Photosynthetic characteristics of Cymbidium plantlet in vitro

The photosynthetic characteristics of the Cymbidium plantlet in vitro cultured on Hyponex-agar medium with 2% sucrose were determined based on the measurements of CO₂ concentration inside and outside of the culture vessels. The CO₂ measurements were made with a gas chromatograph at a PPF (photosynthetic photon flux) of 35, 102 and 226 mol m^-2 s^-1, a chamber air temperature of 15, 25 and 35°C and a CO₂ concentration outside the vessel of approximately 350, 1100 and 3000 ppm. The net photosynthetic rates were determined on individual plantlets and were expressed on a dry weight basis. The steady-state CO₂ concentration during the photoperiod was lower inside the vessel than outside the vessel at any PPF greater than 35 mol m^-2s^-1 and at any chamber air temperature. The photosynthetic response curves relating the net photosynthetic rate, PPF, and CO₂ concentration in the vessel and chamber air temperature were similar to those for Cymbidium plants grown outside and other C₃ plants grown outside under shade. The results indicate that CO₂ enrichment for the plantlets in vitro at a relatively high PPF would promote photosynthesis and hence the growth of chlorophyllous shoots/plantlets in vitro and that the plantlets in vitro would make photoautotrophic growth under environmental conditions favorable for photosynthesis.Abbreviations C_in CO₂ concentration in the culture vessel - C_out CO₂ concentration outside the vessel (in the culture room) - PPF photosynthetic photon flux     

Opposite effects of exogenous sucrose on growth, photosynthesis and carbon metabolism of in vitro plantlets of tomato (L. esculentum Mill.) grown under two levels of irradiances and CO2 concentration

The long-term effects of exogenous sucrose (3 percnt;) on growth, photosynthesis and carbon metabolism ofin vitro tomato plantlets were investigated under two sets of growth conditions that respectively favor source- or sink-limitations of photosynthesis: 1) low photosynthetic photon flux (PPF) (50 μmol m⁻² · s⁻¹) and low CO₂ concentration (400 μmol mol⁻¹) and 2) high PPF (500 μmol m⁻² · s⁻¹ and high CO₂ concentration (4000 μmol mol⁻¹). The supply of sucrose under source-limitation conditions increased the growth, the maximal photosynthetic rate, the chl content, the maximal quantum yield of Photosystem II estimated by the Fv/Fm chl fluorescence ratio as well as the soluble sugars (hexoses, sucrose) and starch contents in roots, young and mature leaves when compared to those of photo-autotrophic plantlets. Also, sucrose feeding under these conditions strongly increased the activity of sucrose synthase (SS) (EC 2.4.1.13) in roots and young leaves whereas the activities of sucrose phosphate synthase (SPS) (EC 2.4.1.14), acid invertase (INV) (EC 3.2.1.26) and ADP-glucose pyrophosphorylase (ADPGppase) (EC 2.7.7.27) were highly stimulated in roots and mature leaves. Contrary to these observations, the supply of sucrose to plantlets developed under high PPF and CO₂ concentration decreased growth and led to a somewhat lower maximal photosynthetic rate relative to photo-autotrophic plantlets. These negative responses to exogenous sucrose were accompanied by stronger accumulations of hexose and starch, larger stimulation of INV in mature leaves developed under conditions of sink limitation than those from source limitation conditions. Moreover, under high PPF and high CO₂ concentration, exogenous sucrose led to a marked repression of the SPS activity and caused much lower stimulations of ADPGppase in mature leaves than those observed at low PPF and low CO₂ concentration. We therefore conclude that under our experimental conditions, the interactive effects of exogenous sucrose and environmental conditions on growth and photosynthesis could be rationalized by the source-sink equilibrium of thein vitro tomato plantlets.     

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.     

