Volatile Metabolites and External CO2Exchange of Wheat Cenoses under Optimal Conditions and Thermal Stress

The effects of elevated temperature (35 and 45°C) on photosynthesis, respiration, and both the qualitative and quantitative compositions of volatile emissions (VE) of wheat (Triticum aestuvumL. cultivar 232) cenoses at light intensities of 70, 150, or 240 W/m²of photosynthetically available radiation (PAR) were studied. At a PAR of 240 W/m², the thermal stabilities of photosynthesis and respiration increased at 35°C and decreased at 45°C. Elevated temperatures nonuniformly changed the rates and direction of VE syntheses. In this process, the highest increase in VE evolution was observed at 70 W/m²and 35°C; the lowest, at 240 W/m². In addition, the concentrations and composition of VE during the repair period differed from the initial values.     

Characteristics of Slow Induction Curve of Chlorophyll Fluorescence and CO2 Exchange for the Assessment of Plant Heat Tolerance at Various Levels of Light Intensity

The heat tolerance of wheat (Triticum aestivum L.) and radish (Raphanus sativus L. var. minor) cenoses exposed to elevated and damaging air temperatures (35°C for 20 h, 45°C for 7 h) under photoculture conditions at various levels of photosynthetically active radiation (PAR) was assessed by measuring characteristics of the slow induction curve of chlorophyll fluorescence at 682 and 734 nm and the CO₂ exchange rate. Irrespective of the illumination level, the exposure of the cenoses to 35°C did not induce irreversible changes in the plant photosynthetic apparatus. The lowest extent of damage to wheat and radish cenoses exposed to 45°C was observed at 150 W/m² of PAR, whereas the highest damage of the plants was observed at an illumination level that was close to the compensation point of the cenose photosynthesis (50–70 W/m² of PAR at air temperature of 24°C). Viability index proved to be the most sensitive characteristic, compared to other characteristics, which were determined by measuring the slow phase of fluorescence induction at 682 and 734 nm. In the cenoses studied, the pattern of changes in the viability index in response to a stress factor was close to the changes in the photosynthetic rate.     

Temperature dependency of bark photosynthesis in beech (Fagus sylvatica L.) and birch (Betula pendula Roth.) trees

Temperature dependencies of stem dark respiration (R(d)) and light-driven bark photosynthesis (A(max)) of two temperate tree species (Fagus sylvatica and Betula pendula) were investigated to estimate their probable influence on stem carbon balance. Stem R(d) was found to increase exponentially with increasing temperatures, whereas A(max) levelled off or decreased at the highest temperatures chosen (35-40 degrees C). Accordingly, a linear relationship between respiratory and assimilatory metabolism was only found at moderate temperatures (10-30 degrees C) and the relationship between stem R(d) and A(max) clearly departed from linearity at chilling (5 degrees C) and at high temperatures (35-40 degrees C). As a result, the proportional internal C-refixation rate also decreased non-linearly with increasing temperature. Temperature response of photosystem II (PSII) photochemistry was also assessed. Bark photochemical yield (Delta F/F(m)') followed the same temperature pattern as bark CO(2) assimilation. Maximum quantum yield of PSII (F(v)/F(m)) decreased drastically at freezing temperatures (-5 degrees C), while from 30 to 40 degrees C only a marginal decrease in F(v)/F(m) was found. In in situ measurements during winter months, bark photosynthesis was found to be strongly reduced. Low temperature stress induced an active down-regulation of PSII efficiency as well as damage to PSII due to photoinhibition. All in all, the benefit of bark photosynthesis was negatively affected by low (<5 degrees C) as well as high temperatures (>30 degrees C). As the carbon balance of tree stems is defined by the difference between photosynthetic carbon gain and respiratory carbon loss, this might have important implications for accurate modelling of stem carbon balance.     

