Using growth analysis to interpret competition between a C3 and a C4 annual under ambient and elevated CO2

Summary Detailed growth analysis in conjunction with information on leaf display and nitrogen uptake was used to interpret competition between Abutilon theophrasti, a C₃ annual, and Amaranthus retroflexus, a C₄ annual, under ambient (350 l l^-1) and two levels of elevated (500 and 700 l l^-1) CO₂. Plants were grown both individually and in competition with each other. Competition caused a reduction in growth in both species, but for different reasons. In Abutilon, decreases in leaf area ratio (LAR) were responsible, whereas decreased unit leaf rate (ULR) was involved in the case of Amaranthus. Mean canopy height was lower in Amaranthus than Abutilon which may explain the low ULR of Amaranthus in competition. The decrease in LAR of Abutilon was associated with an increase in root/shoot ratio implying that Abutilon was limited by competition for below ground resources. The root/shoot ratio of Amaranthus actually decreased with competition, and Amaranthus had a much higher rate of nitrogen uptake per unit of root than did Abutilon. These latter results suggest that Amaranthus was better able to compete for below ground resources than Abutilon. Although the growth of both species was reduced by competition, generally speaking, the growth of Amaranthus was reduced to a greater extent than that of Abutilon. Regression analysis suggests that the success of Abutilon in competition was due to its larger starting capital (seed size) which gave it an early advantage over Amaranthus. Elevated CO₂ had a positive effect upon biomass in Amaranthus, and to a lesser extent, Abutilon. These effects were limited to the early part of the experiment in the case of the individually grown plants, however. Only Amaranthus exhibited a significant increase in relative growth rate (RGR). In spite of the transitory effect of CO₂ upon size in individually grown plants, level of CO₂ did effect final biomass of competitively grown plants. Abutilon grown in competition with Amaranthus had a greater final biomass than Amaranthus at ambient CO₂ levels, but this difference disappeared to a large extent at elevated CO₂. The high RGR of Amaranthus at elevated CO₂ levels allowed it to overcome the difference in initial size between the two species.This study was supported by a grant from the US Department of Energy     

Responses of C4 grasses to atmospheric CO2 enrichment

Summary The growth and photosynethetic responses to atmospheric CO₂ enrichment of 4 species of C₄ grasses grown at two levels of irradiance were studied. We sought to determine whether CO₂ enrichment would yield proportionally greater growth enhancement in the C₄ grasses when they were grown at low irradiance than when grown at high irradiance. The species studied were Echinochloa crusgalli, Digitaria sanguinalis, Eleusine indica, and Setaria faberi. Plants were grown in controlled environment chambers at 350, 675 and 1,000 l 1^-1 CO₂ and 1,000 or 150 mol m^-2 s^-1 photosynthetic photon flux density (PPFD). An increase in CO₂ concentration and PPFD significantly affected net photosynthesis and total biomass production of all plants. Plants grown at low PPFD had significantly lower rates of photosynthesis, produced less biomass, and had reduced responses to increases in CO₂. Plants grown in CO₂-enriched atmosphere had lower photosynthetic capacity relative to the low CO₂ grown plants when exposed to lower CO₂ concentration at the time of measurement, but had greater rate of photosynthesis when exposed to increasing PPFD. The light level under which the plants were growing did not influence the CO₂ compensation point for photosynthesis.     

Diurnal changes in the response of canopy photosynthetic rate to elevated CO2 in a coupled temperature-light environment

The relative increase with elevated CO₂ of canopy CO₂ uptake rate (A), derived from continuous measurements during the day, was examined in full-cover vegetative Lolium perenne canopies after 17 days of regrowth. The stands were grown at ambient (358±50 mol mol^-1) and increased (626±50 mol mol^-1) CO₂ concentration in sunlit growth chambers. Over the entire range of temperature and light conditions (which were strongly coupled and increased simultaneously), A was on average twice as large in high compared to ambient CO₂. This response (called M=A in high CO₂/A in ambient CO₂) could not be explained by changes in canopy conductance for CO₂ diffusion (GC). In spite of interaction and strong coupling between temperature and light intensity, there was evidence that temperature rather than light determined M. Further, high CO₂ treatment was found to alleviate the afternoon depression in A observed in ambient CO₂. A temperature optimum shift or/and a larger carbohydrate sink capacity through altered root/shoot ratio are proposed in explanation.Abbreviations A CO₂ uptake rate - C350 ambient CO₂ treatment - C600 elevated CO₂ treatment - E canopy evapotranspiration rate - GC canopy conductance for CO₂ diffusion - M high CO₂ modification factor     

