Tight control of growth and cell differentiation in photoautotrophically growing moss (<Emphasis Type="Italic">Physcomitrella</Emphasis><Emphasis Type="Italic">patens</Emphasis>) bioreactor cultures

The use of the moss Physcomitrella patens as a production system for heterologous proteins requires highly standardised culture conditions. For this purpose a semi-continuous photoautotrophic bioreactor culture of Physcomitrella was established. This culture grew stably for 7 weeks in a 5-l bioreactor with a dilution rate of 0.22/day. Enrichment of the air for aeration in a batch bioreactor culture with 2% (v/v) CO₂ resulted in an increase in the specific growth rate to 0.57/day. Changes in the pH of the semi-continuous bioreactor culture medium between pH 4.5 and pH 7.0 influenced protonema differentiation; however it did not negatively affect the growth rate compared to uncontrolled pH. The advantages of Physcomitrella as a system for the production of heterologous proteins in plants are discussed.     

The effect of elevated carbon dioxide and ozone on leaf- and branch-level photosynthesis and potential plant-level carbon gain in aspen

Two aspen (Populus tremuloides Michx.) clones, differing in O₃ tolerance, were grown in a free-air CO₂ enrichment (FACE) facility near Rhinelander, Wisconsin, and exposed to ambient air, elevated CO₂, elevated O₃ and elevated CO₂+O₃. Leaf instantaneous light-saturated photosynthesis (P_S) and leaf areas (A) were measured for all leaves of the current terminal, upper (current year) and the current-year increment of lower (1-year-old) lateral branches. An average, representative branch was chosen from each branch class. In addition, the average photosynthetic rate was estimated for the short-shoot leaves. A summing approach was used to estimate potential whole-plant C gain. The results of this method indicated that treatment differences were more pronounced at the plant- than at the leaf- or branch-level, because minor effects within modules accrued in scaling to plant level. The whole-plant response in C gain was determined by the counteracting changes in P_S and A. For example, in the O₃-sensitive clone (259), inhibition of P_S in elevated O₃ (at both ambient and elevated CO₂) was partially ameliorated by an increase in total A. For the O₃-tolerant clone (216), on the other hand, stimulation of photosynthetic rates in elevated CO₂ was nullified by decreased total A.     

Photosynthesis in an invasive grass and native forb at elevated CO2 during an El Niño year in the Mojave Desert

Annual and short-lived perennial plant performance during wet years is important for long-term persistence in the Mojave Desert. Additionally, the effects of elevated CO₂ on desert plants may be relatively greater during years of high resource availability compared to dry years. Therefore, during an El Niño year at the Nevada Desert FACE Facility (a whole-ecosystem CO₂ manipulation), we characterized photosynthetic investment (by assimilation rate-internal CO₂ concentration relationships) and evaluated the seasonal pattern of net photosynthesis (A_net) and stomatal conductance (g_s) for an invasive annual grass, Bromus madritensis ssp. rubens and a native herbaceous perennial, Eriogonum inflatum. Prior to and following flowering, Bromus showed consistent increases in both the maximum rate of carboxylation by Rubisco (V_Cmax) and the light-saturated rate of electron flow (J_max) at elevated CO₂. This resulted in greater A_net at elevated CO₂ throughout most of the life cycle and a decrease in the seasonal decline of maximum midday A_net upon flowering as compared to ambient CO₂. Eriogonum showed significant photosynthetic down-regulation to elevated CO₂ late in the season, but the overall pattern of maximum midday A_net was not altered with respect to phenology. For Eriogonum, this resulted in similar levels of A_net on a leaf area basis as the season progressed between CO₂ treatments, but greater photosynthetic activity over a typical diurnal period. While g_s did not consistently vary with CO₂ in Bromus, it did decrease in Eriogonum at elevated CO₂ throughout much of the season. Since the biomass of both plants increased significantly at elevated CO₂, these patterns of gas exchange highlight the differential mechanisms for increased plant growth. The species-specific interaction between CO₂ and phenology in different growth forms suggests that important plant strategies may be altered by elevated CO₂ in natural settings. These results indicate the importance of evaluating the effects of elevated CO₂ at all life cycle stages to better understand the effects of elevated CO₂ on whole-plant performance in natural ecosystems.     