Modulation of osmotic stress effects on photosynthesis and respiration by temperature in mesophyll protoplast of pea

Exposure of mesophyll protoplast of pea to osmotic stress decreases the rate of photosynthesis while stimulating marginally the respiratory rate of mesophyll protoplasts. The interaction of osmotic and temperature stress during the modulation of photosynthetic and respiratory rates of pea (Pisum sativum var Azad P1) mesophyll protoplasts was investigated. The protoplasts were exposed to either iso-osmotic (0.4 M) or hyper-osmotic (1.0 M) concentration of sorbitol at 15 degrees and 25 degrees C. The rates of photosynthesis and respiration were studied. At optimum temperature of 25 degrees C, there was a decrease in photosynthesis (< 10%) at hyper-osmoticum (osmotic effect), whereas respiration increased marginally (by about 15%). Low temperature (15 degrees C) aggravated the sensitivity of both respiration and photosynthesis to osmotic stress. At 15 degrees C, the decrease in photosynthesis due to osmotic stress was > 35%, while the respiratory rate was stimulated by 30%. The relative proportion of cytochrome pathway decreased by about 50% at both 15 degrees C and 25 degrees C while that of alternative pathway increased, more so, at 15 degrees C, when the mesophyll protoplasts were subjected to hyper-osmoticum stress. The titration experiments showed that extent of engagement of alternative pathway was higher, the slope value was slightly higher for 15 degrees C compared to 25 degrees C. Low temperature modulates the effect of hyper-osmoticum stress on photosynthesis and respiration, and results in increased participation of alternative pathway.     

Temperature regulation in adult quail (Colinus virginianus) during acute thermal stress

1. Evaporative heat loss, O2 consumption, CO2 production, and internal body temperature were measured in unanesthetized, unrestrained bobwhite (Colinus virginianus) at specific ambient temperatures (Ta). 2. No significant change in body temperature occurred at any Ta tested, but metabolic heat production (H) increased from 42.17 W/m2 at Ta 35 degrees C to 102.89 W/m2 at Ta 10 degrees C. 3. Evaporative heat loss (E) increased approximately two-fold from Ta 10-35 degrees C, with E/H increasing exponentially over the same temperature range. 4. No significant change in thermal insulation occurred from Ta 10-30 degrees C. 5. Combined convective and radiative heat transfer for the bobwhite was 2.96 W/m2 X C from Ta 10-35 degrees C.     

Photosynthesis and respiration of a deep-water periphyton community (Macclesfield Bank,South China Sea)

The production parameters of the deep-water periphyton were investigated on the Macclesfield Bank (South China Sea) at depths down to 240 m. At 70–90 m depths the substrate is composed of the remains of dead corals and fragments of porous calcareous material overgrown with red coralline and articulated thalline algae Halimeda sp. At 220–240 m depths the substrate consists of rhodolites, which are individual unattached nodules encrusted mainly with red calcareous coralline algae Lithophyllum sp., Porolithon sp. and red lamellar alga Hypoglossum sp. At all depths the substrate is pierced with green filiform algae Ostreobium sp. and covered with benthic diatom algae. The zooperiphyton in the studied area is comprised of bryozoans, sponges, foraminifers and drilling mollusks. Respiration (R) and the gross (Pg) and net (Pn) primary production of the deepwater periphyton community were determined using the oxygen technique (polarographic electrode) at values of photosynthetically active radiation (PAR) close to natural levels. At 70–90 m depths the Pg of the photoperiphyton was 23.3 mg O₂/(m² h), and the Pn of the community had negative values due to respiration of phytoand mainly zooperiphyton and bacteria. At 220–240 m depths, where less than 0.001% of the surface PAR penetrates, the Pg of the phytoperiphyton decreased to 9.6 mg O₂/(m² h), and the R of the community was 25.9 mg O₂/(m² h). A high efficiency of light energy utilization by the phytoperiphyton was found. The apparent quantum yield (Fa) for algae collected at 70–90 m depths was close to the maximum level of 0.097. The values of Fn that we obtained for 220–240 m depths and calculated from identical data [27], were much higher than theoretical values, which cannot be explained based on modern views on the mechanisms of photosynthesis. Possible sources of errors are discussed. It is proposed that we observed additional evolution of oxygen as the result of H₂O₂ degradation.     

