CO<Subscript>2</Subscript> enrichment affects eco-physiological growth of maize and alfalfa under different water stress regimes in the UAE

Water stress has been reported to alter morphology and physiology of plants affecting chlorophyll content, stomatal size and density. In this study, drought stress mitigating effects of CO₂ enrichment was assessed in greenhouse conditions in the hot climate of UAE. Commercially purchased maize (Zea mays L.) and alfalfa (Medicago sativa L.) were seeded in three different custom-built cage structures, inside a greenhouse. One cage was kept at 1000 ppm CO₂, the second at 700 ppm CO₂, and the third at ambient greenhouse CO₂ environment (i.e. 435 ppm). Three water stress treatments HWS (200 ml per week), MWS (400 ml per week), and CWS (600 ml per week) were given to each cage so that five maize pots and five alfalfa pots in each cage received same water stress treatments. In maize, total chlorophyll content was similar or higher in water stress treatments compared to control for all CO₂ concentrations. Stomatal lengths were higher in enriched CO₂ environments under water stress. At 700 ppm CO₂, stomatal widths decreased as water stress increased from MWS to HWS. At both enriched CO₂ environments, stomatal densities decreased compared to ambient CO₂ environment. In alfalfa, there was no significant increase in total chlorophyll content under enriched CO₂ environments, even though a slight increase was noticed.     

Rapidly diminishing mangrove forests in Myanmar (Burma): a review

IPCC predictions indicate an increase in temperatures by 1.5–7°C in some Amazonian regions during the twenty-first century. These changes could disrupt the present distribution patterns of organisms, including wetland plant species. In this work, we determined in microcosms the effects of scenarios combining elevated temperature and atmospheric CO₂ concentration on the germination and initial growth of the arborescent Amazonian aquatic macrophyte Montrichardia arborescens. Seeds were germinated, and seedlings produced were monitored over a 5-month period in four microcosms: Control: ambient temperature and CO₂ level; Mild: Control + 1.5°C and + 200 ppm CO₂; intermediate: control + 2.5°C and + 400 ppm CO₂; Extreme: Control + 4.5°C and + 850 ppm of CO₂. Rapid light response curves and Fv/Fm values taken in seedlings showed a decrease in electron transportation rate with CO₂ and temperature elevation. Mild and Intermediate treatments stimulated biomass production; Extreme treatment and Control produced similar results. The severe climatic changes expected in the future may negatively influence carbon accumulation in M. arborescens. Since aquatic macrophytes in Amazonian wetlands and wetlands worldwide are key plant species, further studies are needed to predict their fate in a global change perspective.     

Impact of elevated CO<Subscript>2</Subscript> in <Emphasis Type="Italic">Casuarina equisetifolia</Emphasis> rooted stem cuttings inoculated with <Emphasis Type="Italic">Frankia</Emphasis>

Impact of different levels of elevated CO ₂ on the activity of Frankia (Nitrogen-fixing actinomycete) in Casuarina equisetifolia rooted stem cuttings has been studied to understand the relationship between C. equisetifolia, Frankia and CO₂. The stem cuttings of C. equietifolia were collected and treated with 2000 ppm of Indole Butyric Acid (IBA) for rooting. Thus vegetative propagated rooted stem cuttings of C. equisetifolia were inoculated with Frankia and placed in the Open top chambers (OTC) with elevated CO₂ facilities. These planting stocks were maintained in the OTC for 12 months under different levels of elevated CO₂ (ambient control, 600 ppm, 900 ppm). After 12 months, the nodule numbers, bio mass, growth, and photosynthesis of C. equisetifolia rooted stem cuttings inoculated with Frankia were improved under 600 ppm of CO₂. The rooted stem cuttings of C. equisetifolia inoculated with Frankia showed a higher number of nodules under 900 ppm of CO₂ and cuttings without Frankia inoculation exhibited poor growth. Tissue Nitrogen (N) content was also higher under 900 ppm of CO₂ than ambient control and 600 ppm levels. The photosynthetic rate was higher (17.8 μ mol CO₂ m^?2 s^?1) in 900 ppm of CO₂ than in 600 ppm (13.2 μ mol CO₂ m^?2 s^?1) and ambient control (8.3 μ mol CO₂ m^?2 s^?1). This study showed that Frankia can improve growth, N fixation and photosynthesis of C. equietifolia rooted stem cuttings under extreme elevated CO₂ level conditions (900 ppm).     

