Photoautotrophic micropropagation of Spathiphyllum

In order to maximize yield, Spathiphyllum, an ornamental plant, was cultured in vitro in novel culture vessels termed Vitron. The best growth was obtained by culturing plantlets on sugar-free liquid medium under CO₂ enrichment (3 000 μmol mol⁻¹ 24 h⁻¹ d⁻¹) at a low photon flux density (PPFD of 45 μmol m⁻² s⁻¹), suggesting that the novel Vitron culture system is suitable for the photoautotrophic micropropagation of Spathiphyllum.     

Promoting root induction and growth of in vitro macadamia (<Emphasis Type="Italic">Macadamia tetraphylla</Emphasis> L. ‘Keaau’) plantlets using CO<Subscript>2</Subscript>-enriched photoautotrophic conditions

In this study, a rooting protocol was developed for macadamia plantlets with healthy roots and enhanced growth performance, along with enhanced photosynthetic capability. In vitro-grown shoots rooted in vented vessels containing vermiculite as the supporting material exhibited 100% frequency of root induction, whereas when shoots were grown in non-vented vessels containing a solidified Murashige and Skoog (MS) medium, the frequency of root induction was less than 30%. The formation of root with callus, hyperhydricity, and leaf necrosis was observed in this photomixotrophic closed system. The modification of the vented photoautotrophic system with different concentrations of CO₂ and sucrose were investigated using vermiculite as the supporter. The number of roots, root length, root surface area, fresh weight, and dry weight were significantly higher in plantlets grown in CO₂-enriched (1,000 μmol CO₂ mol⁻¹) photoautotrophic conditions. The water content in both root and shoot tissues of plantlets cultured under photoautotrophic conditions was maximized. In addition, shoot and leaf performances were enhanced in plantlets cultured under CO₂-enriched photoautotrophic conditions. The supplementation of sucrose (29–88 mM) to culture media in both ambient and elevated CO₂ conditions affected a reduction in the shoot and root performance of in vitro plantlets. Chlorophyll a, chlorophyll b, and total carotenoids in the leaf tissues of plantlets acclimatized in CO₂-enriched photoautotrophic conditions were enriched, leading to increasing photosynthetic abilities, including chlorophyll fluorescence and net photosynthetic rate. From this investigation, a root induction protocol was established and the production of healthy macadamia plantlets was successfully implemented using CO₂-enriched photoautotrophic conditions.     

Changes in photosynthetic activity,pigment composition,electrolyte leakage,lipid peroxidation,and antioxidant enzymes during ex vitro establishment of micropropagated <Emphasis Type="Italic">Rauvolfia tetraphylla</Emphasis> plantlets

The effects of photosynthetic photon flux density (PPFD) on antioxidant metabolism and photosynthetic properties in leaves during ex vitro establishment of micropropagated Rauvolfia tetraphylla plantlets were investigated. In vitro-propagated plantlets were acclimatized at either 50 (Low-light = LL) or 300 (High-light = HL) μmol m⁻²s⁻¹ photosynthetic PPFD for 4 weeks under controlled conditions. Increases in chlorophyll (Chl) a, b and carotenoid levels were observed in plantlets acclimatized at both light intensities. At transplantation, micropropagated plantlets were not photosynthetically active, but the net photosynthetic rate increased in newly formed leaves over time during acclimatization. The observed differences in pigment contents and photosynthetic rates suggested adaptation of plantlets from heterotrophic to autotrophic mode of nutrition during acclimatization. Changes in activities of antioxidant enzymes were also observed during acclimatization. Superoxide dismutase activity increased in plantlets acclimatized at HL intensities. Likewise, changes in activity of catalase and ascorbate peroxidase were also detected. These observed changes reflected the ability of plants in developing an antioxidant enzymatic defense system aiding in survival against oxidative stress and in reducing release of free radicals.     