Feeding rates of the woodlouse Armadillidium vulgare on herb litters produced at two levels of atmospheric CO2

The consumption and assimilation rates of the woodlouse Armadillidium vulgare were measured on leaf litters from five herb species grown and naturally senesced at 350 and 700 µl l^-1 CO₂. Each type of litter was tested separately after 12, 30 and 45 days of decomposition at 18°C. The effects of elevated CO₂ differed depending on the plant species. In Medicago minima (Fabaceae), the CO₂ treatment had no significant effect on consumption and assimilation. In Tyrimnus leucographus (Asteraceae), the CO₂ treatment had no significant effect on consumption, but the elevated CO₂ litter was assimilated at a lower rate than the ambient CO₂ litter after 30 days of decomposition. In the three other species, Galactites tomentosa (Asteraceae), Trifolium angustifolium (Fabaceae) and Lolium rigidum (Poaceae), the elevated CO₂ litter was consumed and/or assimilated at a higher rate than the ambient CO₂ litter. Examination of the nitrogen contents in these three species of litter did not support the hypothesis of compensatory feeding, i.e. an increase in woodlouse consumption to compensate for low nitrogen content of the food. Rather, the results suggest that in herbs that were unpalatable at the start of the experiment (Galactites, Trifolium and Lolium), more of the the litter produced at 700 µl l^-1 CO₂ was consumed than of that produced at 350 µl l^-1 because inhibitory factors were eliminated faster during decomposition.     

Comparative study of the fermentation of D-glucose/D-xylose mixtures with Pachysolen tannophilus and Candida shehatae

We have performed a comparative analysis of the fermentation of the solutions of the mixtures of D-glucose and D-xylose with the yeasts Pachysolen tannophilus (ATCC 32691) and Candida shehatae (ATCC 34887), with the aim of producing bioethanol. All the experiments were performed in a batch bioreactor, with a constant aeration level, temperature of 30v°C, and a culture medium with an initial pH of 4.5. For both yeasts, the comparison was established on the basis of the following parameters: maximum specific growth rate, biomass productivity, specific rate of substrate consumption (q_s) and of ethanol production (q_E), and overall ethanol and xylitol yields. For the calculation of the specific rates of substrate consumption and ethanol production, differential and integral methods were applied to the kinetic data. From the experimental results, it is deduced that both Candida and Pachysolen sequentially consume the two substrates, first D-glucose and then D-xylose. In both yeasts, the specific substrate-consumption rate diminished over each culture. The values q_s and q_E proved higher in Candida, although the higher ethanol yield was of the same order for both yeasts, close to 0.4 kg kg^у.     

Effect of gaseous composition on cell growth and secondary metabolite production in suspension culture of Stizolobium hassjoo cells

The gaseous composition is an important factor affecting the performance of plant cell cultures. Gaseous metabolites, especially O₂, CO₂ and C₂H₄, play important roles in cell physiology. Forced aeration in bioreactors usually results in poor cell growth and secondary metabolite production. In this work, the effects of gaseous metabolites on cell growth, secondary metabolite formation as well as PPO activity were investigated with respect to Stizolobium hassjoo cell culture producing l-DOPA (3,4-dihydroxyphenylalanine). A device allowing the control of the partial pressures of gaseous metabolites in shake flasks was designed. In addition, a recirculating gas system with a P_O2 controller was designed for a bioreactor. This device could maintain constant P_O2 and P_CO2 in the bioreactor headspace. The results showed that the highest l-DOPA content was attained at P_O2=0.30 atm. Higher P_O2 values retarded cell growth and increased the pH of the culture broth. High P_O2 also enhanced the formation of ethylene and inhibited l-DOPA formation. Carbon dioxide concentrations lower than 5% enhanced cell growth and l-DOPA formation. Cell growth was retarded by 0.3 ppm of ethylene in 2~5 carbon dioxide. Oxygen concentration and D.O. in the broth could be controlled at constant levels in the recirculating culture system. Enrichment of P_O2 up to 0.3 atm during the later stage of cultivation facilitated l-DOPA formation. The interaction among the gaseous metabolites and their influences on cell metabolism and l-DOPA formation were elucidated. This information will facilitate the rational operation of plant cell culture systems producing secondary metabolites.     

Genotypic variation in the response of two perennial grass species to elevated carbon dioxide

Shoot and reproductive biomass of genotypes of Bromus erectus and Dactylis glomerata grown in competition at ambient and elevated CO₂ were examined for 2 consecutive years in order to test whether genetic variation in those traits exists and whether it is maintained over time. At the species level, a positive CO₂ response of shoot biomass of both species was only found in the first year of treatment. At the genotype level, no significant CO₂2genotype interaction was found at any single harvest either for vegetative or reproductive biomass of either species. Analysis over time, however, indicated that there is a potential for evolutionary adaptation only for D. glomerata: (1) repeated measures ANOVA detected a marginally significant CO₂2genotype2time interaction for shoot biomass, because the range of the genotypes CO₂ response increased over time; (2) genotypes that displayed the highest response during the first year under elevated CO₂ also showed the highest response the second year. Null (B. erectus) or weak (D. glomerata) selective potentials of elevated CO₂ were detected in this experiment, but short time series could underestimate this potential with perennial species.     