Impact of In-Situ CO2 Nano-Bubbles Generation on Freezing Parameters of Selected Liquid Foods

The impact of in-situ CO₂ nano-bubbles generation on the freezing properties of soft serve, milk, and apple juice was investigated. Carbonated (0, 1000, and 2000 ppm) liquid foods contained in a tube were submerged and cooled for 90 min in a pre-set ethylene glycol bath (−15 °C). Before the enclosed liquid reached 0 °C, the vibration was discharged through ultrasound in the bath to create nano-bubbles within the carbonated food samples, and the changes in temperature for 90 min of each food were recorded as a freezing curve. The time for onset of nucleation of control soft serve mix was halved in samples with 2000-ppm CO₂ due to the presence of nano-bubbles. Likewise, the nucleation time for milk with and without nano-bubbles at the same CO₂ concentration of 2000 ppm was 7.9 ± 0.1 and 2.8 ± 0.8 min_, respectively. The generation of CO₂ nano-bubbles from 2000-ppm CO₂ level in 10 ^oBx apple juice displayed −9.3 ± 0.3 °C nucleation temperature while the control one had −11.7 ± 0.9 °C.

     

Wet Chemical Colorimetric Estimation of CO: An Update on the Reduced Silver Sol Spectral and Kinetic Transformations to Silver nanoparticle

Measurements of ppm (v/v) level CO_g concentration is conveniently performed by its preconcentration in alkaline absorber solution of Ag⁺-(4)- HCO₂-C₆H₄-SO₂NH₂ complex, followed by a spectral measurement of the reduced silver sol. In this study, the transitory nature of this latter species and its subsequent real-time transformation to silver nanoparticle are presented. These results were based on spectral measurements made under varying concentrations of alkali, (4)-HCO₂-C₆H₄-SO₂NH₂, and Ag⁺ in the absorber solution, and in the presence of a wide range of sampled CO_g concentration. The initially created light yellow colored sol with its broad absorption profile peaking at 380 nm and absorption coefficient 3500?±?300 cm^?1 M^?1 (related to the amount of sampled [CO_g] as standardized by gas chromatographic analysis) changed into the characteristic yellow orange nanoparticle with its plasmon band peak absorption at 425 nm and absorption coefficient 6350?±?300 cm^?1 M^?1. Under different sampling conditions, the respective first-order conversion rates varied between 0.03 and 0.15 h^?1, whereas simultaneous dynamic light scattering measurements revealed steady growth of the averaged particle size ranging from 60 to 300 nm.     

Elevated CO<Subscript>2</Subscript> influences host plant defense response in chickpea against <Emphasis Type="Italic">Helicoverpa armigera</Emphasis>

Global atmospheric concentration of CO₂ is likely to increase from 350 to 750 ppm over the next 100 years. The present studies were undertaken to understand the effects of elevated CO₂ on enzymatic activity and secondary metabolites in chickpea in relation to expression of resistance to pod borer, Helicoverpa armigera. Fifteen-day-old chickpea plants [ICCL 86111—resistant and JG 11—commercial cultivar] grown in the greenhouse were transferred to open-top chambers (OTC) and kept under 350, 550 and 750 ppm of CO₂. Twenty neonates of H. armigera were released on each plant at 7 days after shifting the pots to the OTCs. Un-infested plants were maintained as controls. After 7 days of infestation, the activities of defensive enzymes [peroxidase (POD), polyphenol oxidase (PPO), phenylalanine ammonia lyase (PAL) and tyrosine ammonia lyase (TAL)] and amounts of total phenols and condensed tannins increased with an increase in CO₂ concentration in chickpea. The nitrogen balance index was greater in plants kept at 350 ppm CO₂ than in plants kept under ambient conditions. The H. armigera-infested plants had higher H₂O₂ content; amounts of oxalic and malic acids were greater at 750 ppm CO₂ than at 350 ppm CO₂. Plant damage was greater at 350 ppm than at 550 and 750 ppm CO₂. This information will be useful for understanding effects of increased levels of CO₂ on expression of resistance to insect pests to develop strategies to mitigate the effects of climate change.     