Sagebrush carbon allocation patterns and grasshopper nutrition: the influence of CO2 enrichment and soil mineral limitation

Summary Artemisia tridentata seedlings were grown under carbon dioxide concentrations of 350 and 650 l l^–1 and two levels of soil nutrition. In the high nutrient treatment, increasing CO₂ led to a doubling of shoot mass, whereas nutrient limitation completely constrained the response to elevated CO₂. Root biomass was unaffected by any treatment. Plant root/shoot ratios declined under carbon dioxide enrichment but increased under low nutrient availability, thus the ratio was apparently controlled by changes in carbon allocation to shoot mass alone. Growth under CO₂ enrichment increased the starch concentrations of leaves grown under both nutrient regimes, while increased CO₂ and low nutrient availability acted in concert to reduce leaf nitrogen concentration and water content. Carbon dioxide enrichment and soil nutrient limitation both acted to increase the balance of leaf storage carbohydrate versus nitrogen (C/N). The two treatment effects were significantly interactive in that nutrient limitation slightly reduced the C/N balance among the high-CO₂ plants. Leaf volatile terpene concentration increased only in the nutrient limited plants and did not follow the overall increase in leaf C/N ratio. Grasshopper consumption was significantly greater on host leaves grown under CO₂ enrichment but was reduced on leaves grown under low nutrient availability. An overall negative relationship of consumption versus leaf volatile concentration suggests that terpenes may have been one of several important leaf characteristics limiting consumption of the low nutrient hosts. Digestibility of host leaves grown under the high CO₂ treatment was significantly increased and was related to high leaf starch content. Grasshopper growth efficiency (ECI) was significantly reduced by the nutrient limitation treatment but co-varied with leaf water content.     

Light effects on leaf development and photosynthetic capacity of Hydrocotyle bonariensis Lam.

Rates of net CO₂ uptake were examined in developing leaves of Hydrocotyle bonariensis. Leaves that developed under high photosynthetically active radiation (48 mol m^-2 day^-1 PAR) were smaller, thicker, and reached maximum size sooner than did leaves that developed under low PAR (4.8 mol m^-2 day^-1). Maximum net CO₂ uptake rates were reached after 5 to 6 days expansion for both the low and the high PAR leaves. Leaves grown at high PAR had higher maximum photosynthetic rates and a higher PAR required for light saturation but showed a more rapid decline in rate with age than did low PAR leaves. To assess the basis for the difference observed in photosynthetic rates, CO₂ diffusion conductances and the mesophyll surface available for CO₂ absorption were examined for mature leaves. Stomatal conductance was the largest conductance in all treatments and did not vary appreciably with growth PAR. Mesophyll conductance progressively increased with growth PAR (up to 48 mol m^-2 day^-1) as did the mesophyll surface area per unit leaf area, but the cellular conductance exhibited most of its increase at low PAR (up to 4.8 mol m^-2 day^-1).     

Growth and photosynthesis of Chinese cabbage plants grown under light-emitting diode-based light source

We compared growth and the content of sugar, protein, and photosynthetic pigments, as well as chlorophyll fluorescence parameters in 15- and 27-day-old Chinese cabbage (Brassica chinensis L.) plants grown under a high-pressure sodium (HPS) lamps or a light source built on the basis of red (650 nm) and blue (470 nm) light-emitting diodes (LEDs) with a red to blue photon ratio of 7: 1. One group of plants was grown at a photosynthetic photon flux (PPF) level of 391 ± 24 μ mol/(m² s) (normal level); the other, at a PPF level of 107 ± 9 μ mol/(m² s) (low light). Plants of the third group were firstly grown at the low light and then (on the 12th day) transferred to the normal level. When grown at the normal PPF level, the plants grown under LEDs didn’t differ from plants grown under HPS lamps in shoot fresh weight, but they showed a lower root fresh and dry weights and the lower content of total sugar and sugar reserves in the leaves. No differences in the pigment content and photosystem II quantum yield were found; however, a higher Chl a/b ratio in plants grown under LEDs indicates a different proportion of functional complexes in thylakoid membranes. The response to low light conditions was mostly the same in plants grown under HPS lamps and LEDs; however, LED plants showed a lower growth rate and a higher nonphotochemical fluorescence quenching. In the case of the altered PPF level during growth, the plant photosynthetic apparatus adapted to new conditions of illumination within three days. Plants grown under HPS lamps at a constant normal PPF level and those transferred to the normal PPF level on the 12th day, on the 27th day didn’t differ in shoot fresh weight, but in plants grown under LEDs, the differences were considerable. Our results show that LED-based light sources can be used for plant growing. At the same time, some specific properties of plant photosynthesis and growth under these conditions of illumination were found.     

