Similarity of growth patterns between plantlets and seedlings of Brassica campestris L. under different in vitro environmental conditions

Explants and seeds of Brassica campestris L. were cultured on Murashige & Skoog (1962) medium with and without sucrose in a vessel with different numbers of air changes per hour under different PPF (photosynthetic photon flux) conditions. The growth and development of plantlets in the vessel were similar to those of seedlings when cultured under the same in vitro environmental conditions. The growth and development of seedlings when cultured under the same in vitro environmental conditions. The growth and development of plantlets/seedlings were greater for treatments with a higher number of air changes per hour and a higher PPF regardless of the sucrose concentration in the culture medium.The CO₂ concentration in the vessel with a lower number of air changes per hour decreased to approximately 100 ppm during the photoperiod on day 21 due to the photosynthetic activities of the plantlets/seedlings. The low CO₂ concentration, in turn, reduced the net photosynthetic rate of plantlets/seedlings in the vessel, and thus affected their growth and development.Abbreviations C_in CO₂ concentration in the culture vessel - C_out CO₂ concentration in the culture room - MS mineral composition of Murashige & Skoog (1962) medium - PPF photosynthetic photon flux     

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.     

Effects of increased CO2 levels on growth, photosynthesis, ammonium uptake and cell composition in the macroalga Hypnea spinella (Gigartinales, Rhodophyta)

The red seaweed Hypnea spinella (Gigartinales, Rhodophyta), was cultured at laboratory scale under three different CO₂ conditions, non-enriched air (360?ppm CO₂) and CO₂-enriched air at two final concentrations (750 and 1,600?ppm CO₂), in order to evaluate the influence of increased CO₂ concentrations on growth, photosynthetic capacity, nitrogen removal efficiency, and chemical cellular composition. Average specific growth rates of H. spinella treated with 750 and 1,600?ppm CO₂-enriched air increased by 85.6% and 63.2% compared with non-enriched air cultures. CO₂ reduction percentages close to 12% were measured at 750?ppm CO₂ with respect to 5% and 7% for cultures treated with air and 1,600?ppm CO₂, respectively. Maximum photosynthetic rates were enhanced significantly for high CO₂ treatments, showing P _max values 1.5-fold higher than that for air-treated cultures. N–NH ₄ ⁺ consumption rates were also faster for algae growing at 750 and 1,600?ppm CO₂ than that for non-enriched air cultures. As a consequence of these experimental conditions, soluble carbohydrates increased and soluble protein contents decreased in algae treated with CO₂-enriched air. However, internal C and N contents remained constant at the different CO₂ concentrations. No significant differences in data obtained with both elevated CO₂ treatments, under the assayed conditions, indicate that H. spinella is saturated at dissolved inorganic carbon concentrations close by twice the actual atmospheric levels. The results show that increased CO₂ concentrations might be considered a key factor in order to improve intensively cultured H. spinella production yields and carbon and nitrogen bioremediation efficiencies.     

In deep shade, elevated CO2 increases the vigor of tropical climbing plants

Climbing plants have profound influences on tropical forest dynamics and may take particular advantage from atmospheric CO₂ enrichment, thus potentially enhancing tree turnover. Here we test the effect of a four‐step CO₂‐enrichment on growth of three typical Yucatan (Mexico) climbers, across two low photon flux densities, representing typical understory situations. In pairs of two, species of Gonolobus (Asclepiadaceae), Ceratophytum (Bignoniaceae) and Thinouia (Sapindaceae) were grown on Yucatan forest soil in growth cabinets, which simulated the diurnal climate variation. Biomass increased non‐linearly in response to CO₂ enrichment from 280 (preindustrial) to 420 ppm and 560 ppm, but then (700 ppm) leveled off. The relative effect of CO₂‐enrichment between the two lower (280–420 ppm) CO₂ concentrations was 63% at low light (LL == 42 µmol m^2?2 s^2?1), compared to 37% at high light (HL = 87 µmol m^2?2 s^2?1). This overall response of species pairs was the combined effect of linear and non‐linear responses of the individual species across CO₂ treatments. Plant biomass was 61% larger in HL compared to LL. The species‐specific response depended on the neighbor, a species grew with h, irrespective of plant size. Stem length increased, but not consistently across species and light conditions. Specific stem length (SSL, length per dry mass) declined non‐linearly in all three species as CO₂ concentration increased (more pronounced at LL than at HL). SLA (leaf area per unit leaf dry mass) became lower as CO₂ concentration increased (more pronounced in HL). Enhanced vigor of climbers under elevated CO₂ as documented here may accelerate tropical forest dynamics and lead to greater abundance of early succesional tree species. This could reduce forest carbon stocking in the long run.     