Deschampsia antarctica Desv. primary photochemistry performs differently in plants grown in the field and laboratory

Primary photochemistry of photosystem II (F _v/F _m) of the Antarctic hair grass Deschampsia antarctica growing in the field (Robert Island, Maritime Antarctic) and in the laboratory was studied. Laboratory plants were grown at a photosynthetic photon flux density (PPFD) of 180 μmol m⁻² s⁻¹ and an optimal temperature (13 ± 1.5°C) for net photosynthesis. Subsequently, two groups of plants were exposed to low temperature (4 ± 1.5°C day/night) under two levels of PPFD (180 and 800 μmol m⁻² s⁻¹) and a control group was kept at 13 ± 1.5°C and PPFD of 800 μmol m⁻² s⁻¹. Chlorophyll fluorescence was measured during several days in field plants and weekly in the laboratory plants. Statistically significant differences were found in F _v/F _m (=0.75–0.83), F ₀ and F _m values of field plants over the measurement period between days with contrasting irradiances and temperature levels, suggesting that plants in the field show high photosynthetic efficiency. Laboratory plants under controlled conditions and exposed to low temperature under two light conditions showed significantly lower F _v/F _m and F _m. Moreover, they presented significantly less chlorophyll and carotenoid content than field plants. The differences in the performance of the photosynthetic apparatus between field- and laboratory-grown plants indicate that measurements performed in ex situ plants should be interpreted with caution.     

Physiology of effects of temporary immersion bioreactors on micropropagated pineapple plantlets

Summary Temporary immersion bioreactors are an efficient tool for plant mass propagation because they increase multiplication rate and plant quality. Little knowledge is available on the ecosystem and physiological behavior of plantlets when using this new culture technique. In order to evaluate the effects of the conditions on physiological change of pineapple plantlets, a factorial experiment was conducted, where axillary clusters were cultured under two levels of photosynthetic photon flux (PPF): 30 μmol m⁻²s⁻¹ (low) and 225 μmol m⁻²s⁻¹ (high), using two culture methods (conventional micropropagation in liquid medium and a temporary immersion bioreactor) during the elongation phase. CO₂ concentration in the headspace volume container was measured during a whole cycle of temporary immersion (3h). At the time before the next immersion period, the levels of CO₂ increased significantly to 14171 μmol mol⁻¹ at high PPF. The maximal photosynthetic rate as well as the maximum quantum yield of photosystem II were low for plantlets cultivated in the femporary immersion bioreactor at high PPF. However, these plantlets showed large increases in sugar and nitrogen uptake and also increases in dry weight and foliar area. These results indicate that shoot growth did not totally depend on the photosynthesis process. In vitro pineapple plantlets appeared to use more nutrients in the culture medium than those from photosynthesis. In summary, temporary immersion bioreactor-derived plantlets showed remarkable nutrient uptake, indicating a higher photo-mixotrophic metabolism.     

Seed germination and seedling physiology of Larix kaempferi and Pinus densiflora in seedbeds with charcoal and elevated CO2

We investigated the effect of ectomycorrhizal colonization, charcoal and CO₂ levels on the germination of seeds of Larix kaempferi and Pinus densiflora, and also their subsequent physiological activity and growth. The seeds were sown in brown forest soil or brown forest soil mixed with charcoal, at ambient CO₂ (360 μmol mol⁻¹) or elevated CO₂ (720 μmol mol⁻¹), with or without ectomycorrhiza. The proportions of both conifer seeds that germinated in forest soil mixed with charcoal were significantly greater than for seeds sown in forest soil grown at each CO₂ level (P < 0.05; t-test). However, the ectomycorrhizal colonization rate of each species grown in brown forest soil mixed with charcoal was significantly lower than in forest soil at each CO₂ treatment [CO₂] (P < 0.01; t-test). The phosphorus concentrations in needles of each seedling colonized with ectomycorrhiza and grown in forest soil were greater than in nonectomycorrhizal seedlings at each CO₂ level, especially for L. kaempferi seedlings (P < 0.05; t-test), but the concentrations in seedlings grown in brown forest soil mixed with charcoal were not increased at any CO₂ level. Moreover, the maximum net photosynthetic rate of each seedling for light and CO₂ saturation (P _max) increased when the seedlings were grown with ectomycorrhiza at 720 μmol mol⁻¹ [CO₂]. Ectomycorrhizal colonization led to an increase in the stem diameter of each species grown in each soil treatment at each CO₂ level. However, charcoal slowed the initial growth of both species of seedling, constraining ectomycorrhizal development. These results indicate that charcoal strongly assists seed germination and physiological activity.     

