Photosynthetic limitation by CO<Subscript>2</Subscript> diffusion in drought stressed orange leaves on three rootstocks

Photosynthetic limitations under moderate water deficit were evaluated in ‘Valência’ orange trees grafted on three different rootstocks, in pots. Net CO₂ assimilation rate (A _N), stomatal conductance (g _s), and photosystem II (PS II) operating efficiency ( ) in response to changing intercellular CO₂ partial pressure (C _i) were analyzed under controlled conditions. Drought decreased A _N and g _s, whereas remained unchanged. This resulted in a higher ratio between electron transport rate (ETR) and gross CO₂ assimilation rate (A _G). Since the comparison of A _N–C _i gas exchange curves can lead to incorrect conclusions, a normalization of C _i values () of stressed leaves was applied. Then, the relationship established for irrigated trees between the ETR/A _G ratio and C _i was used to estimate the from ETR/A _G ratios measured under water stress. The response of A _N to suggests that the CO₂ diffusional restriction is the main factor that limits photosynthesis in orange leaves under moderate water deficit.     

DFT study of CO<Subscript>2</Subscript> and H<Subscript>2</Subscript>O co-adsorption on carbon models of coal surface

The moisture content of coal affects the adsorption capacity of CO₂ on the coal surface. Since the hydrogen bonds are formed between H₂O and oxygen functional group, the H₂O cluster more easily adsorbs on the coal micropore than CO₂ molecule. The coal micropores are occupied by H₂O molecules that cannot provide extra space for CO₂ adsorption, which may leads to the reduction of CO₂ adsorption capacity. However, without considering factors of micropore and oxygen functional groups, the co-adsorption mechanisms of CO₂ and adsorbed H₂O molecule are not clear. Density functional theory (DFT) calculations were performed to elucidate the effect of adsorbed H₂O to CO₂ adsorption. This study reports some typical coal-H₂O···CO₂ complexes, along with a detailed analysis of the geometry, energy, electrostatic potential (ESP), atoms in molecules (AIM), reduced density gradient (RDG), and energy decomposition analysis (EDA). The results show that H₂O molecule can more stably adsorb on the aromatic ring surface than CO₂ molecule, and the absolute values of local ESP maximum and minimum of H₂O cluster are greater than CO₂. AIM analysis shows a detailed interaction path and strength between atoms in CO₂ and H₂O, and RDG analysis shows that the interactions among CO₂, H₂O, and coal model belong to weak van der Waals force. EDA indicates that electrostatic and long-range dispersion terms play a primary role in the co-adsorption of CO₂ and H₂O. According to the DFT calculated results without considering micropore structure and functional group, it is shown that the adsorbed H₂O can promote CO₂ adsorption on the coal surface. These results demonstrate that the micropore factor plays a dominant role in affecting CO₂ adsorption capacity, the attractive interaction of adsorbed H₂O to CO₂ makes little contribution.     

Study of Plasma Induced Chemistry by DC Discharges in CO<Subscript>2</Subscript>/N<Subscript>2</Subscript>/H<Subscript>2</Subscript>O Mixtures Above a Water Surface

The chemistry induced by atmospheric pressure DC discharges above a water surface in CO(2)/N(2)/H(2)O mixtures was investigated. The gaseous mixtures studied represent a model prebiotic atmosphere of the Earth. The most remarkable changes in the chemical composition of the treated gas were the decomposition of CO(2) and the production of CO. The concentration of CO increased logarithmically with the increasing input energy density and an increasing initial concentration of CO(2) in the gas. The highest achieved concentration of CO was 4.0 +/- 0.6 vol. %. The production of CO was crucial for the synthesis of organic species, since reactions of CO with some reactive species generated in the plasma, e. g. H* or N* radicals, were probably the starting point in this synthesis. The presence of organic species (including the tentative identification of some amino acids) was demonstrated by the analysis of solid and liquid samples by high-performance liquid chromatography, infrared absorption spectroscopy and proton-transfer-reaction mass spectrometry. Formation of organic species in a completely inorganic CO(2)/N(2)/H(2)O atmosphere is a significant finding for the theory of the origins of life.     

