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.     

Stomatal conductance and not stomatal density determines the long-term reduction in leaf transpiration of poplar in elevated CO<Subscript>2</Subscript>

Using a free-air CO₂ enrichment (FACE) experiment, poplar trees (Populus × euramericana clone I214) were exposed to either ambient or elevated [CO₂] from planting, for a 5-year period during canopy development, closure, coppice and re-growth. In each year, measurements were taken of stomatal density (SD, number mm⁻²) and stomatal index (SI, the proportion of epidermal cells forming stomata). In year 5, measurements were also taken of leaf stomatal conductance (g _s, μmol m⁻² s⁻¹), photosynthetic CO₂ fixation (A, mmol m⁻² s⁻¹), instantaneous water-use efficiency (A/E) and the ratio of intercellular to atmospheric CO₂ (C_i:C_a). Elevated [CO₂] caused reductions in SI in the first year, and in SD in the first 2 years, when the canopy was largely open. In following years, when the canopy had closed, elevated [CO₂] had no detectable effects on stomatal numbers or index. In contrast, even after 5 years of exposure to elevated [CO₂], g _s was reduced, A/E was stimulated, and C_i:C_a was reduced relative to ambient [CO₂]. These outcomes from the long-term realistic field conditions of this forest FACE experiment suggest that stomatal numbers (SD and SI) had no role in determining the improved instantaneous leaf-level efficiency of water use under elevated [CO₂]. We propose that altered cuticular development during canopy closure may partially explain the changing response of stomata to elevated [CO₂], although the mechanism for this remains obscure.     

Changes in growth and photosynthetic patterns of oil palm (<Emphasis Type="Italic">Elaeis guineensis</Emphasis> Jacq.) seedlings exposed to short-term CO<Subscript>2</Subscript> enrichment in a closed top chamber

Three varieties of oil palm seedlings (Deli Yangambi, Deli Urt, Deli AVROS) were exposed to three levels of CO₂ (400, 800, 1,200 μmol/mol) in split plot design to determine growth (net assimilation rate, NAR; relative growth rate, RGR) and photosynthetic patterns of the seedlings under short-term CO₂ exposure of 15 weeks. Increasing CO₂ from 400 to 800 and 1,200 μmol/mol significantly enhanced total biomass and leaf area, net photosynthesis (A) and water use efficiency (WUE) especially from weeks 9 to 15. By the end of week 15, total biomass increased by 113%, and A and WUE by one- and fivefold, respectively, while specific leaf area decreased by 37%. Both enhanced biomass and A under elevated CO₂ were effective in modifying NAR and RGR as shown by high correlation coefficient values (r ² = 0.68 and 0.72; r ² = 0.63 and 0.67, respectively), although WUE seemed to have more influence over the NAR (r ² = 0.97) and RGR (r ² = 0.93). Neither interspecific preference nor its interaction with CO₂ imposed any significant effect on parameters observed. Growth improvement with CO₂ seemed able to produce healthy, bigger and vigorous oil palm seedlings, and the technique may have potential to be developed for use to reduce nursery period.     

Utilization of <Emphasis Type="Italic">Anabaena</Emphasis> sp. in CO<Subscript>2</Subscript> removal processes