Effects of irradiance on growth,photosynthesis, and water use efficiency of seedlings of the chaparral shrub,Ceanothus megacarpus

Summary The effects of irradiance during growth on biomass allocation, growth rates, leaf chlorophyll and protein contents, and on gas exchange responses to irradiance and CO₂ partial pressures of the evergreen, sclerophyllous, chaparral shrub, Ceanothus megacarpus were determined. Plants were grown at 4 irradiances for the growth experiments, 8, 17, 25, 41 nE cm^-2 sec^-1, and at 2 irradiances, 9 and 50 nE cm^-2 sec^-1, for the other comparisons.At higher irradiances root/shoot ratios were somewhat greater and specific leaf weights were much greater, while leaf area ratios were much lower and leaf weight ratios were slightly lower than at lower irradiances. Relative growth rates increased with increasing irradiance up to 25 nE cm^-2 sec^-1 and then leveled off, while unit leaf area rates increased steeply and unit leaf weight rates increased more gradually up to the highest growth irradiance.Leaves grown at 9 nE cm^-2 sec^-1 had less total chlorophyll per unit leaf area and more per unit leaf weight than those grown at 50 nE cm^-2 sec^-1. In a reverse of what is commonly found, low irradiance grown leaves had significantly higher chlorophyll a/b than high irradiance grown leaves. High irradiance grown leaves had much more total soluble protein per unit leaf area and per unit dry weight, and they had much higher soluble protein/chlorophyll than low irradiance grown leaves.High irradiance grown leaves had higher rates of respiration in very dim light, required higher irradiances for photosynthetic saturation and had higher irradiance saturated rates of photosynthesis than low irradiance grown leaves. CO₂ compensation irradiances for leaves of both treatments were very low, <5 nE cm^-2 sec^-1. Leaves grown under low and those grown under high irradiances reached 95% of their saturated photosynthetic rates at 65 and 85 nE cm^-2 sec^-1, respectively. Irradiance saturated rates of photosynthesis were high compared to other chaparral shrubs, 1.3 for low and 1.9 nmol CO₂ cm^-2 sec^-1 for high irradiance grown leaves. A very unusual finding was that leaf conductances to H₂O were significantly lower in the high irradiance grown leaves than in the low irradiance grown leaves. This, plus the differences in photosynthetic rates, resulted in higher water use efficiencies by the high irradiance grown leaves. High irradiance grown leaves had higher rates of photosynthesis at any particular intercellular CO₂ partial pressure and also responded more steeply to increasing CO₂ partial pressure than did low irradiance grown leaves. Leaves from both treatments showed reduced photosynthetic capability after being subjected to low CO₂ partial pressures (100 bars) under high irradiances. This treatment was more detrimental to leaves grown under low irradiances.The ecological implications of these findings are discussed in terms of chaparral shrub community structure. We suggest that light availability may be an important determinant of chaparral community structure through its effects on water use efficiencies rather than on net carbon gain.     

Allocation responses to CO2 enrichment and defoliation by a native annual plant Heterotheca subaxillaris

Among plants grown under enriched atmospheric CO₂, root:shoot balance (RSB) theory predicts a proportionately greater allocation of assimilate to roots than among ambient‐grown plants. Conversely, defoliation, which decreases the plant's capacity to assimilate carbon, is predicted to increase allocation to shoot. We tested these RSB predictions, and whether responses to CO₂ enrichment were modified by defoliation, using Heterotheca subaxillaris, an annual plant native to south‐eastern USA. Plants were grown under near‐ambient (400 μmol mol^?1) and enriched (700 μmol mol^?1) levels of atmospheric CO₂. Defoliation consisted of the weekly removal of 25% of each new fully expanded, but not previously defoliated, leaf from either rosette or bolted plants. In addition to dry mass measurements of leaves, stems, and roots, Kjeldahl N, protein, starch and soluble sugars were analysed in these plant components to test the hypothesis that changes in C:N uptake ratio drive shifts in root:shoot ratio. Young, rapidly growing CO₂‐enriched plants conformed to the predictions of RSB, with higher root:shoot ratio than ambient‐grown plants (P < 0.02), whereas older, slower growing plants did not show a CO₂ effect on root:shoot ratio. Defoliation resulted in smaller plants, among which both root and shoot biomass were reduced, irrespective of CO₂ treatment (P < 0.03). However, H. subaxillaris plants were able to compensate for leaf area removal through flexible shoot allocation to more leaves vs. stem (P < 0.01). Increased carbon availability through CO₂ enrichment did not enhance the response to defoliation, apparently because of complete growth compensation for defoliation, even under ambient conditions. CO₂‐enriched plants had higher rates of photosynthesis (P < 0.0001), but this did not translate into increased final biomass accumulation. On the other hand, earlier and more abundant yield of flower biomass was an important consequence of growth under CO₂ enrichment.     

