Performance of geophytes on extensive green roofs in the United Kingdom

Dwarf geophytes have great potential for use on extensive green roofs because they often come from arid areas and can survive dry and hot summer in a dormant state. However, there has been little research regarding geophytes on green roofs. This experiment was conducted to study the performance of 26 species of geophytes on a green roof during 2005–2006 in Sheffield, UK. The geophytes were grown at two substrate depths (5 cm and 10 cm) of substrate on a green roof without irrigation. To investigate the susceptibility of geophytes to competition from a covering of permanent plants, the geophytes were grown with or without a surface vegetation layer of Sedum album. Overall, the growth, survival rate, regeneration and flowering of geophytes were more successful at a substrate depth of 10 cm than of 5 cm, probably because of improved moisture retention, fewer temperature fluctuations and the protection from digging by animals. The flowering period was limited to spring, therefore, it is recommended to combine with other plant species such as covering plants. Geophyte species did not compete much with S. album and Sedum cover had no significant effects on the growth, survival rate, regeneration and flowering of geophytes in most species. Iris bucharica, Muscari azureum, Tulipa clusiana var. chrysantha, Tulipa humilis, Tulipa tarda and Tulipa turkestanica had good performance at the substrate depth of 5 cm. In addition, Narcissus cyclamineus ‘February gold’ and Tulipa urumiensis exhibited a successful performance at the substrate depth of 10 cm.     

Photosynthesis of field-grown Arracacha (Arracacia xanthorriza Bancroft) cultivars in relation to root-yield

There has been limited research on measuring potential differences in leaf gas exchange of Arracacha (Peruvian parsnip, Arracacia xanthorriza Bancroft) cultivars, as affected by different environments, as well as its relation to storage root-yield. The present paper reports field measurements of leaf CO₂ assimilation rates (A) for five contrasting cultivars grown at two different high-altitude locations. Using a design of plots chosen at random with three repetitions, commercial root production was determined in the two locations at different altitude (1580 and 1930 m). Daily leaf gas exchange was repeatedly monitored with a portable open-mode infrared gas analyzer at different times in both locations during the growth cycle. Root-yield, leaf area and dry weight were measured. Significant differences in leaf photosynthetic rate and in specific leaf area (SLA) were observed among cultivars. Cultivars with high SLA, had high CO₂ assimilation. Mean (A_n) and total (A_tot) of CO₂ assimilation and SLA were significantly correlated with storage root-yield across cultivars and locations. The three cultivars with the greatest commercial root production also had the highest maximum values for A and the highest specific leaf area, indicating that these two parameters can be used to select for highly productive cultivars of A. xanthorriza.     

Green roof cooling and carbon mitigation benefits in a subtropical city

Green roofs are promoted as an effective nature-based urban heat island mitigation strategy. Green roof cooling and energy-saving benefits have been simulated for various climatic zones, but mainly at the building scale. Due to a lack of fact-based information on neighborhood cooling benefits, green roof construction lags and has rarely been incorporated into urban planning actions. This study investigated the thermal benefits and energy savings of green roofs for the central area of the Xianlin Campus of Nanjing University at the neighborhood scale. Three scenarios were simulated for a hot summer day using a validated ENVI-met model: a base case (S0), extensive green roofs (EGRs) (S1), and intensive green roofs (IGRs) (S2). The air temperature cooling benefit from green roofs extended downwards to the pedestrian level. The EGR scenario achieved a maximum 0.29 °C air temperature reduction at the pedestrian level and 0.37 °C at the rooftop level. The IGR scenario achieved a maximum 0.35 °C air temperature reduction at the pedestrian level and 0.45 °C at the rooftop level. EGRs and IGRs reduced energy demands for air-conditioning by 0.39 kWh·m⁻²·d⁻¹ and 0.56 kWh·m⁻²·d⁻¹ and CO₂ emissions by 31,997 kg·d⁻¹ and 45,967 kg·d⁻¹, respectively. These results confirm that green roofs yield substantial cooling and carbon mitigation benefits. Our study provides essential data to establish green roofs as mainstream cooling technology in subtropical cities. The results also imply that urban planners and policymakers may need to embrace the implementation of green roofs in long-term planning and building design practices to improve urban thermal environments, reduce building energy demand, and curb carbon emissions.     