<Emphasis Type="Italic">Petunia</Emphasis> × <Emphasis Type="Italic">hybrida</Emphasis> during transition to flowering as affected by light intensity and quality treatments

Petunia × hybrida was grown under high (H), medium (M) and low (L) light intensity [photoperiod; 16 h d⁻¹, photosynthetic photon flux density (PPFD); 360, 120 and 40 μmol m⁻² s⁻¹, respectively] as well as under end-of-day (EOD) red (R) and far-red (FR) light quality treatments [photoperiod; 14.5 h d⁻¹, PPFD; 30 μmol m⁻² s⁻¹ EOD; 15 min, Control (C) light; without EOD light treatment]. Shoot growth, leaf anatomical and photosynthetic responses as well as the responses of peroxidase (POD) isoforms and their specific activities following transition to flowering (1–6 weeks) were evaluated. Flower bud formation of Petunia × hybrida was achieved at the end of the 4th week for H light treatment and on the end of the 6th week for FR light treatment. No flower bud formation was noticed in the C and R light treatments. H and M light treatments induced lower chlorophyll (Chla, Chlb, Chla+b) concentrations in comparison to L light. On the other hand R and FR light chlorophyll content were similar to C light. Photosynthetic parameters [CO₂ assimilation rate (A), transpiration rate (E) and stomatal conductance (g _s) values] were higher in the H light treated plants in comparison to M and L light treated plants. A, E and g _s values of R and FR light were similar to C light plants. Leaf anatomy revealed that total leaf thickness, thickness of the contained tissues (epidermis, palisade and spongy parenchyma) and relative volume percentages of the leaf histological components were differently affected within the light intensity and the light quality treatments. POD specific activities increased from the 1st to the 6th week during transition to flowering. Native-PAGE analysis revealed the appearance of four anionic POD (A₁–A₄) isoforms in all light treatments. On the basis of the leaf anatomical, photosynthetic and plant morphological responses, the production of high quality Petunia × hybrida plants with optimal flowering times could be achieved through the control of both light intensity and light quality. The appearance of A₁ and A₂ anionic POD isoforms could be also used for successful scheduling under light treatments.     

Application of a novel disposable film culture system to photoautotrophic micropropagation of <Emphasis Type="Italic">Eucalyptus uro-grandis (Urophylia x grandis)</Emphasis>

Summary To overcome various disadvantages of conventional culture vessls for plant micropropagation, we previously developed the photoautotrophic micropropagation technique, with special mention for the first practical film culture system, the ‘Miracle Pack’ (MP), which was made of fluorocarbon polymer film (Neoflo^? PFA film) and supported by a polycarbonate frame. While the PFA film has superior thermal stability, high light transmittance and high gas permeability, making the MP system (MP-PFA) superior to conventional culture vessels for the micropropagation of various plant species, its high cost is a disadvantage. In this study, a possible alternative of lower-cost OTP^? film made of TPX (4-methyl-1-pentane polymer) and CPP (a polypropylene), which possesses similar characteristics to PFA film, is evaluated to develop a novel disposable film culture vesel, termed ‘Vitron’, for culturing Eucalyptus (urophylla x grandis), plantlets. The three film culture systems, MP-PFA, MP-OTP (MP with OTP film), and Vitron, were placed under CO₂ enrichment, low photosynthetic photon flux density (PPFD; 45 μmol m⁻² s⁻¹), and sugar-free medium, using phenol resin foam (Oasis^?) as a substrate. In vitro and ex vitro growth and development of Eucalyptus shoots from the four-leaf stage to the rooting stage were compared for all three culture systems. The effects of the duration and concentration of CO₂ enrichments on in vitro growth of Eucalyptus cultured in the Vitron film system were also examined. The best growth and quality of Eucalyptus plantlets was obtained for the Vitron vessel placed in 3000 ppm CO₂ enrichment for 24 hours per day at low PPFD with sugar-free liquid medium and Oasis as substate. Results of this study suggest that the novel Vitron culture system is suitable for the photoautotrophic micropropagation of Eucalyptus. These authors contributed equally to the research results.     