Effect of increased pCO2 in seawater on survival rate of different developmental stages of the harpacticoid copepod Tigriopus japonicus

The rapid increase in carbon dioxide levels in seawater is causing ocean acidification and is expected to have significant effects on marine life. To explore the ability of the harpacticoid copepod Tigriopus japonicus to adapt to an increased concentration of dissolved carbon dioxide (CO₂) in seawater, we compared the survival rates of adult and nauplius stages at 400, 1000, and 1550?ppm pCO₂ over a 14-day period. The survival rate of T. japonicus dramatically decreased over time with increase in pCO₂ concentration. At 1550?ppm, the survival rate showed a decrease of more than 20% at the end of the experimental period over that at 400?ppm. Furthermore, the survival rate decreased by a greater amount at all concentrations in nauplii than in adults, with a greater effect in wild-collected specimens than in culture-derived individuals. The results suggest that future ocean acidification may negatively influence the sustainability of T. japonicus and thus may eventually influence benthic ecosystems.     

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.     

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.     

Response of tussock tundra to elevated carbon dioxide regimes: analysis of ecosystem CO2 flux through nonlinear modeling

Summary The response of tussock tundra to elevated atmospheric concentrations of CO₂ was measured at Toolik Lake, Alaska in the summer of 1983. Computer-controlled greenhouses were used to determine diurnal ecosystem flux of CO₂ under four treatments: 340 ppm, 510 ppm, and 680 ppm CO₂, as well as 680 ppm CO₂ with a four degree centrigrade increase in temperature. For the seven days of data analyzed, net daily CO₂ flux was significantly different between treatments. Net uptake was positively correlated with CO₂ concentration in the chamber and negatively correlated with temperature. A nonlinear model was used to analyze this data set and to determine some of the reasons for different net CO₂ flux. This model allowed an estimation of light utilization efficiency, total conductance of CO₂, and a comparable measure of total respiration. From this analysis we conclude that nutrient limitations in the arctic decrease the capacity of tundra plants to make use of elevated CO₂ concentrations. The plants respond by decreasing conductance in the presence of elevated CO₂, which results in approximately equal gross uptake rates for the three CO₂ treatments. Apparent changes in system respiration result in higher net uptake under elevated CO₂ but this may be due to biases in the data. The treatment with increased temperature exhibited higher conductances and, consequently, higher gross uptake of CO₂ than the other treatments. Higher temperatures, however, also increase respiration with the result being lower net uptake than would be expected in the absence of temperature inscreases.     

Effects of elevated CO2 and temperature on plant growth and herbivore defensive chemistry