Influence of ultraviolet-B (UV-B) radiation on photosynthetic and growth characteristics in field-grown cassava (Manihot esculentum Crantz)

The effects of ultraviolet-B (UV-B between 290 and 320 nm) on photosynthesis and growth characteristics were investigated in field grown cassava (Manihot esculentum Crantz). Plants were grown at ambient and ambient plus a 5.5kJ m^?2 d^?1 supplementation of UV-B radiation for 95 d. The supplemental UV-B fluence used in this experiment simulated a 15% depletion in stratospheric ozone at the equator (0°N). Carbon dioxide exchange, oxygen evolution, and the ratio of variable to maximum fluorescence (F_v/F_m) were determined for fully expanded leaves after 64–76 d of UV-B exposure. AH plants were harvested after 95 d of UV-B exposure, assayed for chlorophyll and UV-B absorbing compounds, and separated into leaves, petioles, stems and roots. Exposure to UV-B radiation had no effect on in situ rates of photosynthesis or dark respiration. No difference in the concentration of UV-B absorbing compounds was observed between treatments. A 2-d daytime diurnal comparison of F_v to F_m ratios indicated a significant decline in F_v/F_m ratios and a subsequent increase in photoinhibition under enhanced UV-B radiation if temperature or PPF exceeded 35°C or 1800μmol m^?2 s^?1, respectively. However, UV-B effects on fluorescence kinetics appeared to be temporal since maximal photosynthetic rates as determined by oxygen evolution at saturated CO₂ and PPF remained unchanged. Although total biomass was unaltered with UV-B exposure, alterations in the growth characteristics of cassava grown with supplemental UV-B radiation are consistent with auxin destruction and reduced apical dominance. Changes in growth included an alteration of biomass partitioning with a significant increase in shoot/root ratio noted for plants receiving supplemental UV-B radiation. The increase in shoot/root ratio was due primarily to a significant decrease in root weight (–32%) with UV-B exposure. Because root production determines the harvest-able portion of cassava, UV-B radiation may still influence the yield of an important tropical agronomic species, even though photosynthesis and total dry biomass may not be directly affected.     

Photosynthetic responses to elevated CO2and O3 in field-grown potato(Solanum tuberosum)

Potato plants (Solanum tuberosum L. cv. Bintje) were grown to maturity in open-top chambers under three carbon dioxide (CO₂; ambient and 24 h d⁻¹ seasonal mean concentrations of 550 and 680 μmol mol⁻¹) and two ozone levels (O₃; ambient and an 8 h d⁻¹ seasonal mean of 50 nmol mol⁻¹). Chlorophyll content, photosynthetic characteristics, and stomatal responses were determined to test the hypothesis that elevated atmospheric CO₂ may alleviate the damaging influence of O₃ by reducing uptake by the leaves. Elevated O₃ had no detectable effect on photosynthetic characteristics, leaf conductance, or chlorophyll content, but did reduce SPAD values for leaf 15, the youngest leaf examined. Elevated CO₂ also reduced SPAD values for leaf 15, but not for older leaves; destructive analysis confirmed that chlorophyll content was decreased. Leaf conductance was generally reduced by elevated CO₂, and declined with time in the youngest leaves examined, as did assimilation rate (A). A generally increased under elevated CO₂, particularly in the older leaves during the latter stages of the season, thereby increasing instantaneous transpiration efficiency. Exposure to elevated CO₂ and/or O₃ had no detectable effect on dark-adapted fluorescence, although the values decreased with time. Analysis of the relationships between assimilation rate and intercellular CO₂ concentration and photosynthetically active photon flux density showed there was initially little treatment effect on CO₂-saturated assimilation rates for leaf 15. However, the values for plants grown under 550 μmol mol⁻¹ CO₂ were subsequently greater than in the ambient and 680 μmol mol⁻¹ treatments, although the beneficial influence of the former treatment declined sharply towards the end of the season. Light-saturated assimilation was consistently greater under elevated CO₂, but decreased with time in all treatments. The values decreased sharply when leaves grown under elevated CO₂ were measured under ambient CO₂, but increased when leaves grown under ambient CO₂ were examined under elevated CO₂. The results obtained indicate that, although elevated CO₂ initially increased assimilation and growth, these beneficial effects were not necessarily sustained to maturity as a result of photosynthetic acclimation and the induction of earlier senescence.     