Effects of elevated CO<Subscript>2</Subscript> on foliar chemistry of saplings of nine species of tropical tree

This study examined the effects of elevated CO₂ on secondary metabolites for saplings of tropical trees. In the first experiment, nine species of trees were grown in the ground in open-top chambers in central Panama at ambient and elevated CO₂ (about twice ambient). On average, leaf phenolic contents were 48% higher under elevated CO₂. Biomass accumulation was not affected by CO₂, but starch, total non-structural carbohydrates and C/N ratios all increased. In a second experiment with Ficus, an early successional species, and Virola, a late successional species, treatments were enriched for both CO₂ and nutrients. For both species, nutrient fertilization increased plant growth and decreased leaf carbohydrates, C/N ratios and phenolic contents, as predicted by the carbon/nutrient balance hypothesis. Changes in leaf C/N levels were correlated with changes in phenolic contents for Virola (r=0.95, P<0.05), but not for Ficus. Thus, elevated CO₂, particularly under conditions of low soil fertility, significantly increased phenolic content as well as the C/N ratio of leaves. The magnitude of the changes is sufficient to negatively affect herbivore growth, survival and fecundity, which should have impacts on plant/herbivore interactions.     

Vitis vinifera culture in a non-conventional bioreactor: the reciprocating plate bioreactor

This paper is concerned with the potential use of a reciprocating plate bioreactor (RPB) for suspended plant cell cultures. The agitation mechanism of the RPB system, a plate stack, was first evaluated in pure water and in pseudocells medium of 20, 40 and 60% of PCV. As the pseudocell concentration increases, the oxygen mass transfer coefficient, K_La, significantly decreases. Correlations were established for each plate stack and concentration with good prediction of K_La. Three fermentations were performed with Vitis vinifera cells, two in the RPB system and one in shake flasks. Shake flask cultures showed better performance whereas the first fermentation performed with the RPB showed the lowest performance. The lower growth observed was attributed to the operating conditions for aeration and the dissolved oxygen control strategy. CO₂ stripping in the initial portion of the fermentation led to lower biomass growth. The second fermentation, with more appropriate operating conditions, appears to follow the trend of shake flask cultures but was terminated after 5 days due to contamination. The RPB has the potential to be used for suspended plant cell cultures but significant research needs to be performed to find optimal operating conditions but, more importantly, to make appropriate modifications to ensure the sterility of the bioreactor over long time periods.     

Tree seedling growth in natural deep shade: functional traits related to interspecific variation in response to elevated CO2

The mechanisms for species-specific growth responses to changes in atmospheric CO₂ concentration within narrow ecological groups of species, such as shade-tolerant, late-successional trees, have rarely been addressed and are not well understood. In this study the underlying functional traits for interspecific variation in the biomass response to elevated CO₂ were explored for seedlings of five late-successional temperate forest tree species (Fagus sylvatica, Acer pseudoplatanus, Quercus robur, Taxus baccata, Abies alba). The seedlings were grown in the natural forest understorey in very low and low light microsites (an average of 1.3% and 3.4% full sun in this experiment), and were exposed to either current ambient CO₂ concentrations, 500, or 660 µl CO₂ l^-1 in 36 open-top chambers (OTC) over two growing seasons. Even across the narrow range of successional status and shade tolerance, the study species varied greatly in photosynthesis, light compensation point, leaf dark respiration (R_d), leaf nitrogen concentration, specific leaf area (SLA), leaf area ratio (LAR), and biomass allocation among different plant parts, and showed distinct responses to CO₂ in these traits. No single species combined all characteristics traditionally considered as adaptive to low light conditions. At very low light, the CO₂ stimulation of seedling biomass was related to increased LAR and decreased R_d, responses that were observed only in Fagus and Taxus. At slightly higher light levels, interspecific differences in the biomass response to elevated CO₂ were reversed and correlated best with leaf photosynthesis. The data provided here contribute to a mechanistic process-based understanding of distinct response patterns in co-occurring tree species to elevated CO₂ in natural deep shade. I conclude that the high variation in physiological and morphological traits among late-successional species, and the consequences for their responses to slight changes in resource availability, have previously been underestimated. The commonly used broad definitions of functional groups of species may not be sufficient for the understanding of recruitment success and dynamic changes in species composition of old-growth forests in response to rising concentrations of atmospheric CO₂.     