This paper focuses on modelling the growth rate and exopolysaccharides production of Anabaena sp. ATCC 33047, to be used in carbon dioxide removal and biofuels production. For this, the influence of dilution rate, irradiance and aeration rate on the biomass and exopolysaccharides productivity, as well as on the CO₂ fixation rate, have been studied. The productivity of the cultures was maximum at the highest irradiance and dilution rate assayed, resulting to 0.5 g_bio l⁻¹ day⁻¹ and 0.2 g_eps l⁻¹ day⁻¹, and the CO₂ fixation rate measured was 1.0 gCO₂ l⁻¹ day⁻¹. The results showed that although Anabaena sp. was partially photo-inhibited at irradiances higher than 1,300 μE m⁻² s⁻¹, its growth rate increases hyperbolically with the average irradiance inside the culture, and so does the specific exopolysaccharides production rate. The latter, on the other hand, decreases under high external irradiances, indicating that the exopolysaccharides metabolism hindered by photo-damage. Mathematical models that consider these phenomena have been proposed. Regarding aeration, the yield of the cultures decreased at rates over 0.5 v/v/min or when shear rates were higher than 60 s⁻¹, demonstrating the existence of thus existence of stress damage by aeration. The behaviour of the cultures has been verified outdoors in a pilot-scale airlift tubular photobioreactor. From this study it is concluded that Anabaena sp. is highly recommended to transform CO₂ into valuable products as has been proved capable of metabolizing carbon dioxide at rates of 1.2 gCO₂ l⁻¹ day⁻¹ outdoors. The adequacy of the proposed equations is demonstrated, resulting to a useful tool in the design and operation of photobioreactors using this strain.     

Down-regulation of Rubisco activity under combined increases of CO<Subscript>2</Subscript> and temperature minimized by changes in Rubisco k<Subscript>cat</Subscript> in wheat

Increases in growth temperature have been observed to affect photosynthesis differently under long-term exposure to ambient- and twice ambient-air CO₂ concentrations. This study investigates the causes of this interaction in wheat (Triticum aestivum L.) grown in the field over two consecutive years under temperature gradient chambers in ambient (370 μmol mol⁻¹) or elevated (700 μmol mol⁻¹) atmospheric CO₂ concentrations and at ambient or ambient +4°C temperatures, with either a low or a high nitrogen supply. The photosynthesis-internal CO₂ response curves and the activity, activation state, k_cat and amount of Ribulose-1, 5-bisphosphate carboxylase/oxygenase (Rubisco) were measured, as well as the soluble protein concentration in flag leaves at ear emergence and 8–15 days after anthesis. A high nitrogen supply increased V_cmax, the Rubisco amount and activity and soluble protein contents, but did not significantly change the Rubisco k_cat. Both elevated CO₂ and above ambient temperatures had negative effects on V_cmax and Rubisco activity, but at elevated CO₂, an increase in temperature did not decrease V_cmax or Rubisco activity in relation to ambient temperature. The amounts of Rubisco and soluble protein decreased with elevated CO₂ and temperature. The negative impact of elevated CO₂ on Rubisco properties was somewhat counteracted at elevated temperatures by an increase in k_cat. This effect can diminish the detrimental effects on photosynthesis of combined increases of CO₂ and temperature.     

The effects of enhanced ultraviolet-B and nitrogen supply on growth,photosynthesis and nutrient status of <Emphasis Type="Italic">Abies faxoniana</Emphasis> seedlings

Abies faxoniana is a key species in reforestation processes in the southeast of the Qinghai-Tibetan Plateau of China. The changes in growth, photosynthesis and nutrient status of A. faxoniana seedlings exposed to enhanced ultraviolet-B (UV-B), nitrogen supply and their combination were investigated. The experimental design included two levels of UV-B treatments (ambient UV-B, 11.02 KJ m⁻² day⁻¹; enhanced UV-B, 14.33 KJ m⁻² day⁻¹) and two nitrogen levels (0; 20 g N m⁻²). The results indicated that: (1) enhanced UV-B significantly caused a marked decline in growth parameters, net photosynthetic rate (Pn), photosynthetic pigments and F _v/F _m, (2) supplemental nitrogen supply increased the accumulation of total biomass, Pn, photosynthetic pigments and F _v/F _m under ambient UV-B, whereas supplemental nitrogen supply reduced Pn, and not affect biomass under enhanced UV-B, (3) enhanced UV-B or nitrogen supply changed the concentration of nutrient elements of various organs.     