The growth of <Emphasis Type="Italic">Chlorella sorokiniana</Emphasis> as influenced by CO<Subscript>2</Subscript>, light,and flue gases

In order to achieve recognition as environmentally friendly production, flue gases should be used as a CO₂ source for growing the microalgae Chlorella sorokiniana when used for hydrogen production. Flue gases from a waste incinerator and from a silicomanganese smelter were used. Before testing the flue gases, the algae were grown in a laboratory at 0.04, 1.3, 5.9, and 11.0 % (v/v) pure CO₂ gas mixed with fresh air. After 5 days of growth, the dry biomass per liter algal culture reached its maximum at 6.1 % CO₂. A second experiment was conducted in the laboratory at 6.2 % CO₂ at photon flux densities (PFD) of 100, 230, and 320 μmol photons m^?2 s^?1. After 4 days of growth, increasing the PFD increased the biomass production by 67 and 108 % at the two highest PFD levels, as compared with the lowest PFD. A bioreactor system containing nine daylight-exposed tubes and nine artificial light-exposed tubes was installed on the roof of the waste incinerator. The effect of undiluted flue gas (10.7 % CO₂, 35.8 ppm NO _x , and 38.6 ppm SO₂), flue gas diluted with fresh air to give 4.2 % CO₂ concentration, and 5.0 % pure CO₂ gas was studied in daylight (21.4?±?9.6 mol photons m^?2 day^?1 PAR, day length 12.0 h) and at 135 μmol photons m^?2 s^?1 artificial light given 24 h day^?1 (11.7?±?0.0 mol photons m^?2 day^?1 PAR). After 4 days’ growth, the biomass production was the same in the two flue gas concentrations and the 5 % pure CO₂ gas control. The biomass production was also the same in daylight and artificial light, which meant that, in artificial light, the light use efficiency was about twice that of daylight. The starch concentration of the algae was unaffected by the light level and CO₂ concentration in the laboratory experiments (2.5–4.0 % of the dry weight). The flue gas concentration had no effect on starch concentration, while the starch concentration increased from about 1.5 % to about 6.0 % when the light source changed from artificial light to daylight. The flue gas from the silicomanganese smelter was characterized by a high CO₂ concentration (about 17 % v/v), low oxygen concentration (about 4 %), about 100 ppm NO _x , and 1 ppm SO₂. The biomass production using flue gas significantly increased as compared with about 5 % pure CO₂ gas, which was similar to the biomass produced at a CO₂ concentration of 10–20 % mixed with N₂. Thus, the enhanced biomass production seemed to be related to the low oxygen concentration rather than to the very high CO₂ concentration.     

Effects of elevated CO2 and temperature on the growth,elemental composition,and cell size of two marine diatoms: potential implications of global climate change

Two pennate diatoms, Amphora coffeaeformis and Nitzschia ovalis, were used to evaluate potential responses to the future CO₂ and temperature increases with respect to cell-specific growth rate, elemental composition, size, population growth rate, and carrying capacity. Diatoms were subjected to four different treatments over a 2 week period (approximately 4 generations): a control (28°C and present-day CO₂, ~400 ppm), high CO₂ (28°C with high CO₂, ~750 ppm), high temperature (31°C and present-day CO₂, ~400 ppm), and greenhouse-effect treatment (31°C with high CO₂, ~750 ppm). The results indicated that both the cell-specific growth rates and the carrying capacity of A. coffeaeformis decreased at the higher temperature treatment, whereas N. ovalis did not differ among all treatments. No significant difference was found in either species’ elemental cell composition, but higher C:N and C:P ratios were observed for A. coffeaeformis and N. ovalis, respectively, in high CO₂ and greenhouse-effect treatments. Smaller cell sizes were observed for both species under the greenhouse-effect treatment, a phenomenon that could alter benthic food webs in the future.     

