Combined effects of CO2 concentration and nutrient status on the biomass production and nutrient uptake of birch seedlings (Betula pendula)

Birch seedlings (Betula pendula) were grown for four months in a greenhouse at three nutrient levels (fertilization of 0, 100 and 500 kg ha^-1 monthy) and at four CO₂ concentrations (350, 700, 1050 and 1400 ppm). The effect of CO₂ concentration on the biomass production depended on the nutrient status. When mineralization of the soil material was the only source of nutrients (0 kg ha^-1), CO₂ enhancement reduced the biomass production slightly, whereas the highest production increase occurred at a fertilization of 100 kg ha^-1, being over 100% between 350 and 700 ppm CO₂. At 500 kg ha^-1 the production increase was smaller, and the production decreased beyond a CO₂ concentration of 700 ppm. The CO₂ concentration had a slight effect on the biomass distribution, the leaves accounting for the highest proportion at the lowest CO₂ concentration (350 ppm). An increase in nutrient status led to a longer growth period and increased the nutrient concentrations in the plants, but the CO₂ concentration had no effect on the growth rhythm and higher CO₂ reduced the nutrient concentrations.     

Rising CO2, secondary plant metabolism,plant-herbivore interactions and litter decomposition

A brief account is given of the ecological significance of quantitatively important secondary plant compounds, mainly those of a phenolic nature, in herbivory and decomposition. Phenolic compounds accumulate to a greater extent in slow-growing species than in fast-growing ones, particularly when soil conditions (nutrients, water) restrict growth. Two hypotheses to explain the increased concentration of phenolics when soil conditions are unfavorable are presented. The first hypothesis (the carbon supply model of secondary plant metabolism) considers the increased levels of non-structural carbohydrates as the major trigger. The second hypothesis (the amino acid diversion model of secondary plant metabolism) states that increased accumulation of phenolics stems from a decreased use of a common precursor (phenylalanine or tyrosine) for protein synthesis. Current experimental evidence, though still fairly limited, supports the second hypothesis, but further testing is required before the first model can be rejected. So far, there is very little evidence for a direct effect of atmospheric CO₂ on the concentration of secondary compounds in higher plants. However, there are likely to be indirect effects, due to a stronger limitation by the nitrogen supply in plants whose growth has been promoted by atmospheric CO₂. It is concluded that it is very likely that phenolic compounds accumulate to a greater extent in plants exposed to elevated CO₂, due to a greater limitation of nutrients, rather than as a direct effect of elevated CO₂.     

Effects of elevated CO2 and temperature on secondary compounds in the needles of Scots pine (Pinus sylvestris L.)

The aim of this study was to evaluate the long-term effects of elevated CO₂ concentration (doubling of ambient CO₂ concentration) and temperature (2–6°C elevation) on the concentration and content of secondary compounds in the needles of Scots pine (Pinus sylvestris L.) saplings grown in closed-top environmental chambers. The chamber treatments included (1) ambient temperature and CO₂, (2) ambient temperature and elevated CO₂, (3) elevated temperature and ambient CO₂, and (4) elevated temperature and elevated CO₂. The needle sampling and analyses of monoterpenes, HPLC-phenolics and condensed tannins in current- and 1-year-old needles were made in two consecutive years. The results showed that the effects of elevation of CO₂ and temperature were greatest on the monoterpene concentration in the needles while the concentration of HPLC-phenolics remained almost unaffected by the changed growing conditions. Most of the observed decrease in monoterpene concentration was caused by the CO₂ enrichment while the effect of elevated temperature alone was not as significant. The accumulation of condensed tannins tended to increase due to the elevation of CO₂ alone compensating the reduced carbon allocation to monoterpenes. Overall, the responses of the concentrations of secondary compounds to the elevation of CO₂ and temperature are variable and depend strongly on the properties and characteristics of each compound as well as on the interrelation between the production of these compounds and the primary production of trees.     