Abundance and Diversity of CO<Subscript>2</Subscript>-fixing Bacteria in Grassland Soils Close to Natural Carbon Dioxide Springs

Gaseous conditions at natural CO₂ springs (mofettes) affect many processes in these unique ecosystems. While the response of plants to extreme and fluctuating CO₂ concentrations ([CO₂]) is relatively well documented, little is known on microbial life in mofette soil. Therefore, it was the aim of this study to investigate the abundance and diversity of CO₂-fixing bacteria in grassland soils in different distances to a natural carbon dioxide spring. Samples of the same soil type were collected from the Stavešinci mofette, a natural CO₂ spring which is known for very pure CO₂ emissions, at different distances from the CO₂ releasing vents, at locations that clearly differed in soil CO₂ efflux (from 12.5 to over 200 μmol CO₂ m⁻² s⁻¹ yearly average). Bulk and rhizospheric soil samples were included into analyses. The microbial response was followed by a molecular analysis of cbbL genes, encoding for the large subunit of RubisCO, a carboxylase which is of crucial importance for C assimilation in chemolitoautotrophic microbes. In all samples analyzed, the “red-like” type of cbbL genes could be detected. In contrast, the “green-like” type of cbbL could not be measured by the applied technique. Surprisingly, a reduction of “red-like” cbbL genes copies was observed in bulk soil and rhizosphere samples from the sites with the highest CO₂ concentrations. Furthermore, the diversity pattern of “red-like” cbbL genes changed depending on the CO₂ regime. This indicates that only a part of the autotrophic CO₂-fixing microbes could adapt to the very high CO₂ concentrations and adverse life conditions that are governed by mofette gaseous regime. Urška Videmšek, Alexandra Hagn, Michael Schloter, and Dominik Vodnik contributed equally to this study.     

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.     

Carbon balance in a monospecific stand of an annual herb <Emphasis Type="Italic">Chenopodium album</Emphasis> at an elevated CO<Subscript>2</Subscript> concentration

Elevated CO₂ enhances carbon uptake of a plant stand, but the magnitude of the increase varies among growth stages. We studied the relative contribution of structural and physiological factors to the CO₂ effect on the carbon balance during stand development. Stands of an annual herb Chenopodium album were established in open-top chambers at ambient and elevated CO₂ concentrations (370 and 700 μmol mol⁻¹). Plant biomass growth, canopy structural traits (leaf area, leaf nitrogen distribution, and light gradient in the canopy), and physiological characteristics (leaf photosynthesis and respiration of organs) were studied through the growing season. CO₂ exchange of the stand was estimated with a canopy photosynthesis model. Rates of light-saturated photosynthesis and dark respiration of leaves as related with nitrogen content per unit leaf area and time-dependent reduction in specific respiration rates of stems and roots were incorporated into the model. Daily canopy carbon balance, calculated as an integration of leaf photosynthesis minus stem and root respiration, well explained biomass growth determined by harvests (r ² = 0.98). The increase of canopy photosynthesis with elevated CO₂ was 80% at an early stage and decreased to 55% at flowering. Sensitivity analyses suggested that an alteration in leaf photosynthetic traits enhanced canopy photosynthesis by 40–60% throughout the experiment period, whereas altered canopy structure contributed to the increase at the early stage only. Thus, both physiological and structural factors are involved in the increase of carbon balance and growth rate of C. album stands at elevated CO₂. However, their contributions were not constant, but changed with stand development.     

Seasonal physiological responses and biomass growth in a bioenergy crop (<Emphasis Type="Italic">Phalaris arundinacea</Emphasis> L.) under elevated temperature and CO<Subscript>2</Subscript>, subjected to different water regimes in boreal conditions

