Impact of elevated CO<Subscript>2</Subscript> in <Emphasis Type="Italic">Casuarina equisetifolia</Emphasis> rooted stem cuttings inoculated with <Emphasis Type="Italic">Frankia</Emphasis>

Impact of different levels of elevated CO ₂ on the activity of Frankia (Nitrogen-fixing actinomycete) in Casuarina equisetifolia rooted stem cuttings has been studied to understand the relationship between C. equisetifolia, Frankia and CO₂. The stem cuttings of C. equietifolia were collected and treated with 2000 ppm of Indole Butyric Acid (IBA) for rooting. Thus vegetative propagated rooted stem cuttings of C. equisetifolia were inoculated with Frankia and placed in the Open top chambers (OTC) with elevated CO₂ facilities. These planting stocks were maintained in the OTC for 12 months under different levels of elevated CO₂ (ambient control, 600 ppm, 900 ppm). After 12 months, the nodule numbers, bio mass, growth, and photosynthesis of C. equisetifolia rooted stem cuttings inoculated with Frankia were improved under 600 ppm of CO₂. The rooted stem cuttings of C. equisetifolia inoculated with Frankia showed a higher number of nodules under 900 ppm of CO₂ and cuttings without Frankia inoculation exhibited poor growth. Tissue Nitrogen (N) content was also higher under 900 ppm of CO₂ than ambient control and 600 ppm levels. The photosynthetic rate was higher (17.8 μ mol CO₂ m^?2 s^?1) in 900 ppm of CO₂ than in 600 ppm (13.2 μ mol CO₂ m^?2 s^?1) and ambient control (8.3 μ mol CO₂ m^?2 s^?1). This study showed that Frankia can improve growth, N fixation and photosynthesis of C. equietifolia rooted stem cuttings under extreme elevated CO₂ level conditions (900 ppm).     

Effect of cement industry flue gas simulation on the physiology and photosynthetic performance of <Emphasis Type="Italic">Chlorella sorokiniana</Emphasis>

Cement plants account for significant emissions of CO₂ and other pollutants into the atmosphere. As a means for its mitigation, we tested the effect of a cement industry-based flue gas simulation (FGS — 18% CO₂, 9% O₂, 300 ppm NO₂, 140 ppm SO₂) on the green alga, Chlorella sorokiniana. Culture pH, cell density, cell viability and productivity, specific growth rates, photosynthetic performance, and biochemical composition were monitored. The treatments consisted of different FGS volumes (0.1, 0.3, 0.8, 1.5, 6, and 48 L day^?1) that were applied in a series of laboratory-scale semi-continuous batch cultures under controlled conditions. Controls were exposed to 18% CO₂ enriched air. Cell density showed that C. sorokiniana was able to grow in all treatments, but compared to the controls, low pH (~ 5.0) caused by 48 L FGS day^?1 led to 27% decrease in specific growth rate. Increasing FGS exposure decreased maximum and operational quantum yields obtained by pulse amplitude modulated fluorometry, while photochemical quenching remained constant (~ 0.93). The α and rETR _max parameters calculated from rapid light curves decreased with increasing FGS exposure. Total proteins and carbohydrates (per cell basis) increased after 6 and 48 L FGS day^?1, which can be advantageous for biotechnological applications, but cell productivity (cells L^?1 day^?1) decreased. Despite the effects in physiology, C. sorokiniana could withstand a pH range of 6.0–5.0 imposed by 48 L FGS day^?1. Overall, C. sorokiniana can be considered a robust species in flue gas bioremediation.     

Photosynthetic characteristics and nitrogen allocation in the black locust (<Emphasis Type="Italic">Robinia pseudoacacia</Emphasis> L.) grown in a FACE system

Key message

The black locust is adapted to elevated [CO ₂ ] through changes in nitrogen allocation characteristics in leaves.