Effect of CO2 enrichment and nitrogen availability on resource acquisition and resource allocation in a grass,Bromus mollis

Summary The effects of CO₂ enrichment on the growth, biomass partitioning, photosynthetic rates, and leaf nitrogen concentration of a grass, Bromus mollis (C₃), were investigated at a favorable and a low level of nitrogen availability. Despite increases in root: shoot ratios, leaf nitrogen concentrations were decreased under CO₂ enrichment at both nitrogen levels. For the low-nitrogen treatment, this resulted in lower photosynthetic rates measured at 650 l/l for the CO₂-enriched plants, compared to photosynthetic rates measured at 350 l/l for the non-enriched plants. At higher nitrogen availability, photosynthetic rates of plants grown and measured at 650 l/l were greater than photosynthetic rates of the non-enriched plants measured at 350 l/l. Water use efficiency, however, was increased in enriched plants at both nitrogen levels. CO₂ enrichment stimulated vegetative growth at both high and low nitrogen during most of the vegetative growth phase but, at the end of the experiment, total biomass of the high and low CO₂ treatments did not differ for plants grown at low nitrogen availability. While not statistically significant, CO₂ tended to stimulate seed production at high nitrogen and to decrease it at low nitrogen.     

Effects of atmospheric CO2 enrichment, water status and applied nitrogen on water- and nitrogen-use efficiencies of wheat

Atmospheric CO₂ levels are expected to exceed 700 mol mol^–1 by the end of the 21st century. The influence of increased CO₂ concentration on crop plants is of major concern. This study investigated water- and nitrogen-use efficiency (WUE and NUE, respectively, were defined by the amount of biomass accumulated per unit water or N uptake) of spring wheat (Triticum aestivumL.) grown under two atmospheric CO₂ concentrations (350 and 700 mol mol^–1), two soil moisture treatments (well-watered and drought) and five nitrogen amendment treatments. Results showed that enriched CO₂ concentration increased canopy WUE, and more N supply led to higher WUE under the increased CO₂. Canopy WUE was significantly lower in well-watered treatments than in drought treatment, but increased with the increased N supply. Elevated CO₂ reduced the apparent recovery fraction of applied N by the plant root system (N_r, defined as the ratio of the increased N uptake to N applied), but increased the NUE and agronomic N efficiency (NAE, defined as the ratio of the increased biomass to N applied). Water limitation and high N application reduced the N_r, NUE and NAE, indicating a poor N efficiency. In addition, there was a close relationship between the root mass ratio and NUE. Canopy WUE was negatively related to the root mass ratio and NUE. Our results indicated that CO₂ enrichment enhanced WUE more at high N application, but increased NUE more when N application was less.     

Photosynthetic inhibition after long-term exposure to elevated levels of atmospheric carbon dioxide

The effect of long-term exposure to elevated levels of CO₂ on biomass partitioning, net photosynthesis and starch metabolism was examined in cotton. Plants were grown under controlled conditions at 350, 675 and 1000 l l^-1 CO₂. Plants grown at 675 and 1000 l l^-1 had 72% and 115% more dry weight respectively than plants grown at 350 l l^-1. Increases in weight were partially due to corresponding increases in leaf starch. CO₂ enrichment also caused a decrease in chlorophyll concentration and a change in the chlorophyll a/b ratio. High CO₂ grown plants had lower photosynthetic capacity than 350 l l^-1 grown plants when measured at each CO₂ concentration. Reduced photosynthetic rates were correlated with high internal (non-stomatal) resistances and higher starch levels. It is suggested that carbohydrate accumulation causes a decline in photosynthesis by feedback inhibition and/or physical damage at the chloroplast level.Abbreviations Ci internal CO₂ concentration - Chl chlorophyll - DMSO dimethylsulfoxide - HSD honestly significant difference (procedure) - MCW methanolchloroform-water - Pi inorganic phosphate - S.E.M. standard error of mean     

Leaf and canopy responses of Lolium perenne to long-term elevated atmospheric carbon-dioxide concentration