Light responses of photosynthesis and transpiration of two tomato cultivars under ambient and altered CO2 and O2

Young plants of two tomato (Lycopersicon esculentum L.) cultivars, ‘Sonatine’ and ‘F6-IVT’, were examined for whole plant photosynthesis and transpiration in a closed gas-exchange system under different light levels and a combination of high or low oxygen (21 or 1%) and high or low carbon dioxide concentrations (1850 or 550 mg m^?3). With saturating light, both cultivars showed approximately equivalent increases in photosynthesis in response to lowering the oxygen concentration, raising the carbon dioxide, or both. Under non-saturating light, ‘F6-IVT’ responded positively to lowered oxygen but CO₂ had little effect. In ‘Sonatine’, changes in O₂ as well as CO₂ gave photosynthetic enhancement under low light. Stomates responded primarily to CO₂ with little response to O₂. As a result of the stomatal behavior to light, plant water-use efficiency in the short term peaked at moderate light levels, was enhanced by low O₂, but was enhanced most by high CO₂, regardless of O₂ concentration.     

The physiology of Cymbidium plantlets cultured in vitro under conditions of high carbon dioxide and low photosynthetic photon flux density

Summary

Cymbidium plantlets were grown in vitro under conditions of high CO₂ and low photosynthetic photon flux density using the Miracle Packt culture system. Shoots and roots of plantlets showed differential growth characteristics. Shoot growth was not different in plantlets cultured under CO₂-enriched (CDE) and non-enriched (NCDE) conditions. Root growth was promoted in plantlets cultured under CDE in the presence or absence of 2% sucrose (S) with rockwool (R) as the supporting material. Growth was poor in plantlets cultured in 1% agar. Root growth was best in plantlets cultured under CDE R+S. Sucrose is still an important component for root growth under CDE conditions even though CO₂ can be used as an alternative carbon source. Photosynthetic measurements (CO₂ uptake and total Rubisco activity) showed the presence of active and operational photosynthetic machinery in plantlets cultured under CDE and NCDE conditions. The apparent lack of photoautotrophy (as evident from the lack of starch grains in chloroplasts) in plantlets cultured under NCDE conditions is not the result of a lesser potential for photoautotrophy; rather it is a consequence of sub-optimal CO₂ concentrations within the culture vessels.     

Greenhouse gas fluxes in an open air humidity manipulation experiment

Air moisture is one of the main factors causing the greenhouse effect, but humidity has not been thoroughly studied at the ecosystem level. In 2006 a free-air humidity manipulation (FAHM) facility was established in Estonia to investigate the effect of humidity on the performance of two tree species—silver birch (Betula pendula Roth.) and hybrid aspen (Populus tremula L. × P. tremuloides Michx.). The trial is located on an Endogleyic Planosol of former arable land and offers the opportunity to change relative air humidity through controlled artificial misting and drying. We measured the CO₂, CH₄ and N₂O emission from the FAHM system using closed chamber and gas-chromatograph techniques from July 2009 to October 2010. Measurements were carried out once a month in three humidification (h) plots and in three control (c) plots. The vegetation period was rainy in 2009, but the next summer was relatively dry. The dry summer interacted better with the humidification. The CO₂ flux decreased when the air moisture was higher than in the control plots. The soil acted as a sink for methane. Less CH₄ was oxidized in the soil with increased humidity. Emission of N₂O did not correlate with air humidity, although one could observe a clear tendency that there was a smaller N₂O flux during the period with increased humidity. Expectedly, CO₂ emission and CH₄ consumption demonstrated strong positive correlations with soil temperature.     