Abstract

The black locust (Robinia pseudoacacia L.) is an invasive woody legume within Japan. This prolific species has a high photosynthetic rate and growth rate, and undergoes symbiosis with N₂-fixing micro-organisms. To determine the effect of elevated CO₂ concentration [CO₂] on its photosynthetic characteristics, we studied the chlorophyll (Chl) and leaf nitrogen (N) content, and the leaf structure and N allocation patterns in the leaves and acetylene reduction activity after four growing seasons, in R. pseudoacacia. Our specimens were grown at ambient [CO₂] (370 μmol mol^?1) and at elevated [CO₂] (500 μmol mol^?1), using a free air CO₂ enrichment (FACE) system. Net photosynthetic rate at growth [CO₂] (A _growth) and acetylene reduction activity were significantly higher, but maximum carboxylation rate of RuBisCo (V _cmax), maximum rate of electron transport driving RUBP regeneration (J _max), net photosynthetic rate under enhanced CO₂ concentration and light saturation (A _max), the N concentration in leaf, and in leaf mass per unit area (LMA) and ribulose-1,5-bisphosphate carboxylase oxygenase (RuBisCo) content were significantly lower grown at elevated [CO₂] than at ambient [CO₂]. We also found that RuBisCo/N were less at elevated [CO₂], whereas Chl/N increased significantly. Allocation characteristics from N in leaves to photosynthetic proteins, N_L (Light-harvesting complex: LHC, photosystem I and II: PSI and PSII) and other proteins also changed. When R. pseudoacacia was grown at elevated [CO₂], the N allocation to RuBisCo (N_R) decreased to a greater extent but N_L and N remaining increased relative to specimens grown at ambient [CO₂]. We suggest that N remobilization from RuBisCo is more efficient than from proteins of electron transport (N_E), and from N_L. These physiological responses of the black locust are significant as being an adaptation strategy to global environmental changes.

     

Photosynthetic capacity of the capsule wall and its contribution to carbon fixation and seed yield in castor (<Emphasis Type="Italic">Ricinus communis</Emphasis> L.)

Defoliation occurs in castor due to several reasons, but the crop has propensity to compensate for the seed yield. Photosynthetic efficiency in terms of functional (gas exchange and chlorophyll fluorescence) and structural characteristics (photosynthetic pigment profiles and anatomical properties) of castor capsule walls under light- and dark-adapted conditions was compared with that of leaves. Capsule wall showed high intrinsic efficiency of photosystem II (F _v/F _m, 0.82) which was comparable to leaves (F _v/F _m, 0.80). With increasing photon flux densities (PFD), actual quantum yields and photochemical quenching coefficients of the capsule walls were similar to that in leaves, while electron transport rates reached a maximum corresponding to about 118 % of the leaves. However, maximum net photosynthetic rate of the capsule walls (2.60 µmol CO₂ m^?2 s^?1) was less than one-fourth of the leaves (15.67 µmol CO₂ m^?2 s^?1) at the CO₂ concentration of 400 µmol mol^?1, and the difference was attributed to about 80 % lower stomatal density and the 75 % lower total chlorophyll content of capsule walls than the leaves. Furthermore, seed weight in dark-adapted capsules was 2.70–12.42 % less as compared to the capsules developed under light. The results indicate that castor capsule walls are photosynthetically active (about 15–30 % of the leaves) and contribute significantly to carbon fixation and seed yield accounting for 10 % photoassimilates towards seed weight.     

Factors underlying genotypic differences in the induction of photosynthesis in soybean [Glycine max (L.) Merr.]

Crop leaves are subject to continually changing light levels in the field. Photosynthetic efficiency of a crop canopy and productivity will depend significantly on how quickly a leaf can acclimate to a change. One measure of speed of response is the rate of photosynthesis increase toward its steady state on transition from low to high light. This rate was measured for seven genotypes of soybean [Glycine max (L.) Merr.]. After 10 min of illumination, cultivar ‘UA4805’ (UA) had achieved a leaf photosynthetic rate (P_n) of 23.2 μmol · m^?2 · s^?1, close to its steady‐state rate, while the slowest cultivar ‘Tachinagaha’ (Tc) had only reached 13.0 μmol · m^?2 · s^?1 and was still many minutes from obtaining steady state. This difference was further investigated by examining induction at a range of carbon dioxide concentrations. Applying a biochemical model of limitations to photosynthesis to the responses of P_n to intercellular CO₂ concentration (C_i), it was found that the speed of apparent in vivo activation of ribulose‐1:5‐bisphosphate carboxylase/oxygenase (Rubisco) was responsible for this difference. Sequence analysis of the Rubisco activase gene revealed single nucleotide polymorphisms that could relate to this difference. The results show a potential route for selection of cultivars with increased photosynthetic efficiency in fluctuating light.     