We investigated the seasonal variability of effects of elevated temperature (+3.5°C), CO₂ elevation (700 μmol mol⁻¹) and varying water regimes (high to low water content) on physiological responses and biomass growth of reed canary grass (Phalaris arundinacea L., local field-grown cultivar) grown in a boreal environment. In controlled environment greenhouses, various physiological and growth parameters of grass, i.e., light-saturated net photosynthetic rates (P _nmax), water use efficiency (WUE) and optimal photochemical efficiency of photosystem II (F _v/F _m), and leaf area development and biomass of plant organs (leaf, stem, coarse, and fine root) were measured. During the early measurement periods, elevated temperature enhanced leaf photosynthesis and above-ground biomass of reed canary grass; however, this resulted in earlier senescence and lower biomass at the end of measurement period, compared to ambient temperature. This effect was more pronounced under water limitation. Elevated CO₂ enhanced P _nmax, WUE, and leaf area and total plant biomass (above- and below-ground) over growing season. The explanation for imbalance between stimulated photosynthesis and increase in above-ground biomass was that CO₂ enrichment causes a greater increase in the plant’s root system. The combination of elevated temperature and CO₂ slightly increases the growth of plant. Adequate water availability favored photosynthesis and biomass growth of reed canary grass. The temperature- and drought-induced stresses were partially mitigated by elevated CO₂. Other cultivars should be tested in order to identify those that are better adapted to elevated temperatures and CO₂ and variable water levels.     

Photosynthetic responses of apricot (<Emphasis Type="Italic">Prunus armeniaca</Emphasis> L.) to photosynthetic photon flux density,leaf temperature,and CO<Subscript>2</Subscript> concentration

Two cultivars (Katy and Erhuacao) of apricot (Prunus armeniaca L.) were evaluated under open-field and solar-heated greenhouse conditions in northwest China, to determine the effect of photosynthetic photon flux density (PPFD), leaf temperature, and CO₂ concentration on the net photosynthetic rate (P _N). In greenhouse, Katy registered 28.3 μmol m⁻² s⁻¹ for compensation irradiance and 823 μmol m⁻² s⁻¹ for saturation irradiance, which were 73 and 117 % of those required by Erhuacao, respectively. The optimum temperatures for cvs. Katy and Erhuacao were 25 and 35 °C in open-field and 22 and 30 °C in greenhouse, respectively. At optimal temperatures, P _N of the field-grown Katy was 16.5 μmol m⁻² s⁻¹, 21 % less than for a greenhouse-grown apricot. Both cultivars responded positively to CO₂ concentrations below the CO₂ saturation concentration, whereas Katy exhibited greater P _N (18 %) and higher carboxylation efficiency (91 %) than Erhuacao at optimal CO₂ concentration. Both cultivars exhibited greater photosynthesis in solar-heated greenhouses than in open-field, but Katy performed better than Erhuacao under greenhouse conditions.     

Growth of three cattail (<Emphasis Type="Italic">Typha</Emphasis>) taxa in response to elevated CO<Subscript>2</Subscript>

The establishment of non-native species and the increase in atmospheric CO₂, in combination, have the ability to alter current ecosystems. Previous studies have shown that invasive species tend to respond more strongly to CO₂ than natives, but these comparisons have been of different and unrelated species. To assess how response to CO₂ might be related to invasiveness per se, we compared a native (Typha latifolia) with a congeneric invasive (Typha angustifolia), as well as their hybrid (T. × glauca). All three taxa are common components of wetland vegetation, often occurring in near monocultures. An open-top chamber experiment was used to examine the effects of elevated and ambient CO₂ concentrations on the three taxa. All three increased rhizome biomass by 40% in elevated CO₂. Although the absolute increase did not differ among taxa, the invasive T. angustifolia had a much higher proportional response in biomass and photosynthetic rate (45 and 40% respectively). The weaker response of the two larger taxa native T. latifolia (16 and 2%) and hybrid T. × glauca (−4% and −1%) was possibly driven by soil nutrient deficiency, such that they were not able to benefit from increased CO₂. However, under low nutrients the smaller species T. angustifolia may become more a problematic invader in the future.     