普通土壤栽培增施CO2和有机土栽培对日光温室秋黄瓜产量和品质的影响

在日光温室条件下,研究了普通土壤栽培增施CO₂及有机土栽培对黄瓜产量和营养品质的影响,并对比了两种栽培方式下CO₂的变化。结果表明：有机土栽培与增施CO₂的普通土壤栽培均在上午提高了温室内CO₂浓度,使温室中CO₂浓度在上午光合作用最强的时期显著高于普通土壤栽培,最终表现为黄瓜生长优于普通土壤栽培。生理分析表明：普通土壤栽培增施CO₂和有机土栽培均可增加黄瓜叶片叶绿素含量,并显著提高了植株的根系活力和净光合速率。增施CO₂对盛果期黄瓜果实中可溶性固形物和VC含量有显著提高作用,分别提高10.21%和7.23%;而有机土栽培下黄瓜总糖和粗蛋白含量显著高于其他处理。黄瓜盛果期增施CO₂增产效果明显,单株产量较对照显著提高,与有机土栽培产量相当。增施CO₂对黄瓜产量的影响主要在采收中后期;而有机土栽培对黄瓜产量的影响主要是在采收的前中期。有机土栽培不仅改善了根区环境,还对温室CO₂浓度有很好改善作用,可以不用增施CO₂而实现优质高产。     

Comparison of establishment methods for extensive green roofs in southern Sweden

The most common technique for establishment of thin extensive green roofs in Sweden has been using prefabricated vegetation mats. Our study investigated (1) how the establishment of green roofs in Sweden was influenced by the establishment method (prefabricated vegetation mat, plug-plant, shoot), substrate composition and species mixture, and (2) whether on-site construction was a possible alternative. The establishment of the vegetation, which in all cases consisted of succulent species, was recorded using the quadrate point intercept method in fixed plots and the success measured as frequency cover.Prefabricated vegetation mats had higher succulent plant cover than on-site constructed roofs. There was no difference in succulent plant cover between plots established using plug-plants compared to shoots. Shoot-established plots had more moss than the other establishment methods. The commercial substrate ‘Roof soil’ had significantly higher succulent plant cover than the other substrates, which might be related to a higher nutrient content. The organic content of the non-commercial substrates was rapidly decomposed. The standard species mixture produced a higher cover than both the mix developed for northern conditions and the mix with an increased proportion of big leaved species. The total cover of the plots was mainly dependent on the cover of two species: Sedum album (L.) and Sedum acre (L.). Few species managed to establish spontaneously but the establishment of woody species highlighted the need for proper maintenance.     

The responses of photosynthetic capacity,chlorophyll fluorescence and chlorophyll content of nectarine (Prunus persica var. Nectarina Maxim) to greenhouse and field grown conditions

Three nectarine (Prunus persica var. Nectarina Maxim.) cultivars grown under solar-heated greenhouse and open-field in northwest China, were tested to evaluate their photosynthetic and chlorophyll fluorescence response to both growth conditions, and whether nectarine plants acclimate to the solar-heated greenhouse growth condition. Comparisons of light-saturated photosynthetic capacity (Amax) and CO₂-saturated photosynthetic capacity (RuBPmax) indicated that each cultivar (Z, Zao-Hongzhu; H, Hua-Guang; Y, Yan-Guang) maintained similar rates of light-saturated and CO₂-saturated carbon assimilation when grown in both conditions. The curve of diurnal variation of net photosynthetic (P_N) rate showed double peaks in open-field but single when grown in greenhouse. Compared with open-field-grown plants, a significant increase of daily average P_N was found in Z but decreased in Y in greenhouse. The diurnal variation of F_v/F_m indicate that plants grown in greenhouse experience less photoinhibition than in open-field condition. A reduction in chlorophyll (chl) a/b ratio in leaves of greenhouse grown plants with significant increase in chlorophyll (chl) b content were obtained. The results suggest that some nectarine cultivars have the ability to acclimate to the solar-heated greenhouse growth condition.     

Can microbial inoculants boost soil food webs and vegetation development on newly constructed extensive green roofs?