Characterization of backcross introgression lines derived from <Emphasis Type="Italic">Oryza nivara</Emphasis> accessions for photosynthesis and yield

Improvement of photosynthetic traits is a promising strategy to break the yield potential barrier of major food crops. Leaf photosynthetic traits were evaluated in a set of high yielding Oryza sativa, cv. Swarna?×?Oryza nivara backcross introgression lines (BILs) along with recurrent parent Swarna, both in wet (Kharif) and dry (Rabi) seasons in normal irrigated field conditions. Net photosynthesis (P_N) ranged from 15.37 to 23.25 µmol (CO₂) m^?2 s^?1 in the BILs. Significant difference in P_N was observed across the seasons and genotypes. Six BILs showed high photosynthesis compared with recurrent parent in both seasons. Chlorophyll content showed minimum variation across the seasons for any specific BIL but significant variation was observed among BILs. Significant positive association between photosynthetic traits and yield traits was observed, but this association was not consistent across seasons mainly due to contrasting weather parameters in both seasons. BILs 166s and 248s with high and consistent photosynthetic rate exhibited stable high yield levels in both the seasons compared to the recurrent parent Swarna. There is scope to exploit photosynthetic efficiency of wild and weedy rice to identify genes for improvement of photosynthetic rate in cultivars.     

Acclimation of shade-tolerant and light-resistant <Emphasis Type="Italic">Tradescantia</Emphasis> species to growth light: chlorophyll <Emphasis Type="Italic">a</Emphasis> fluorescence,electron transport,and xanthophyll content

In this study, we have compared the photosynthetic characteristics of two contrasting species of Tradescantia plants, T. fluminensis (shade-tolerant species), and T. sillamontana (light-resistant species), grown under the low light (LL, 50–125 µmol photons m^?2 s^?1) or high light (HL, 875–1000 µmol photons m^?2 s^?1) conditions during their entire growth period. For monitoring the functional state of photosynthetic apparatus (PSA), we measured chlorophyll (Chl) a emission fluorescence spectra and kinetics of light-induced changes in the heights of fluorescence peaks at 685 and 740 nm (F ₆₈₅ and F ₇₄₀). We also compared the light-induced oxidation of P₇₀₀ and assayed the composition of carotenoids in Tradescantia leaves grown under the LL and HL conditions. The analyses of slow induction of Chl a fluorescence (SIF) uncovered different traits in the LL- and HL-grown plants of ecologically contrasting Tradescantia species, which may have potential ecophysiological significance with respect to their tolerance to HL stress. The fluorometry and EPR studies of induction events in chloroplasts in situ demonstrated that acclimation of both Tradescantia species to HL conditions promoted faster responses of their PSA as compared to LL-grown plants. Acclimation of both species to HL also caused marked changes in the leaf anatomy and carotenoid composition (an increase in Violaxanthin?+?Antheraxantin?+?Zeaxanthin and Lutein pools), suggesting enhanced photoprotective capacity of the carotenoids in the plants grown in nature under high irradiance. Collectively, the results of the present work suggest that the mechanisms of long-term PSA photoprotection in Tradescantia are based predominantly on the light-induced remodeling of pigment-protein complexes in chloroplasts.     

Effects of Gamma Stress and Carbon Dioxide on Eight Bioactive Flavonoids and Photosynthetic Efficiency in <Emphasis Type="Italic">Centella asiatica</Emphasis>