Suitability of the alkalistable carbonic anhydrase from a polyextremophilic bacterium <Emphasis Type="Italic">Aeribacillus pallidus</Emphasis> TSHB1 in biomimetic carbon sequestration

Carbonic anhydrase (CA) was produced from the polyextremophilic (halotolerant, moderately thermophilic and alkaliphilic) bacterium Aeribacillus pallidus TSHB1 isolated from water and sediment samples of Choti Anhoni hot spring of Pipariya, Madhya Pradesh (India), is being reported to be suitable for carbon sequestration. Growth and CA production were inhibited at higher CO₂ concentration (5–10 %). Under optimized culture variables (tryptone 0.8 %, yeast extract 0.08 %, glucose 1 %, micronutrient solution 1 %, inoculums size 1.10 %, agitation 200 at pH 8, and temperature 55 °C), 3.7-fold higher CA production was attained than that under unoptimized conditions. The zymogram analysis of the partially purified CA revealed an activity band corresponding to 32 kDa. The enzyme is stable in the pH range between 8.0 and 11.0 with T _1/2 of 40, 15, and 8 min at 60, 70, and 80 °C, respectively. The CA of A. pallidus displayed a marked enhancement in the rate of CaCO₃ precipitation from aqueous CO₂. The CA-aided formation of CaCO₃ was 42.5 mg mg^?1 protein. Scanning electron microscopy revealed the formation of rhomboid calcite crystals. This is the first report on the production and applicability of CA from the polyextremophilic A. pallidus in carbon sequestration.     

Impact of Different Carbon Dioxide Concentrations in the Olfactory Response of Sipha flava (Hemiptera: Aphididae) and its Predators

The increasing level CO₂ may altered host plant physiology and hence affect the foraging behavior of herbivore insects and predator. Hence, the aim of this study was provides evidence that host plants grown at different levels of CO₂ can alter the choice behavior of aphid, Sipha flava and their natural enemies, Cycloneda sanguinea and Diomus seminulus. The plant used was Pennisetum purpureum, cultivar Cameron Piracicaba growing in greenhouse (mean value of CO₂?=?440 ppm), climatic chamber with constant value of CO₂?=?500 ppm and climatic chamber with fluctuating CO₂ (mean value?=?368 ppm). A glass Y-shape olfactometer was used to verify the insects responses towards elephant grass plants cultivated under different conditions. The aphids were statistically more attracted by plants grown with constant CO₂ level (500 ppm) than by plants grown with fluctuating CO₂ level or plants grown in greenhouse. There was no difference in S. flava preference to non-infested versus infested plants by conspecifics. The predator C. sanguinea did not show difference between plants grown with constant CO₂ level and infested or not with S. flava. However, the predator D. seminulus showed higher preference to plants grown with constant CO₂ level and infested with S. flava. This study showed that the response of S. flava and its predators were affected by plants grown under different levels of CO₂.     

Decreased Percentages of the Peripheral Blood T-Cell Subsets and the Serum IL-2 Contents in Chickens Fed on Diets Excess in Fluorine

Three hundred 1-day-old Avian broilers were divided into four groups and fed on control diet (F 23 ppm) and high-fluorine diets (400 ppm, high-fluorine group I; 800 ppm, high-fluorine group II; 1,200 ppm, high-fluorine group III) for 42 days (n?=?75/group). The percentages of CD ₄ ⁺ and CD ₈ ⁺ T cells were decreased in three high-fluorine groups when compared with those of control group. Meanwhile, the CD ₄ ⁺ /CD ₈ ⁺ ratio were lower in high-fluorine group II at 28 days of age and in high-fluorine group III at 42 days of age than in control group. Also, the serum interleukin-2 (IL-2) contents were decreased in three high-fluorine groups when compared with those of control group. Histopathologically, the thymus became hypocellular in three high-fluorine groups. It was concluded that dietary fluorine excess (400~1,200 ppm) reduced the percentages of T-lymphocyte subsets and the serum IL-2 contents, and cellular immune function could be affected in chickens.     

Effect of Vanadium on the Subset and Proliferation of Peripheral Blood T Cells, and Serum Interleukin-2 Content in Broilers