Green roofs are a key to providing nature-based solutions in cities. However, most green roofs installed in the Northern hemisphere are shallow, stonecrop planted systems (“extensive” green roofs), which have been shown to support limited biodiversity and could be more effective at providing ecosystem services. One issue with this type of extensive green roof is that rootzones are almost sterile on construction, relying on natural colonisation to provide a soil food web. This is a slow process, meaning plant growth can also be slow. Our aim was to determine if a soil food web could be introduced when the green roof is built. We applied microbial inoculants (mycorrhizal fungi and bacteria (Bacillus spp.)) to a new green roof and monitored plant growth and the soil food web (bacteria, mycorrhizal fungi and microarthropods). Different inoculants altered the composition of microarthropod communities, potentially impacting later succession. In particular, bacterial inoculants increased microarthropod populations. This is one of the first studies to demonstrate that the addition of microbial inoculants impacts not only plant growth, but also faunal components of the soil food web, which could have implications for long-term resilience. Bacteria were effective at aiding mycorrhizal colonisation of plants roots, but this colonisation had no impact on the growth of our selected stonecrops, Sedum album, Petrosedum reflexum and Phedimus spurius. We suggest that if a beneficial mycorrhiza could be found to promote the growth of these specific species on green roofs, bacteria could be effective “helper” species to aid colonisation. This study enables green roof researchers and the industry to justify further exploration of the impact of microbial inoculants on green roofs.     

Effect of intermittent as compared to continuous CO2 enrichment on growth and flowering of Chrysanthemum × morifolium Ramat. and Saintpaulia ionantha H. Wendl

Plants of three cultivars of Saintpaulia ionantha and Chrysanthemum × morifolium were grown until flowering at 335 (normal) or 900 μl l⁻¹ CO₂ (high). Continuous high CO₂ concentration increased the final dry weights from 76 to 123% in Saintpaulia and from 15 to 32% in Chrysanthemum compared to the normal concentration. Changing the CO₂ concentration from normal to high (intermittent) in intervals of 1 h resulted in dry weights intermediate to that of constant normal or constant high CO₂ concentrations in both species. Morning and evening enrichment gave the same effect as 1-h intermittent enrichment in Saintpaulia. High CO₂ concentration given every other day gave the same effect as 1 h intermittent CO₂ in Chrysanthemum. Increased dry weights were accompanied by more and larger leaves in Saintpaulia, and mainly by thicker and longer stem and more lateral breaks in Chrysanthemum.Time to flowering was significantly reduced by CO₂ enrichment in Saintpaulia, but was generally not affected in Chrysanthemum. Number of flowers and flowerbuds was increased by CO₂ application in both species. Constant high CO₂ concentration generally had effects superior to that of the intermittent treatments.     

Response of tomato plants to saline water as affected by carbon dioxide supplementation. II. Physiological responses

Summary

Photosynthesis of tomato plants (Lycopersicon esculentum (L.) Mill. cv. F144) was studied under conditions of CO₂ supplementation and salinity. The purpose of the study was to elucidate the mechanisms underlying the effects of salinity on the acclimation of tomato plants to CO₂ supplementation. Plants were grown under either low (355.mmol mol^–1) or elevated (1200.6.50 mmol mol^–1) CO₂ and were irrigated with low concentrations of mixed salts. The highest salinity level (E.C. 7 dS m–1) was that used to produce quality tomatoes in the Negev highlands, in Israel. During early development (three weeks after planting), the net photosynthetic rate of the leaves was much higher under elevated CO₂, and other than a slight decrease in quantum yield efficiency as measured by fluorescence (DF/F 9 ^m ), no signs of acclimation to high levels of CO₂ were apparent. Clear acclimation to high CO₂ concentration was evide t ten weeks after planting when the net photosynthetic rate, photosynthetic capacity, and carboxylation efficiency of leaves of non-salinized plants were strongly suppressed under elevated CO₂. This was accompanied by reductions in carboxylation efficiency, Rubisco activity and PSII quantum yield, and an increased accumulation of leaf soluble sugars. The reduction in photosynthetic capacity in the high CO₂ plants was less in plants grown at the highest salinity level. This was correlated with an increase in the PSII quantum yield parameters (F_v/F_m) and DF/F 9 m ) but not with Rubisco activity which was affected by the CO₂ treatments only. These results explain the effects of high CO₂ on yields in tomatoes grown at high levels of salt (Li et al., 1999).     