Leaf respiration of snow gum in the light and dark. Interactions between temperature and irradiance

We investigated the effect of temperature and irradiance on leaf respiration (R, non-photorespiratory mitochondrial CO(2) release) of snow gum (Eucalyptus pauciflora Sieb. ex Spreng). Seedlings were hydroponically grown under constant 20 degrees C, controlled-environment conditions. Measurements of R (using the Laisk method) and photosynthesis (at 37 Pa CO(2)) were made at several irradiances (0-2,000 micromol photons m(-2) s(-1)) and temperatures (6 degrees C-30 degrees C). At 15 degrees C to 30 degrees C, substantial inhibition of R occurred at 12 micromol photons m(-2) s(-1), with maximum inhibition occurring at 100 to 200 micromol photons m(-2) s(-1). Higher irradiance had little additional effect on R at these moderate temperatures. The irradiance necessary to maximally inhibit R at 6 degrees C to 10 degrees C was lower than that at 15 degrees C to 30 degrees C. Moreover, although R was inhibited by low irradiance at 6 degrees C to 10 degrees C, it recovered with progressive increases in irradiance. The temperature sensitivity of R was greater in darkness than under bright light. At 30 degrees C and high irradiance, light-inhibited rates of R represented 2% of gross CO(2) uptake (v(c)), whereas photorespiratory CO(2) release was approximately 20% of v(c). If light had not inhibited leaf respiration at 30 degrees C and high irradiance, R would have represented 11% of v(c). Variations in light inhibition of R can therefore have a substantial impact on the proportion of photosynthesis that is respired. We conclude that the rate of R in the light is highly variable, being dependent on irradiance and temperature.     

Temperature response of photosynthesis and internal conductance to CO2: results from two independent approaches

The internal conductance to CO(2) transfer from intercellular spaces to chloroplasts poses a major limitation to photosynthesis, but few studies have investigated its temperature response. The aim of this study was to determine the temperature response of photosynthesis and internal conductance between 10 degrees C and 35 degrees C in seedlings of a deciduous forest tree species, Quercus canariensis. Internal conductance was estimated via simultaneous measurements of gas exchange and chlorophyll fluorescence ("variable J method"). Two of the required parameters, the intercellular photocompensation point (C(i)*) and rate of mitochondrial respiration in the light (R(d)), were estimated by the Laisk method. These were used to calculate the chloroplastic photocompensation point (Gamma*) in a simultaneous equation with g(i). An independent estimate of internal conductance was obtained by a novel curve-fitting method based on the curvature of the initial Rubisco-limited portion of an A/C(i) curve. The temperature responses of the rate of Rubisco carboxylation (V(cmax)) and the RuBP limited rate of electron transport (J(max)) were determined from chloroplastic CO(2) concentrations. The rate of net photosynthesis peaked at 24 degrees C. C(i)* was similar to reports for other species with a C(i)* of 39 micromol mol(-1) at 25 degrees C and an activation energy of 34 kJ mol(-1). Gamma* was very similar to the published temperature response for Spinacia oleracea from 20 degrees C to 35 degrees C, but was slightly greater at 10 degrees C and 15 degrees C. J(max) peaked at 30 degrees C, whereas V(cmax) did not reach a maximum between 10 degrees C and 35 degrees C. Activation energies were 49 kJ mol(-1) for V(cmax) and 100 kJ mol(-1) for J(max). Both methods showed that internal conductance doubled from 10 degrees C to 20 degrees C, and then was nearly temperature-independent from 20 degrees C to 35 degrees C. Hence, the temperature response of internal conductance could not be fitted to an Arrhenius function. The best fit to estimated g(i) was obtained with a three-parameter log normal function (R(2)=0.98), with a maximum g(i) of 0.19 mol m(-2) s(-1) at 29 degrees C.     