Multiple shoot induction and leaf and flower bud abscission of Annonacultures as affected by types of ventilation

Nodal explants of Annona squamosa L. and Annona muricata L. were cultured in vitro under various types of ventilation: airtight vessel (sealed condition; number of air exchange 0.1 h^–1), natural ventilation (via a polypropylene membrane; number of air exchange 1.5 h^–1), and forced ventilation (5.0 cm³ min^–1 in a 60 cm³ vessel; number of air exchange 5.0 h^–1). In both species, numbers of leaves, leaf areas and numbers of nodes per shoot increased with improving standards of ventilation, while leaf abscissions were substantially reduced; all the leaves had abscised in the airtight vessels after 12–15 days, but none had done so with forced ventilation. Flower-bud abscission in A. muricatashowed a similar trend after 21 days. These effects were associated with reductions in the accumulation of ethylene within the culture vessels, produced by increasing the efficiency of ventilation; ethylene was not detected in those fitted with a forced ventilation system. CO₂ concentrations in culture headspaces and the net photosynthetic rates of the plantlets were also evaluated. CO₂ concentrations decreased well below the ambient in the natural and airtight vessels; however, under forced ventilation, CO₂ concentrations were significantly higher during the photoperiod, compared to those of the natural ventilation and airtight vessel treatments. In general, net photosynthetic rates per unit leaf area increased with increasing photosynthetic photon flux (PPF) and rates were highest in plantlets grown under forced ventilation, intermediate under natural ventilation and lowest in the airtight vessels.Eighteen different media were investigated for their effects on multiple shoot induction in both species. The best medium for multiple shoot induction and growth in A. squamosa was Murashige and Skoog medium (MS) + 6-benzylaminopurine (BA; 1.5 mg l^–1) + casein hydrolysate (1.0 g l^–1) and for A. muricata MS + BA (1.0 mg l^–1) + naphthaleneacetic acid (NAA; 0.1 mg l^–1).     

Influence of in vitro growth conditions on in vitro and ex vitro photosynthetic rates of easy- and difficult-to-acclimatize sea oats (Uniola paniculata L.) genotypes

Net photosynthetic rates (P _n) of easy (EK 16-3) and difficult-to-acclimatize (EK 11-1) sea oats genotypes were examined under the following culture conditions: (1) photoautotrophic [sugar-free medium, high photosynthetic photon flux (PPF), high vessel ventilation rates and CO₂ enrichment, (PA)]; (2) modified photomixotrophic [sugar-containing medium diluted with sugar-free medium over time, high PPF, and high vessel ventilation rates (PM)]; (3) modified photomixotrophic enriched [same as PM with CO₂ enrichment, (PME)]; or (4) conventional photomixotrophic [sugar-containing medium, low PPF, and low vessel ventilation rates (control)]. Regardless of genotype, plantlets cultured under PA conditions died within 2 wk, whereas under PM and PME conditions, plantlets increased their P _n. After 6 wk, P _n per gram dry weight was 1.7 times greater in EK 16-3 than EK 11-1 plantlets cultured under PME conditions. In vitro-produced leaves of EK 16-3 plantlets were elongated with expanded blades, whereas EK 11-1 produced short leaves without expanded blades, especially under control conditions. After in vitro culture, EK 16-3 PME plantlets exhibited the highest dry weights among treatments. EK 16-3 PME and EK 16-3 PM had similarly high survivability, shoot and root dry weights and leaf lengths ex vitro compared to EK 16-3 control and EK 11-1 PM and PME plantlets. Ex vitro growth, survivability and P _n per leaf area of either genotype were not affected by CO₂ enrichment under modified photomixotrophic conditions. These results suggest that growth and survivability of sea oats genotypes with different acclimatization capacities can be enhanced by optimizing culture conditions.     