Gas exchange and chlorophyll fluorescence responses of <Emphasis Type="Italic">Pinus radiata</Emphasis> D. Don seedlings during and after several storage regimes and their effects on post-planting survival

Post-storage gas exchange parameters like CO₂ assimilation, stomatal conductance, transpiration, water use efficiency and intercellular CO₂ concentrations, together with several chlorophyll a fluorescence parameters: F_o, F_v, F_v/F_m, F_m/F_o and F_v/F_o were examined in radiata pine (Pinus radiata D. Don) seedlings that were stored for 1, 8 or 15 days at 4° or 10°C with or without soil around the roots. Results were analysed in relation to post-storage water potential and electrolyte leakage in order to forecast their vitality (root growth potential) following cold storage, and post-planting survival potential under optimal conditions. During storage at 4° and 10°C, photosynthesis was reduced, being more pronounced in bare-root seedlings than in seedlings with soil around the roots. The depletion of CO₂ assimilation seemed not to be solely a stomatal effect as effects on chloroplasts contributed to this photosynthetic inhibition. Thus, the fall in the ratios F_v/F_m, F_v/F_o and F_m/F_o indicated photochemical apparatus damage during storage. Photosynthetic rate was positively correlated with the root growth index and new root length showing that new root growth is dependent primarily on current photosynthesis. Pre-planting exposure of bare-root radiata pine seedlings to temperatures of 10°C for more than 24 h during transportation or storage is not recommended.     

Experimental behavior of a whole cell immobilized dextransucrase biocatalyst in batch and packed bed reactors

Dextransucrases from Leuconostoc mesenteroides have been used to produce a diversity of controlled structure oligosaccharides with potential industrial applications. This is the case of !(1̄) branched glucooligosaccharides produced by L. mesenteroides NRRL B-1299 dextransucrase. In order to establish an industrial scale process with the immobilized enzyme, a biocatalyst was produced by whole cell entrapment in alginate beads. The main physical and physicochemical properties of the biocatalyst were determined and the hydrodynamic behavior in a packed bed reactor studied. It was possible to produce spherical beads of 0.2 cm diameter containing the insoluble part of L. mesenteroides culture (cells and insoluble polymer) with an activity of 4 IU/g. Immobilization yield reached 93% with an effectiveness factor of 0.995 for particles of d_p < 0.2 cm. Due to the complexity of dextransucrase mechanism and kinetics, data obtained from initial rate measurements failed to describe the results obtained from the batch and continuous reactors. Therefore, apparent K_M and V_max data were used for the reactor modeling. It was found that under the conditions studied, the reaction rate was controlled by external mass transfer limitations.     

Four-year growth dynamics of beech-spruce model ecosystems under CO2 enrichment on two different forest soils

To elucidate how atmospheric CO₂ enrichment, enhanced nutrient supply and soil quality interact to affect regrowth of temperate forests, young Fagus sylvatica and Picea abies trees were grown together in large model ecosystems. Identical communities were established on a nutrient-poor acidic and on a more fertile calcareous soil and tree growth, leaf area index, fine root density and soil respiration monitored over four complete growing seasons. Biomass responses to CO₂ enrichment and enhanced N supply at the end of the experiment reflected compound interest effects of growth stimulation during the first two to three seasons rather than persistent stimulation over the whole duration of the experiment. Whereas biomass of Picea was enhanced in elevated CO₂ on both soils, Fagus responded negatively to CO₂ on acidic but positively on calcareous soil. Biomass of both species profited from enhanced N supply on the poor acidic soil only. Leaf area index on both soils was greater in high N supply as a consequence of a stimulation early in the experiment, but was unaffected by CO₂ enrichment. Fine root density on acidic soil was increased in high N supply, but this did not stimulate soil respiration rate. In contrast, elevated CO₂ stimulated both fine root density and soil CO₂ efflux on calcareous soil, especially towards the end of the experiment. Our experiment suggests that future species dominance in beech-spruce forests is likely to change in response to CO₂ enrichment, but this response is subject to complex interactions with environmental factors other than CO₂, particularly soil type.     