Increased atmospheric CO₂ and gamma irradiation have a significant impact on the plant photosynthetic apparatus and organic compound production. In this study, we evaluated the effect of elevated CO₂ on the photosynthetic efficiency and production of defensive secondary metabolites (flavonoids) induced by gamma irradiation as a physical elicitor in Centella asiatica. Irradiated and non-irradiated 10-week-old plants of C. asiatica were exposed to 400 and 800 μmol mol^?1 of atmospheric CO₂ in growth chambers for 2 h every day until six weeks. A CO₂-enriched atmosphere initially improved the photosynthetic efficiency and ameliorated the detrimental impact of gamma irradiation on the photosynthetic apparatus, increasing carbon allocation into the flavonoid pathway. Elevated CO₂ combined with gamma irradiation resulted in the highest concentration of flavonoids in C. asiatica tissues compared with the other treatments. There was an enhancement in rutin (2.49 fold), naringin (2.15 fold), fisetin (4.07 fold), and morin (4.62 fold) with rising CO₂ concentrations from 400 to 800 μmol mol^?1 in the irradiated plants. With increasing CO₂ concentration, the compensation point and the respiration declined, whereas the apparent quantum yield and the maximum net photosynthesis (A _max) rate increased. The efficiency of photosystem II (PSII) was improved in the irradiated plants grown under high concentrations of CO₂. The total carbohydrate concentration reached the maximum value at the highest level of CO₂, followed by gamma irradiation combined with the highest level of CO₂. Irradiated plants of C. asiatica grown under elevated CO₂ could be superior to non-irradiated plants due to increased carbon availability both for the flavonoid biosynthesis and for the photosynthetic pathway.     

Gas exchange,carbon balance and stomatal traits in wild and cultivated rice (<Emphasis Type="Italic">Oryza sativa</Emphasis> L.) genotypes

Carbon balancing within the plant species is an important feature for climatic adaptability. Photosynthesis and respiration traits are directly linked with carbon balance. These features were studied in 20 wild rice accessions Oryza spp., and cultivars. Wide variation was observed within the wild rice accessions for photosynthetic oxygen evolution or photosynthetic rate (A), dark (R _d), and light induced respiration (LIR) rates, as well as stomatal density and number. The mean rate of A varied from 10.49 μmol O₂ m^?2 s^?1 in cultivated species and 13.09 μmol O₂ m^?2 s^?1 in wild spp., The mean R _d is 2.09 μmol O₂ m^?2 s^?1 and 2.31 μmol O₂ m^?2 s^?1 in cultivated and wild spp., respectively. Light induced Respiration (LIR) was found to be almost twice in wild rice spp., (16.75 μmol O₂ m^?2 s^?1) compared to cultivated Oryza spp., Among the various parameters, this study reveals LIR and A as the key factors for positive carbon balance. Stomatal contribution towards carbon balance appears to be more dependent on abaxial surface where several number of stomata are situated. Correlation analysis indicates that R _d and LIR increase with the increase in A. In this study, O. nivara (CR 100100, CR 100097), O. rufipogon (IR 103404) and O. glumaepatula (IR104387) were identified as potential donors which could be used in rice breeding program. Co-ordination between gas exchange and patchiness in stomatal behaviour appears to be important for carbon balance and environmental adaptation of wild rice accessions, therefore, survival under harsh environment.     

Genetic engineering of polyamine metabolism changes <Emphasis Type="Italic">Medicago truncatula</Emphasis> responses to water deficit

In the current scenario of climate change and increasing water scarcity there is an increased need to combine research efforts for the development of abiotic stress resistant crops, specifically plants able to support water deficit (WD). Polyamines (PAs) have been described as being involved in the regulation of many physiological processes and a variety of stress responses in plants. Arginine decarboxylase (ADC) is considered a key enzyme of the polyamine (PA) biosynthetic pathway. In this study, a T₂ transgenic homozygous line of Medicago truncatula expressing the oat Adc under the control of CaMV 35S was obtained and was shown to have higher leaf accumulation of putrescine, spermidine and norspermidine compared to wild type plants. The photosynthetic parameters, leaf internal CO₂ concentration (Ci), net CO₂ assimilation rate (A), transpiration (E) and stomatal conductance (gs) of transformed and untransformed lines during WD and water deficit recovery experiments were measured by IRGA (infrared gas analyzer) and compared over time. Two light intensities were used, growth light intensity (391 μmol m^?2 s^?1) and saturating light intensity (1044 μmol m^?2 s^?1). Independently of the light intensity, and under WD, the transgenic line stood out with increased Ci, A, E and gs; suggesting a possible benefit of the augmented PAs under such disturbing environmental conditions. We showed that the constitutive expression of the oat Adc gene improve the physiological responses to WD and that WD recovered transgenic plants had higher seed yield, suggesting a possible benefit of PA metabolism manipulation in legumes.     