Elevated CO<Subscript>2</Subscript> mitigates the adverse effects of drought on daytime net ecosystem CO<Subscript>2</Subscript> exchange and photosynthesis in a Florida scrub-oak ecosystem

Drought is a normal, recurrent feature of climate. In order to understand the potential effect of increasing atmospheric CO₂ concentration (C _a) on ecosystems, it is essential to determine the combined effects of drought and elevated C _a (EC) under field conditions. A severe drought occurred in Central Florida in 1998 when precipitation was 88 % less than the average between 1984 and 2002. We determined daytime net ecosystem CO₂ exchange (NEE) before, during, and after the drought in the Florida scrub-oak ecosystem exposed to doubled C _a in open-top chamber since May 1996. We measured diurnal leaf net photosynthetic rate (P _N) of Quercus myrtifolia Willd, the dominant species, during and after the drought. Drought caused a midday depression in NEE and P _N at ambient CO₂ concentration (AC) and EC. EC mitigated the midday depression in NEE by about 60 % compared to AC and the effect of EC on leaf P _N was similar to its effect on NEE. Growth in EC lowered the sensitivity of NEE to air vapor pressure deficit under drought. Thus EC would help the scrub-oak ecosystem to survive the consequences of the effects of rising atmospheric CO₂ on climate change, including increased frequency of drought, while simultaneously sequestering more anthropogenic carbon.     

Effects of exogenous H<Subscript>2</Subscript>O<Subscript>2</Subscript> on the content of endogenous H<Subscript>2</Subscript>O<Subscript>2</Subscript>, activities of catalase and hydrolases,and cell ultrastructure in tobacco leaves

It was shown that tobacco leaf treatment with 100 mM H₂O₂ increased their content of endogenous H₂O₂ and activities of catalase and hydrolases (acid phosphatase, proteases, and RNase) and also caused various changes in the cell structure. In this case, programmed cell death (PCD) occurred in some cells, which was observed as chromatin condensation, cytoplasm collapse, etc. In the meantime, many cells displayed organelle activation rather than PCD. It is suggested that cells that undergo H₂O₂-dependent PCD release signaling molecules inducing protective mechanisms against oxidative stress in neighboring cells not exhibiting PCD.     

An estimation of CO<Subscript>2</Subscript> fixation capacity in mangrove forest using two methods of CO<Subscript>2</Subscript> gas exchange and growth curve analysis

In many coastal areas of South-East Asia, attempts have been made to revive coastal ecosystem by initiating projects that encourage planting of mangrove trees. Compared to the terrestrial trees, mangrove trees possess a higher carbon fixation capacity. It becomes a very significant option for clean development mechanism (CDM) program. However, a reliable method to estimate CO₂ fixation capacity of mangrove trees has not been established. Acknowledging the above fact, we decided to set up an estimation method for the CDM program, using gas exchange analysis to estimate mangrove productivity, we put into consideration the net CO₂ fixation of reforested Kandelia candel (5-, 10-, and 15-year-old stand). This was estimated by gas exchange analysis and growth curve analysis. In growth curve analysis, we drew a growth curve of a single stand using data of above- and below-ground biomass. In the gas exchange analysis, we calculated CO₂ fixation capacity by (1) measuring respiration rate of each organ of stand and calculating respiratory CO₂ emission from above- to below-ground biomass. (2) Measuring the single-leaf photosynthetic rate in response to light intensity and calculating the photosynthetic CO₂ absorption. (3) We also developed a model for the diurnal changes in temperature, and monthly averages based on one-day estimation of CO₂ absorption and emission, which we corrected by this model in order to estimate the net CO₂ fixation capacity in response to temperature. Comparing the biomass accumulation of the two methods constructed for the same forest, the above-ground biomass accumulation of 10-year-old forest (34.3 ton ha⁻¹ yr⁻¹) estimated by gas exchange analysis was closely compared to those of growth curve analysis (26.6 ton ha⁻¹ yr⁻¹), suggesting that the gas exchange analysis was capable of estimating mangrove productivity. The validity of the estimated CO₂ fixation capacity by the gas exchange analysis and the growth curve analysis was also discussed.     

