Higher Photosynthetic Potential Research Articles

Growth of elaborate microbial pinnacles in Lake Vanda, Antarctica

Microbial pinnacles in ice-covered Lake Vanda, McMurdo Dry Valleys, Antarctica, extend from the base of the ice to more than 50m water depth. The distribution of microbial communities, their photosynthetic potential, and pinnacle morphology affects the local accumulation of biomass, which in turn shapes pinnacle morphology. This feedback, plus environmental stability, promotes the growth of elaborate microbial structures. In Lake Vanda, all mats sampled from greater than 10m water depth contained pinnacles with a gradation in size from <1-mm-tall tufts to pinnacles that were centimeters tall. Small pinnacles were cuspate, whereas larger ones had variable morphology. The largest pinnacles were up to ~30cm tall and had cylindrical bases and cuspate tops. Pinnacle biomass was dominated by cyanobacteria from the morphological and genomic groups Leptolyngbya, Phormidium, and Tychonema. The photosynthetic potential of these cyanobacterial communities was high to depths of several millimeters into the mat based on PAM fluorometry, and sufficient light for photosynthesis penetrated ~5mm into pinnacles. The distribution of photosynthetic potential and its correlation to pinnacle morphology suggests a working model for pinnacle growth. First, small tufts initiate from random irregularities in prostrate mat. Some tufts grow into pinnacles over the course of ~3years. As pinnacles increase in size and age, their interiors become colonized by a more diverse community of cyanobacteria with high photosynthetic potential. Biomass accumulation within this subsurface community causes pinnacles to swell, expanding laminae thickness and creating distinctive cylindrical bases and cuspate tops. This change in shape suggests that pinnacle morphology emerges from a specific distribution of biomass accumulation that depends on multiple microbial communities fixing carbon in different parts of pinnacles. Similarly, complex patterns of biomass accumulation may be reflected in the morphology of elaborate ancient stromatolites.

High C3 photosynthetic capacity and high intrinsic water use efficiency underlies the high productivity of the bioenergy grass Arundo donax.

Arundo donax has attracted interest as a potential bioenergy crop due to a high apparent productivity. It uses C3 photosynthesis yet appears competitive with C4 grass biomass feedstock’s and grows in warm conditions where C4 species might be expected to be that productive. Despite this there has been no systematic study of leaf photosynthetic properties. This study determines photosynthetic and photorespiratory parameters for leaves in a natural stand of A. donax growing in southern Portugal. We hypothesise that A. donax has a high photosynthetic potential in high and low light, stomatal limitation to be small and intrinsic water use efficiency unusually low. High photosynthetic rates in A. donax resulted from a high capacity for both maximum Rubisco (Vc,max 117 μmol CO2 m−2 s−1) and ribulose-1:5-bisphosphate limited carboxylation rate (Jmax 213 μmol CO2 m−2 s−1) under light-saturated conditions. Maximum quantum yield for light-limited CO2 assimilation was also high relative to other C3 species. Photorespiratory losses were similar to other C3 species under the conditions of measurement (25%), while stomatal limitation was high (0.25) resulting in a high intrinsic water use efficiency. Overall the photosynthetic capacity of A. donax is high compared to other C3 species, and comparable to C4 bioenergy grasses.

The effect of photosynthesis parameters on leaf lifespan

Leaf longevity (LL) varies widely among higher plants. LL is a sum of the functional component LLf (the duration of active photosynthesis) and the nonfunctional component LLn (duration of the period during which photosynthesis does not occur). LLn corresponds to the period of winter dormancy in the case of evergreen boreal species. The photosynthetic potential of the leaf (PPL)—that is, the maximal possible amount of CO2 fixed during the leaf lifespan—is inferred from the dynamics of the maximal rate of photosynthesis (Pa) during LLf. Pa reaches a peak value (Pa max) during leaf “maturation.” The photosynthetic potential depends on the functional lifespan to a greater degree than on the maximal rate of photosynthesis. The PPL/LLf ratio determines the rate of realization of the photosynthetic potential during the lifetime of the leaf. LLf is strongly and positively correlated to LL, and LL can therefore be considered a parameter determining the rate of PPL realization, along with LLf (for a first approximation). The prolonged LLf characteristic of evergreen species gives them an advantage—a higher photosynthetic potential than that of deciduous species. Consequently, PPL is realized more slowly in evergreen species than in deciduous species. An increase of LLf and LL is accompanied by an increase of leaf construction cost (LCCa) and a decrease of the photosynthesis rate, with the decrease per unit dry weight (Pm) being much more pronounced than that per unit leaf area (Pa). This points to a much higher contribution of cell wall weight to the total dry weight of longlived leaves of evergreen species than to that of short-lived leaves of deciduous species. Unidirectional changes of PPL and LCCa stabilize leaf payback (LP). Species with a short (long) LLf and high (low) rate of PPL realization are characteristic of early (late) succession and habitats with favorable (unfavorable) environmental conditions for photosynthesis and growth, since these species are more competitive under said conditions. Species with a high rate of PPL realization have an advantage in competition under conditions favorable for photosynthesis and growth, since they use environmental resources for rapid growth and expansion. The rate of photosynthetic potential realization characterizes the aging rate of the leaf.