Effect of Light Intensity, Carbon Dioxide Concentration, and Leaf Temperature on Gas Exchange of Spray Carnation Plants

The rates of CO₂ assimilation by potted spray carnation plants(cv. Cerise Royalette) were determined over a wide range oflight intensities (45–450 W m^–2 PAR), CO₂ concentrations(200–3100 vpm), and leaf temperatures (5–35 °C).Assimilation rates varied with these factors in a way similarto the response of single leaves of other temperate crops, althoughthe absolute values were lower. The optimal temperature forCO₂ assimilation was between 5 and 10 °C at 45 W m^–2PAR but it increased progressively with increasing light intensityand CO₂ concentration up to 27 °C at 450 W m^–2 PARand 3100 vpm CO₂ as expressed by the equation TOpt = –6.47-h 2.336 In G + 0.031951 where C is CO₂ concentration in vpmand I is photo-synthetically active radiation in W m^–2.CO₂ enrichment also increased stomatal resistance, especiallyat high light intensities. The influence of these results on optimalization of temperaturesand CO₂ concentrations for carnation crops subjected to dailylight variation, and the discrepancy between optimal temperaturesfor growth and net photosynthesis, are discussed briefly     

Temperature response of mesophyll conductance. Implications for the determination of Rubisco enzyme kinetics and for limitations to photosynthesis in vivo

CO(2) transfer conductance from the intercellular airspaces of the leaf into the chloroplast, defined as mesophyll conductance (g(m)), is finite. Therefore, it will limit photosynthesis when CO(2) is not saturating, as in C3 leaves in the present atmosphere. Little is known about the processes that determine the magnitude of g(m). The process dominating g(m) is uncertain, though carbonic anhydrase, aquaporins, and the diffusivity of CO(2) in water have all been suggested. The response of g(m) to temperature (10 degrees C-40 degrees C) in mature leaves of tobacco (Nicotiana tabacum L. cv W38) was determined using measurements of leaf carbon dioxide and water vapor exchange, coupled with modulated chlorophyll fluorescence. These measurements revealed a temperature coefficient (Q(10)) of approximately 2.2 for g(m), suggesting control by a protein-facilitated process because the Q(10) for diffusion of CO(2) in water is about 1.25. Further, g(m) values are maximal at 35 degrees C to 37.5 degrees C, again suggesting a protein-facilitated process, but with a lower energy of deactivation than Rubisco. Using the temperature response of g(m) to calculate CO(2) at Rubisco, the kinetic parameters of Rubisco were calculated in vivo from 10 degrees C to 40 degrees C. Using these parameters, we determined the limitation imposed on photosynthesis by g(m). Despite an exponential rise with temperature, g(m) does not keep pace with increased capacity for CO(2) uptake at the site of Rubisco. The fraction of the total limitations to CO(2) uptake within the leaf attributable to g(m) rose from 0.10 at 10 degrees C to 0.22 at 40 degrees C. This shows that transfer of CO(2) from the intercellular air space to Rubisco is a very substantial limitation on photosynthesis, especially at high temperature.     

PHYSIOLOGICAL RESPONSES TO TEMPERATURE AND IRRADIANCE IN SPIROGYRA (ZYGNEMATALES, CHAROPHYCEAE)1

Spirogyra Link (1820) is an anabranched filamentous green alga that forms free-floating mats in shallow waters. It occurs widely in static waters such as ponds and ditches, sheltered littoral areas of lakes, and stow-flowing streams. Field observations of its seasonal distribution suggest that the 70-μm-wide filament form of Spirogyra should have a cool temperature and high irradiance optimum for net photosynthesis. Measurements of net photosynthesis and respiration were marie at 58 combinations of tight and temperature in a controlled environment facility. Optimum conditions were 25°C and 1500 μmol photons m⁻² s⁻¹, at which net photosynthesis averaged 75.7 mg O₂ gdm⁻¹ h⁻¹. Net photosynthesis was positive at temperatures from 5° to 35°C at most irradiances except at combinations of extremely low irradiances and high temperatures (7 and 23 μmol photons m⁻² s⁻¹ at 30°C and 7, 23, and 35 μmol photons m⁻² s⁻¹ at 35°C). Respiration rates increased with both temperature and prior irradiance. Light-enhanced respiration rates were significantly greater than dark respiration rates following irradiances of 750 μmol photons m⁻² s⁻¹ or greater. Polynomials were fitted to the data to generate response surfaces; such response surfaces can be used to represent net photosynthesis and respiration in ecological models. The data indicate that the alga can tolerate the cool water and high irradiances characteristic of early spring but cannot maintain positive net photosynthesis under conditions of high temperature and low light (e.g. when exposed to self-shading ).     