Hydrothermal Stability of Adenine Under Controlled Fugacities of N<Subscript>2</Subscript>, CO<Subscript>2</Subscript> and H<Subscript>2</Subscript>

An experimental study has been carried out on the stability of adenine (one of the five nucleic acid bases) under hydrothermal conditions. The experiments were performed in sealed autoclaves at 300 degrees C under fugacities of CO(2), N(2) and H(2) supposedly representative of those in marine hydrothermal systems on the early Earth. The composition of the gas phase was obtained from the degradation of oxalic acid, sodium nitrite and ammonium chloride, and the oxidation of metallic iron. The results of the experiments indicate that after 200 h, adenine is still present in detectable concentration in the aqueous phase. In fact, the concentration of adenine does not seem to be decreasing after approximately 24 h, which suggests that an equilibrium state may have been established with the inorganic constituents of the hydrothermal fluid. Such a conclusion is corroborated by independent thermodynamic calculations.     

Components of CO<Subscript>2</Subscript> exchange in leaves of C<Subscript>3</Subscript> species with different ability of starch accumulation

Using a radiogasometric method the rates of photorespiratory and respiratory decarboxylations of primary and stored photosynthates in the leaves of two groups of C₃ species, differing in the ability of starch accumulation, were determined. One group included starch-accumulating (SA) species with rates of starch synthesis on the average 38 % the rate of photosynthesis [Solanum tuberosum L., Arabidopsis thaliana (L.) Heynh, Helianthus annuus L., and Plantago lanceolata L.]. The second group represented starch-deficient (SD) species with rates of starch synthesis less than 8 % the rate of photosynthesis (Secale cereale L., Triticum aestivum L., Hordeum vulgare L., and Poa trivialis L.). In SA species the rate of respiration in the dark was significantly higher than in SD species. No differences were found in the rates of photosynthesis, photorespiration, and respiration under irradiation. Thus, the degree of inhibition of respiration by irradiation was in SA species higher than in SD species. It is concluded that starch does not provide substrates for respiratory and photorespiratory decarboxylations in irradiated photosynthesizing leaves.     

Molecular properties of metal difluorides and their interactions with CO<Subscript>2</Subscript> and H<Subscript>2</Subscript>O molecules: a DFT investigation

A computational study of metal difluorides (MF₂; M = Ca to Zn) and their interactions with carbon dioxide and water molecules was performed. The structural parameter values obtained and the results of AIM analysis and energy decomposition analysis indicated that the Ca–F bond is weaker and less ionic than the bonds in the transition metal difluorides. A deformation density plot revealed the stablizing influence of the Jahn–Teller effect in nonlinear MF₂ molecules (e.g., where M= Sc, Ti, Cr). An anaysis of the metal K-edge peaks of the difluorides showed that shifts in the edge energy were due to the combined effects of the ionicity, effective nuclear charge, and the spin state of the metal. The interactions of CO₂ with ScF₂ (Scc3 geometry) and TiF₂ (Tic2 geometry) caused CO₂ to shift from its usual linear geometry to a bent geometry (η²(C=O) binding mode), while it retained its linear geometry (η¹(O) binding mode) when it interacted with the other metal difluorides. Energy decomposition analysis showed that, among the various geometries considered, the Scc3 and Tic2 geometries possessed the highest interaction energies and orbital interaction energies. Heavier transition metal difluorides showed stronger affinities for H₂O, whereas the lighter transition metal (Sc and Ti) difluorides preferred CO₂. Overall, the results of this study suggest that fluorides of lighter transition metals with partially filled d orbitals (e.g., Sc and Ti) could be used for CO₂ capture under moist conditions.