The relationship between leaf photosynthetic capacity (p _{n, max}), net canopy CO₂- and H₂O-exchange rate (NCER and E _t, respectively) and canopy dry-matter production was examined in Lollium perenne L. cv. Vigor in ambient (363±30 l· l^-1) and elevated (631±43 l·l^-1) CO₂ concentrations. An open system for continuous and simultaneous regulation of atmospheric CO₂ concentration and NCER and E _t measurement was designed and used over an entire growth cycle to calculate a carbon and a water balance. While NCER_max of full-grown canopies was 49% higher at elevated CO₂ level, stimulation of p _n, max was only 46% (in spite of a 50% rise in one-sided stomatal resistance for water-vapour diffusion), clearly indicating the effect of a higher leaf-area index under high CO₂ (approx. 10% in one growing period examined). A larger amount of CO₂-deficient leaves resulted in higher canopy dark-respiration rates and higher canopy light compensation points. The structural component of the high-CO₂ effect was therefore a disadvantage at low irradiance, but a far greater benefit at high irradiance. Higher canopy darkrespiration rates under elevated CO₂ level and low irradiance during the growing period are the primary causes for the increase in dry-matter production (19%) being much lower than expected merely based on the NCER_max difference. While total water use was the same under high and low CO₂ levels, water-use efficiency increased 25% on the canopy level and 87% on a leaf basis. In the course of canopy development, allocation towards the root system became greater, while stimulation of shoot dry-matter accumulation was inversely affected. Over an entire growing season the root/shoot production ratio was 22% higher under high CO₂ concentration.Abbreviations and symbols C350 ambient CO₂, 363±30 l·l^-1 - C600 high CO₂, 631±43 l·l^-1 - c _a atmospheric CO₂ level - c _i CO₂ concentration in the intracellular spaces of the leaf - E_t canopy evapotranspiration - I _o canopy light compensation point - NCER canopy CO₂-exchange rate - p _n leaf photosynthetic rate - PPFD photosynthetic photon flux density - r _a leaf boundary-layer resistance - RD canopy dark-respiration rate - r _s stomatal resistance - WUE water use efficiency     

Effects of long-term elevated atmospheric carbon dioxide onLolium perenne andTrifolium repens,using a simple photosynthesis model

Changes in gross canopy photosynthetic rate (PGc), produced by long-term exposure to an elevated atmospheric CO₂ level (626±50 µmol mol^-1), were modelled forLolium perenne L. cv. Vigor andTrifolium repens L. cv. Blanca, using a simple photosynthesis model, based on biochemical and physiological information (leaf gross CO₂ uptake in saturating light, P_max, and leaf quantum efficiency, ) and structural vegetation parameters (leaf area index, LAI, canopy extinction coefficient, k, leaf transmission, M). Correction of PGc for leaf respiration allowed comparison with previously measured canopy net CO₂ exchange rates, with the average divergence from model prediction amounting to about 6%. Sensitivity analysis showed that for a three-week old canopy, the PGc increase in high CO₂ could be attributed largely to changes in P_max and , while differences in canopy architecture were no longer important for the PGc-stimulation (which they were in the early growth stages). As a consequence of this increasing LAI with canopy age, the gain of daytime CO₂ uptake is progressively eroded by the increasing burden of canopy respiration in high-CO₂ grownLolium perenne. Modelling canopy photosynthesis in different regrowth stages after cutting (one week, two weeks,...), revealed that the difference in a 24-h CO₂ balance between the ambient and the high CO₂ treatment is reduced with regrowth time and completely disappears after 6 weeks.Abbreviations C350 ambient CO₂ treatment - C625 high CO₂ treatment - k canopy extinction coefficient - LAI leaf area index - LAI_max fitted LAI-maximum - M leaf transmission - NCER net CO₂ exchange rate - PGc gross canopy photosynthetic rate - Q photosynthetic photon flux density - Q₀ photosynthetic photon flux density at the top of the canopy - RDc canopy dark respiration rate - RDl leaf dark respiration rate - t regrowth time after cutting - T air temperature - leaf quantum efficiency - _LAI rate of initial LAI-increase with time     

Temperature effects on the photosynthetic response of C3 plants to long-term CO2 enrichment