Forest carbon balance under elevated CO2

Free-air CO₂ enrichment (FACE) technology was used to expose a loblolly pine (Pinus taeda L.) forest to elevated atmospheric CO₂ (ambient + 200 µl l^-1). After 4 years, basal area of pine trees was 9.2% larger in elevated than in ambient CO₂ plots. During the first 3 years the growth rate of pine was stimulated by ~26%. In the fourth year this stimulation declined to 23%. The average net ecosystem production (NEP) in the ambient plots was 428 gC m^-2 year^-1, indicating that the forest was a net sink for atmospheric CO₂. Elevated atmospheric CO₂ stimulated NEP by 41%. This increase was primarily an increase in plant biomass increment (57%), and secondarily increased accumulation of carbon in the forest floor (35%) and fine root increment (8%). Net primary production (NPP) was stimulated by 27%, driven primarily by increases in the growth rate of the pines. Total heterotrophic respiration (R_h) increased by 165%, but total autotrophic respiration (R_a) was unaffected. Gross primary production was increased by 18%. The largest uncertainties in the carbon budget remain in separating belowground heterotrophic (soil microbes) and autotrophic (root) respiration. If applied to temperate forests globally, the increase in NEP that we measured would fix less than 10% of the anthropogenic CO₂ projected to be released into the atmosphere in the year 2050. This may represent an upper limit because rising global temperatures, land disturbance, and heterotrophic decomposition of woody tissues will ultimately cause an increased flux of carbon back to the atmosphere.     

Minimum fluidization velocity and friction factor in a liquid-solid inverse fluidized bed reactor

In the present study the hydrodynamic characteristics (bed expansion and pressure drop) of low-density polyethylene (LDPE) and polypropylene (PP) are studied in a liquid-solid inverse fluidized bed reactor as a function of particle diameter, liquid viscosity and density. The bed expansion and pressure drop data are used to determine the minimum fluidization velocity, U_mf and friction factor, P. It was found that the U_mf increased with an increase in the particle diameter and a decrease in solid density and was independent of initial bed height (solid loading). In addition, the U_mf decreased with an increase in the CMC concentration. The friction factor Reynolds number plot was found similar to that of classical fluidization. Dimensionless equations were proposed for the. prediction of the friction factor and the U_mf.     

Estimation of axial dispersion in horizontal rotating tubular bioreactor by means of a structured model

A horizontal rotating tubular bioreactor (HRTB) is designed as the combination of a "thin layer bioreactor" and a "biodisc" reactor. The investigation of mixing in HRTB was done by the temperature step method in a wide range of process conditions [residence time (t_z=360036000 s) and bioreactor rotation speed (n=0.0830.917 s^у)]. In all experiments heat losses were detected. A mathematical model based on "tank in series" concept was developed to describe the mixing in HRTB - a "spiral flow" model (SFM) which has incorporated heat losses. However, the simulations of SFM could be used for calculation of temperature response curves for the case when there is no heat losses. These corrected curves were used then to estimate Bodenstein number as a parameter of standard dispersion model (SDM). The obtained Bodenstein numbers were in the range 10-17. The simulations showed that SFM was more capable to describe the mixing in HRTB giving better fitting with experimental measurements than SDM, indicating that mixing pattern in HRTB is too complex to be described with this relatively simple, one-parameter model.     

Very high productivity of the C4 aquatic grass Echinochloa polystachya in the Amazon floodplain confirmed by net ecosystem CO2 flux measurements

Fluxes of CO₂ and H₂O vapour from dense stands of the C4 emergent macrophyte grass Echinochloa polystachya were measured by eddy covariance in both the low water (LW) and high water (HW, flooded) phases of the annual Amazon river cycle at Manaus, Brazil. Typical clear-sky midday CO₂ uptake rates by the vegetation stand (including detritus, sediment or water surface) were 30 and 35 µmol CO₂ (ground) m^-2 s^-1 in the LW and HW periods, respectively. A rectangular hyperbola model fitted the responses of "instantaneous" (20- or 30-min average) net CO₂ exchange rates to incident photosynthetic photon flux densities (PFD) well. Stand evaporation rates were linearly related to PFD. The major difference in CO₂ uptake rates between the two periods was the larger respiration flux during LW due to the CO₂ efflux from sediment, roots and litter. Integrated 20- or 30-min fluxes were used to derive relationships between daily CO₂ and H₂O vapour fluxes and incident radiation. The daily CO₂ fluxes were almost linearly related to incident radiation, but there was evidence of saturation at the highest daily radiation totals. Annual productivity estimated from the daily model in 1996-1997 agreed closely with that previously estimated for 1985-1986 from a leaf-scale photosynthetic model, but were some 15% less than those derived at that time from biomass harvests. Both CO₂ uptake and water use efficiency were comparable with those found in fertilised maize fields in warm temperate conditions.     

