm), and plants were either subjected to or not subjected to herbivory by their target biological control agents. There was an overall increase in biomass production and C:N across all species at elevated CO2, both in the absence and presence of biological control, although C:N of M. aquaticum and biomass of A. filiculoides with herbivory were not constant with this trend. Insect feeding damage was reduced by elevated CO2, except for S. molesta. Thus, we can expect that plants will respond differently to CO2 increase, but the general trend suggests that these species will become more challenging to manage through biological control in future.

Elucidating relationship between nitrous oxide emission and functional soil microbes from tropical lowland rice soil exposed to elevated CO2: A path modelling approach

Understanding the effect of elevated atmospheric CO2 on nitrous oxide (N2O) emission and plant-microbe interactions in rice soils is of great significance for predicting the long-term response of rice ecosystems to elevated CO2 concentration. Elevated atmospheric CO2 concentration has the potential to augment rice production and alter the soil nitrogen (N) dynamics. Because N2O emission is controlled by microbial activity, we reasoned that changes in soil N dynamics and activity of soil microbes may affect N2O flux from rice soil. In order to examine the influence of elevated CO2, different N doses and varying moisture regimes on N2O emission from rice soil, we designed a field experiment with 3 CO2 levels [C1 = ambient CO2 (400 ± 10 μmol mol−1), C2 = elevated CO2 (550 ± 20 μmol mol−1), C3 = elevated CO2 (700 ± 20 μmol mol−1)], 3 N doses [No = No nitrogen, N1 = 100 kg ha−1, N2 = 150 kg ha−1] and 2 moisture regimes (M1 = well watered, M2 = water deficit stress upto −60 kPa). In this study, path analyses using partial least square path modelling (PLS‐PM) approach was used to distinguish the direct and indirect factors influencing N2O emission under ambient and elevated CO2 conditions. Significant increase was found for labile N fractions such as microbial biomass-N (32 %; p ≤ 0.03) whereas significant decrease was found for NH4+-N (40 %; p ≤ 0.0005) and NO3--N (32 %; p ≤ 0.001) concentration under elevated over ambient CO2. Rhizospheric denitrifier population was increased (39 %; p ≤ 0.001) whereas, nitrifier population decreased (41 %; p ≤ 0.001) under elevated as compared to ambient CO2. Exposure of elevated CO2 decreased (20 %; p ≤ 0.001) N mineralization whereas it increased N2O emission (43 %; p ≤ 0.001). Elevated CO2 level increased activities of β- glucosidase, urease and fluorescein diacetate showing significant effects on soil N dynamics. Path modelling (PLS-PM) approach indicated a direct effect of nitrifiers and denitrifiers population on N2O emission and the effect was more pronounced under elevated CO2 as compared to ambient CO2 levels. The developed predictive models for N2O emission clarifies that the effect of varying CO2 levels is more pronounced at rice vegetative stage than reproductive stage.

How do elevated atmosphere CO2 and temperature alter the physiochemical properties of starch granules and rice taste?

Elevated atmospheric CO2 (EC) and temperature (ET) strongly affect agricultural production, but the mechanism through which EC and/or ET influence starch granules and their relationship to cooked rice taste remain largely unknown. Therefore, a field experiment using a popular japonica cultivar grown in a temperature/free-air CO2 enrichment environment was conducted to investigate the responses of volume and fine structure of starch granules and their formation physiology to EC (+200 ppm) and/or ET (+1 °C) in 2015–2016. EC markedly enhanced the activity of soluble-starch synthase and granule-bound starch synthase by 28.0% and 27.9% respectively, thereby increasing the long chains and the volume of starch granules. However, EC decreased the activity of starch-branch enzyme by 7.5% possibly via the pathway of ethylene signalling (EC prominently decreased the ethylene evolution rate of rice grains by 28.8%), resulting in a remarkable decrease in α-1′6 glucosidic bonds and significant increase in the iodine-binding capacity and double helix in starch molecules. These EC-induced changes in morphology and fine structure of starch granules synergistically altered the thermal properties of rice flour and eventually improved the cohesiveness and taste of cooked rice, as suggested by the significant relationships between them. ET partially offset the beneficial EC effects in most cases. However, few remarkable CO2 × temperature or CO2 × year effects were detected, indicating that the effects of EC on starch granules and rice taste less varied with meteorological conditions. These findings have important implications on rice palatability and for the development of adaptive strategies in the starch industry in future environment.

Composition and activity of nitrifier communities in soil are unresponsive to elevated temperature and CO2, but strongly affected by drought

Nitrification is a fundamental process in terrestrial nitrogen cycling. However, detailed information on how climate change affects the structure of nitrifier communities is lacking, specifically from experiments in which multiple climate change factors are manipulated simultaneously. Consequently, our ability to predict how soil nitrogen (N) cycling will change in a future climate is limited. We conducted a field experiment in a managed grassland and simultaneously tested the effects of elevated atmospheric CO2, temperature, and drought on the abundance of active ammonia-oxidizing bacteria (AOB) and archaea (AOA), comammox (CMX) Nitrospira, and nitrite-oxidizing bacteria (NOB), and on gross mineralization and nitrification rates. We found that N transformation processes, as well as gene and transcript abundances, and nitrifier community composition were remarkably resistant to individual and interactive effects of elevated CO2 and temperature. During drought however, process rates were increased or at least maintained. At the same time, the abundance of active AOB increased probably due to higher NH4+ availability. Both, AOA and comammox Nitrospira decreased in response to drought and the active community composition of AOA and NOB was also significantly affected. In summary, our findings suggest that warming and elevated CO2 have only minor effects on nitrifier communities and soil biogeochemical variables in managed grasslands, whereas drought favors AOB and increases nitrification rates. This highlights the overriding importance of drought as a global change driver impacting on soil microbial community structure and its consequences for N cycling.