To assess the long-term effect of increased CO₂ and temperature on plants possessing the C₃ photosynthetic pathway, Chenopodium album plants were grown at one of three treatment conditions: (1) 23 °C mean day temperature and a mean ambient partial pressure of CO₂ equal to 350 bar; (2) 34 °C and 350 bar CO₂; and (3) 34 °C and 750 bar CO₂. No effect of the growth treatments was observed on the CO₂ reponse of photosynthesis, the temperature response of photosynthesis, the content of Ribulose-1,5-bisphosphate carboxylase (Rubisco), or the activity of whole chain electron transport when measurements were made under identical conditions. This indicated a lack of photosynthetic acclimation in C. album to the range of temperature and CO₂ used in the growth treatments. Plants from every treatment exhibited similar interactions between temperature and CO₂ on photosynthetic activity. At low CO₂ (< 300 bar), an increase in temperature from 25 to 35 °C was inhibitory for photosynthesis, while at elevated CO₂ (> 400 bar), the same increase in temperature enhanced photosynthesis by up to 40%. In turn, the stimulation of photosynthesis by CO₂ enrichment increased as temperature increased. Rubisco capacity was the primary limitation on photosynthetic activity at low CO₂ (195 bar). As a consequence, the temperature response of A was relatively flat, reflecting a low temperature response of Rubisco at CO₂ levels below its k_m for CO₂. At elevated CO₂ (750 bar), the temperature response of electron transport appeared to control the temperature dependency of photosynthesis above 18 °C. These results indicate that increasing CO₂ and temperature could substantially enhance the carbon gain potential in tropical and subtropical habitats, unless feedbacks at the whole plant or ecosystem level limit the long-term response of photosynthesis to an increase in CO₂ and temperature.Abbreviations A net CO₂ assimilation rate - C _a ambient partial pressure of CO₂ - C _i intercellular partial pressure of CO₂ - Rubisco Ribulose-1,5-bisphosphate carboxylase - VPD vapor pressure difference between leaf and air     

The effect of long term CO2 enrichment on the growth,biomass partitioning and mineral nutrition of Sitka spruce (Picea sitchensis (Bong.) Carr.)

Sitka spruce [Picea sitchensis (Bong.) Carr.] seedlings were grown for 3 years in an outside control plot or in ambient (355 mol mol^-1) or elevated (ambient + 350 mol mol^-1) atmospheric CO₂ environments, within open top chambers (OTCs) at the Institute of Terrestrial Ecology, Edinburgh. Sequential harvests were carried out at the end of each growing season and throughout the 1991 growing season, five in all. Plants grown in elevated CO₂ had, (i) 35 and 10% larger root/shoot ratios at the end of the first and third season, respectively, (ii) significantly higher summer leader extension relative growth rates, which declined more rapidly in early autumn than ambient grown plants, (iii) after three growing seasons a significantly increased mean annual relative growth rate, (iv) consistently lower foliar nutrient concentrations, and (v) after two growing seasons smaller total projected needle areas. Plants grown inside OTCs were taller, heavier and had a smaller root/shoot ratio than those grown outside the chambers. There was no effect of CO₂ concentration on Sitka spruce leaf characteristics, although leaf area ratio, specific leaf area and leaf weight ratio all fell throughout the course of the 3 year experiment.     

Effects of CO2 enrichment,nutrient addition,and fungal endophyte-infection on the growth of two grasses

Summary Increasing atmospheric carbon dioxide (CO₂) concentration is expected to increase plant productivity and alter plant/plant interactions, but little is known about its effects on symbiotic interactions with microorganisms. Interactions between perennial ryegrass, Lolium perenne (a C3 plant), and purpletop grass, Tridens flavus (a C4 plant), and their clavicipitaceous fungal endophytes (Acremonium lolii and Balansia epichloe, respectively) were investigated by growing the grasses under 350 and 650 l l^– 1 CO₂ at two nutrient levels. Infected and uninfected perennial ryegrass responded with increased growth to both CO₂ enrichment and nutrient addition. Biomass and leaf area of infected and uninfected plants responded similarly to CO₂ enrichment. When growth analysis parameters were calculated, there were significant increases in relative growth rate and net assimilation rate of infected plants compared to uninfected plants, although the differences remained constant across CO₂ and nutrient treatments. Growth of purpletop grass did not increase with CO₂ enrichment or nutrient addition and there were no significant differences between infected and uninfected plants. CO₂ enrichment did not alter the interactions between these two host grasses and their endophytic-fungal symbionts.     