Net CO2 storage in mediterranean olive and peach orchards

Agricultural practices can play an important role in atmospheric CO₂ emission and fixation. In this study, we present results on carbon fluxes in the biomass of two typical Mediterranean orchards indicating that proper canopy management coupled with other agricultural techniques could increase the absorption of atmospheric CO₂ and its storage. We also discuss the potential environmental contribution of the orchards to enhancement of both soil and air quality. Trials were carried out in southern Italy on olive (Olea europaea L.) and peach orchards (Prunus persica L.) at different age and plant densities. At the end of each vegetative season, values of fixed atmospheric CO₂ were calculated by measuring dry matter accumulation and partitioning in the different plant organs. In the early years, sequestered CO₂ was primarily distributed in the permanent structures and in the root system while in mature orchards the fixed CO₂ was distributed in leaves, pruning materials and fruit. Significant differences in amounts of fixed CO₂ were observed in peach orchards cultivated using different planting and training strategies. The results underline the importance of training system, plant density and cultivation techniques in the absorption of atmospheric CO₂ and its storage as organic matter in the soil.     

Responses of morphology and drought tolerance of Sedum lineare to watering regime in green roof system: A root perspective

The presence of drought tolerant vegetation is essential for the longevity of an extensive green roof when irrigation is not installed. Earlier studies have examined performance of green roof plants under contrasting watering regimes and found that higher watering frequency provided better growth and survival rates. The effect of early watering regimes on the subsequent response of plants to persistent drought stress in extensive green roofs, however, has not been extensively studied. In order to evaluate the effects of watering regime during the establishment period of Sedum lineare on its growth and drought tolerance, two greenhouse experiments using simulated green roofs were conducted. It was found in the first experiment that a 2-day-interval watering regimen at the early planting stage produced greater root biomass and root size than those of 6-day- and 13-day-interval watering, indicating that deficit watering tended to induce thinner roots in S. lineare. In the second experiment, the remaining plants were subsequently subjected to a 28-day drought treatment. The roots of plants watered at 13-day-interval maintained the highest respiration activity among all plants during the drought period. Results suggest that an appropriate deficit watering regimen at the early planting stage may lead to smaller root size and higher root:shoot ratios in S. lineare, and thereby improve its drought tolerance performance on extensive green roofs.     

Plant establishment on a green roof under extreme hot and dry conditions: The importance of leaf succulence in plant selection

Plant selection for extensive green roofs has largely been based on cool, temperate climate research. However, as green roof implementation in hotter and drier climates increases, there is a need to evaluate plant performance under these climatic conditions. Succulents have been shown to be successful in hot and dry green roofs, although survival differs between species and the role of leaf succulence in survival has not been fully explored. For non-succulent plants, habitats with conditions similar to green roofs (‘habitat templates’) have been used to select plants, although few studies have discussed the performance of these selections under green roof conditions. Therefore, we evaluated establishment of 32 plant species on an unirrigated extensive (125 mm deep) green roof in Melbourne, Australia over a 42 week period (from winter through summer into autumn). Plants were selected on the basis of life-form, succulence, appropriate habitat templates and/or successful use on green roofs internationally. Climatic conditions during the experiment were often extreme, with evaporation regularly exceeding rainfall and a hot and dry summer (mean maximum air temperature 35 °C and 80.6 mm total rainfall), leading to roof temperatures of 65 °C. After 42 weeks, only succulent plants remained alive and only three of the succulent species had 100% survival. Survival was positively related to the degree of leaf succulence (g H₂O leaf area cm⁻¹) making this a useful trait for plant selection for unirrigated green roofs in hot, dry climates. The failure of most species, despite being chosen from appropriate habitats, demonstrates the need to evaluate potential plants on green roofs under extreme climatic conditions. Supplementary irrigation may be essential to sustain non-succulent species during extreme weather in hot and dry climates.     