Concentration of atmospheric CO₂ and temperature have both been rising for the last three decades. In this century, the temperature has been predicted to rise by 2–5 °C and the CO₂ concentration to double. These changes may affect the primary and secondary metabolism of plants and thus have implications for other trophic levels. However, the biotic interactions in changing climate conditions are poorly known. In this study, two questions were addressed: (i) How will climate change affect growth and the amounts of secondary compounds in flexible plant species? and (ii) How will this affect herbivores living on this species. Four clones of the dark‐leaved willow (Salix myrsinifolia (Salisb.)) seedlings were grown in closed‐top chambers with two controlled factors: concentration of atmospheric CO₂ and temperature (T). There were four combinations of these factors, each combination replicated four times (total of 16 chambers): (i) Control CO₂ (350 ppm) and control T, (ii) Elevated CO₂ (700 ppm) and control T, (iii) Control CO₂ and elevated T (2 °C), and (iv) Elevated CO₂ and elevated T. Stem growth and aerial biomass of the plants were determined; and the leaf phenolics, nitrogen and water concentrations were analysed. In addition the growth rate of larvae and feeding preference of adults of a specialist herbivore, the chrysomelid beetle Phratora vitellinae (L.), on the treated willow leaves were measured. Elevated temperature and CO₂ concentration increased the stem biomass and elevated CO₂ increased leaf biomass and total aerial biomass of the willows. Patterns of biomass allocation were different in different temperature treatments. At elevated temperature there was less branch and leaf material in relation to stems than at the control temperature. Moreover, patterns of biomass allocation differed among clones. CO₂ enhancement increased the specific leaf weight (SLW) and reduced both water and nitrogen content of the leaves, however, leaf area was unaffected by the treatments. Carbon dioxide (CO₂) and T enhancement reduced the concentrations of several phenolic compounds in the leaves. Phenolic compounds, nutrients, and water in the leaves might be diluted partly due to increased carbon allocation to different structures (e.g. thickening of cell wall and increase of trichomes, etc.). In some cases plant clones showed specific responses to treatments. The CO₂ enhancement reduced the relative growth rate (RGR) of the beetle larvae, and in contrast, temperature elevation increased it. Adult beetles did not clearly discriminate between willow leaves grown in different T and CO₂ environments, but tended to eat more leaf material from chambers with doubled CO₂ concentration. At elevated CO₂ adult beetles may need to eat more leaf material in order to reproduce, which may in turn prolong the life cycles, increasing the risk of being eaten and possibly affecting ability to overwinter successfully. Overall, climate change may significantly modify the dynamic interaction between willow and beetle populations.     

Effect of elevated CO2 concentration on seedling growth rate and photosynthesis inHevea brasiliensis

To study the effect of elevated CO₂ concentration on plant growth and photosynthesis, two clones ofHevea brasiliensis were grown in polybags and exposed to elevated concentration (700±25ppm) for 60 days. There was higher biomass accumulation, leaf area and better growth when compared to ambient air grown plantso From A/Ci curves it is clear that photosynthetic rates increases with increase in CO₂ concentrations. After 60 days of exposure to higher CO₂ concentration, a decrease in the carbon assimilation rate was noticed.     

A rhizolysimeter facility for studying the dynamics of crop and soil processes: description and evaluation

Increased atmospheric carbon dioxide (CO₂) concentration will likely cause changes in plant productivity and composition that might affect soil decomposition processes. The objective of this study was to test to what extent elevated CO₂ and N fertility-induced changes in residue quality controlled decomposition rates. Cotton (Gossypium hirsutum L.) was grown in 8-l pots and exposed to two concentrations of CO₂ (390 or 722 μmol mol^-1) and two levels of N fertilization (1.0 or 0.25 g l^-1 soil) within greenhouse chambers for 8 wks. Plants were then chemically defoliated and air-dried. Leaf, stem and root residues were assayed for total non-structural carbohydrates (TNC), lignin (LTGA), proanthocyanidins (PA), C and N. Respiration rates of an unsterilized sandy soil (Lakeland Sand) mixed with residues from the various treatments were determined using a soda lime trap to measure CO₂ release. At harvest, TNC and PA concentrations were 17 to 45% higher in residues previously treated with elevated CO₂ compared with controls. Leaf and stem residue LTGA concentrations were not significantly affected by either the elevated CO₂ or N fertilization treatments, although root residue LTGA concentration was 30% greater in plants treated with elevated CO₂. The concentration of TNC in leaf residues from the low N fertilization treatment was 2.3 times greater than that in the high N fertilization treatment, although TNC concentration in root and stem residues was suppressed 13 to 23% by the low soil N treatment. PA and LTGA concentrations in leaf, root and stem residues were affected by less than 10% by the low N fertilization treatment. N concentration was 14 to 44% lower in residues obtained from the elevated CO₂ and low N fertilization treatments. In the soil microbial respiration assay, cumulative CO₂ release was 10 to 14% lower in soils amended with residues from the elevated CO₂ and low N fertility treatments, although treatment differences diminished as the experiment progressed. Treatment effects on residue N concentration and C:N ratios appeared to be the most important factors affecting soil microbial respiration. The results of our study strongly suggest that, although elevated CO₂ and N fertility may have significant impact on post-harvest plant residue quality of cotton, neither factor is likely to substantially affect decomposition. Thus, C cycling might not be affected in this way, but via simple increases in plant biomass production. This revised version was published online in June 2006 with corrections to the Cover Date.     