Effect of 24-Epibrassinolide on Chlorophyll Fluorescence and Photosynthetic CO<Subscript>2</Subscript> Assimilation in <Emphasis Type="Italic">Vicia faba</Emphasis> Plants Treated with the Photosynthesis-Inhibiting Herbicide Terbutryn

Simultaneous measurements of chlorophyll (Chl) fluorescence and CO₂ assimilation (A) in Vicia faba leaves were taken during the first weeks of growth to evaluate the protective effect of 24-epibrassinolide (EBR) against damage caused by the application of the herbicide terbutryn (Terb) at pre-emergence. V. faba seeds were incubated for 24 h in EBR solutions (2 × 10⁻⁶ or 2 × 10⁻⁵ mM) and immediately sown. Terb was applied at recommended doses (1.47 or 1.96 kg ha⁻¹) at pre-emergence. The highest dose of Terb strongly decreased CO₂ assimilation, the maximum quantum yield of PSII photochemistry in the dark-adapted state (F _V/F _M), the nonphotochemical quenching (NPQ), and the effective quantum yield (ΔF/F′_M) during the first 3–4 weeks after plant emergence. Moreover, Terb increased the basal quantum yield of nonphotochemical processes (F ₀/F _M)_, the degree of reaction center closure (1 − q _p), and the fraction of light absorbed in PSII antennae that was dissipated via thermal energy dissipation in the antennae (1 − F′_V/F′_M). The herbicide also significantly reduced plant growth at the end of the experiment as well as plant length, dry weight, and number of leaves. The application of EBR to V. faba seeds before sowing strongly diminished the effect of Terb on fluorescence parameters and CO₂ assimilation, which recovered 13 days after plant emergence and showed values similar to those of control plants. The protective effect of EBR on CO₂ assimilation was detected at a photosynthetic photon flux density (PFD) of 650 μmol m⁻² s⁻¹ and the effect on ΔF/F′_M and photosynthetic electron transport (J) was detected under actinic lightings up to 1750 μmol m⁻² s⁻¹. The highest dose of EBR also counteracted the decrease in plant growth caused by Terb, and plants registered the same growth values as controls.     

Effects of temperature,photosynthetic photon flux density,photoperiod and O<Subscript>2</Subscript> and CO<Subscript>2</Subscript> concentrations on growth rates of the symbiotic dinoflagellate, <Emphasis Type="Italic">Amphidinium</Emphasis> sp.

Symbiotic dinoflagellates of the species Amphidinium are expected to be pharmaceutically useful microalgae because they produce antitumor macrolides. A microalgae production system with a large number of cells at a high density has been developed for the efficient production of macrolide compounds. In the present study, the effects of culture conditions on the cellular growth rate of dinoflagellates were investigated to determine the optimum culture conditions for obtaining high yields of microalgae. Amphidinium species was cultured under conditions with six temperature levels (21–35°C), six levels of photosynthetic photon flux density (15–70 μmol photons m⁻² s⁻¹), three levels of CO₂ concentration (0.02–0.1%), and three levels of O₂ concentration (0.2–21%). The number of cells cultured in a certain volume of solution was monitored microscopically and the cellular growth rate was expressed as the specific growth rate. The maximum specific growth rate was 0.022 h⁻¹ at a temperature of 26°C and O₂ concentration of 5%, and the specific growth rate was saturated at a CO₂ concentration of 0.05%, a photosynthetic photon flux density of 35 μmol photons m⁻² s⁻¹ and a photoperiod of 12 h day⁻¹ upon increasing each environmental parameter. The results demonstrate that Amphidinium species can multiply efficiently under conditions of relatively low light intensity and low O₂ concentration.     