Performance of native succulents,forbs, and grasses on an extensive green roof over four years in subtropical Australia

To achieve enduring low-maintenance green roofs that provide maximum benefit in the subtropics, plants need to be well adapted to the local climate with extensive green coverage. The use of native plants contributes to ecological restoration, yet there is very limited information available on their performance in the subtropics. This study aimed to determine the performance of nine species of Australian native forbs, succulents, and grasses in monofunctional and functionally-mixed plant communities on an extensive green roof in Brisbane over four years. Green coverage and survival were monitored via image analysis and observational visits. Forbs established slowly, but successfully (82 % green coverage, 67 % survival after four years) with species Hibbertia scandens (100 % survival) and Dianella brevipedunculata (58 % survival and extensive recruitment) performing the best. Grasses, including Themeda triandra, Poa labillardieri and Cymbopogon refractus, achieved a fast initial green coverage (47 % after 10 months), but showed high seasonal variability and declined to 2 %. Contrary to expectations, succulents performed poorly (<5 % green coverage, 14 % survival). Green coverage had an inverse trend to plant survival in successful plots (forbs, functionally-mixed) indicating a gap-filling effect by high performing species. Survival was more strongly linked to individual species than to functional type or plant community arrangement. Based on the results of this study, we recommend consideration of functionally-mixed green roof plantings with a variety of indigenous plants including forbs for low maintenance and resilient green coverage in the subtropics. Habitats that provided suitable plant species for this study were coastal headlands, dunes, montane areas, and open eucalypt forests. Analogous habitats in other regions can be explored to find new native plant species to increase the plant palette of potentially suitable species. It would be beneficial to trial more plants from these habitats over multiple years to increase the knowledge of suitable species available to green roof designers.     

Abscisic acid alleviates the deleterious effects of cold stress on ‘Sultana’ grapevine (Vitis vinifera L.) plants by improving the anti-oxidant activity and photosynthetic capacity of leaves

The effects of exogenous application of abscisic acid (ABA) on anti-oxidant enzyme activities and photosynthetic capacity in ‘Sultana’ grapevine (Vitis vinifera L.) were investigated under cold stress. When vines had an average of 15 leaves, 0 (control), 50, 100, or 200 µM ABA was sprayed to run-off on all leaves of each plant. Twenty-four hours after foliar spraying with ABA, half (n = 5) of the water-only control vines and half (n = 5) of each group of ABA-treated plants were subjected to 4°C for 12 h, followed by a recovery period of 3 d under greenhouse conditions (25°/18°C day/night). The remaining plants in each treatment group were kept at 24°C. Cold stress increased H₂O₂ and malondialdehyde (MDA) concentrations in vine leaves, whereas all foliar ABA treatments significantly reduced their levels. Chilled plants showed marked increases in their total soluble protein contents in response to each ABA treatment. ABA significantly increased the activities of superoxide dismutase, peroxidase, catalase, and ascorbate peroxidase in cold-stressed grapevine leaves. In contrast, cold stress markedly decreased the rates of leaf photosynthesis (A) and evaporation (E), stomatal conductance (g_s), and chlorophyll concentrations in leaves, but increased intercellular CO₂ concentrations (C_i) in leaves. Treatment with all concentrations of ABA resulted in lower leaf A, E, and g_s values, but higher C_i values at 24°C. However, following cold stress, ABA-treated vines showed higher leaf A, E, and g_s values, but lower C_i values compared to control vines without ABA treatment. The application of 50–200 µM ABA allowed chilled vines to recover more quickly when re-exposed to normal temperatures, enabling the vines to resume their photosynthetic capacity more efficiently following cold stress. These results showed that, by stimulating anti-oxidant enzyme systems and alleviating cold-induced stomatal limitations, ABA reduced the inhibitory effect of cold stress on the rate of CO₂ fixation in ‘Sultana’ grapevine plants.     