Carbon Dioxide and Methane Fluxes From Tree Stems,Coarse Woody Debris,and Soils in an Upland Temperate Forest

Forest soils and canopies are major components of ecosystem CO₂ and CH₄ fluxes. In contrast, less is known about coarse woody debris and living tree stems, both of which function as active surfaces for CO₂ and CH₄ fluxes. We measured CO₂ and CH₄ fluxes from soils, coarse woody debris, and tree stems over the growing season in an upland temperate forest. Soils were CO₂ sources (4.58 ± 2.46 µmol m^?2 s^?1, mean ± 1 SD) and net sinks of CH₄ (?2.17 ± 1.60 nmol m^?2 s^?1). Coarse woody debris was a CO₂ source (4.23 ± 3.42 µmol m^?2 s^?1) and net CH₄ sink, but with large uncertainty (?0.27 ± 1.04 nmol m^?2 s^?1) and with substantial differences depending on wood decay status. Stems were CO₂ sources (1.93 ± 1.63 µmol m^?2 s^?1), but also net CH₄ sources (up to 0.98 nmol m^?2 s^?1), with a mean of 0.11 ± 0.21 nmol m^?2 s^?1 and significant differences depending on tree species. Stems of N. sylvatica, F. grandifolia, and L. tulipifera consistently emitted CH₄, whereas stems of A. rubrum, B. lenta, and Q. spp. were intermittent sources. Coarse woody debris and stems accounted for 35% of total measured CO₂ fluxes, whereas CH₄ emissions from living stems offset net soil and CWD CH₄ uptake by 3.5%. Our results demonstrate the importance of CH₄ emissions from living stems in upland forests and the need to consider multiple forest components to understand and interpret ecosystem CO₂ and CH₄ dynamics.     

Adaptive photosynthetic strategies of the Mediterranean maquis species according to their origin

In consideration of their origin the adaptive strategies of the evergreen species of the Mediterranean maquis were analysed. Rosmarinus officinalis L., Erica arborea L., and Erica multiflora L. had the lowest net photosynthetic rate (P_N) in the favourable period [7.8±0.6 μmol(CO₂) m^?2s^?1, mean value], the highest P_N decrease (on an average 86 % of the maximum) but the highest recovery capacity (>70 % of the maximum) at the first rainfall in September. Cistus incanus L. and Arbutus unedo L. had the highest P_N during the favourable period [15.5±5.2 μmol(CO₂) m^?2s^?1, mean value], 79 % decrease during drought, and a lower recovery capacity (on an average 54 %). Quercus ilex L., Phillyrea latifolia L., and Pistacia lentiscus L. had an intermediate P_N in the favourable period [9.2±1.3 μmol(CO2) m^?2s^?1, mean value], a lower reduction during drought (on an average 63 %), and a range from 62 % (Q. ilex and P. latifolia) to 39 % (P. lentiscus) of recovery capacity. The Mediterranean species had higher decrease in P_N and stomatal conductance during drought and a higher recovery capacity than the pre-Mediterranean species. Among the pre-Mediterranean species, P. latifoliahad the best adaptation to long drought periods also by its higher leaf mass per area (LMA) which lowered leaf temperature thus decreasing transpiration rate during drought. Moreover, its leaf longevity determined a more stable leaf biomass during the year. Among the Mediteranean species, R. officinalis was the best adapted species to short drought periods by its ability to rapidly recover. Nevertheless, R. officinalis had the lowest tolerance to high temperatures by its P_N dropping below half its maximum value when leaf temperature was over 33.6°C. R. officinalismay be used as a bioindicator species of global change.     

Light, temperature and nutrients as factors in photosynthetic adjustment to an elevated concentration of carbon dioxide