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     

Effect of sucrose,light, and carbon dioxide on plantain micropropagation in temporary immersion bioreactors

In vitro physiology and carbon metabolism can be affected by the sink–source relationship. The effect of different sucrose concentrations (10, 30, and 50 g L⁻¹), light intensities (80 and 150 μmol m⁻² s⁻¹), and CO₂ levels (375 and 1,200 μmol mol⁻¹) were tested during plantain micropropagation in temporary immersion bioreactors. Activities of pyruvate kinase, phosphoenol pyruvate carboxylase, and the photosynthesis rate were recorded. From the morphological and practical point of view, the best results were obtained when plants were cultured with 30 g L⁻¹ sucrose, 80 μmol m⁻² s⁻¹ light intensity, and 1,200 μmol mol⁻¹ CO₂ concentration. This treatment improved leaf and root development, reduced respiration during in vitro culture, and increased starch level at the end of the hardening phase. In addition to that, the number of competent plants was increased from 80.0% to 91.0% at the end of the in vitro phase and the survival percentage from 95.71% to 99.80% during ex vitro hardening.     

Acclimation of the summer annual species, Lolium temulentum, to CO2 enrichment

Lolium temulentum L. Ba 3081 was grown hydroponically in air (350 μmol mol⁻¹ CO₂) and elevated CO₂ (700 μmol mol⁻¹ CO₂) at two irradiances (150 and 500 μmol m⁻² s⁻¹) for 35 days at which point the plants were harvested. Elevated CO₂ did not modify relative growth rate or biomass at either irradiance. Foliar carbon-to-nitrogen ratios were decreased at elevated CO₂ and plants had a greater number of shorter tillers, particularly at the lower growth irradiance. Both light-limited and light-saturated rates of photosynthesis were stimulated. The amount of ribulose-1,5-bisphosphate carboxylase-oxygenase (Rubisco) protein was increased at elevated CO₂, but maximum extractable Rubisco activities were not significantly increased. A pronounced decrease in the Rubisco activation state was found with CO₂ enrichment, particularly at the higher growth irradiance. Elevated-CO₂-induced changes in leaf carbohydrate composition were small in comparison to those caused by changes in irradiance. No CO₂-dependent effects on fructan biosynthesis were observed. Leaf respiration rates were increased by 68% in plants grown with CO₂ enrichment and low light. We conclude that high CO₂ will only result in increased biomass if total light input favourably increases the photosynthesis-to-respiration ratio. At low irradiances, biomass is more limited by increased rates of respiration than by CO₂-induced enhancement of photosynthesis. Received: 23 February 1999 / Accepted: 15 June 1999     

Impact of in vitro CO2 enrichment and sugar deprivation on acclimatory responses of Phalaenopsis plantlets to ex vitro conditions

We assessed the effect of growth at either 400 μmol mol^?1 (ambient) or 1000 μmol mol^?1 (elevated) CO₂ and 0 g L^?1 (deprivation) or 30 g L^?1 (supplementation) sugar on morphological traits, photosynthetic attributes and intrinsic elements of the CAM pathway using the CAM orchid Phalaenopsis ‘Amaglade’. The growth of shoot (retarded) and root (induced) was differently affected by CO₂ enrichment and mixotrophic regime (+sugar). The Fv/Fm ratio was 14% more in CO₂-enriched treatment than at ambient level during in vitro growth. At elevated level of CO₂ and sugar treatment, the content of Chl(a + b), Chl a/b and Chl/Car was enhanced while carotenoid content remained unaltered. During in vitro growth, gas-exchange analysis indicated that increased uptake of CO₂ accorded with the increased rate of transpiration and unchanged stomatal conductance at elevated level of CO₂ under both photo- and mixotrophic growth condition. At elevated level of CO₂ and sugar deprivation, activities of Rubisco (26.4%) and PEPC (74.5%) was up-regulated. Among metabolites, the content of sucrose and starch was always higher under CO₂ enrichment during both in vitro and ex vitro growth. Our results indicate that plantlets grown under CO₂ enrichment developed completely viable photosynthetic apparatus ready to be efficiently transferred to ex vitro condition that has far-reaching implications in micropropagation of Phalaenopsis.     