Elevated CO<Subscript>2</Subscript> ameliorated oxidative stress induced by elevated O<Subscript>3</Subscript> in <Emphasis Type="Italic">Quercus mongolica</Emphasis>

Using open top chambers, the effects of elevated O₃ (80 nmol mol⁻¹) and elevated CO₂ (700 μmol mol⁻¹), alone and in combination, were studied on young trees of Quercus mongolica. The results showed that elevated O₃ increased malondialdehyde content and decreased photosynthetic rate after 45 days of exposure, and prolonged exposure (105 days) induced significant increase in electrolyte leakage and reduction of chlorophyll content. All these changes were alleviated by elevated CO₂, indicating that oxidative stress on cell membrane and photosynthesis was ameliorated. After 45 days of exposure, elevated O₃ stimulated activities of superoxide dismutase (SOD, EC 1.15.1.1) and ascorbate peroxidase (APX, EC 1.11.1.11), but the stimulation was dampened under elevated CO₂ exposure. Furthermore, ascorbate (AsA) and total phenolics contents were not higher in the combined gas treatment than those in elevated O₃ treatment. It indicates that the protective effect of elevated CO₂ against O₃ stress was achieved hardly by enhancing ROS scavenging ability after 45 days of exposure. After 105 days of exposure, elevated O₃ significantly decreased activities of SOD, catalase (CAT, EC 1.11.1.6) and APX and AsA content. Elevated CO₂ suppressed the O₃-induced decrease, which could ameliorate the oxidative stress in some extent. In addition, elevated CO₂ increased total phenolics content in the leaves both under ambient O₃ and elevated O₃ exposure, which might contribute to the protection against O₃-induced oxidative stress as well.     

Influence of irradiance on photosynthesis and PSII photochemical efficiency in maize during short-term exposure at high CO<Subscript>2</Subscript> concentration

This work aimed to evaluate if gas exchange and PSII photochemical activity in maize are affected by different irradiance levels during short-term exposure to elevated CO₂. For this purpose gas exchange and chlorophyll a fluorescence were measured on maize plants grown at ambient CO₂ concentration (control CO₂) and exposed for 4 h to short-term treatments at 800 μmol(CO₂) mol⁻¹ (high CO₂) at a photosynthetic photon flux density (PPFD) of either 1,000 μmol m⁻² s⁻¹ (control light) or 1,900 μmol m⁻² s⁻¹ (high light). At control light, high-CO₂ leaves showed a significant decrease of net photosynthetic rate (P _N) and a rise in the ratio of intercellular to ambient CO₂ concentration (C _i/C _a) and water-use efficiency (WUE) compared to control CO₂ leaves. No difference between CO₂ concentrations for PSII effective photochemistry (Φ_PSII), photochemical quenching (q_p) and nonphotochemical quenching (NPQ) was detected. Under high light, high-CO₂ leaves did not differ in P _N, C _i/C _a, Φ_PSII and NPQ, but showed an increase of WUE. These results suggest that at control light photosynthetic apparatus is negatively affected by high CO₂ concentration in terms of carbon gain by limitations in photosynthetic dark reaction rather than in photochemistry. At high light, the elevated CO₂ concentration did not promote an increase of photosynthesis and photochemistry but only an improvement of water balance due to increased WUE.     

Phenol biodegradation by the thermoacidophilic archaeon <Emphasis Type="Italic">Sulfolobus solfataricus</Emphasis> 98/2 in a fed-batch bioreactor