The Regulatory Role of Inflorescence Leaves in Fruit-setting by Sweet Orange (Citrus sinensis)

Inflorescence leaves improve fruit set on sweet orange trees. We sought an explanation for this effect in terms of carbon demand by developing fruit versus potential supply from adjacent leaves. Our assessment was based upon measurements of fruit growth, leaf photosynthesis and ¹⁴C distribution patterns in plants grown under controlled conditions. Leafy inflorescences had sufficient foliar surface (1.24 dm²) and photosynthetic capacity (CO₂ 10.1 mg · dm^-2· h^-1) to support early development of fruits on the same shoot, and to make a substantial contribution towards subsequent growth. ¹⁴C-assimilates derived from new leaves were distributed towards adjacent fruit which showed strong competition for labelled substrate. By contrast, fruit borne on leafless inflorescences had to obtain all their assimilates from older leaves whose photosynthetic capacity (CO₂ 3.5–4.6 mg · dm^-2· h^-1) and individual area (0.2 dm²) were generally insufficient to wholly sustain fruit growth, so that a large number of old-leaves were needed; these fruit would be more susceptible to competition from other sinks.     

Acquisition and within-plant allocation of 13C and 15N in CO2-enriched Quercus robur plants

We assessed the effects of doubling atmospheric CO₂ concentration, [CO₂], on C and N allocation within pedunculate oak plants (Quercus robur L.) grown in containers under optimal water supply. A short-term dual ¹³CO₂ and ¹⁵NO₃^? labelling experiment was carried out when the plants had formed their third growing flush. The 22-week exposure to 700 μl l^?1 [CO₂] stimulated plant growth and biomass accumulation (+53% as compared with the 350 μl l^?1 [CO₂] treatment) but decreased the root/shoot biomass ratio (-23%) and specific leaf area (-18%). Moreover, there was an increase in net CO₂ assimilation rate (+37% on a leaf dry weight basis; +71% on a leaf area basis), and a decrease in both above- and below-ground CO₂ respiration rates (-32 and -26%, respectively, on a dry mass basis) under elevated [CO₂]. ¹³C acquisition, expressed on a plant mass basis or on a plant leaf area basis, was also markedly stimulated under elevated [CO₂] both after the 12-h ¹³CO₂ pulse phase and after the 60-h chase phase. Plant N content was increased under elevated CO₂ (+36%), but not enough to compensate for the increase in plant C content (+53%). Thus, the plant C/N ratio was increased (+13%) and plant N concentration was decreased (-11%). There was no effect of elevated [CO₂] on fine root-specific ¹⁵N uptake (amount of recently assimilated ¹⁵N per unit fine root dry mass), suggesting that modifications of plant N pools were merely linked to root size and not to root function. N concentration was decreased in the leaves of the first and second growing flushes and in the coarse roots, whereas it was unaffected by [CO₂] in the stem and in the actively growing organs (fine roots and leaves of the third growth flush). Furthermore, leaf N content per unit area was unaffected by [CO₂]. These results are consistent with the short-term optimization of N distribution within the plants with respect to growth and photosynthesis. Such an optimization might be achieved at the expense of the N pools in storage compartments (coarse roots, leaves of the first and second growth flushes). After the 60-h ¹³C chase phase, leaves of the first and second growth flushes were almost completely depleted in recent ¹³C under ambient [CO₂], whereas these leaves retained important amounts of recently assimilated ¹³C (carbohydrate reserves?) under elevated [CO₂].     

Transpiration does not control growth and nutrient supply in the amphibious plant Mentha aquatica