Gas exchange of Ginkgo biloba leaves at different CO2 concentration levels

One and a half year-old Ginkgo saplings were grown for 2 years in 7 litre pots with medium fertile soil at ambient air CO₂ concentration and at 700 μmol mol⁻¹ CO₂ in temperature and humidity-controlled cabinets standing in the field. In the middle of the 2nd season of CO₂ enrichment, CO₂ exchange and transpiration in response to CO₂ concentration was measured with a mini-cuvette system. In addition, the same measurements were conducted in the crown of one 60-year-old tree in the field. Number of leaves/tree was enhanced by elevated CO₂ and specific leaf area decreased significantly.CO₂ compensation points were reached at 75–84 μmol mol⁻¹ CO₂. Gas exchange of Ginkgo saplings reacted more intensively upon CO₂ than those of the adult Ginkgo. On an average, stomatal conductance decreased by 30% as CO₂ concentration increased from 30 to 1000 μmol mol⁻¹ CO₂. Water use efficiency of net photosynthesis was positively correlated with CO₂ concentration levels. Saturation of net photosynthesis and lowest level of stomatal conductance was reached by the leaves of Ginkgo saplings at >1000 μmol mol⁻¹ CO₂. Acclimation of leaf net CO₂ assimilation to the elevated CO₂ concentration at growth occurred after 2 years of exposure. Maximum of net CO₂ assimilation was 56% higher at ambient air CO₂ concentration than at 700 μmol mol⁻¹ CO₂.     

Photosynthesis in willows (Salix × dasyclados) grown at different CO2 concentrations and fertilization levels

Summary Willows (Salix x dasyclados) were grown for 4 months in growth chambers at four nutrient and CO₂ levels, and photosynthesis measurements were made during the latter half of this period. Photosynthesis became saturated at lower light intensities at low CO₂ concentrations than at higher ones. The effect of CO₂ concentration on photosynthesis was greater at higher temperatures. The willows grown at the highest CO₂ concentration (1000 ppm) had a lower photosynthetic capacity than the others when measured at various concentrations. The effect of nutrient status on photosynthesis clearly increased with rising CO₂ concentrations. Although photosynthetic acclimation took place to a certain extent at higher CO₂ concentrations, photosynthesis still remained higher the higher the growth concentration was. At each CO₂ level photosynthesis increased contemporaneously with leaf nitrogen content, but at each fertilization level a rise in CO₂ concentration slightly increased photosynthesis and reduced the nitrogen content. The relative increase in photosynthesis achieved by a rise in CO₂ was greater than the corresponding increase in biomass growth, whereas the effect of fertilization was greater on biomass growth than on the rate of photosynthesis in the same willows.     

Effect of doubled CO<Subscript>2</Subscript> on morphology: Inhibition of stomata development in growing birch (<Emphasis Type="Italic">Betula platyphylla</Emphasis> Suk.) leaves