The short-term stimulation of the net rate of carbon dioxide exchange of leaves by elevated concentrations of CO₂ usually observed in C₃ plants sometimes does not persist. Experiments were conducted to test whether the patterns of response to the environment during growth were consistent with the hypotheses that photosynthetic adjustment to elevated CO₂ concentration is due to (1) feedback inhibition or (2) nutrient stress. Soybean [Glycine max (L.) Merr. cv. Williams] and sugar beet (Best vulgaris L. cv. Mono Hye-4) were grown from seed at 350 and 700 μl^? CO₂, at 20 and 25°C, at a photon flux density of 0.5 and 1.0 mmol m^?2 S^?1 and with three nutrient regimes until the third trifoliolate leaf of soybean or the sixth leaf of sugar beet had finished expanding. Net rates of CO₂ exchange of the most recently expanded leaves were then measured at both 350 and 700 μl 1^?1 CO₂. Plants grown at the elevated CO₂ concentration had net rates of leaf CO₂ exchange which were reduced by 33% in sugar beet and 23% in soybean when measured at 350 μl 1^?1 CO₂ and when averaged over all treatments. Negative photosynthetic adjustment to elevated CO₂ concentration was not greater at 20 than at 25°C, was not greater at a photon flux density of 1.0 than at 0.5 mmol m^?2 S^?1 and was not greater with limiting nutrients. Furthermore, in soybean, negative photosynthetic adjustment could be induced by a single night at elevated CO₂ concentration, with net rates of CO₂ exchange the next day equal to those of leaves of plants grown from seed at the elevated concentration of CO₂. These patterns do not support either the feedback-inhibition or the nutrient-stress hypothesis of photosynthetic adjustment to elevated concentrations of CO₂.     

The growth of <Emphasis Type="Italic">Chlorella sorokiniana</Emphasis> as influenced by CO<Subscript>2</Subscript>, light,and flue gases

In order to achieve recognition as environmentally friendly production, flue gases should be used as a CO₂ source for growing the microalgae Chlorella sorokiniana when used for hydrogen production. Flue gases from a waste incinerator and from a silicomanganese smelter were used. Before testing the flue gases, the algae were grown in a laboratory at 0.04, 1.3, 5.9, and 11.0 % (v/v) pure CO₂ gas mixed with fresh air. After 5 days of growth, the dry biomass per liter algal culture reached its maximum at 6.1 % CO₂. A second experiment was conducted in the laboratory at 6.2 % CO₂ at photon flux densities (PFD) of 100, 230, and 320 μmol photons m^?2 s^?1. After 4 days of growth, increasing the PFD increased the biomass production by 67 and 108 % at the two highest PFD levels, as compared with the lowest PFD. A bioreactor system containing nine daylight-exposed tubes and nine artificial light-exposed tubes was installed on the roof of the waste incinerator. The effect of undiluted flue gas (10.7 % CO₂, 35.8 ppm NO _x , and 38.6 ppm SO₂), flue gas diluted with fresh air to give 4.2 % CO₂ concentration, and 5.0 % pure CO₂ gas was studied in daylight (21.4?±?9.6 mol photons m^?2 day^?1 PAR, day length 12.0 h) and at 135 μmol photons m^?2 s^?1 artificial light given 24 h day^?1 (11.7?±?0.0 mol photons m^?2 day^?1 PAR). After 4 days’ growth, the biomass production was the same in the two flue gas concentrations and the 5 % pure CO₂ gas control. The biomass production was also the same in daylight and artificial light, which meant that, in artificial light, the light use efficiency was about twice that of daylight. The starch concentration of the algae was unaffected by the light level and CO₂ concentration in the laboratory experiments (2.5–4.0 % of the dry weight). The flue gas concentration had no effect on starch concentration, while the starch concentration increased from about 1.5 % to about 6.0 % when the light source changed from artificial light to daylight. The flue gas from the silicomanganese smelter was characterized by a high CO₂ concentration (about 17 % v/v), low oxygen concentration (about 4 %), about 100 ppm NO _x , and 1 ppm SO₂. The biomass production using flue gas significantly increased as compared with about 5 % pure CO₂ gas, which was similar to the biomass produced at a CO₂ concentration of 10–20 % mixed with N₂. Thus, the enhanced biomass production seemed to be related to the low oxygen concentration rather than to the very high CO₂ concentration.     