The effect of elevated carbon dioxide and fertilization on primary and secondary metabolites in birch,Betula pendula (Roth)

Seedlings of European white birch (Betula pendula Roth) were grown in growth chambers for one growth season under four carbon dioxide regimes (350, 700, 1050 and 1400 ppm) and at three fertilization levels (0, 100 and 500 kg ha^–1 monthly). The soluble carbohydrates and secondary phenolics in the leaves and stems were analysed. It was found that fertilizer addition reduced the amounts of glucose and fructose while sucrose remained almost unaffected. The sugar content of leaves increased at 700 ppm and 1050 ppm of CO₂ and decreased at the highest CO₂ concentration (1400 ppm). The amounts of proanthocyanidins and flavonoids in leaves decreased with fertilization addition and increased with CO₂ enrichment. The production of simple phenolic glucosides varied according to the fertilization and CO₂ treatments. The triterpenoid content of stems seemed to increase with fertilization and CO₂-addition. Our results indicate that the production of phytochemicals in the birch seedlings is very sensitive to both fertilization and CO₂ addition, which is in agreement with earlier studies, and thus provide some support for the hypothesis of carbon allocation to plant defence when there is an excess of carbon and nutrient. The considerable variation in the production of secondary components may indicate that the synthesis of these defensive metabolites can be regulated by a plant to certain extent, depending on the ability of the plant to acclimate to changes in the physical environment.     

CO2 fixation in stem slices of Picea abies (L.) Karst: microautoradiographic studies

Summary Microautoradiography was used to show that chlorophyllous cells of young Picea abies stem slices are able to fix ¹⁴CO₂, in the dark as well as in the light. The amount of ¹⁴CO₂ fixed in the dark is much lower than that in the light. In the dark the concentration of radioactive label is equally high in all chlorophyllous cells of the stem. In the light, however, a gradient of radioactive assimilates extends from the stem surface to its centre, with the highest concentration being located in the phelloderm and the outer one-third of the cortex. This is in spite of even illumination and CO₂ supply across the whole stem slice. In the dark, stem slices with and without bark show the same amount of radioactive label in the chlorophyllous cells of xylem, perimedullary region and pith. In the light, however, the concentration of radioactive assimilates in these cells is much higher in stem slices with bark than in stem slices without bark. It is assumed therefore that light fixation products of phelloderm and cortex are transported radially into the tissue inside the cambium.     

Response of Forest Trees to Increased Atmospheric CO 2

The CO ₂ fertilization hypothesis stipulates that rising atmospheric CO ₂ has a positive effect on tree growth due to increasing availability of carbon. The objective of this paper is to compare the recent literature related to both field CO ₂ -enriched experiments with trees and empirical dendrochronological studies detecting CO ₂ fertilization effects in tree-rings. This will allow evaluation of tree growth responses to atmospheric CO ₂ enrichment by combining evidence from both ecophysiology and tree-ring research. Based on considerable experimental evidence of direct CO ₂ fertilization effect (increased photosynthesis, water use efficiency, and above- and belowground biomass), and predications from the interactions of enriched CO ₂ with temperature, nitrogen and drought, we propose that warm, moderately drought-stressed ecosystems with an ample nitrogen supply might be the most CO ₂ responsive ecosystems. Empirical tree-ring studies took the following three viewpoints on detecting CO ₂ fertilization effect in tree-rings: 1) finding evidence of CO ₂ fertilization effect in tree-rings, 2) attributing growth enhancement to favorable climate rather than atmospheric CO ₂ enrichment, and 3) considering that tree growth enhancement might be caused by synergistic effects of several factors such as favorable climate change, CO ₂ fertilization, and anthropogenic atmospheric deposition (e.g., nitrogen). At temperature-limiting sites such as high elevations, nonfindings of CO ₂ fertilization evidence could be ascribed to the following possibilities: 1) cold temperatures, a short season of cambial division, and nitrogen deficiency that preclude a direct CO ₂ response, 2) old trees past half of their maximum life expectancy and consequently only a small increase in biomass increment due to CO ₂ fertilization effect might be diminished, 3) the elimination of age/size-related trends by statistical detrending of tree-ring series that might remove some long-term CO ₂ -related trends in tree-rings, and 4) carbon partitioning and growth within a plant that is species-specific. Our review supports the atmospheric CO ₂ fertilization effect hypothesis, at least in trees growing in semi-arid or arid conditions because the drought-stressed trees could benefit from increased water use efficiency to enhance growth.     