Open image in new window

Graphical abstract Interaction of metal difluorides with carbon dioxide and water

     

Abscisic acid-induced apoplastic H<Subscript>2</Subscript>O<Subscript>2</Subscript> accumulation up-regulates the activities of chloroplastic and cytosolic antioxidant enzymes in maize leaves

The histochemical and cytochemical localization of abscisic acid (ABA)-induced H₂O₂ production in leaves of maize (Zea mays L.) plants were examined, using 3,3-diaminobenzidine (DAB) and CeCl₃ staining, respectively, and the relationship between ABA-induced H₂O₂ production and ABA-induced subcellular activities of antioxidant enzymes was studied. H₂O₂ generated in response to ABA treatment was detected within 0.5 h in major veins of the leaves and maximized at about 2–4 h. In mesophyll and bundle sheath cells, ABA-induced H₂O₂ accumulation was observed only in apoplast, and the greatest accumulation occurred in the walls of mesophyll cells facing large intercellular spaces. Meanwhile, ABA treatment led to a significant increase in the activities of the leaf chloroplastic and cytosolic antioxidant enzymes superoxide dismutase (SOD), ascorbate peroxidase (APX) and glutathione reductase (GR), and pretreatment with the NADPH oxidase inhibitor diphenyleneiodonium (DPI), the O ₂ ⁻ scavenger Tiron and the H₂O₂ scavenger dimethylthiourea (DMTU) almost completely arrested the increase in the activities of these antioxidant enzymes. Our results indicate that the accumulation of apoplastic H₂O₂ is involved in the induction of the chloroplastic and cytosolic antioxidant enzymes. Moreover, an oxidative stress induced by paraquat (PQ), which generates O ₂ ⁻ and then H₂O₂ in chloroplasts, also up-regulated the activities of the chloroplastic and cytosolic antioxidant enzymes, and the up-regulation was blocked by the pretreatment with Tiron and DMTU. These data suggest that H₂O₂ produced at a specific cellular site could coordinate the activities of antioxidant enzymes in different subcellular compartments.     

Photosynthetic CO<Subscript>2</Subscript> uptake in seedlings of two tropical tree species exposed to oscillating elevated concentrations of CO<Subscript>2</Subscript>

Do short-term fluctuations in CO₂ concentrations at elevated CO₂ levels affect net CO₂ uptake rates of plants? When exposed to 600 μl CO₂ l^?1, net CO₂ uptake rates in shoots or leaves of seedlings of two tropical C₃ tree species, teak (Tectona grandis L. f.) and barrigon [Pseudobombax septenatum (Jacq.) Dug.], increased by 28 and 52% respectively. In the presence of oscillations with half-cycles of 20 s, amplitude of ca. 170 μl CO₂ l^?1 and mean of 600 μl CO₂ l^?1, the stimulation in net CO₂ uptake by the two species was reduced to 19 and 36%, respectively, i.e. the CO₂ stimulation in photosynthesis associated with a change in exposure from 370 to 600 μl CO₂ l^?1 was reduced by a third in both species. Similar reductions in CO₂-stimulated net CO₂ uptake were observed in T. grandis exposed to 40-s oscillations. Rates of CO₂ efflux in the dark by whole shoots of T. grandis decreased by 4.8% upon exposure of plants grown at 370 μl CO₂ l^?1 to 600 μl CO₂ l^?1. The potential implications of the observations on CO₂ oscillations and dark respiration are discussed in the context of free-air CO₂ enrichment (FACE) systems in which short-term fluctuations of CO₂ concentration are a common feature.     

Photosynthetic sunfleck utilization potential of understory saplings growing under elevated CO<Subscript>2</Subscript> in FACE