Impacts of enhanced UVB radiation on photosynthetic characteristics of the marine diatom <Emphasis Type="Italic">Phaeodactylum tricornutum</Emphasis> (Bacillariophyceae,Heterokontophyta)

Solar ultraviolet B (UVB) irradiance at the Earth’s surface is increasing due to anthropogenic influences. To evaluate the effects of enhanced UVB radiation on photosynthetic characteristics of the marine diatom Phaeodactylum tricornutum, the species was exposed to four levels of UVB radiation, 0, 0.25, 0.75, and 1.50 KJ m^?2 day^?1 for 7 days. Effects of UVB stress on net photosynthetic rate, net respiration rate, variable chlorophyll (Chl) fluorescence parameters, Chl a and carotenoid contents, and UV-absorbing compounds (UVACs) were investigated. Results showed that there were no significant differences in terms of net respiration rate or maximal photochemical efficiency of photosystem II (F_v/F_m) between the treatments in the short or long term. However, enhanced UVB radiation at an intensity of 0.16 W m^?2 had a negative effect on the net photosynthetic rate, electron transport rate, and on the pathway of excess energy dissipation over the short term (1 to 5 days). Carotenoid and UVACs content increased under UVB radiation. Photosynthetic parameters were unaffected by UVB radiation on the seventh day indicating that P. tricornutum can adapt to UVB radiation in the long term. Results of the present study indicate that there is a dynamic balance between damage and adaptation in microalgae that enables them to adapt to UVB-induced photosystem alterations during both short-term and long-term exposure.     

Physiological and Biochemical Mechanisms Preventing Cd Toxicity in the New Hyperaccumulator <Emphasis Type="Italic">Abelmoschus manihot</Emphasis>

Abelmoschus manihot, an ornamental plant, was examined for phytoremediation purposes in accordance with the ability to accumulate cadmium and physiological mechanisms of cadmium tolerance. A net photosynthetic rate (A _N) glasshouse experiment for 60 days was conducted to investigate the influence of different cadmium amounts (0–100 mg kg^?1) on the growth, biomass, photosynthetic performance, reactive oxygen species (ROS) production, antioxidative enzyme activities, Cd uptake and accumulation of A. manihot. Exposure to cadmium enhanced plant growth even at 100 mg kg^?1, without showing symptoms of visible damage. The cadmium concentration of shoots (stems or leaves) and roots was more than the critical value of 100 mg kg^?1 and reached 126.17, 185.26 and 210.24 mg kg^?1, respectively. BCF values of A. manihot plants exceeded the reference value 1.0 for all the Cd treatments, and TF values were greater than 1 at 15–60 mg kg^?1 Cd treatment. The results also showed that cadmium concentrations of 60 mg kg^?1 or less induced a significant enhancement in plant net photosynthetic rate (A _N), stomatal conductance (G _s), transpiration rate (T _r), photosynthetic pigments and F _v/F _m. These parameters were slightly decreased at the higher concentration (100 mg kg^?1). The ROS production (O₂ ^?, H₂O₂) and antioxidative response including SOD, CAT and POD were significantly enhanced by increasing cadmium. These results suggest that A. manihot can be considered as a Cd-hyperaccumulator and the hormetic effects may be taken into consideration in remediation of Cd contamination soil.     

Physiological responses of <Emphasis Type="Italic">Abies faxoniana</Emphasis> populations from different elevations to increased CO<Subscript>2</Subscript> and N application

The altitude-related responses to the increased application of CO₂, N, and their combination were investigated in two Abies faxoniana populations, which originated from a subalpine coniferous forest at elevations of 2,580 and 3,200 m using closed-top chambers. The two contrasting populations were subjected to two CO₂ regimes (350 and 700 µmol mol^?1) and two N levels (0 and 5 g N m^?2 year^?1). Their net photosynthetic rate, non-structural carbohydrate concentration, and photosynthetic N use efficiency (PNUE) increased under elevated CO₂. However, the increases detected in the high-elevation (HE) population were significantly greater than those found in the low-elevation (LE) population. Under elevated CO₂ and N application, the maximal carboxylation rate (V _cmax) increased in HE population, whereas no effects were found on V _cmax in LE population. The C to N ratio decreased under N application in both populations. N application also induced the HE population to show greater increases in free amino acids, soluble proteins, N concentration, and PNUE than LE population. These results suggested that the population from HE was more sensitive to elevated CO₂ and (or) N application than LE population. Results of this study provided valuable knowledge for predicting forest development under increased atmospheric CO₂ concentration and (or) N deposition.     