English

Carbon dioxide is a green house gas, responsible for potential threat of global climate change. Reduction and stabilization of such green house gas concentration is of utmost importance. Photosynthesis in green plants achieves natural carbon dioxide fixation with algae having higher photosynthetic potential than terrestrial plants. A biocatalyst in the form of carbonic anhydrase enzyme was used in the experiment in order to fix the carbon dioxide. The catalyst was supplied externally in modified Zarrouk media which was without sodium bicarbonate. This enzyme efficiently converted carbon dioxide into bicarbonate at ambient temperature and pressure producing 3,072mg/L and 27,805mg/L of bicarbonate 30 and 240 seconds respectively. Spirulina was released in the flasks containing modified Zarrouk media with bicarbonate synthesized by the activity of externally supplied carbonic anhydrase. The growth of Spirulina was observed for 120h and found comparable with the growth observed in standard Zarrouk media.

Optimizing illumination in the greenhouse using a 3D model of tomato and a ray tracer.

Reduction of energy use for assimilation lighting is one of the most urgent goals of current greenhouse horticulture in the Netherlands. In recent years numerous lighting systems have been tested in greenhouses, yet their efficiency has been very difficult to measure in practice. This simulation study evaluated a number of lighting strategies using a 3D light model for natural and artificial light in combination with a 3D model of tomato. The modeling platform GroIMP was used for the simulation study. The crop was represented by 3D virtual plants of tomato with fixed architecture. Detailed data on greenhouse architecture and lamp emission patterns of different light sources were incorporated in the model. A number of illumination strategies were modeled with the calibrated model. Results were compared to the standard configuration. Moreover, adaptation of leaf angles was incorporated for testing their effect on light use efficiency (LUE). A Farquhar photosynthesis model was used to translate the absorbed light for each leaf into a produced amount of carbohydrates. The carbohydrates produced by the crop per unit emitted light from sun or high pressure sodium lamps was the highest for horizontal leaf angles or slightly downward pointing leaves, and was less for more upward leaf orientations. The simulated leaf angles did not affect light absorption from inter-lighting LED modules, but the scenario with LEDs shining slightly upward (20°) increased light absorption and LUE relative to default horizontal beaming LEDs. Furthermore, the model showed that leaf orientation more perpendicular to the string of LEDs increased LED light interception. The combination of a ray tracer and a 3D crop model could compute optimal lighting of leaves by quantification of light fluxes and illustration by rendered lighting patterns. Results indicate that illumination efficiency increases when the lamp light is directed at most to leaves that have a high photosynthetic potential.