Partitioning of photosynthetic electron flow between CO2 and O2 reduction in a C3 leaf (Phaseolus vulgaris L.) at different CO2 concentrations and during drought stress

Photosystem II chlorophyll fluorescence and leaf net gas exchanges (CO₂ and H₂O) were measured simultaneously on bean leaves (Phaseolus vulgaris L.) submitted either to different ambient CO₂ concentrations or to a drought stress. When leaves are under photorespiratory conditions, a simple fluorescence parameter F/ F_m (B. Genty et al. 1989, Biochem. Biophys. Acta 990, 87–92; F = difference between maximum, F_m, and steady-state fluorescence emissions) allows the calculation of the total rate of photosynthetic electron-transport and the rate of electron transport to O₂. These rates are in agreement with the measurements of leaf O₂ absorption using ¹⁸O₂ and the kinetic properties of ribulose-1,5bisphosphate carboxylase/oxygenase. The fluorescence parameter, F/F_m, showed that the allocation of photosynthetic electrons to O₂ was increased during the desiccation of a leaf. Decreasing leaf net CO₂ uptake, either by decreasing the ambient CO₂ concentration or by dehydrating a leaf, had the same effect on the partitioning of photosynthetic electrons between CO₂ and O₂ reduction. It is concluded that the decline of net CO₂ uptake of a leaf under drought stress is only due, at least for a mild reversible stress (causing at most a leaf water deficit of 35%), to stomatal closure which leads to a decrease in leaf internal CO₂ concentration. Since, during the dehydration of a leaf, the calculated internal CO₂ concentration remained constant or even increased we conclude that this calculation is misleading under such conditions.Abbreviations Ca, Ci ambient, leaf internal CO₂ concentrations - F_m, F_o, F_s maximum, minimal, steady-state fluorescence emission - F_v variable fluorescence emission - PPFD photosynthetic photon flux density - q_p, q_N photochemical, non-photochemical fluorescence quenching - Rubisco ribulose-1,5-bisphosphate carboxylase/oxygenase     

Effect of CO2 enhancement in an outdoor algal production system usingTetraselmis

One of the objectives of microalgal culture is to provide reliable production technology for important live aquaculture feed organisms. Presented here are the results of experiments designed to provide a better understanding of the relationship between inorganic carbon availability and algal production.Our results suggest that through additions of CO₂ gas we were able to maintain sufficient dissolved carbon to stabilize outdoor algal cultures. Increases in the rate of addition of CO₂ increased levels of dissolved CO₂, total dissolved inorganic carbon (CO₂), and decreased pH in the growth medium. This translated into improved buffering capacity of the culture medium and higher growth rate. A minimum of 2.4 mM CO₂ was found necessary to maintain a maximal growth rate of 0.7 doublings/day. We also found that the increased productivity more than offsets the cost of adding the CO₂.     

Decomposition of litter produced under elevated CO2: Dependence on plant species and nutrient supply

We investigated the effect of CO₂ concentration and soilnutrient availability during growth on the subsequent decomposition andnitrogen (N) release from litter of four annual grasses that differ inresource requirements and native habitat. Vulpia microstachys isa native grass found on California serpentine soils, whereas Avenafatua, Bromus hordaceus, and Lolium multiflorum areintroduced grasses restricted to more fertile sandstone soils (Hobbs & Mooney 1991). Growth in elevated CO₂ altered litter C:N ratio,decomposition, and N release, but the direction and magnitude of thechanges differed among plant species and nutrient treatments. ElevatedCO₂ had relatively modest effects on C:N ratio of litter,increasing this ratio in Lolium roots (and shoots at high nutrients),but decreasing C:N ratio in Avena shoots. Growth of plants underelevated CO₂ decreased the decomposition rate of Vulpialitter, but increased decomposition of Avena litter from the high-nutrient treatment. The impact of elevated CO₂ on N loss fromlitter also differed among species, with Vulpia litter from high-CO₂ plants releasing N more slowly than ambient-CO₂litter, whereas growth under elevated CO₂ caused increased Nloss from Avena litter. CO₂ effects on N release in Lolium and Bromus depended on the nutrient regime in whichplants were grown. There was no overall relationship between litter C:Nratio and decomposition rate or N release across species and treatments.Based on our study and the literature, we conclude that the effects ofelevated CO₂ on decomposition and N release from litter arehighly species-specific. These results do not support the hypothesis thatCO₂ effects on litter quality consistently lead to decreasednutrient availability in nutrient-limited ecosystems exposed to elevatedCO₂.     