Temperature preference and respiration of acaridid mites

The thermal preferences in a grain mass and respiration at various temperatures in mites (Acari: Acarididae) of medical and economical importance [Acarus siro (L. 1758), Dermatophagoides farinae Hughes 1961, Lepidoglyphus destructor (Schrank 1871), and Tyrophagus putrescentiae (Schrank 1781)] were studied under laboratory conditions. Based on the distribution of mites in wheat, Triticum aestivum L., grain along a thermal gradient from 10 to 40 degrees C, L. destructor, D. farinae, and A. siro were classified as eurythermic and T. putrescentiae as stenothermic. The lowest preferred temperature was found for D. farinae (28 degrees C), followed by A. siro (28.5 degrees C), L. destructor (29.5 degrees C), and T. putrescentiae (31.5 degrees C). The relationship between the respiration rate and the temperature was similar for all four mite species. The highest respiration was found in the range from 31 to 33 degrees C. This is approximately 2 degrees C higher than the preferred temperature of these species. The lower temperature threshold of respiration ranged from 1 to 5 degrees C and the upper threshold ranged from 45 to 48 degrees C. Acclimatization of A. siro to temperature regimes of 5, 15, and 35 degrees C resulted in thermal preferences between 9 and 12 degrees C, 9 and 20 degrees C, and 28 and 35 degrees C, respectively. The respiration rate of acclimatized specimens increased with the temperature, reaching a maximum at 29.0 degrees C for mites acclimatized at 5 and 15 degrees C and a maximum at 33.7 degrees C for those acclimatized at 30 degrees C.     

Gas exchange by pods and subtending leaves and internal recycling of CO(2) by pods of chickpea (Cicer arietinum L.) subjected to water deficits

Terminal drought markedly reduces leaf photosynthesis of chickpea (Cicer arietinum L.) during seed filling. A study was initiated to determine whether photosynthesis and internal recycling of CO(2) by the pods can compensate for the low rate of photosynthesis in leaves under water deficits. The influence of water deficits on the rates of photosynthesis and transpiration of pods and subtending leaves in chickpea (cv. Sona) was investigated in two naturally-lit, temperature-controlled glasshouses. At values of photosynthetically active radiation (PAR) of 900 micromol m(-2) s(-1) and higher, the rate of net photosynthesis of subtending leaves of 10-d-old pods was 24 and 6 micromol m(-2) s(-1) in the well-watered (WW) and water-stressed (WS) plants when the covered-leaf water potential (Psi) was -0.6 and -1.4 MPa, respectively. Leaf photosynthesis further decreased to 4.5 and 0.5 micromol m(-2) s(-1) as Psi decreased to -2.3 and -3.3 MPa, respectively. At 900--1500 micromol m(-2) s(-1) PAR, the net photosynthetic rate of 10-d-old pods was 0.9-1.0 micromol m(-2) s(-1) in the WW plants and was -0.1 to -0.8 micromol m(-2) s(-1) in the WS plants. The photosynthetic rates of both pods and subtending leaves decreased with age, but the rate of transpiration of the pods increased with age. The rates of respiration and net photosynthesis inside the pods were estimated by measuring the changes in the internal concentration of CO(2) of covered and uncovered pods during the day. Both the WW and WS pods had similar values of internal net photosynthesis, but the WS pods showed significantly higher rates of respiration suggesting that the WS pods had higher gross photosynthetic rates than the WW pods, particularly in the late afternoon. When (13)CO(2) was injected into the gas space inside the pod, nearly 80% of the labelled carbon 24 h after injection was observed in the pod wall in both the WW and WS plants. After 144 h the proportion of (13)C in the seed had increased from 19% to 32% in both treatments. The results suggest that internal recycling of CO(2) inside the pod may assist in maintaining seed filling in water-stressed chickpea.     