Few studies have evaluated elevated CO₂ responses of trees in variable light despite its prevalence in forest understories and its potential importance for sapling survival. We studied two shade-tolerant species (Acer rubrum, Cornus florida) and two shade-intolerant species (Liquidambar styraciflua, Liriodendron tulipifera) growing in the understory of a Pinus taeda plantation under ambient and ambient+200 ppm CO₂ in a free air carbon enrichment (FACE) experiment. Photosynthetic and stomatal responses to artificial changes in light intensity were measured on saplings to determine rates of induction gain under saturating light and induction loss under shade. We expected that growth in elevated CO₂ would alter photosynthetic responses to variable light in these understory saplings. The results showed that elevated CO₂ caused the expected enhancement in steady-state photosynthesis in both high and low light, but did not affect overall stomatal conductance or rates of induction gain in the four species. Induction loss after relatively short shade periods (<6 min) was slower in trees grown in elevated CO₂ than in trees grown in ambient CO₂ despite similar decreases in stomatal conductance. As a result leaves grown in elevated CO₂ that maintained induction well in shade had higher carbon gain during subsequent light flecks than was expected from steady-state light response measurements. Thus, when frequent sunflecks maintain stomatal conductance and photosynthetic induction during the day, enhancements of long-term carbon gain by elevated CO₂ could be underestimated by steady-state photosynthetic measures. With respect to species differences, both a tolerant, A. rubrum, and an intolerant species, L. tulipifera, showed rapid induction gain, but A. rubrum also lost induction rapidly (c. 12 min) in shade. These results, as well as those from independent studies in the literature, show that induction dynamics are not closely related to species shade tolerance. Therefore, it cannot be concluded that shade-tolerant species necessarily induce faster in the variable light conditions common in understories. Although our study is the first to examine dynamic photosynthetic responses to variable light in contrasting species in elevated CO₂, studies on ecologically diverse species will be required to establish whether shade-tolerant and -intolerant species show different photosynthetic responses in elevated CO₂ during sunflecks. We conclude that elevated CO₂ affects dynamic gas exchange most strongly via photosynthetic enhancement during induction as well as in the steady state. Received: 1 April 1999 / Accepted: 16 August 1999     

Decades-long effects of high CO<Subscript>2</Subscript> concentration on soil nitrogen dynamics at a natural CO<Subscript>2</Subscript> spring

The effects of high atmospheric CO₂ concentration ([CO₂]) on ecosystem processes have been explored using temporal facilities such as open-top-chambers and free-air CO₂ enrichment. However, the effects of high [CO₂] on soil properties takes decades and may not be captured by short-term experiments. Natural CO₂ springs provide a unique opportunity to study the long-term effects of high [CO₂]. In this study, we investigated soil properties at a natural CO₂ spring. We found that the amounts of total carbon (C) and nitrogen (N) stored in the soil at the high [CO₂] site exceeded those in the reference site by 60 and 30%, respectively. The effects of high [CO₂] were large in the upper slope position where the canopy openness was high and plants grew faster, but no effects were detected in the lowest position where the canopy openness was lower (half of that at the upper slope position). In contrast, effects of high [CO₂] on soil N dynamics, such as N mineralization and nitrification rates, did not exhibit a slope gradient. This suggests that effects of high [CO₂] differed among soil stoichiometric characteristics and N dynamics. These complicated effects of high [CO₂] imply that the future effects of high [CO₂] on ecosystems could vary widely in conjunction with environmental conditions such as light availability and/or topographic conditions.     

Comparison of CO<Subscript>2</Subscript> and H<Subscript>2</Subscript>O fluxes over grassland vegetations measured by the eddy-covariance technique and by open system chamber

Measurements of CO₂ and H₂O fluxes were carried out using two different techniques—eddy-covariance (EC) and open system gas exchange chamber (OC)—during two-years’ period (2003–2004) at three different grassland sites. OC measurements were made during fourteen measurement campaigns. We found good agreement between the OC and EC CO₂ flux values (n = 63, r ² = 0.5323, OC F_CO2 = −0.6408+0.9508 EC F_CO2). The OC F_H2O values were consistently lower than those measured by the EC technique, probably caused by the air stream difference inside and outside the chamber. Adjusting flow rate within the chamber to the natural conditions would be necessary in future OC measurements. In comparison with EC, the OC proved to be a good tool for gas exchange measurements in grassland ecosystems.     