Effects of elevated atmospheric CO2 and temperature on the management of powdery mildew of zucchini

AbstractThe impact of combined environmental factors, such as temperature and CO2, on the control of the powdery mildew of zucchini, caused by Podosphaera xanthii, and of different control measures has been studied on plants grown in phytotrons. Five experimental trials were conducted, and the powdery mildew severity of both treated and untreated zucchini plants was found to be significantly affected by the interaction between temperature (three different regimes: 16–18; 18–22; 22–26°C), CO2 (two concentrations: 400–450 and 800–850 ppm) and the treatments. However, at the end of the trials, the efficacy of all the products was not affected by the different, tested environmental conditions. Sulphur consistently provided the highest disease control (75%–85% efficacy). Among the resistant inducers that were tested, calcium oxide was the most effective, in terms of powdery mildew control under all the conditions tested in phytotrons, reducing disease severity from 46% to 61%. Foliar applications of phosphite (14%–28% efficacy), Ampelomyces quisqualis (12%–23% efficacy) and potassium silicate (13%–24% efficacy) only slightly reduced the disease severity for all the tested temperature regimes and CO2 concentrations, compared to the untreated control. The results obtained under our experimental conditions show that a possible increase in CO2 concentration and temperature, which is expected for the next few years, should not influence the efficacy of the tested resistance inducers or of sulphur against powdery mildew on zucchini. Moreover, the suppressive effect of calcium oxide is in light of its possible use in greenhouses for zucchini powdery mildew control under 400–450 ppm of CO2 and under enriched condition of 800–850 ppm of CO2.

Land management and climate change determine second‐generation bioenergy potential of the US Northern Great Plains

AbstractBioenergy with carbon capture and storage (BECCS) has been proposed as a potential climate mitigation strategy raising concerns over trade‐offs with existing ecosystem services. We evaluate the feasibility of BECCS in the Upper Missouri River Basin (UMRB), a landscape with diverse land use, ownership, and bioenergy potential. We develop land‐use change scenarios and a switchgrass (Panicum virgatum L.) crop functional type to use in a land‐surface model to simulate second‐generation bioenergy production. By the end of this century, average annual switchgrass production over the UMRB ranges from 60 to 210 Tg dry mass/year and is dependent on the Representative Concentration Pathway for greenhouse gas emissions and on land‐use change assumptions. Under our simple phase‐in assumptions this results in a cumulative total production of 2,000–6,000 Tg C over the study period with the upper estimates only possible in the absence of climate change. Switchgrass yields decreased as average CO2 concentrations and temperatures increased, suggesting the effect of elevated atmospheric CO2 was small because of its C4 photosynthetic pathway. By the end of the 21st century, the potential energy stored annually in harvested switchgrass averaged between 1 and 4 EJ/year assuming perfect conversion efficiency, or an annual electrical generation capacity of 7,000–28,000 MW assuming current bioenergy efficiency rates. Trade‐offs between bioenergy and ecosystem services were identified, including cumulative direct losses of 1,000–2,600 Tg C stored in natural ecosystems from land‐use change by 2090. Total cumulative losses of ecosystem carbon stocks were higher than the potential ~300 Tg C in fossil fuel emissions from the single largest power plant in the region over the same time period, and equivalent to potential carbon removal from the atmosphere from using biofuels grown in the same region. Numerous trade‐offs from BECCS expansion in the UMRB must be balanced against the potential benefits of a carbon‐negative energy system.

Elevated CO2 mitigates the negative effect of CeO2 and Cr2O3 nanoparticles on soil bacterial communities by alteration of microbial carbon use

The interactive effects of elevated atmospheric CO2 and nanoparticles (NPs) on the structure and function of soil bacterial community remain unknown. Here we compared the impacts of CeO2 (nCeO2) and Cr2O3 (nCr2O3) nanoparticles on the taxonomic compositions and functional attributes of bacterial communities under elevated CO2 (eCO2). The stimulated enzyme activities (dehydrogenase, acid phosphatase and urease), increased microbial biomass carbon (MBC), and higher bacterial alpha-diversity were observed under the combined effects of eCO2 and NPs compared to the single NP treatment, indicating eCO2 could mitigate the adverse effect of NPs on soil microorganisms. NPs and eCO2 are important factors influencing the alpha- and beta-diversity (17% and 18% of variations were explained) as well as functional profile (20% and 26% of variations were explained) of bacterial communities. Rising CO2 level promoted the resilience of NP-resistant bacterial populations, primarily the members of Alphaproteobacteria, Gammaproteobacteria and Bacteroidia, which are also characterized by the fast carbon use capability. Moreover, the significantly (P < 0.05) higher metabolic quotient (qCO2), reduced available carbon and overrepresented carbon metabolism genes at eCO2vs. ambient CO2 (aCO2) indicate the acceleration of available carbon turnover in NP-exposed soils. Correlation analysis revealed that mitigation of NPs toxicity by eCO2 could be attributed to the remarkable decline of bioavailable metals disassociated from NPs and available carbon level, as well as promotion of the rapid carbon-metabolizing microbes. Our study pointed out the positive role of eCO2 in alleviating the adverse effect of NPs on microbiological soil environment, and results can serve as important basis in establishing guidelines for lowering the ecotoxicity of NPs.