Human exposure to 2450 MHz CW energy at levels outside the IEEE C95.1 standard does not increase core temperature

Permission was received from the Brooks AFB Institutional Review Board and the AF Surgeon General's Office to exceed the peak power density (PD = 35 mW/cm(2)) we had previously studied during partial body exposure of human volunteers at 2450 MHz. Two additional peak PD were tested (50 and 70 mW/cm(2)). The higher of these PD (normalized peak local SAR = 15.4 W/kg) is well outside the IEEE C95.1 guidelines for partial body exposure, as is the estimated whole body SAR approximately 1.0 W/kg. Seven volunteers (four males, three females) were tested at each PD in three ambient temperatures (T(a) = 24, 28, and 31 degrees C) under our standard protocol (30 min baseline, 45 min RF exposure, 10 min baseline). The thermophysiological data (esophageal and six skin temperatures, metabolic heat production, local sweat rate, and local skin blood flow) were combined with comparable data at PD = 0, 27, and 35 mW/cm(2) from our 1999 study to generate response functions across PD. No change in esophageal temperature or metabolic heat production was recorded at any PD in any T(a). At PD = 70 mW/cm(2), skin temperature on the upper back (irradiated directly) increased 4.0 degrees C in T(a) = 24 degrees C, 2.6 degrees C in T(a) = 28 degrees C, and 1.8 degrees C in T(a) = 31 degrees C. These differences were primarily due to the increase in local sweat rate, which was greatest in T(a) = 31 degrees C. Also at PD = 70 mW/cm(2), local skin blood flow on the back increased 65% over baseline levels in T(a) = 31 degrees C, but only 40% in T(a) = 24 degrees C. Although T(a) becomes an important variable when RF exposure exceeds the C95.1 partial body exposure limits, vigorous heat loss responses of blood flow and sweating maintain thermal homeostasis efficiently. It is also clear that strong sensations of heat and thermal discomfort will motivate a timely retreat from a strong RF field, long before these physiological responses are exhausted. Published 2001 Wiley-Liss, Inc.     

Physiological responses of Opuntia ficus-indica to growth temperature

The influences of various day/night air temperatures on net CO₂ uptake and nocturnal acid accumulation were determined for Opuntia ficus-indica, complementing previous studies on the water relations and responses to photosynthetically active radiation (PAR) for this widely cultivated cactus. As for other Crassulacean acid metabolism (CAM) plants, net nocturnal CO₂ uptake had a relatively low optimal temperature, ranging from 11°C for plants grown at day/night air temperatures of 10°C/0°C to 23°C at 45°C/35°C. Stomatal opening, which occurred essentially only at night and was measured by changes in water vapor conductance, progressively decreased as the measurement temperature was raised. The CO₂ residual conductance, which describes chlorenchyma properties, had a temperature optimum a few degrees higher than the optimum for net CO₂ uptake at all growth temperatures. Nocturnal CO₂ uptake and acid accumulation summed over the whole night were maximal for growth temperatures near 25°C/15°C, CO₂ uptake decreasing more rapidly than acid accumulation as the growth temperature was raised. At day/night air temperatures that led to substantial nocturnal acid accumulation (25°C/15°C.). 90% saturation of acid accumulation required a higher total daily PAR than at non-optimal growth temperatures (10°C/0°C and 35°C/25°C). Also, the optimal temperature of net CO₂ uptake shifted downward when the plants were under drought conditions at all three growth temperatures tested, possibly reflecting an increased fractional importance of respiration at the higher temperatures during drought. Thus, water status, ambient PAR, and growth temperatures must all be considered when predicting the temperature response of gas exchange for O. ficus-indica and presumably for other CAM plants.     

Low clouds and cloud immersion enhance photosynthesis in understory species of a southern Appalachian spruce-fir forest (USA)