Toxic at low concentrations, phenol is one of the most common organic pollutants in air and water. In this work, phenol biodegradation was studied in extreme conditions (80°C, pH = 3.2) in a 2.7 l bioreactor with the thermoacidophilic archaeon Sulfolobus solfataricus 98/2. The strain was first acclimatized to phenol on a mixture of glucose (2000 mg l⁻¹) and phenol (94 mg l⁻¹) at a constant dissolved oxygen concentration of 1.5 mg l⁻¹. After a short lag-phase, only glucose was consumed. Phenol degradation then began while glucose was still present in the reactor. When glucose was exhausted, phenol was used for respiration and then for biomass build-up. After several batch runs (phenol < 365 mg l⁻¹), specific growth rate (μ_X) was 0.034 ± 0.001 h⁻¹, specific phenol degradation rate (q_P) was 57.5 ± 2 mg g⁻¹ h⁻¹, biomass yield (Y_X/P) was 52.2 ± 1.1 g mol⁻¹, and oxygen yield factor ( \textY_{\textX/\textO 2} ) \left( {{\text{Y}}_{{{\text{X}}/{\text{O}}_{ 2} }} } \right) was 9.2 ± 0.2 g mol⁻¹. A carbon recovery close to 100% suggested that phenol was exclusively transformed into biomass (35%) and CO₂ (65%). Molar phenol oxidation constant ( \textY_{\textO 2 /\textP} ) \left( {{\text{Y}}_{{{\text{O}}_{ 2} /{\text{P}}}} } \right) was calculated from stoichiometry of phenol oxidation and introducing experimental biomass and CO₂ conversion yields on phenol, leading to values varying between 4.78 and 5.22 mol mol⁻¹. Respiratory quotient was about 0.84 mol mol⁻¹, very close to theoretical value (0.87 mol mol⁻¹). Carbon dioxide production, oxygen demand and redox potential, monitored on-line, were good indicators of growth, substrate consumption and exhaustion, and can therefore be usefully employed for industrial phenol bioremediation in extreme environments.     

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.     

Soil Organic Carbon Accumulation in Intensively Managed <Emphasis Type="Italic">Phyllostachys praecox</Emphasis> Stands

Area of bamboo forest (Phyllostachys praecox) has rapidly increased in southern China during the last 20 years due to its high economic value. Aims of this study were to analyse the temporal and spatial variations of soil organic matter (SOM) in heavily winter mulched bamboo stands and to estimate potential for carbon sequestration. Total of 60 soil profiles with 0–15 years of bamboo plantation were sampled from three towns in Lin’an County. Results showed that with increased plantation years, SOM decreased slightly at the beginning (1–5 years), and then rose up steadily. Based on the average of the three locations, the highest SOM content of 75.82 g/kg was the surface layer (0–10 cm) of the 15 years. As plantation year increased, the variation of SOM in the surface layer (0–10 cm) was represented by a parabolic shape, and in the second layer (10–20 cm), it was a similar mode, but less vigorous. Soil organic carbon (SOC) storage significantly increased during 5 to 15 years after it reached full production, and the calculated annual SOC increment in 0–40 cm soil profile was about 6.3 t C/ha/year. Therefore, extended Phyllostachys praecox forests can be considered as one option for countering CO₂ emissions and regional climate change.     

Responses of tropical native and invader C<Subscript>4</Subscript> grasses to water stress,clipping and increased atmospheric CO<Subscript>2</Subscript> concentration

The invasion of African grasses into Neotropical savannas has altered savanna composition, structure and function. The projected increase in atmospheric CO₂ concentration has the potential to further alter the competitive relationship between native and invader grasses. The objective of this study was to quantify the responses of two populations of a widespread native C₄ grass (Trachypogon plumosus) and two African C₄ grass invaders (Hyparrhenia rufa and Melinis minutiflora) to high CO₂ concentration interacting with two primary savanna stressors: drought and herbivory. Elevated CO₂ increased the competitive potential of invader grasses in several ways. Germination and seedling size was promoted in introduced grasses. Under high CO₂, the relative growth rate of young introduced grasses was twice that of native grass (0.58 g g⁻¹ week⁻¹ vs 0.25 g g⁻¹ week⁻¹). This initial growth advantage was maintained throughout the course of the study. Well-watered and unstressed African grasses also responded more to high CO₂ than did the native grass (biomass increases of 21–47% compared with decreases of 13–51%). Observed higher water and nitrogen use efficiency of invader grasses may aid their establishment and competitive strength in unfertile sites, specially if the climate becomes drier. In addition, high CO₂ promoted lower leaf N content more in the invader grasses. The more intensive land use, predicted to occur in this region, may interact with high CO₂ to fincreasesavor the African grasses, as they generally recovered faster after simulated herbivory. The superiority of invader grasses under high CO₂ suggests further in their competitive strength and a potential increased rate of displacement of the native savannas in the future by grasslands dominated by introduced African species.