Effect of increased salinity on CO2 assimilation,O2 evolution and the δ13C values of leaves of Plantago maritima L. developed at low and high NaCl levels

The effect of increased salinity on photosynthesis was studied in leaves of Plantago maritima L. that developed while plants were at low and high NaCl levels. In leaves that developed while plants were grown at 50 mol·m^-3, exposure to 200 and 350 mol·m^-3 NaCl resulted in reductions in net CO₂ assimilation and stomatal conductance. The decline in CO₂ assimilation in plants at 200 and 350 mol·m^-3 NaCl occurred almost exclusively at high intercellular CO₂ concentrations. The initial slope of the CO₂ assimilation-intercellular CO₂ (A-C _i) curve, determined after salinity was increased, was identical or very similar to that measured initially. In contrast to the reductions observed in CO₂ assimilation, there were no significant differences in O₂ evolution rates measured at 5% CO₂ among leaves from plants exposed to higher salinity and plants remaining at low salinity.Leaves that developed while plants were at increased salinity levels also had significantly lower net CO₂ assimilation rates than plants remaining at 50 mol·m^-3 NaCl. The lower CO₂ assimilation rates in plants grown at 200 and 350 mol·m^-3 NaCl were a result of reduced stomatal conductance and low intercellular CO₂ concentration. There were no significant differences among treatments for O₂ evolution rates measured at high CO₂ levels. The increased stomatal limitation of photosynthesis was confirmed by measurements of the ¹³C/¹²C composition of leaf tissue. Water-use efficiency was increased in the plants grown at high salinity.Abbreviations and symbols A net CO₂ assimilation rate - C _a ambient CO₂ concentration - C _i intercellular CO₂ concentration - ¹³C isotopic ratio (¹³C/¹²C) expressed relative to a standard - RuBP ribulose-1,5-bisphosphate     

Leaf and canopy responses to elevated CO2 in a pine forest under free-air CO2 enrichment

Physiological responses to elevated CO₂ at the leaf and canopy-level were studied in an intact pine (Pinus taeda) forest ecosystem exposed to elevated CO₂ using a free-air CO₂ enrichment (FACE) technique. Normalized canopy water-use of trees exposed to elevated CO₂ over an 8-day exposure period was similar to that of trees exposed to current ambient CO₂ under sunny conditions. During a portion of the exposure period when sky conditions were cloudy, CO₂-exposed trees showed minor (7%) but significant reductions in relative sap flux density compared to trees under ambient CO₂ conditions. Short-term (minutes) direct stomatal responses to elevated CO₂ were also relatively weak (5% reduction in stomatal aperture in response to high CO₂ concentrations). We observed no evidence of adjustment in stomatal conductance in foliage grown under elevated CO₂ for nearly 80 days compared to foliage grown under current ambient CO₂, so intrinsic leaf water-use efficiency at elevated CO₂ was enhanced primarily by direct responses of photosynthesis to CO₂. We did not detect statistical differences in parameters from photosynthetic responses to intercellular CO₂ (A _net-C _i curves) for Pinus taeda foliage grown under elevated CO₂ (550 mol mol^–1) for 50–80 days compared to those for foliage grown under current ambient CO₂ from similar-sized reference trees nearby. In both cases, leaf net photosynthetic rate at 550 mol mol^–1 CO₂ was enhanced by approximately 65% compared to the rate at ambient CO₂ (350 mol mol^–1). A similar level of enhancement under elevated CO₂ was observed for daily photosynthesis under field conditions on a sunny day. While enhancement of photosynthesis by elevated CO₂ during the study period appears to be primarily attributable to direct photosynthetic responses to CO₂ in the pine forest, longer-term CO₂ responses and feedbacks remain to be evaluated.     

Loblolly pine grown under elevated CO2 affects early instar pine sawfly performance

Seedlings of loblolly pine Pinus taeda (L.), were grown in open-topped field chambers under three CO₂ regimes: ambient, 150 l l^–1 CO₂ above ambient, and 300 l l^–1 CO₂ above ambient. A fourth, non-chambered ambient treatment was included to assess chamber effects. Needles were used in 96 h feeding trials to determine the performance of young, second instar larvae of loblolly pine's principal leaf herbivore, red-headed pine sawfly, Neodiprion lecontei (Fitch). The relative consumption rate of larvae significantly increased on plants grown under elevated CO₂, and needles grown in the highest CO₂ regime were consumed 21% more rapidly than needles grown in ambient CO₂. Both the significant decline in leaf nitrogen content and the substantial increase in leaf starch content contributed to a significant increase in the starch:nitrogen ratio in plants grown in elevated CO₂. Insect consumption rate was negatively related to leaf nitrogen content and positively related to the starch:nitrogen ratio. Of the four volatile leaf monoterpenes measured, only -pinene exhibited a significant CO₂ effect and declined in plants grown in elevated CO₂. Although consumption changed, the relative growth rates of larvae were not different among CO₂ treatments. Despite lower nitrogen consumption rates by larvae feeding on the plants grown in elevated CO₂, nitrogen accumulation rates were the same for all treatments due to a significant increase in nitrogen utilization efficiency. The ability of this insect to respond at an early, potentially susceptible larval stage to poorer food quality and declining levels of a leaf monoterpene suggest that changes in needle quality within pines in future elevated-CO₂ atmospheres may not especially affect young insects and that tree-feeding sawflies may respond in a manner similar to herb-feeding lepidopterans.     