Growth and net photosynthetic rates of <Emphasis Type="Italic">Hosta</Emphasis> ‘blue vision’ during acclimatization in bright,natural light with CO<Subscript>2</Subscript> enrichment

Summary Hosta ‘Blue Vision’, a shade-adapted perennial, was successfully acclimatized in high, natural light conditions in the research Acclimatron^TM at Clemson University, Clemson, SC during the summer of 2000. The supplemental CO₂ levels achieved during acclimatization were 710±113, 2396±121, and 5641±119 μmol mol⁻¹, approximately 2×, 6×, and 15× ambient CO₂. Plants were maintained in H₂O-saturated atmospheres and protected from temperature increases associated with high light intensity. In the 5 wk following ex vitro transfer, plantlet roots grew at the 2× CO₂ level, but shoot biomass was unaffected. Results for the 6× and 15× CO₂ levels were comparable and provided the best plantlet growth. The “doubling time’ that is characteristic of exponential growth was 10.8 and 9.8 d for root and shoot dry weights, respectively. There was no indication of light saturation of net photosynthetic rate (NPR) over the photosynthetic photon flux density (PPFD) range of 100–1200 μmolm⁻²s⁻¹ experienced during this study. An interaction between CO₂ and light intensity levels was detected for NPR of Hosta ‘Blue Vision’ with CO₂ saturation occurring at approximately 2800 μmol mol⁻¹. regardless of light level. Furthermore, at the optimal CO₂ level, NPR increased quadratically as light intensity increased, and NPR was greatest at the maximum light intensity (PPFD: 1200 μmol m⁻²s⁻¹).     

Growth,Stomatal Conductance,Photosynthetic Rate,Ribulose-1,5-Bisphosphate Carboxylase/Oxygenase and Phosphoenolpyruvate Carboxylase Activities during Rooting and Acclimatisation of Rosa Hybrida Plantlets

The rooting of shoots of micropropagated Rosa hybrida cv. Madame Delbard was conducted on MS medium with 30 kg m^–3 sucrose or on hydroponic medium (containing less mineral salts), under higher photosynthetic photon flux density (PPFD) (100 in comparison with 45 µmol m^–2 s^–1) and flushed by ambient air [AC, 340 µmol(CO₂) mol^–1] or by CO₂-enriched air (EC, 2 500 µmol mol^–1) and lower relative humidity (80–90 % vs. 96–99 %). This cultivation led to plantlets with longer roots and adventitious root formation. Net photosynthetic rate and ribulose-1,5-bisphosphate carboxylase/oxygenase (RuBPCO) activities, RuBPCO/phosphoenolpyruvate carboxylase activities ratio, and starch accumulation increased under these conditions. After 14 d, plantlets had functional stomata and could be acclimated on open benches without gradual decrease in relative humidity. The percentage of survival was higher when the rooting took place in EC than in AC. However, the advantage acquired during rooting phase by plantlets cultured in liquid medium was not maintained after 4 weeks of acclimatisation.     

Growth and photosynthetic response of <Emphasis Type="Italic">Fagus crenata</Emphasis> seedlings to ozone and/or elevated carbon dioxide

We investigated the effects of ozone (O₃) and/or elevated CO₂ concentration ([CO₂]) on growth and photosynthetic traits of Fagus crenata seedlings. Two-year-old seedlings were grown in four experimental treatments comprising two O₃ treatments (charcoal-filtered air and 100 nmol mol⁻¹ O₃; 6 h/day, 3 days/week) in combination with two CO₂ treatments (350 and 700 μmol mol⁻¹) for 18 weeks in environmental control growth chambers. The four treatments were designated as control, elevated O₃, elevated CO₂, and elevated CO₂ + O₃. Dry matter growth of the seedlings was greater in elevated CO₂ + O₃ than in elevated CO₂. In elevated CO₂ + O₃, a marked increase of second-flush leaves, considered a compensative response to O₃, was observed. The net photosynthetic rate of first-flush leaves in elevated CO₂ + O₃ increased earlier and was maintained for a longer period of time than that in elevated CO₂. Because emergence of second-flush leaves of F. crenata is greatly affected by the amount of assimilation products of first-flush leaves in current year, we consider that an early increase in the net photosynthetic rate of first-flush leaves contributed to the marked increase in second-flush leaf emergence under elevated CO₂ + O₃. These results imply that we must account for changes in compensative capacity with respect to not only morphological traits but also phenological traits and physiological functions such as photosynthesis when evaluating effects of O₃ on F. crenata under elevated [CO₂].     