High-altitude forests of the southern Appalachian Mountains (USA) are frequently immersed in clouds, as are many mountain forests. They may be particularly sensitive to predicted increases in cloud base altitude with global warming. However, few studies have addressed the impacts of immersion on incident sunlight and photosynthesis. Understory sunlight (photosynthetically active radiation, PAR) was measured during clear, low cloud, and cloud-immersed conditions at Mount Mitchell and Roan Mountain, NC (USA) along with accompanying photosynthesis in four representative understory species. Understory PAR was substantially less variable on immersed vs. clear days. Photosynthesis became light-saturated between ～100 and 400 μmol · m(-2) · s(-1) PAR for all species measured, corresponding closely to the sunlight environment measured during immersion. Estimated daily carbon gain was 26% greater on clear days at a more open canopy site but was 22% greater on immersed/cloudy days at a more closed canopy site. F(v)/F(m) (maximum photosystem II efficiency) in Abies fraseri seedlings exposed to 2.5 min full sunlight was significantly reduced (10%), indicating potential reductions in photosynthesis on clear days. In addition, photosynthesis in microsites with canopy cover was nearly 3-fold greater under immersed (2.6 mmol · m(-2) · h(-1)) vs. clear conditions (0.9 mmol · m(-2) · h(-1)). Thus, cloud immersion provided more constant PAR regimes that enhanced photosynthesis, especially in shaded microsites. Future studies are needed to predict the survival of these refugial forests under potential changes in cloud regimes.     

Uptake and biotransformation of 2,4,6-trinitrotoluene (TNT) by microplantlet suspension culture of the marine red macroalga Portieria hornemannii

Microplantlets of the marine red macroalga Portieria hornemannii efficiently removed the explosive compound 2,4,6-trinitrotoluene (TNT) from seawater. Photosynthetic, axenic microplantlets (1.2 g FW/L) were challenged with enriched seawater medium containing dissolved TNT at concentrations of 1.0, 10, and 50 mg/L. At 22 degrees C and initial TNT concentrations of 10 mg/L or less, TNT removal from seawater was 100% within 72 h, and the first-order rate constant for TNT removal ranged from 0.025 to 0.037 L/gFW h under both illuminated conditions (153 microE/m(2)s, 14:10 LD photoperiod) and dark conditions. Two immediate products of TNT biotransformation, 2-amino-4,6-dinitrotoluene and 4-amino-2,6-dintrotoluene, were identified in the liquid culture medium, with a maximum material balance recovery of 29 mole%. Only trace levels of these products and residual TNT were found within the fresh cell biomass. Removal of TNT by P. hornemannii microplantlets at initial concentrations of 1.0 or 10 mg/L did not affect the respiration rate. At an initial TNT concentration of 10 mg/L, net photosynthesis decreased towards zero, commensurate with the removal of dissolved TNT from seawater, whereas at an initial TNT concentration of 1.0 mg/L, the net photosynthesis rate was not affected.     

Biogeochemical processes in the algal-bacterial mats of the Urinskii alkaline hot spring

The structure and production characteristics of microbial communities from the Urinskii alkaline hot spring (Buryat Republic, Russia) have been investigated. A distinctive characteristic of this hot spring is the lack of sulfide in the issuing water. The water temperature near the spring vents ranged from 69 to 38.5 degrees C and pH values ranged from 8.8 to 9.2. The total mineralization of water was less than 0.1 g/liter. Temperature has a profound effect on the species composition and biogeochemical processes occurring in the algal-bacterial mats of the Urinskii hot spring. The maximum diversity of the phototrophic community was observed at the temperatures 40 and 46 degrees C. A total of 12 species of cyanobacteria, 4 species of diatoms, and one species of thermophilic anoxygenic phototrophic bacteria, Chloroflexus aurantiacus, have been isolated from mat samples. At temperatures above 40 degrees C, the filamentous cyanobacterium Phormidium laminosum was predominant; its cell number and biomass concentration were 95.1 and 63.9%, respectively. At lower temperatures, the biomass concentrations of the cyanobacterium Oscillatoria limosa and diatoms increased (50.2 and 36.4%, respectively). The cyanobacterium Mastigocladus laminosus, which is normally found in neutral or slightly acidic hydrothermal systems, was detected in microbial communities. As the diatom concentration increases, so does the dry matter concentration in mats, while the content of organic matter decreases. The concentrations of proteins and carbohydrates reached their maximum levels at 45-50 degrees C. The maximum average rate of oxygenic photosynthesis (2.1 g C/m2 day), chlorophyll a content (343.4 mg/m2), and cell number of phototrophic microorganisms were observed at temperatures from 45 to 50 degrees C. The peak mass of bacterial mats (56.75 g/m2) occurred at a temperature of 65-60 degrees C. The maximum biomass concentration of phototrophs (414.63 x 10(-6) g/ml) and the peak rate of anoxygenic photosynthesis [0.42 g C/(m2 day)] were observed at a temperature of 35-40 degrees C.     