A correlation between changes in luminescence decay kinetics and the appearance of a CO2-accumulating mechanism in Scenedesmus obliquus

In experiments with the unicellular green algae Scenedesmus obliquus a correlation was found between the presence of the CO₂-accumulating mechanism and the appearance of polyphasic luminescence decay kinetics. A potentiometric titration method was used to measure and calculate photosynthetic carbon uptake.Polyphasic luminescence decay kinetics was found when the algae showed photosynthetic characteristics typical of algae adapted to low-CO₂ conditions. When high-CO₂ grown algae were transferred to low-CO₂ conditions they gradually developed polyphasic decay kinetics during the first 25–30 minutes. When low-CO₂ grown algae were transferred to high-CO₂ conditions the polyphasic decay kinetics disappeared. To account for these results a working hypothesis is presented on the basis of the energy requirement for a CO₂-accumulating mechanism.     

Effects of elevated CO2 and nitrogen on nutrient uptake in ponderosa pine seedlings

This paper reports on the results of a controlled-environment study on the effects of CO₂ (370, 525, and 700 mol mol^-1) and N [0, 200, and 400 g N g soil^-1 as (NH₄)SO₄] on ponderosa pine (Pinus ponderosa) seedlings. Based upon a review of the literature, we hypothesized that N limitations would not prevent a growth response to elevated CO₂. The hypothesis was not supported under conditions of extreme N deficiency (no fertilizer added to a very poor soil), but was supported when N limitations were less severe but still suboptimal (lower rate of fertilization). The growth increases in N-fertilized seedlings occurred mainly between 36 and 58 weeks without any additional N uptake. Thus, it appeared that elevated CO₂ allowed more efficient use of internal N reserves in the previously-fertilized seedlings, whereas internal N reserves in the unfertilized seedlings were insufficient to allow this response. Uptake rates of other nutrients were generally proportional to growth. Nitrogen treatment caused reductions in soil exchangeable K⁺, Ca²⁺, and Mg²⁺ (presumably because of nitrification and NO₃ ^- leaching) but increases in extractable P (presumably due to stimulation of phosphatase activity).The results of this and other seedling studies show that elevated CO₂ causes a reduction in tissue N concentration, even under N-rich conditions. The unique response of N is consistent with the hypothesis that the efficiency of Rubisco increases with elevated CO₂. These results collectively have significant implications for the response of mature, N-deficient forests to evevated CO₂.     

Elevated CO2 alters anatomy,physiology, growth,and reproduction of red mangrove (Rhizophora mangle L.)