Cross-talks between Ca<Superscript>2+</Superscript>/CaM and H<Subscript>2</Subscript>O<Subscript>2</Subscript> in abscisic acid-induced antioxidant defense in leaves of maize plants exposed to water stress

Here we examined whether Ca²⁺/Calmodulin (CaM) is involved in abscisic acid (ABA)-induced antioxidant defense and the possible relationship between CaM and H₂O₂ in ABA signaling in leaves of maize (Zea mays L.) plants exposed to water stress. An ABA-deficient mutant vp5 and its wild type were used for the experimentation. We found that water stress enhanced significantly the contents of CaM and H₂O₂, and the activities of chloroplastic and cytosolic superoxide dismutase (SOD), ascorbate peroxidase (APX) and glutathione reductase (GR), and the gene expressions of the CaM1, cAPX, GR1 and SOD4 in leaves of wild-type maize. However, the increases mentioned above were almost arrested in vp5 plants and in the wild-type plants pretreated with ABA biosynthesis inhibitor tungstate (T), suggesting that ABA is required for water stress-induced H₂O₂ production, the enhancement of CaM content and antioxidant defense. Besides, we showed that the up-regulation of water stress-induced antioxidant defense was almost completely blocked by pretreatment with Ca²⁺ inhibitors, CaM antagonists and reactive oxygen (ROS) manipulators. Moreover, the analysis of time course of CaM and H₂O₂ production under water stress showed that the increase in CaM content preceded that of H₂O₂. These results suggested that Ca²⁺/CaM and H₂O₂ were involved in the ABA-induced antioxidant defense under water stress, and the increases of Ca²⁺/CaM contents triggered H₂O₂ production, which inversely affected the contents of CaM. Thus, a cross-talk between Ca²⁺/CaM and H₂O₂ may play a pivotal role in the ABA signaling.     

The effects of elevated atmospheric CO<Subscript>2</Subscript> and nitrogen amendments on subsurface CO<Subscript>2</Subscript> production and concentration dynamics in a maturing pine forest

Profiles of subsurface soil CO₂ concentration, soil temperature, and soil moisture, and throughfall were measured continuously during the years 2005 and 2006 in 16 locations at the free air CO₂ enrichment facility situated within a temperate loblolly pine (Pinus taeda L.) stand. Sampling at these locations followed a 4 by 4 replicated experimental design comprised of two atmospheric CO₂ concentration levels (ambient [CO₂]^a, ambient + 200 ppmv, [CO₂]^e) and two soil nitrogen (N) deposition levels (ambient, ambient + fertilization at 11.2 g_N m⁻² year⁻¹). The combination of these measurements permitted indirect estimation of belowground CO₂ production and flux profiles in the mineral soil. Adjacent to the soil CO₂ profiles, direct (chamber-based) measurements of CO₂ fluxes from the soil–litter complex were simultaneously conducted using the automated carbon efflux system. Based on the measured soil CO₂ profiles, neither [CO₂]^e nor N fertilization had a statistically significant effect on seasonal soil CO₂, CO₂ production, and effluxes from the mineral soil over the study period. Soil moisture and temperature had different effects on CO₂ concentration depending on the depth. Variations in CO₂ were mostly explained by soil temperature at deeper soil layers, while water content was an important driver at the surface (within the first 10 cm), where CO₂ pulses were induced by rainfall events. The soil effluxes were equal to the CO₂ production for most of the time, suggesting that the site reached near steady-state conditions. The fluxes estimated from the CO₂ profiles were highly correlated to the direct measurements when the soil was neither very dry nor very wet. This suggests that a better parameterization of the soil CO₂ diffusivity is required for these soil moisture extremes.     

Intrinsic changes in photosynthetic parameters of carrot leaves under increasing CO<Subscript>2</Subscript> concentrations and soil moisture regimes