Two-year old birch (Betula platyphylla Suk.) seedlings were grown in climatic chambers for 7 weeks under various conditions: (1) ambient CO₂ concentration (350 ppm) and an ordinary nitrogen content in soil (2 mM NH₄NO₃); (2) ambient CO₂ concentration and a high nitrogen rate (16 mM NH₄NO₃); (3) doubled CO₂ concentration (700 ppm) and ordinary nitrogen content, and (4) doubled CO₂ concentration and a high nitrogen rate. Doubled CO₂ concentration in combination with the high nitrogen rate activated mostly seedling growth, e.g., stem thickening and leaf initiation. In this treatment, the maximum rate of apparent photosynthesis (A _max) was twice as high as in control seedlings. At doubled CO₂ concentration and ordinary nitrogen content, we observed the phenomenon of stomata absence from the upper leaf surface and doubling their number on the lower surface, whereas, at doubled CO₂ concentration and a high nitrogen rate, stomata partition was essentially similar as in control leaves. The conclusion is that, when the balance between CO₂ concentration and nitrogen rate is shifted, doubled CO₂ concentration exerts a morphotropic effect on differentiation of young epidermal tissue.Translated from Fiziologiya Rastenii, Vol. 52, No. 2, 2005, pp. 198–202.Original Russian Text Copyright © 2005 by Mao, Y.-J. Wang, X.-W. Wang, Voronin.This revised version was published online in April 2005 with a corrected cover date.     

Effect of CO2 and light on survival and growth of rice regenerants grownin vitro on sugar-free medium

Rice (Oryza sativa L.) plantlets regenerated from callus (rice regenerants) were grownin vitro during the preparation stage either on a 1/4 strength N6 gellan gum (4 g l^-1) medium without sucrose (SFM) or with 30 g l^-1 sucrose (SCM), and under CO₂ concentrations of 0.4, 2, 10, 50 or 100 mmol mol^-1, a photoperiod of 24 h and a photosynthetic photon flux density (PPFD) of 125 mol m^-2 s^-1. Rice regenerants were also grownin vitro on SFM or SCM under CO₂ concentration of 50 mmol mol^-1, a photoperiod of 12 or 24 h and a PPFD of 80 or 125 mol m^-2 s^-1. All rice regenerants grew successfully on SFM under CO₂ concentrations of 50 or 100 mmol mol^-1. Increasing the CO₂ concentration increased the survival percentage, shoot length and shoot and root dry weights of rice regenerants grown on SFM. Increasing CO₂ concentration had no significant effect on the survival or growth of rice regenerants grown on SCM. Survival percentages of rice regenerants grown on SCM were less than 80% for each of the CO₂ concentrations. A photoperiod of 24 h under CO₂ enrichment improved the survival and growth of rice regenerants grown on SFM, and increased the survival percentage and shoot dry weight of rice regenerants grown on SCM.     

Effect of elevated CO2 on tropical soda apple and its biological control agent Gratiana boliviana (Coleoptera: Chrysomelidae)

Rising atmospheric CO₂ levels could have drastic effects on the performance of invasive weeds and their insect herbivores. Despite the importance of biological control as an effective management tool for environmental weeds, there have been few studies on the potential impact of climate change on the future efficacy of biological control. The objective of the present study was to evaluate the effect of elevated CO₂ on the performance of tropical soda apple Solanum viarum (Solanaceae) and its biological control agent Gratiana boliviana (Coleoptera: Chrysomelidae). We established three levels of CO₂ in environmental growth chambers: ambient (400 ppm), medium (580 ppm) and high (780 ppm). Plants growing at the high level had greater biomass compared to those growing at the ambient and medium levels of CO₂. Leaf water content and the amount of leaf nitrogen were reduced at high compared to ambient or medium CO₂ levels. G. boliviana immature survival and developmental time were negatively affected at high CO₂ but not at medium or ambient levels. Adults were lighter and smaller when reared at the high CO₂ level compared to ambient and medium treatments, while adult fecundity was higher at the medium CO₂ level. Leaf area consumed by fifth instars was lower when feeding on plants grown at the high CO₂ level either inside a Petri dish or on potted plants. These results suggest that beetle performance may be diminished under future climate. However, further studies should incorporate other factors such as temperature and precipitation as well as the evolutionary potential of herbivores and plants to adapt to a changing climate.     