Mangroves, woody halophytes restricted to protected tropical coasts, form some of the most productive ecosystems in the world, but their capacity to act as a carbon source or sink under climate change is unknown. Their ability to adjust growth or to function as potential carbon sinks under conditions of rising atmospheric CO₂ during global change may affect global carbon cycling, but as yet has not been investigated experimentally. Halophyte responses to CO₂ doubling may be constrained by the need to use carbon conservatively under water-limited conditions, but data are lacking to issue general predictions. We describe the growth, architecture, biomass allocation, anatomy, and photosynthetic physiology of the predominant neotropical mangrove tree, Rhizophora mangle L., grown solitarily in ambient (350 ll^–1) and double-ambient (700 ll^–1) CO₂ concentrations for over 1 year. Mangrove seedlings exhibited significantly increased biomass, total stem length, branching activity, and total leaf area in elevated CO₂. Enhanced total plant biomass under high CO₂ was associated with higher root:shoot ratios, relative growth rates, and net assimilation rates, but few allometric shifts were attributable to CO₂ treatment independent of plant size. Maximal photosynthetic rates were enhanced among high-CO₂ plants while stomatal conductances were lower, but the magnitude of the treatment difference declined over time, and high-CO₂ seedlings showed a lower P_max at 700 ll^–1 CO₂ than low-CO₂ plants transferred to 700 ll^–1 CO₂: possible evidence of downregulation. The relative thicknesses of leaf cell layers were not affected by treatment. Stomatal density decreased as epidermal cells enlarged in elevated CO₂. Foliar chlorophyll, nitrogen, and sodium concentrations were lower in high CO₂. Mangroves grown in high CO₂ were reproductive after only 1 year of growth (fully 2 years before they typically reproduce in the field), produced aerial roots, and showed extensive lignification of the main stem; hence, elevated CO₂ appeared to accelerate maturation as well as growth. Data from this long-term study suggest that certain mangrove growth characters will change flexibly as atmospheric CO₂ increases, and accord with responses previously shown in Rhizophora apiculata. Such results must be integrated with data from sea-level rise studies to yield predictions of mangrove performance under changing climate.     

Microplankton respiratory activity and CO2 production rates in the Otranto Strait (Mediterranean Sea)

Respiratory activity and metabolic CO₂production of the microplankton in the Otranto Strait (Mediterranean Sea) were determined by monitoring the Electron Transport System activity. Ten stations were repeatedly investigated during two oceanographic surveys in February–March and August 1994. Respiratory activity and CO₂ production, estimated from the surface to the bottom, were higher in the euphotic layers (0-200 m) during summer (mean values: Winter = 0.024 μg C h⁻¹ dm⁻³; Summer = 0.042 μg C h⁻¹ dm⁻³); in the aphotic zone (deeper than 200 m), the rates were similar throughout different seasons (0.013 and 0.014 μg C h⁻¹ dm⁻³, respectively). A comparison with data collected by other authors from the euphotic layers of the Mediterranean Sea was made. Respiratory activities decreased from Western to Eastern Mediterranean Basins. The values of CO₂ production, integrated between 200 and 1000 m in the Otranto Strait (mean value 237.7 mg C m⁻² d⁻¹), were compared with other data collected from the Mediterranean Sea as well as from the Pacific, Atlantic and Indian Oceans. The comparison showed the Otranto Strait to be a site of organic matter oxidation. This revised version was published online in August 2006 with corrections to the Cover Date.     

Land plants of amphibious Littorella uniflora (L.) Aschers. maintain utilization of CO2 from the sediment

Summary Submerged macrophytes of the isoetid life form derive the majority of their CO₂ for photosynthesis from the sediment. The experiments described here were designed to test the hypothesis that root uptake of CO₂ is important also in the terrestrial form of Littorella uniflora. The results of ¹⁴CO₂ experiments showed that sediment CO₂ contributed 56% of the total fixation at 0.1mm CO₂ in the rhizosphere, 83% at 0.5mm and 96% at 2.5mm. Sediment CO₂ in emergent Littorella stands ranged from 0.1 to 1.0mm and averaged 0.5mm. Measurements of the net CO₂ exchange over the leaves showed an even higher dependence of the sediment as CO₂ source. Littorella leaves had no stomata at the base and densities (ca. 100 mm^–2) typical of terrestrial plants at the tip, allowing sediment-derived CO₂ to be supplied along the length of the leaf. The stomata permit supply of CO₂ from the air during periods of reduced sediment CO₂ concentrations (e.g. if the sediment dries up) and regulate transpiration.     