A controlled growth chamber experiment was conducted to investigate the short-term water use and photosynthetic responses of 30-d-old carrot seedlings to the combined effects of CO₂ concentration (50–1 050 μmol mol⁻¹) and moisture deficits (−5, −30, −55, and −70 kPa). The photosynthetic response data was fitted to a non-rectangular hyperbola model. The estimated parameters were compared for effects of moisture deficit and elevated CO₂ concentration (EC). The carboxylation efficiency (α) increased in response to mild moisture stress (−30 kPa) under EC when compared to the unstressed control. However, moderate (−55 kPa) and extreme (−70 kPa) moisture deficits reduced α under EC. Maximum net photosynthetic rate (P _Nmax) did not differ between mild water deficit and unstressed controls under EC. Moderate and extreme moisture deficits reduced P _Nmax by nearly 85 % compared to controls. Dark respiration rate (R _D) showed no consistent response to moisture deficit. The CO₂ compensation concentration (Γ) was 324 μmol mol⁻¹ for −75 kPa and ranged 63–93 μmol mol⁻¹ for other moisture regimes. Interaction between moisture deficit and EC was noticed for P _N, ratio of intercellular and ambient CO₂ concentration (C _i/C _a), stomatal conductance (g _s ), and transpiration rate (E). P _N was maximum and C _i/C _a was minimum at −30 kPa moisture deficit and at C _a of 350 μmol mol⁻¹. The g _s and E showed an inverse relationship at all moisture deficit regimes and EC. Water use efficiency (WUE) increased with moisture deficit up to −55 kPa and declined thereafter. EC showed a positive influence towards sustaining P _N and increasing WUE only under mild moisture stress, and no beneficial effects of EC were noticed at moderate or extreme moisture deficits.     

Emissions of CO<Subscript>2</Subscript>, CH<Subscript>4</Subscript> and N<Subscript>2</Subscript>O from undisturbed,drained and mined peatlands in Estonia

The aim of this study is to estimate emissions of greenhouse gases CO₂, CH₄ and N₂O, and the effects of drainage and peat extraction on these processes, in Estonian transitional fens and ombrotrophic bogs. Closed-chamber-based sampling lasted from January to December 2009 in nine peatlands in Estonia, covering areas with different land-use practices: natural (four study sites), drained (six sites), abandoned peat mining (five sites) and active peat mining areas (five sites). Median values of soil CO₂ efflux were 1,509, 1,921, 2,845 and 1,741 kg CO₂-C ha^?1 year^?1 from natural, drained, abandoned and active mining areas, respectively. Emission of CH₄-C (median values) was 85.2, 23.7, 0.07 and 0.12 kg ha^?1 year^?1, and N₂O-N ?0.05, ?0.01, 0.18 and 0.19 kg ha^?1 year^?1, respectively. There were significantly higher emissions of CO₂ and N₂O from abandoned and active peat mining areas, whereas CH₄ emissions were significantly higher in natural and drained areas. Significant Spearman rank correlation was found between soil temperature and CO₂ flux at all sites, and CH₄ flux with high water level at natural and drained areas. Significant increase in CH₄ flux was detected for groundwater levels above 30 cm.     

The relationship between leaf and ecosystem CO<Subscript>2</Subscript> exchanges in a maize field

The relationship between leaf photosynthetic rate (A) in a vegetation canopy and the net ecosystem CO₂ exchange (NEE) over an entire ecosystem is not well understood. The aim of the present study is to assess the coordinated changes in NEE derived with eddy covariance, A measured in leaf cuvette, and their associations in a rainfed maize field. The light response-curves were estimated for the carbon assimilation rate at both the leaf and ecosystem scales. NEE and A synchronically changed throughout the day and were greater around noon and persisted longer during rapid growth periods. The leaf A had a similar pattern of daytime changes in the top, middle, and bottom leaves. Only severe leaf ageing led to a significant decline in the maximum efficiency of photosystem II (PSII) photochemistry. The greater maximum NEE was associated with a higher ecosystem quantum yield. NEE was positively and significantly correlated with the leaf A averaged based on the vertical distribution of leaf area. The finding highlights the feasibility of assessing NEE by leaf CO₂ exchange because of most of experimental data obtained with leaf cuvette methods; and also implies that simultaneously enhancing leaf photosynthetic rate, electron transport rate, net carbon assimilation at whole ecosystem might play a critical role for the enhancement of crop productivity.     

CO<Subscript>2</Subscript> bio-mitigation using microalgae

Microalgae are a group of unicellular or simple multicellular photosynthetic microorganisms that can fix CO(2) efficiently from different sources, including the atmosphere, industrial exhaust gases, and soluble carbonate salts. Combination of CO(2) fixation, biofuel production, and wastewater treatment may provide a very promising alternative to current CO(2) mitigation strategies.