The purpose of this 42-day study was to investigate the effects of dietary excess vanadium on immune function by determining changes of the subsets and proliferation function of peripheral blood T cells. Four hundred twenty 1-day-old avian broilers were divided into six groups and fed on a corn–soybean basal diet as control diet or the same diet amended to contain 5, 15, 30, 45, and 60 ppm vanadium supplied as ammonium metavanadate. In comparison with those of the control group, the percentages of CD ₃ ⁺ , CD ₃ ⁺ CD ₄ ⁺ , and CD ₃ ⁺ CD ₈ ⁺ were decreased in 45 and 60 ppm groups from 14 to 42 days of age, and the percentages of CD ₃ ⁺ and CD ₃ ⁺ CD ₄ ⁺ were increased in 5 ppm group at 42 days of age. The CD ₄ ⁺ /CD ₈ ⁺ ratio was increased in 45 and 60 ppm groups at 28 days of age. Meanwhile, the proliferation function of peripheral blood T cell were decreased in 30, 45, and 60 ppm groups from 14 to 42 days of age. Also, the serum interleukin-2 contents were decreased in 45 and 60 ppm groups from 14 to 42 days of age and increased in 5 ppm group at 28 days of age. Histopathologically, hypocellularity appeared in the thymus in 45 and 60 ppm groups. It was concluded that dietary vanadium in excess of 30 ppm reduced the percentages of peripheral blood T-cell subsets and the proliferation function and serum interleukin-2 contents. The cellular immune function was finally impaired in broilers.     

Energetic assessment of fixation of CO<Subscript>2</Subscript> and subsequent biofuel production using <Emphasis Type="Italic">B. cereus</Emphasis> SM1 isolated from sewage treatment plant

The ongoing work on global warming resulting from green house gases (GHGs) has led to explore the possibility of bacterial strains which can fix carbon dioxide (CO₂) and can generate value-added products. The present work is an effort in this direction and has carried out an exhaustive batch experiments for the fixation of CO₂ using B. Cereus SM1 isolated from sewage treatment plant (STP). The work has incorporated 5-day batch run for gaseous phase inlet CO₂ concentration of 13 ± 1 % (%v/v). 84.6 (±5.76) % of CO₂ removal was obtained in the gaseous phase at mentioned CO₂ concentration (%v/v). Energetic requirement for CO₂ fixation was assessed by varying Fe[II] ion concentration (0–200 ppm) on the per-day basis. The cell lysate obtained from CO₂ fixation studies (Fe[II] ion = 100 ppm) was analyzed using Fourier transformation infrared spectroscopy (FTIR) and gas chromatography-mass spectroscopy (GC–MS). This analysis confirmed the presence of fatty acids and hydrocarbon as valuable products. The hydrocarbons were found in the range of C₁₁–C₂₂ which is equivalent to light oil. The obtained fatty acids were found in the range of C₁₁–C₁₉. The possibility of fatty acid conversion to biodiesel was explored by carrying out the transesterification reaction. The yield of biodiesel was obtained as 86.5 (±0.048) % under the transesterification reaction conditions. Results of this research work can provide the valuable information in the implementation of biomitigation of CO₂ at real scenario.     

Antifeedant,larvicidal and growth inhibitory activities of fractions from Clerodendrum phlomidis Linn. F. against bhendi fruit borer Earias vittella Fab

Antifeedant, larvicidal and growth inhibitory activities of 12 fractions from chloroform extract of Clerodendrum phlomidis Linn. F. were evaluated against Earias vittella. Among the fractions, fraction 5 showed promising antifeedant activity of 86.94% at 1000 ppm followed by 500 ppm concentration with the least LC₅₀ and LC₉₀ values of 120.15 and 1027.92 ppm, respectively, with significant Chi-square values. Fraction 5 had maximum larvicidal activity of 86.38% at 1000 ppm concentration with the least LC₅₀ and LC₉₀ values of 245.42 and 1010.99 ppm, respectively, with significant Chi-square value of 51.33 (p ≤ 0.05). Fractions 5 and 6 reduced the adult emergence to 0% at 1000 ppm concentration. According to our knowledge, this is the first report of fractions from C. phlomidis for activity against E. vittella. The study clearly suggests that the fraction from C. phlomidis could be used to develop a new botanical formulation to manage economically important pests.     

Coexpression and characterization of the human large-conductance Ca2+-activated K+ channel α + β1 subunits in HEK293 cells

Large-conductance Ca²⁺-activated K⁺ channel is formed by a tetramer of the pore-forming α-subunit and distinct accessory β-subunits (β1–β4) which contribute to BK_Ca channel molecular diversity. Accumulative evidences indicate that not only α-subunit alone but also the α + β subunit complex and/or β-subunit might play an important role in modulating various physiological functions in most mammalian cells. To evaluate the detailed pharmacological and biophysical properties of α + β1 subunit complex or β1-subunit in BK_Ca channel, we established an expression system that reliably coexpress hSloα + β1 subunit complex in HEK293 cells. The coexpression of hSloα + β1 subunit complex was evaluated by western blotting and immunolocalization, and then the single-channel kinetics and pharmacological properties of expressed hSloα + β1 subunit complex were investigated by cell-attached and outside-out patches, respectively. The results in this study showed that the expressed hSloα + β1 subunit complex demonstrated to be fully functional for its typical single-channel traces, Ca²⁺-sensitivity, voltage-dependency, high conductance (151 ± 7 pS), and its pharmacological activation and inhibition.     