Elevated CO2 reduces field decomposition rates of Betula pendula (Roth.) leaf litter

The effect of elevated atmospheric CO₂ and nutrient supply on elemental composition and decomposition rates of tree leaf litter was studied using litters derived from birch (Betula pendula Roth.) plants grown under two levels of atmospheric CO₂ (ambient and ambient +250 ppm) and two nutrient regimes in solar domes. CO₂ and nutrient treatments affected the chemical composition of leaves, both independently and interactively. The elevated CO₂ and unfertilized soil regime significantly enhanced lignin/N and C/N ratios of birch leaves. Decomposition was studied using field litter-bags, and marked differences were observed in the decomposition rates of litters derived from the two treatments, with the highest weight remaining being associated with litter derived from the enhanced CO₂ and unfertilized regime. Highly significant correlations were shown between birch litter decomposition rates and lignin/N and C/N ratios. It can be concluded, from this study, that at levels of atmospheric CO₂ predicted for the middle of the next century a deterioration of litter quality will result in decreased decomposition rates, leading to reduction of nutrient mineralization and increased C storage in forest ecosystems. However, such conclusions are difficult to generalize, since tree responses to elevated CO₂ depend on soil nutritional status.     

Decline in gypsy moth (Lymantria dispar) performance in an elevated CO2 atmosphere depends upon host plant species

Plant species differ broadly in their responses to an elevated CO₂ atmosphere, particularly in the extent of nitrogen dilution of leaf tissue. Insect herbivores are often limited by the availability of nutrients, such as nitrogen, in their host plant tissue and may therefore respond differentially on different plant species grown in CO₂-enriched environments. We reared gyspy moth larvae (Lymantria dispar) in situ on seedlings of yellow birch (Betula allegheniensis) and gray birch (B. populifolia) grown in an ambient (350 ppm) or elevated (700 ppm) CO₂ atmosphere to test whether larval responses in the elevated CO₂ atmosphere were species-dependent. We report that female gypsy moths (Lymantria dispar) reared on gray birch (Betula populifolia) achieved similar pupal masses on plants grown at an ambient or an elevated CO₂ concentration. However, on yellow birch (B. allegheniensis), female pupal mass was 38% smaller on plants in the elevated-CO₂ atmosphere. Larval mortality was significantly higher on yellow birch than gray birch, but did not differ between the CO₂ treatments. Relative growth rate declined more in the elevated CO₂ atmosphere for larvae on yellow birch than for those on gray birch. In preference tests, larvae preferred ambient over elevated CO₂-grown leaves of yellow birch, but showed no preference between gray birch leaves from the two CO₂ atmospheres. This differential response of gypsy moths to their host species corresponded to a greater decline in leaf nutritional quality in the elevated CO₂ atmosphere in yellow birch than in gray birch. Leaf nitrogen content of yellow birch dropped from 2.68% to 1.99% while that of gray birch leaves only declined from 3.23% to 2.63%. Meanwhile, leaf condensed tannin concentration increased from 8.92% to 11.45% in yellow birch leaves while gray birch leaves only increased from 10.72% to 12.34%. Thus the declines in larval performance in a future atmosphere may be substantial and host-species-specific.     

Urea additions and defoliation affect plant responses to elevated CO2 in a C3 grass from Yellowstone National Park

A common grass from Yellowstone National Park, Stipa occidentalis, was grown in a factorial experiment to determine if its response to the direct effects of elevated CO₂ would be affected by defoliation, and urea additions simulating the N in a urine hit. Plants were grown in tall pots (to mimic rooting depth in the field) in growth chambers under elevated (700 ppm) and ambient (370 ppm) CO₂, were defoliated or left undefoliated, and given N-supply rates based on field mineralization rates (untreated) or with an additional 40 g N/m². Growth increases in response to elevated CO₂ were largest when plants remained unclipped and received urea additions, and were found primarily in crowns and roots (storage organs). Aboveground biomass, which is the part of the plant consumed by grazing mammals, was not affected by elevated CO₂. The elevated CO₂ treatment caused a reduction in leaf percent N. However, there was a significant interaction between the CO₂ and urea treatments, resulting in a larger difference in leaf percent N between urea-treated and control plants under elevated than under ambient CO₂. Hence, elevations in atmospheric CO₂ may cause an increase in the amount of urine-hit-induced spatial variability in temperate grasslands. Since food quantity remained largely unchanged in response to elevated CO₂, and forage N content went down, grazing mammals may be negatively affected by increases in atmospheric CO₂.     