Effects of desiccation and CO2 concentrations on emersed photosynthesis in Porphyra haitanensis (Bangiales,Rhodophyta), a species farmed in China

The effects on photosynthesis of CO₂ and desiccation in Porphyra haitanensis were investigated to establish the effects of increased atmospheric CO₂ on this alga during emersion at low tides. With enhanced desiccation, net photosynthesis, dark respiration, photosynthetic efficiency, apparent carboxylating efficiency and light saturation point decreased, while the light compensation point and CO₂ compensation point increased. Emersed net photosynthesis was not saturated by the present atmospheric CO₂ level (about 350?ml?m^?3), and doubling the CO₂ concentration (700?ml?m^?3) increased photosynthesis by between 31% and 89% at moderate levels of desiccation. The relative enhancement of emersed net photosynthesis at 700?ml?m^?3 CO₂ was greater at higher temperatures and higher levels of desiccation. The photosynthetic production of Porphyra haitanensis may benefit from increasing atmospheric CO₂ concentration during emersion.     

The effect of elevated CO2 concentration and soil pH on the relationship between plant growth and rhizosphere denitrification potential

The effect of CO₂ concentration on plant growth and the size of the rhizosphere denitrifier population was investigated for ryegrass grown at 3 different soil pH values (pH 4.3, 5.9 and 7.0). Soil microcosms were planted with ryegrass and maintained under constant growth conditions at either ambient (450ppm) or elevated (720ppm) CO₂ concentration. At harvest, the rhizosphere soil was collected and subjected to a potential denitrification assay to provide an estimate of the size of the denitrifier population present. Ryegrass dry matter production varied across the pH range studied and contrary to other studies, elevated CO₂ concentration did not consistently increase growth. Plant growth was reduced by ≈ 35% and 23% at pH 4.3 and pH 5.9, respectively, under elevated CO₂ concentration. At pH 7.0, however, plant growth was increased by ≈ 45% under elevated CO₂. Potential denitrification rates within the rhizosphere followed a similar pattern to plant growth in the different treatments, suggesting that plant growth and the size of denitrifier population within the rhizosphere are coupled. This study investigates the relationship between plant growth and rhizosphere denitrification potential, thereby providing an estimate of the size of the denitrifier population under increased CO₂ concentration and soil pH.     

Influence of enhanced CO2 on growth and photosynthesis of the red algaeGracilaria sp. andG. chilensis

The influence of elevated CO₂ concentrations on growth and photosynthesis ofGracilaria sp. andG. chilensis was investigated in order to procure information on the effective utilization of CO₂. Growth of both was enhanced by CO₂ enrichment (air + 650 ppm CO₂, air + 1250 ppm CO₂, the enhancement being greater inGracilaria sp. Both species increased uptake of NO₃ ^– with CO₂ enrichment. Photosynthetic inorganic carbon uptake was depressed inG. chilensis by pre-culture (15 days) with CO₂ enrichment, but little affected inGracilaria sp. Mass spectrometric analysis showed that O₂ uptake was higher in the light than in the dark for both species and in both cases was higher inGracilaria sp. The higher growth enhancement inGracilaria sp. was attributed to greater depression of photorespiration by the enrichment of CO₂ in culture.     

Release of resource constraints allows greater carbon allocation to secondary metabolites and storage in winter wheat

The atmospheric CO₂ concentration ([CO₂]) is rapidly increasing, and this may have substantial impact on how plants allocate metabolic resources. A thorough understanding of allocation priorities can be achieved by modifying [CO₂] over a large gradient, including low [CO₂], thereby altering plant carbon (C) availability. Such information is of critical importance for understanding plant responses to global environmental change. We quantified the percentage of daytime whole‐plant net assimilation (A) allocated to night‐time respiration (R), structural growth (SG), nonstructural carbohydrates (NSC) and secondary metabolites (SMs) during 8 weeks of vegetative growth in winter wheat (Triticum aestivum) growing at low, ambient and elevated [CO₂] (170, 390 and 680 ppm). R/A remained relatively constant over a large gradient of [CO₂]. However, with increasing C availability, the fraction of assimilation allocated to biomass (SG + NSC + SMs), in particular NSC and SMs, increased. At low [CO₂], biomass and NSC increased in leaves but decreased in stems and roots, which may help plants achieve a functional equilibrium, that is, overcome the most severe resource limitation. These results reveal that increasing C availability from rising [CO₂] releases allocation constraints, thereby allowing greater investment into long‐term survival in the form of NSC and SMs.