Response of Cassava canopy to mid-day pseudo sunrise induced by solar eclipse

Variations in CO₂ concentration over a cassava canopy were measured during a solar eclipse at Thiruvananthapuram, India. The analysis presented attempts to differentiate between the eclipse effect and the possible effect of thick clouds, taking CO₂ as a proxy for photosynthesis. CO₂ and water vapor were measured at a rate of 10 Hz, and radiation at 1 Hz, together with other meteorological parameters. A rapid reduction in CO₂ observed post-peak eclipse, due apparently to intense photosynthesis, appears similar to what happens at daybreak/post-sunrise. The increase in CO₂ (4 ppm) during peak eclipse, with radiation levels falling below the photosynthesis cut-off for cassava, indicates domination of respiration due to the light-limiting conditions.     

Effects of Multi-nutrient Additions on GHG Fluxes in a Temperate Grassland of Northern China

Human activities have substantially enhanced the availability of important nutrient elements such as nitrogen (N), phosphorus (P), and potassium (K) in ecosystems worldwide. However, how the concurrent increase in all of these nutrients will affect greenhouse gas (that is, CO₂, N₂O, CH₄) levels remains unknown. In a temperate steppe of northern China, a 2-year field experiment was conducted to examine the effects of multi-nutrient additions on GHG fluxes from 2009 to 2010. Four levels of annual nutrient loads were mimicked: 0 g NPK (control), 15.5 g P m^?2 and 19.5 g K m^?2 as KH₂PO₄ (PK), 10 g N m^?2 as NH₄NO₃ plus PK (10N + PK), and 20 g N m^?2 plus PK (20N + PK) per year. The results show that multi-nutrient additions led to significant increases in net primary production (NPP) and soil temperature (ST), a significant decrease in soil moisture (SM) in 2010, and no significant changes in other soil parameters. Seasonal patterns differed greatly for different GHG fluxes in response to different nutrient treatments, largely as a result of differences in influential factors. The 10N + PK treatment significantly increased CO₂ uptake, whereas the 20N + PK treatment significantly decreased CO₂ uptake. The application of P and K without additional N significantly enhanced CH₄ uptake, whereas the two N + PK treatments significantly enhanced N₂O emissions. Significant positive, linear relationships were found between cumulative CO₂ uptake and soil total nitrogen (TN), microbial biomass carbon, and microbial biomass nitrogen, whereas significant negative, linear relationships were found with NPP, SM, and the C/N ratio. Significant positive, linear relationships were found between cumulative N₂O emission and ST, TN, NPP, and total organic carbon, whereas no relationships were found between cumulative CH₄ uptake and any soil parameters. CO₂ flux was related to N₂O flux temporally, to a certain extent, for all the treatments. In the control, N₂O flux showed a negative, linear relationship with CH₄ flux, whereas no regular relationships were detected between CO₂ and CH₄ fluxes in any treatment. Our findings imply that increasing nutrient deposition will change the magnitude, patterns, and relationships among GHG uptakes and emissions in the future.     

Does plant size affect growth responses to water availability at glacial,modern and future CO<Subscript>2</Subscript> concentrations?

Plant responses to carbon (C) and water availability are strongly connected. Thus, we can learn much about the responses of modern plants to rising atmospheric carbon dioxide (CO₂) by studying their performance under a range of carbon and water availabilities, including very low CO₂ as in past glacial periods. We hypothesized that, especially in shallow soils, the positive effects of high CO₂ and the negative effects of low CO₂ on growth response to drought are moderated by plant size-driven feedbacks through transpiration and soil water depletion. We grew two temperate annual C₃ species, Avena sativa and Chenopodium album, in glacial (180 ppm), modern (400 ppm) and future (700 ppm) CO₂ levels and five soil water regimes in climate chambers. In both species, low CO₂ resulted in a much lower relative growth rate, biomass and total leaf area than at ambient CO₂ with higher water availability, but this difference disappeared steadily towards severe drought conditions. Elevated CO₂ increased relative growth rate, plant biomass and total leaf area of both species slightly compared with ambient CO₂. These results were especially pronounced under drought. Our results support the hypothesis that, in annuals, plant size modulates the negative drought effect at low CO₂. However, plant size-mediated effects of high CO₂ on growth response to drought were inconclusive. Further experiments should reveal the interactive effects of CO₂ and water regimes in environments closer to a field setting, both in shallow and in deep soils with unconstrained rooting, as well as in mixed communities.     