Leaf cavity CO2 concentrations and CO2 exchange in onion,Allium cepa L.

Onion (Allium cepa L.) plants were examined to determine the photosynthetic role of CO₂ that accumulates within their leaf cavities. Leaf cavity CO₂ concentrations ranged from 2250 L L^–1 near the leaf base to below atmospheric (<350 L L^–1) near the leaf tip at midday. There was a daily fluctuation in the leaf cavity CO₂ concentrations with minimum values near midday and maximum values at night. Conductance to CO₂ from the leaf cavity ranged from 24 to 202 mol m^–2 s^–1 and was even lower for membranes of bulb scales. The capacity for onion leaves to recycle leaf cavity CO₂ was poor, only 0.2 to 2.2% of leaf photosynthesis based either on measured CO₂ concentrations and conductance values or as measured directly by ¹⁴CO₂ labeling experiments. The photosynthetic responses to CO₂ and O₂ were measured to determine whether onion leaves exhibited a typical C₃-type response. A linear increase in CO₂ uptake was observed in intact leaves up to 315 L L^–1 of external CO₂ and, at this external CO₂ concentration, uptake was inhibited 35.4±0.9% by 210 mL L^–1 O₂ compared to 20 mL L^–1 O₂. Scanning electron micrographs of the leaf cavity wall revealed degenerated tissue covered by a membrane. Onion leaf cavity membranes apparently are highly impermeable to CO₂ and greatly restrict the refixation of leaf cavity CO₂ by photosynthetic tissue.Abbreviations C_a external CO₂ concentration - C_i intercellular CO₂ concentration - CO₂ compensation concentration - PPFR photosynthetic photon fluence rate     

Effects of elevated CO2 on plant growth and nutrient partitioning of rice (Oryza sativa L.) at rapid tillering and physiological maturity

Abstract

This work investigates the relationship between plant growth, grain yield, nutrient acquisition and partitioning in rice (Oryza sativa L.) under elevated CO₂. Plants were grown hydroponically in growth chambers with a 12-h photoperiod at either 370 or 700 µmol CO₂ mol^?1 concentration. Plant dry mass (DM), grain yield and macro- and micronutrient concentrations of vegetative organs and grains were determined. Elevated CO₂ increased biomass at tillering, and this was largely due to an increase in root mass by 160%. Elevated CO₂ had no effect on total nutrient uptake (N, P, K, Mg and Ca). However, nutrient partitioning among organs was significantly altered. N partitioning to leaf blades was significantly decreased, whereas the N partitioning into the leaf sheaths and roots was increased. Nutrient use efficiency of N, P, K, and Mg in all organs was significantly increased at elevated CO₂. At harvest maturity, grain yield was increased by 27% at elevated CO₂ while grain (protein) concentration was decreased by a similar magnitude (28%), suggesting that critical nutrient requirements for rice might need to be reassessed with global climate change.     

Products of CO2 fixation and 14C labelling pattern of alanine in Methanobacterium thermoautotrophicum pulse-labelled with 14CO2

The incorporation of ¹⁴CO₂ by an exponentially growing culture of the autotrophic bacterium Methanobacterium thermoautotrophicum has been studied. The distribution of radioactivity during 2s–120s incubation periods has been analyzed by chromatography and radioautography. After a 2 s incubation most of the radioactivity of the ethanolsoluble fraction was present in the amino acids alanine, glutamate, glutamine and aspartate, whereas phosphorylated compounds were only weakly labelled. The percentage of the total radioactivity fixed, which was contained in the principal early labelled amino acid alanine, increased in the first 20 s and only then decreased, indicating that alanine is derived from primary products of CO₂ fixation.The labelling patterns of alanine produced during various incubation times have been determined by degradation. After a 2 s ¹⁴CO₂ pulse, 61% of the radioactivity was located in C-1, 23% in C-2, and 16% in C-3. The results are consistent with the operation of a previously proposed autotrophic CO₂ assimilation pathway which involves the formation of acetyl CoA from 2 CO₂ via one-carbon unit intermediates, followed by the reductive carboxylation of acetyl CoA to pyruvate.