Inter- and intra-generic differences in growth,reproduction, and fitness of nine herbaceous annual species grown in elevated CO2 environments

In assessing the capacity of plants to adapt to rapidly changing global climate, we must elucidate the impacts of elevated carbon dioxide on reproduction, fitness and evolution. We investigated how elevated CO₂ influenced reproduction and growth of plants exhibiting a range of floral morphologies, the implications of shifts in allocation for fitness in these species, and whether related taxa would show similar patterns of response. Three herbaceous, annual species each of the genera Polygonum, Ipomoea, and Cassia were grown under 350 or 700 ppm CO₂. Vegetative growth and reproductive output were measured non-destructively throughout the full life span, and vegetative biomass was quantified for a subsample of plants in a harvest at first flowering. Viability and germination studies of seed progeny were conducted to characterize fitness precisely. Early vegetative growth was often enhanced in high-CO₂ grown plants of Polygonum and Cassia (but not Ipomoea). However, early vegetative growth was not a strong predictor of subsequent reproduction. Phenology and production of floral buds, flowers, unripe and abscised fruits differed between CO₂ treatments, and genera differed in their reproductive and fitness responses to elevated CO₂. Polygonum and Cassia species showed accelerated, enhanced reproduction, while Ipomoea species generally declined in reproductive output in elevated CO₂. Seed quality and fitness (in terms of viability and percentage germination) were not always directly correlated with quantity produced, indicating that output alone may not reliably indicate fitness or evolutionary potential. Species within genera typically responded more consistently to CO₂ than unrelated species. Cluster analyses were performed separately on suites of vegetative and reproductive characters. Some species assorted within genera when these reproductive responses were considered, but vegetative responses did not reflect taxonomic affinity in these plants. Congeners may respond similarly in terms of reproductive output under global change, but fitness and prognoses of population persistence and evolutionary performance can be inferred only rarely from examination of vegetative characters alone.     

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     

Prolonged Growth of Young Spruce (<Emphasis Type="Italic">Picea koraiensis</Emphasis> Nakai) Plants at Double Atmospheric CO<Subscript>2</Subscript> Concentration Stimulates the Preferential Growth of Thick Roots

Two-year-old young spruce (Picea koraiensis Nakai) plants were grown in a climatic chamber during three summer months at double atmospheric CO₂ concentration, sufficient content of soil inorganic nitrogen, and diurnal variation of temperature and illuminance, which simulate natural growth conditions. The control plants were grown in another climatic chamber under the same conditions, but at atmospheric CO₂ concentration (350 ppm). CO₂ exchange was measured with a Li-Cor 6400 infra-red gas analyzer in attached leaves placed in a climatic chamber in the morning under growth conditions and saturating light 1200 μE/(m² s) in June, July, and August. In addition, dry weights of needles, leafless shoot parts of plant, fraction of thick (more than 0.5 mm in diameter) and thin (less than 0.5 mm in diameter) roots were recorded. The data were used to plot CO₂ exchange rates as a function of carbon dioxide concentration and to calculate the increment of shoot and root phytomass. The maximum gas exchange rates in the treated and control plants similarly depended on CO₂ concentration. The slope of the CO₂ dependence curve, which corresponded to the kinetic characteristic V _m /K _M of photosynthetic carboxylation, increased monotonically during the experiment. To the end of observation period, the proportion of thick roots in plant phytomass significantly increased in the plants grown at double atmospheric CO₂ concentration, as compared to the control plants. Thus, the increase in the rate of photosynthetic gas exchange in plants grown for three months at double atmospheric CO₂ concentration was only due to the increase in CO₂, the substrate of Rubisco carboxylation activity. We found no differences in the CO₂ characteristic for Rubisco between the treated and control plants. The ratio of needle to thin roots in the treated and control plants was similar and did not change during the experiment. The excess of photoassimilates in the treated, as compared to the control plants, was preferentially used for thick root growth. This result shows that photosynthesis in young spruce forests can deposit excess atmospheric CO₂ in the soil horizon in the form of thick root phytomass. __________ Translated from Fiziologiya Rastenii, Vol. 52, No. 5, 2005, pp. 741–746. Original Russian Text Copyright ? 2005 by Mao, Y.-J. Wang, Zhu, X.-W. Wang, Sun, Zhou, Voronin.     