Mentha aquatica L. was grown at different nutrient availabilities in water and in air at 60% RH. The plants were kept at 600 mmol m^?3 free CO₂ dissolved in water (40 times air equilibrium) and at 30 mmol m^?3 CO₂ in air to ensure CO₂ saturation of growth in both environments. We quantified the transpiration-independent water transport from root to shoot in submerged plants relative to the transpiration stream in emergent plants and tested the importance of transpiration in sustaining nutrient flux and shoot growth. The acropetal water flow was substantial in submerged Mentha aquatica, reaching 14% of the transpiration stream in emergent plants. The transpiration-independent mass flow of water from the roots, measured by means of tritiated water, was diverted to leaves and adventitious shoots in active growth. The plants grew well and at the same rates in water and air, but nutrient fluxes to the shoot were greater in plants grown in air than in those that were submerged when they were rooted in fertile sediments. Restricted O₂ supply to the roots of submerged plants may account for the smaller nutrient concentrations, though these exceeded the levels required to saturate growth. In hydroponics, the root medium was aerated and circulated between submerged and emergent plants to minimize differences in medium chemistry, and here the two growth forms behaved similarly and could fully exploit nutrient enrichment. It is concluded that the lack of transpiration from leaf surfaces in a vapour-saturated atmosphere, or under water, is not likely to constrain the transfer of nutrients from root to shoot in herbaceous plants. Nutrient deficiency under these environmental conditions is more likely to derive from restricted development and function of the roots in waterlogged anoxic soils or from low porewater concentrations of nutrients.     

Interactive effects of elevated atmospheric CO2, mycorrhization and drought on long-distance transport of reduced sulphur in young pedunculate oak trees (Quercus robur L.)

Pedunculate oak (Quercus robur L.) was germinated and grown under nutrient non-limiting conditions for a total of 10–15 weeks at ambient CO₂ concentration and 1100 μmol mol^–1 CO₂ either in the presence or the absence of the mycorrhizal fungus Laccaria laccata. Half of the oak trees of these treatments were exposed to drought during final growth by suspending the water supply for 21 d. Mycorrhization and elevated atmospheric CO₂ each enhanced total plant biomass per tree. Whereas additional biomass accumulation of trees grown under elevated CO₂ was mainly attributed to increased growth of lateral roots, mycorrhization promoted shoot growth. Water deficiency reduced biomass accumulation without affecting relative water content, but this effect was more pronounced in mycorrhizal as compared to non-mycorrhizal trees. Elevated CO₂ partially prevented the development of drought stress, as indicated by leaf water potential, but did not counteract the negative effects of water deficiency on growth during the time studied. Enhanced biomass accumulation requires adaption in protein synthesis and, as a consequence, enhanced allocation of reduced sulphur produced in the leaves to growing tissues. Therefore, allocation of reduced sulphur from oak leaves was studied by flap-feeding radiolabelled GSH, the main long-distance transport form of reduced sulphur, to mature oak leaves. Export of radiolabel proceeded almost exclusively in basipetal direction to the roots. The rate of export of radioactivity out of the fed leaves was significantly enhanced under elevated CO₂, irrespective of mycorrhization. A higher proportion of the exported GSH was transported to the roots than to basipetal stem sections under elevated CO₂ as compared to ambient CO₂. Mycorrhization did not affect ³⁵S export out of the fed leaves, but the distribution of radiolabel between stem and roots was altered in preference of the stem. Trees exposed to drought did not show appreciable export of the ³⁵S radioactivity fed to the leaves when grown under ambient CO₂. Apparently, drought inhibited basipetal transport of reduced sulphur at the level of phloem loading and/or phloem transport. Elevated CO₂ seemed to counteract this effect of drought stress to some extent, since higher leaf water potentials and improved ³⁵S export out of the fed leaves was observed in oak trees exposed to drought and elevated CO₂ as compared to trees exposed to drought and ambient CO₂.     

Photoautotrophic culture conditions and photosynthetic photon flux influence growth of <Emphasis Type="Italic">Lilium</Emphasis> bulblets <Emphasis Type="Italic">in vitro</Emphasis>

Summary Lilium Asiatic hybrid ‘Mona’ bulblets were cultured in vitro for 100 d under photoautotrophic (CO₂-enriched conditions and without sucrose in the medium) and heterotrophic (non-enriched CO₂ conditions and sucrose-supplemented medium) methods and under various levels of photosynthetic photon flux (PPF). Bulblet growth and net photosynthetic rate (NPR) were analyzed. CO₂₋ and PPF-enriched conditions enhanced the overall growth of bulblets, scale leaves, and roots. Heterotrophic conditions enhanced bulblet growth but higher PPF levels were inhibitory to the development of scale leaves. These results indicate the CO₂₋ and PPF-enriched conditions (photoautotrophic conditions) are beneficial for the production of high-quality bulblets of Asiatic hybrid lilies in vitro     