Adaptive temperature regulation in the little bird in winter: predictions from a stochastic dynamic programming model

Stomatal CO₂ responsiveness and photosynthetic capacity vary greatly among plant species, but the factors controlling these physiological leaf traits are often poorly understood. To explore if these traits are linked to taxonomic group identity and/or to other plant functional traits, we investigated the short-term stomatal CO₂ responses and the maximum rates of photosynthetic carboxylation (V _cmax) and electron transport (J _max) in an evolutionary broad range of tropical woody plant species. The study included 21 species representing four major seed plant taxa: gymnosperms, monocots, rosids and asterids. We found that stomatal closure responses to increased CO₂ were stronger in angiosperms than in gymnosperms, and in monocots compared to dicots. Stomatal CO₂ responsiveness was not significantly related to any of the other functional traits investigated, while a parameter describing the relationship between photosynthesis and stomatal conductance in combined leaf gas exchange models (g ₁) was related to leaf area-specific plant hydraulic conductance. For photosynthesis, we found that the interspecific variation in V _cmax and J _max was related to within leaf nitrogen (N) allocation rather than to area-based total leaf N content. Within-leaf N allocation and water use were strongly co-ordinated (r ² = 0.67), such that species with high fractional N investments into compounds maximizing photosynthetic capacity also had high stomatal conductance. We conclude that while stomatal CO₂ responsiveness of tropical woody species seems poorly related to other plant functional traits, photosynthetic capacity is linked to fractional within-leaf N allocation rather than total leaf N content and is closely co-ordinated with leaf water use.     

Influence of phosphorus and nitrogen on photosynthetic parameters and growth in <Emphasis Type="Italic">Vicia faba</Emphasis> L.

The influence of phosphorus (P) and nitrogen (N) supply on biomass, leaf area, photon saturated photosynthetic rate (P_max), quantum yield efficiency (α), intercellular CO₂ concentration (C_i), and carboxylation efficiency (CE) was investigated in Vicia faba. The influence of P on N accumulation, biomass, and leaf area production was also investigated. An increase in P supply was consistently associated with an increase in N accumulation and N productivity in terms of biomass and leaf area production. Furthermore, P increased the photosynthetic N use efficiency (NUE) in terms of P_max and α. An increase in P supply was also associated with an increase in CE and a decrease in C_i. Under variable daily meteorological conditions specific leaf nitrogen content (N_L), specific leaf phosphorus content (P_L), specific leaf area (δ_L), root mass fraction (R_f), P_max, and α remained constant for a given N and P supply. A monotonic decline in the steady-state value of R_f occurred with increasing N supply. δ_L increased with increasing N supply or with increasing N_L. We tested also the hypothesis that P supply positively affects both N demand and photosynthetic NUE by influencing the upper limit of the asymptotic values for P_max and CE, and the lower limit for C_i in response to increasing N.     

Ecotypes of <Emphasis Type="Italic">Gracilaria caudata</Emphasis> (Gracilariales,Rhodophyta): physiological and morphological approaches considering life history phases

On the Brazilian coast, the red alga Gracilaria caudata J. Agardh is exploited for agar production. In view of its economic importance for potential mariculture, this work aimed to elucidate and characterize ecotypes along an extended Brazilian coastline by evaluating the effects of irradiance (70 and 150 μmol photons m^?2 s^?1) on the number of differentiated branches, growth rates (GRs), photosynthesis parameters, and pigment content of female gametophytes and tetrasporophytes from three distinct geographical areas: Ceará State (CE), Bahia State (BA), and São Paulo State (SP). Compared to low irradiance, high irradiance promoted higher GRs and a greater number of differentiated branches, as well as maximum electron transport rate (ETR_max) and maximum photosynthesis (P _max) in both phases. However, irrespective of population or irradiance, tetrasporophytes had higher ETR_max (3.30 μmol e^? m^?2 s^?1) than gametophytes (2.54 μmol e^? m^?2 s^?1), corroborating the hypothesis that tetrasporophytes have better physiological performance than gametophytes, implicating correspondingly better adaptive abilities. Under high irradiance, regardless of the period of cultivation (14 or 28 days), strains from CE presented the highest GR (15% day^?1) when compared to strains from SP (14% day^?1) and BA (13% day^?1). CE strains also had the highest number of differentiated branches and P _max. Based on these results, we suggest that CE strains are the best candidates for future experimental mariculture tests. Importantly, overall differences in physiological performance among the strains from different populations give evidence of intraspecific diversity, thus supporting the hypothesis of ecotypic differentiation and allowing this study to define different G. caudata ecotypes.