Physiological effects of kaolin applications in well-irrigated and water-stressed walnut and almond trees

BACKGROUND AND AIMS: Kaolin applications have been used to mitigate the negative effects of water and heat stress on plant physiology and productivity with variable results, ranging from increased to decreased yields and photosynthetic rates. The mechanisms of action of kaolin applications are not clear: although the increased albedo reduces leaf temperature and the consequent heat stress, it also reduces the light available for photosynthesis, possibly offsetting benefits of lower temperature. The objective of this study was to investigate which of these effects are prevalent and under which conditions. METHODS: A 6% kaolin suspension was applied on well-irrigated and water-stressed walnut (Juglans regia) and almond (Prunus dulcis) trees. Water status (i.e. stem water potential, psi(s)), gas exchange (i.e. light-saturated CO2 assimilation rate, Amax; stomatal conductance, g(s)), leaf temperature (T(l)) and physiological relationships in treated and control trees were then measured and compared. KEY RESULTS: In both species, kaolin did not affect the daily course of psi(s) whereas it reduced Amax by 1-4 micromol CO2 m(-2) s(-1) throughout the day in all combinations of species and irrigation treatments. Kaolin did not reduce g(s) in any situation. Consequently, intercellular CO2 concentration (C(i)) was always greater in treated trees than in controls, suggesting that the reduction of Amax with kaolin was not due to stomatal limitations. Kaolin reduced leaf temperature (T(l)) by about 1-3 degrees C and leaf-to-air vapour pressure difference (VPD(l)) by about 0.1-0.7 kPa. Amax was lower at all values of g(s), T(l) and VPD(l) in kaolin-treated trees. Kaolin affected the photosynthetic response to the photosynthetically active radiation (PAR) in almond leaves: kaolin-coated leaves had similar dark respiration rates and light-saturated photosynthesis, but a higher light compensation point and lower apparent quantum yield, while the photosynthetic light-response curve saturated at higher PAR. When these parameters were used to model the photosynthetic response curve to PAR, it was estimated that the kaolin film allowed 63% of the incident PAR to reach the leaf. CONCLUSIONS: The main effect of kaolin application was the reduction, albeit minor, of photosynthesis, which appeared to be related to the shading of the leaves. The reduction in T(l) and VPD(l) with kaolin did not suffice to mitigate the adverse effects of heat and water stress on Amax.     

Acclimation of Photosynthesis and Dark Respiration of a Submersed Angiosperm beneath Ice in a Temperate Lake

Ceratophyllum demersum L. remained physiologically active beneath ice of a southeastern Michigan lake. The effect of seasonally low photosynthetic photon flux density (PPFD) and cold but nonfreezing temperature on whole-plant physiology was studied. Net photosynthesis was measured at six temperatures and 12 PPFDs. Net photosynthesis, soluble protein concentration, ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco) protein concentration, and Rubisco activity of winter plants were 32, 31, 33, and 70% lower, respectively, than those of plants collected in the summer. Optimum temperatures for net photosynthesis of winter and summer plants were 5 and 30[deg]C, respectively. Dark respiration of winter plants was up to 313% greater than that of summer plants. Reduced Rubisco activity and increased dark respiration interacted to reduce net photosynthesis. Interaction of reduced net photosynthesis and increased dark respiration increased CO2 and light compensation points and the light saturation point of winter plants. Growth of C. demersum was limited by the ambient phosphorus concentration of lake water during summer. Apical stem segments of winter-collected plants had 54 and 35% more phosphorus and nitrogen, respectively, than summer-collected plants. Physiologically active perennation beneath ice enabled C. demersum to accumulate phosphorus during the winter when it was most abundant. Partial uncoupling of phosphorus acquisition from utilization may reduce phosphorus limitation upon growth during the summer when phosphorus concentration is seasonally the lowest.