Growth of In vitro banana (Musa SPP.) shoots under photomixotrophic and photoautotrophic conditions

Summary In vitro banana (Musa spp.) shoots were cultured under photomixotrophic (30 gl⁻¹ sucrose and 0.2 h⁻¹ number of air exchanges of culture vessels) and photoautotrophic (0 gl⁻¹ sucrose and 3.9 h⁻¹ number of air exchanges) conditions for 28 d in 370 cm³ Magenta boxes (GA7-type) containing 70 ml of half-strength Murashige and Skoog (MS) medium with 22.2 μM N⁶-benzyladenine (BA). The effects of varying CO₂ concentration (475 or 1340 μmol mol⁻¹) and light intensity (photosynthetic photon flux (PPF) of 100 or 200 μmol m⁻² s⁻¹) were investigated. Fresh and dry weights of banana shoots grown photomixotrophically were significantly greater on day 28 than those grown photoautotrophically. Photoautorophic shoots had a larger number of unfolded leaves and greater leaf area than photomixotrophic plants by days 14 and 28, regardless of CO₂ concentration. The shoot fresh and dry weights on day 14 in photoautotrophic conditions were significantly greater at PPF of 200 μmol m⁻² s⁻¹ than at 100 μmol m⁻² s⁻¹. The increase in net photosynthetic rate of photoautotrophic banana shoots was significant compared with photomixotrophic shoots. The multiplication ratio of in vitro banana shoots grown photoautotrophically in a 28-d culture period was the greatest at 100 μmol m⁻² s⁻¹ PPF and 475 μmol mol⁻¹ CO₂.     

The effect of elevated CO2 on diel leaf growth cycle, leaf carbohydrate content and canopy growth performance of Populus deltoides

Image sequence processing methods were applied to study the effect of elevated CO₂ on the diel leaf growth cycle for the first time in a dicot plant. Growing leaves of Populus deltoides, in stands maintained under ambient and elevated CO₂ for up to 4 years, showed a high degree of heterogeneity and pronounced diel variations of their relative growth rate (RGR) with maxima at dusk. At the beginning of the season, leaf growth did not differ between treatments. At the end of the season, final individual leaf area and total leaf biomass of the canopy was increased in elevated CO₂. Increased final leaf area at elevated CO₂ was achieved via a prolonged phase of leaf expansion activity and not via larger leaf size upon emergence. The fraction of leaves growing at 30–40% day^?1 was increased by a factor of two in the elevated CO₂ treatment. A transient minimum of leaf expansion developed during the late afternoon in leaves grown under elevated CO₂ as the growing season progressed. During this minimum, leaves grown under elevated CO₂ decreased their RGR to 50% of the ambient value. The transient growth minimum in the afternoon was correlated with a transient depletion of glucose (less than 50%) in the growing leaf in elevated CO₂, suggesting diversion of glucose to starch or other carbohydrates, making this substrate temporarily unavailable for growth. Increased leaf growth was observed at the end of the night in elevated CO₂. Net CO₂ exchange and starch concentration of growing leaves was higher in elevated CO₂. The extent to which the transient reduction in diel leaf growth might dampen the overall growth response of these trees to elevated CO₂ is discussed.     

Elevated CO2 may impair the beneficial effect of arbuscular mycorrhizal fungi on the mineral and phytochemical quality of lettuce

Arbuscular mycorrhizal fungi (AMF) can improve growth and nutritional quality of greenhouse‐grown lettuces cultivated at ambient CO₂. Moreover, mycorrhizal symbiosis is predicted to be important in defining plant responses to elevated atmospheric CO₂ concentrations. Our main objective was to assess the effects of elevated CO₂ on growth and nutritional quality of greenhouse‐grown lettuces inoculated or not with AMF. Results showed that the accumulation of mineral nutrients (e.g. P, Cu, Fe) and antioxidant compounds (carotenoids, phenolics, anthocyanins, ascorbate) induced by AMF in leaves of lettuces cultivated at ambient CO₂ may diminish or disappear under elevated CO₂. It is hypothesized that a relevant quantity of photoassimilates could be used for improving shoot growth and spreading mycorrhizal colonization in detriment to the secondary metabolism. However, important differences can be found among different cultivars of lettuces.