The effects of elevated CO2 on seed production and seedling recruitment in a sheep-grazed pasture

Seed production and seedling recruitment were measured over 2 years under ambient (360 ppm) and elevated (475 ppm) atmospheric CO₂ in a free air carbon dioxide enrichment (FACE) experiment, carried out in a sheep-grazed pasture on dry, sandy soil in New Zealand. In both years elevated CO₂ led to more dispersed seeds of the grasses Anthoxanthum odoratum, Lolium perenne and Poa pratensis, the legumes Trifolium repens and T. subterraneum and the herbs Hypochaeris radicata and Leontodon saxatilis. The increased seed dispersal in A. odoratum, H. radicata, Leontodon saxatilis and T. repens reflected both more inflorescences per unit area and more seeds per inflorescence under elevated CO₂. The increased seed dispersal in Lolium perenne, P. pratensis and T. subterraneum was due solely to more inflorescences per unit area. The number of seedlings that emerged and survived to at least 7 months of age was increased by elevated CO₂ for H. radicata, Leontodon saxatilis, T. repens and T. subterraneum in both years and for A. odoratum and Lolium perenne in the first year. For species where increased seedling recruitment was noted, there was a significant positive correlation between seed production in summer and seedling emergence in the following autumn and winter, and sowing 200 extra seeds per species m^-2 resulted in more seedlings compared to unsown controls. Elevated CO₂ did not affect seedling survival in any species. There was no measurable effect of elevated CO₂ on canopy and soil surface conditions or soil moisture at the time of seedling emergence. The results suggest the dominant effect of elevated CO₂ on seedling recruitment in this pasture was an indirect one, reflecting effects on the number of seeds produced. The biomass of H. radicata, Leontodon saxatilis, T. repens and T. subterraneum in the above-ground vegetation was greater under elevated than ambient CO₂. However, the size of individual seedlings and mature plants of these four species was unaffected by elevated CO₂. The results indicate an important way elevated CO₂ influenced plant species composition in this pasture was through changes in the pattern of seedling recruitment.     

General relationship for volumetric oxygen transfer coefficient (k L a) prediction in tower bioreactors utilizing immobilized cells

A general relationship for prediction of the volumetric oxygen transfer coefficient (k_La) in a tower bioreactor utilizing immobilized Penicillium chrysogenum as function of air superficial velocity, suspension rheological parameters and liquid physical properties is proposed in this study. The relationship was applied to three different systems and a good agreement between the calculated values and the experimental data was obtained.     

Elevated CO2 influences nutrient availability in young beech-spruce communities on two soil types

The objectives of this study were to investigate how different soil types and elevated N deposition (0.7 vs 7 g N m^-2a^-1) influence the effects of elevated CO₂ (370 vs 570 µmol CO₂ mol^-1) on soil nutrients and net accumulation of N, P, K, S, Ca, Mg, Fe, Mn, and Zn in spruce (Picea abies) and beech (Fagus sylvatica). Model ecosystems were established in large open-top chambers on two different forest soils: a nutrient-poor acidic loam and a nutrient-rich calcareous sand. The response of net nutrient accumulation to elevated atmospheric CO₂ depended upon soil type (interaction soil 2 CO₂, P<0.05 for N, P, K, S, Ca, Mg, Zn) and differed between spruce and beech. On the acidic loam, CO₂ enrichment suppressed net accumulation of all nutrients in beech (P<0.05 for P, S, Zn), but stimulated it for spruce (P<0.05 for Fe, Zn) On the nutrient-rich calcareous sand, increased atmospheric CO₂ enhanced nutrient accumulation in both species significantly. Increasing the N deposition did not influence the CO₂ effects on net nutrient accumulation with either soil. Under elevated atmospheric CO₂, the accumulation of N declined relative to other nutrients, as indicated by decreasing ratios of N to other nutrients in tree biomass (all ratios: P<0.001, except the N to S ratio). In both the soil and soil solution, elevated CO₂ did not influence concentrations of base cations and available P. Under CO₂ enrichment, concentrations of exchangeable NH₄⁺ decreased by 22% in the acidic loam and increased by 50% in the calcareous sand (soil 2 CO₂, P<0.001). NO₃^- concentrations decreased by 10-70% at elevated CO₂ in both soils (P<0.01).