Responses of Gmelina arborea, a tropical deciduous tree species, to elevated atmospheric CO2: Growth, biomass productivity and carbon sequestration efficacy

The photosynthetic response of trees to rising CO₂ concentrations largely depends on source-sink relations, in addition to differences in responsiveness by species, genotype, and functional group. Previous studies on elevated CO₂ responses in trees have either doubled the gas concentration (>700 μmol mol⁻¹) or used single large addition of CO₂ (500-600 μmol mol⁻¹). In this study, Gmelina arborea, a fast growing tropical deciduous tree species, was selected to determine the photosynthetic efficiency, growth response and overall source-sink relations under near elevated atmospheric CO₂ concentration (460 μmol mol⁻¹). Net photosynthetic rate of Gmelina was ∼30% higher in plants grown in elevated CO₂ compared with ambient CO₂-grown plants. The elevated CO₂ concentration also had significant effect on photochemical and biochemical capacities evidenced by changes in F_V/F_M, ABS/CSm, ET₀/CSm and RuBPcase activity. The study also revealed that elevated CO₂ conditions significantly increased absolute growth rate, above ground biomass and carbon sequestration potential in Gmelina which sequestered ∼2100 g tree⁻¹ carbon after 120 days of treatment when compared to ambient CO₂-grown plants. Our data indicate that young Gmelina could accumulate significant biomass and escape acclimatory down-regulation of photosynthesis due to high source-sink capacity even with an increase of 100 μmol mol⁻¹ CO₂.     

Changes in photosynthetic capability and carbohydrate production in an epiphytic CAM orchid plantlet exposed to super-elevated CO2

The effects on growth in super-elevated (1%) CO₂ in terms of photosynthetic capability and carbohydrate production were studied in an epiphytic CAM (Crassulacean acid metabolism) orchid plantlet, Mokara Yellow (Arachnis hookeriana×Ascocenda Madame Kenny). The growth of the plantlets was greatly enhanced after growing for 3 months at 1% CO₂ compared with the control plantlets (0.035% CO₂). CO₂ enrichment produced more than a 2-fold increase in dry matter production. The enhanced root growth at 1% CO₂ led to a higher root:shoot ratio. Plantlets grown at super-elevated CO₂ had higher F_v/F_m values, a higher photochemical quenching (q_P) and a relatively lower non-photochemical quenching (q_N). CO₂ at 1% appeared to enhance the utilization of captured light energy in the orchid plantlets. CO₂ enrichment also increased contents of soluble sugars (glucose and sucrose) and starch in the orchid plantlets. The extra starch formed under 1% CO₂ did not cause a disruption of the chloroplasts. Chlorophyll content was higher and a clear granal stacking was evident in young leaves and roots of plantlets grown at 1% CO₂. An extensive thylakoid system was observed in the young leaf chloroplasts of the CO₂-enriched plantlets indicating an improved development of the photosynthetic apparatus when compared to that of the control plantlets. The increased photosynthetic capacity and enhanced growth of the epiphytic roots under CO₂ enrichment would facilitate the generation of more photoassimilates and acquisition of essential resources, thereby increasing the survival rate of orchid plantlets under stressful field conditions.     

Long-term responses of the green-algal lichen Parmelia caperata to natural CO2 enrichment

Acclimation to elevated CO₂ was investigated in Parmelia caperata originating from the vicinity of a natural CO₂ spring, where the average daytime CO₂ concentration was 729 ± 39 μmol mol⁻¹ dry air. Thalli showed no evidence of a down-regulation in photosynthetic capacity following long-term exposure to CO₂ enrichment in the field; carboxylation efficiency, total Ribulose bisphosphate carboxylase/oxygenase (Rubisco) content, apparent quantum yield of CO₂ assimilation, and the light-saturated rate of CO₂ assimilation (measured under ambient and saturating CO₂ concentrations) were similar in thalli from the naturally CO₂ enriched site and an adjacent control site where the average long-term CO₂ concentration was about 355 μmol mol⁻¹. Thalli from both CO₂ environments exhibited low CO₂ compensation points and early saturation of CO₂ uptake kinetics in response to increasing external CO₂ concentrations, suggesting the presence of an active carbon-concentrating mechanism. Consistent with the lack of significant effects on photosynthetic metabolism, no changes were found in the nitrogen content of thalli following prolonged exposure to elevated CO₂. Detailed intrathalline analysis revealed a decreased investment of nitrogen in Rubisco in the pyrenoid of algae located in the elongation zone of thalli originating from elevated CO₂, an effect associated with a reduction in the percentage of the cell volume occupied by lipid bodies and starch grains. Although these differences did not affect the photosynthetic capacity of thalli, there was evidence of enhanced limitations to CO₂ assimilation in lichens originating from the CO₂-enriched site. The light-saturated rate of CO₂ assimilation measured at the average growth CO₂ concentration was found to be significantly lower in thalli originating from a CO₂-enriched atmosphere compared with that of thalli originating and measured at ambient CO₂. At lower photosynthetic photon flux densities, the light compensation point of net CO₂ assimilation was significantly higher in thalli originating from elevated CO₂, and this effect was associated with higher usnic acid content. Received: 8 May 1998 / Accepted: 22 January 1999     