Remote Sensing of Solar-excited Plant Fluorescence as a Measure of Photosynthetic Rate

Leaf level net photosynthetic rates (P _N) of laurel oak (Quercus hemispherica) juveniles grown under contrasting nutrient and CO₂ regimes were negatively correlated with red to far-red ratios, R/FR (690/760 nm), steady-state, solar-excited fluorescence ratios (r ² = 0.66, n = 12) measured across 12 plant canopies. Laurel oak juveniles that had been subjected to nitrogen stress over a period of a year demonstrated higher R/FR than their counterparts that had been provided with sufficient nitrogen. Plants that had been grown at elevated CO₂ concentrations, EC [700 mol (CO₂) mol^-1] also exhibited significantly higher R/FR when subjected to normal ambient carbon dioxide concentrations than their counterparts grown under ambient concentrations, AC [380 mol (CO₂) mol^-1]. All fluorescence measurements were obtained by observing a multi-plant canopy using a unique solar-blind passive sensor. This sensor, which utilizes Fraunhofer-line discrimination techniques, detects radiation at the cores of the lines comprising the atmospheric oxygen A- and B-bands, centered at 762 and 688 nm, respectively. These results support the use of solar-excited steady-state plant fluorescence as a potential tool for remote measurement of canopy radiation use efficiency.     

Influence of Etherel and Gibberellic Acid on Carbon Metabolism,Growth, and Essential Oil Accumulation in Spearmint (Mentha Spicata)

Controlled environment chamber and glasshouse studies were conducted on six herbaceous annual species grown at 350 (AC) and 700 (EC) mol(CO₂) mol^-1 to determine whether growth at EC resulted in acclimation of the apparent quantum yield of photosynthesis (QY) measured at limiting photosynthetic photon flux density (PPFD), or in acclimation of net photosynthetic rate (P _N) measured at saturating PPFD. It was also determined whether acclimation in P _N at limiting PPFD was correlated with acclimation of carboxylation efficiency or ribulose-1,5-bisphosphate (RuBP) regeneration rate measured at saturating PPFD. Growth at EC reduced both the QY and P _N at limiting PPFD in three of the six species. The occurrence of photosynthetic acclimation measured at a rate limiting PPFD was independent of whether photosynthetic acclimation was apparent at saturating measurement PPFD. At saturating measurement PPFD, acclimation to EC in the apparent carboxylation efficiency and RuBP regeneration capacity also occurred independently. Thus at least three components of the photosynthetic system may adjust independently when leaves are grown at EC. Estimates of photosynthetic acclimation at both high and low PPFD are necessary to accurately predict photosynthesis at the whole plant or canopy level as [CO₂] increases.     

Elevated CO2 and leaf shape: Are dandelions getting toothier?

Heteroblastic leaf development in Taraxacum officinale is compared between plants grown under ambient (350 ppm) vs. elevated (700 ppm) CO₂ levels. Leaves of elevated CO₂ plants exhibited more deeply incised leaf margins and relatively more slender leaf laminae than leaves of ambient CO₂ plants. These differences were found to be significant in allometric analyses that controlled for differences in leaf size, as well as analyses that controlled for leaf developmental order. The effects of elevated CO₂ on leaf shape were most pronounced when plants were grown individually, but detectable differences were also found in plants grown at high density. Although less dramatic than in Taraxacum, significant effects of elevated CO₂ on leaf shape were also found in two other weedy rosette species, Plantago major and Rumex crispus. These observations support the long-standing hypothesis that leaf carbohydrate level plays an important role in regulating heteroblastic leaf development, though elevated C0₂ may also affect leaf development through direct hormonal interactions or increased leaf water potential. In Taraxacum, pronounced modifications of leaf shape were found at CO₂ levels predicted to occur within the next century.