Root restriction-induced limitation to photosynthesis in tomato (Lycopersicon esculentum Mill.) leaves

Root restriction often depresses photosynthetic capacity and the mechanism for this reduction, however, remains unclear. To identify the mechanism by which root restriction affects the photosynthetic characteristics, tomato (Lycopersicon esculentum Mill.) seedlings were subjected to root restriction stress with or without supplemental aeration to the nutrient solution. With the development of the root restriction stress, CO₂ assimilation rate was decreased only in confined plants without supplemental aeration. There were also significant decreases in leaf water potential, stomatal conductance (g_s), intercellular CO₂ concentration (C_i), and increases in the stomatal limitation (l) and the xylem sap ABA concentration. Meanwhile, the maximum carboxylation rate of Rubisco (V_cmax) and the capacity for ribulose-1,5-bisphosphate regeneration (J_max) also decreased, followed by substantial reductions in the quantum yield of PSII electron transport (Φ_PSII). Additionally, root restriction resulted in accumulation of carbohydrates in various plant tissues irrespective of aeration conditions. It is likely that root restriction-induced depression of photosynthesis was mimicked by water stress.     

Culture method and photosynthetic photon flux affect photosynthesis,growth and survival of Limonium ‘Misty Blue’ in vitro

Microcuttings (shoots each with two leaves) of Limonium ‘Misty Blue’ were cultivated in vitro for 28 days under photoautotrophic (sucrose-free culture medium; CO₂ and photosynthetic photon flux (PPF) enriched conditions), photomixotrophic (medium with 30 g l⁻¹ sucrose; CO₂ and PPF enriched conditions) and heterotrophic (medium with 30 g l⁻¹ sucrose; CO₂ non-enriched conditions) methods. Several growth variables were measured during and at the end of cultivation: shoot fresh and dry weight, percentage of shoot dry matter, root fresh weight, number of leaves, leaf area, chlorophyll and sugar content of leaves, stomatal density and size, net photosynthetic rate (NPR) and percent survival of plantlets ex vitro. Plantlets grown in photoautotrophic and photomixotrophic methods had more leaves, high chlorophyll and sugar contents, high NPR, and showed high percent survival. However, these plantlets possessed less number of stomata per square millimeter. In contrast, the plantlets grown by the heterotrophic method showed decreased values of these growth variables except for the number of stomata per square millimeter. These results indicate that CO₂ enrichment for plantlets in vitro at a relatively high PPF would promote photosynthesis and hence growth of chlorophyllous explants/plantlets in vitro. The resulting plantlets were acclimatized better and sooner on ex vitro transplantation.     

Effect of CO2 enrichment on photosynthesis,growth and yield of tomato

Net photosynthesis of tomato plants was measured as CO₂ uptake in various light intensities, CO₂ concentrations, O₂ concentrations and temperatures during short-term experiments. Net photosynthesis increased significantly with increasing CO₂ concentration at all light intensities, even at the lowest one. The optimal temperature for photosynthesis increased with CO₂ enrichment. The changes in photosynthesis when the $\text{CO}{}_2\text{O}{}_2$ ratio was varied suggest that the effect of CO₂ enrichment is a result of a reduction in photorespiration.To determine whether the increase in photosynthesis caused by CO₂ enrichment would produce a greater yield, tomato plants were cultivated from seed to harvest in a tightly-closed greenhouse that was enriched with CO₂ continuously during the entire growing-period. The control greenhouse was ventilated by openings in the roof and door. The temperature of the 2 greenhouses was kept the same. Plants enriched with CO₂ showed a significant increase in fresh and dry weight and yield of tomatoes. The results are discussed in relation to earlier work in which CO₂ enrichment was discontinued when there was a need for ventilation.