Gas exchange and growth responses to elevated CO2 and light levels in the CAM species Opuntia ficus-indica

Gas exchange and dry-weight production in Opuntia ficus-indica, a CAM species cultivated worldwide for its fruit and cladodes, were studied in 370 and 750 μmol mol⁻¹ CO₂ at three photosynthetic photon flux densities (PPFD: 5, 13 and 20 mol m⁻² d⁻¹). Elevated CO₂ and PPFD enhanced the growth of basal cladodes and roots during the 12-week study. A rise in the PPFD increased the growth of daughter cladodes; elevated CO₂ enhanced the growth of first-daughter cladodes but decreased the growth of the second-daughter cladodes produced on them. CO₂ enrichment enhanced daily net CO₂ uptake during the initial 8 weeks after planting for both basal and first-daughter cladodes. Water vapour conductance was 9 to 15% lower in 750 than in 370 μmol mol⁻¹ CO₂. Cladode chlorophyll content was lower in elevated CO₂ and at higher PPFD. Soluble sugar and starch contents increased with time and were higher in elevated CO₂ and at higher PPFD. The total plant nitrogen content was lower in elevated CO₂. The effect of elevated CO₂ on net CO₂ uptake disappeared at 12 weeks after planting, possibly due to acclimation or feedback inhibition, which in turn could reflect decreases in the sink strength of roots. Despite this decreased effect on net CO₂ uptake, the total plant dry weight at 12 weeks averaged 32% higher in 750 than in 370 μmol mol⁻¹ CO₂. Averaged for the two CO₂ treatments, the total plant dry weight increased by 66% from low to medium PPFD and by 37% from medium to high PPFD.     

The study of microclimate in response to different plant community association in tropical moist deciduous forest from northern India

The data on microclimate were collected between 2010 and 2011 in five forest communities (dry miscellaneous, sal mixed, lowland miscellaneous, teak and savannah) in a tropical moist deciduous forest in Katerniaghat Wildlife Sanctuary, Uttar Pradesh, India to compare how vegetation structure affects microclimate. Diurnal variations in microclimatic variables [photosynthetically active radiation (PAR) at forest understory level, air temperature, soil surface temperature, ambient CO₂, air absolute humidity] were measured with LI-COR 840, LI-COR 191, LI-COR 190 SZ, LI-1400-101 and LI-1400-103 (LI-COR; Lincoln, NE, USA) at centre of three 0.5 ha plots in each forest community. The diurnal trend in microclimatic parameters showed wide variations among communities. PAR at forest floor ranged from 0.0024 to 1289.9 (μmol m⁻²s⁻¹) in post-monsoon season and 0.0012 to 1877.3 (μmol m⁻²s⁻¹) in mid-winter season. Among the five communities, the highest PAR value was observed in savannah and lowest in sal mixed forest. All the forest communities received maximum PAR at forest floor between 1000 and 1200 h. The ambient air temperature ranged from 19.15 to 26.69°C in post-monsoon season and 11.31 to 23.03°C in mid-winter season. Soil temperature ranged from 13.54 to 36.88°C in post-monsoon season and 6.39 to 29.17°C in mid-winter season. Ambient CO₂ ranged from 372.16 to 899.14 μmol mol⁻¹ in post-monsoon season and 396.65 to 699.65 μmol mol⁻¹ in mid-winter season. In savannah ecosystem, diurnal trend of ambient CO₂ was totally different from rest four communities. According to Canonical correspondence analysis, PAR and ambient CO₂ are most important in establishment of forest community, among microclimatic variables.