Rheological Properties of Aqueous Dispersions of Xanthan Gum Containing Different Chloride Salts Are Impacted by both Sizes and Net Electric Charges of the Cations

Xanthan gum (XG) is one of the most effective thickener agents used worldwide. In foods products, one of the factors affecting its physical properties is the ionic strength of the medium. Though it is well known that XG rheological properties in aqueous media depend on both type and concentration of electrolytes, correlations between such dispersion properties and molecular aspects of dispersed XG chains are still to be more deeply studied. Thus, in the present study, aqueous XG dispersions [200 mg?(100 mL)^?1] added of Na, K, Mg or Ca chlorides (ionic strength 50 mM or 100 mM) were rheologically characterized, and the corresponding results were explained based on different physicochemical analyses. Comparing to the control (unsalted XG dispersion), KCl and CaCl₂ tended to produce a more drastic decrease of apparent viscosities of XG dispersions than NaCl and MgCl₂. In dynamic-oscillatory assays, the predominance of elastic character over viscous character was more evident for XG dispersions containing KCl and CaCl₂, in particular at frequencies > 0.1 Hz. XG dispersions containing KCl or CaCl₂ also presented smaller pH and |ζ-potentials| values, as well as greater densities and average hydrodynamic diameters of dispersed XG chains, when compared to respective counterparts containing NaCl or MgCl₂. As the decreasing order of the cations radii is K⁺?>?Ca²⁺ ≈ Na⁺?>?Mg²⁺, our results allowed deducing that not only the net electric charges of the cations, but also their sizes, should be considered when analyzing the effect of chloride salts on rheological properties of XG aqueous dispersions, according to the desired for this hydrocolloid (weak thickener, strong thickener or pro-gelling agent).     

Do changes in flood pulse duration disturb soil carbon dioxide emissions in semi-arid floodplains?

In semi-arid floodplains the average times between floods have been cited to drive metabolic and biogeochemical responses during the subsequent flooding pulse. However, the interaction effects of flood pulse duration and the length of time between floods on the carbon budget are not well understood. Using field experiments, flood pulses—dry cycles were simulated (SF plots—short flood/dry cycles: 15 flood days + 7 dry + 15 flood and LF plots—long flood/dry cycles: 21 flood + 14 dry + 21 flood) in a semi-arid floodplain in Central Spain, in order to study the effects on soil CO₂ emissions. Differences on soil water content among SF, LF and control plots were statistically significant throughout the experiment (p < 0.01). Soil CO₂ emission rates during drying time were significantly related with the duration of previous flooding and inter-flooding intervals (R ² = 0.52–0.64, p = 0.03). During the first stage of desiccation, the high soil water content appears to limit aerobic metabolism. Soil respiration rates similar to those of control plots measurements occurred 1–2 weeks later. Then, soil respiration increased to a maximum rate which was delayed 5–8 weeks, as high soil water content limited microbial activity. While more than 7 days of inundation promoted denitrification, organic nutrients supplied by flood water increased 1% soil respiration during drying. Differences between SF and LF plots in soil CO₂ emissions only appeared after floodplain soil had been subjected to two consecutive flood-dry cycles; 70 days after the second inundation ended, CO₂ fluxes achieved similar values in all treatments. Daily soil CO₂ emission rates during the entire study period (117 days) were comparable, independently of the flood duration and the time between floods (75.76 ± 1.59 and 77.94 ± 0.45 mmol CO₂ m^?2 day^?1, in SF and LF, respectively). Flood disturbance affects site-specific microbial processes, but only during very short time periods. The mechanism by which soil microbial communities cope or adapt to new conditions needs to be reassessed in future research in order to determine the long-term effects of hydrological changes in the soil carbon balance of semi-arid floodplains.