不同温度下CO2浓度增高对坛紫菜生长和叶绿素荧光特性的影响

Atmospheric CO 2 concentration is predicted to nearly double by the end of this century.There are a large number of reports on the effects of elevated atmospheric CO 2 concentrations on seaweeds.However,the investigation concerning the impacts of combined effects of elevated atmospheric CO 2 concentrations and temperature on seaweeds is very limited.In the present study,the red seaweed Porphyra haitanensis(Bangiales,Rhodophyta) was cultured under four different conditions:(1) 15 ℃ + 390μmol/mol CO 2,(2) 15 ℃ + 700μmol/mol CO 2,(3) 25 ℃ + 390μmol/mol CO 2,(4) 25 ℃ + 700μmol /mol CO 2,in order to examine the combined effects of the elevated CO 2 concentrations and temperature on growth,some biochemical components and chlorophyll fluorescence in this commercially important species.The results indicated that the growth response of P.haitanensis to elevated CO 2 in seawater was temperature dependent,with the enhancement of growth resulting from elevated CO 2 being remarkable greater at lower growth temperature(15 ℃) with respect to 25 ℃.The CO 2 conditions in culture exerted a much pronounced influence on the contents of Chlorophyll a(Chl a) and Carotenoid(Car) than temperature did.15 ℃-grown P.haitanensis exhibited much higher maximum relative electron transport rate(rETR max) in comparison with 25 ℃-grown thalli,regardless of the CO 2 concentrations in culture.This indicated that P.haitanensis displayed a higher photosynthetic potential at low growth temperature than high growth temperature.Meanwhile,extra CO 2 in the culture had no significant impact on rETR max in P.haitanensis.The characters of chlorophyll fluorescence were determined under different measurement temperatures using Junior-PAM.The increase of measurement temperature from 10 to 30 ℃ made a negligible effect on rETR max,the photosynthetic light use efficiency of electron transport(α,the initial slope of the rapid light curves) and maximum photochemical quantum yield values(F v / F m),regardless of the growth conditions.However,the values of rETR max 、α and F v / F m were reduced drastically when the measurement temperatures were above 30 ℃,with the decline being much pronounced in 15 ℃-grown algae than 25 ℃-grown algae.Our results suggested that high temperatures(30—40 ℃) in the short-term inhibited the photosynthetic capacity of P.haitanensis,which might be associated with the damage in photosystem Ⅱ(PSⅡ) reaction centre and a concomitant reduction of electrons transport rate.Meanwhile,25 ℃-grown algae showed a higher tolerance to high temperature stress than 15 ℃-grown algae did,since 15 ℃-grown algae displayed greater downtrend in the values of rETR max 、α and F v / F m when the measurement temperatures rose to 30 ℃.The results also showed that the value of rETR max was lower in P.haitanensis thalli grown under CO 2 enriched air with respect to non-enriched air when the algae were subjected to the high temperatures,indicating that,compared to normal CO 2 growth conditions,elevated CO 2 growth conditions might repress the ability of photosynthetic electron transport of algae when subjected to short-term high temperature stress.

COMPARISON OF RESISTANCE TO LIGHT STRESS IN TOXIC AND NON-TOXIC STRAINS OF MICROCYSTIS AERUGINOSA (CYANOPHYTA)(1).

Blooms of Microcystis aeruginosa (Kützing) Kützing occur frequently in many freshwater ecosystems around the world, but the role of environmental factors in promoting the growth and determining the proportion of toxic and non-toxic strains still requires more investigation. In this study, four strains (toxic CPCC299 & FACHB905 and non-toxic CPCC632 & FACHB315) were exposed to high light (HL) condition, similar to light intensity found at the surface of a bloom, to evaluate their sensitivity to photoinhibition. We also estimated their capacity to recover from this HL stress. For all strains, our results showed an increased inhibition of the photosynthetic activity with HL treatment time. When comparing the extent of photoinhibition between strains, both toxic strains were more resistant to the treatment and recovered completely their photosynthetic capacity after 3 h, while non-toxic strains needed more time to recover. For toxic strains, the rETR under HL was higher compared to the rETR under low light (LL) control condition despite 50% photoinhibition. This suggests that the detrimental effect of high light (HL; up to 2 h) is outweighed by their higher photosynthetic potential. This conclusion did not stand for non-toxic strains, and indicates their preference for LL environment. We also demonstrated that a LL/HL cycle induced a 259% increase in cell yield for a toxic strain and a decrease by 22% for a non-toxic strain. This also indicates that toxic strains have higher tolerance to HL in a fluctuating light environment. Our data demonstrated that difference of sensitivity to HL between strains can modify the competitive outcome between toxic and non-toxic strains and may affect bloom toxicity.

Comparison of the performance of several hybrid poplar clones and their potential suitability for use in northern China

Abstract The performance of 14 North American hybrid poplar clones was evaluated near Beijing in short-rotation plantations grown at a 1 × 1 m spacing. Significant clonal differences were found in eco-physiological and morphological characteristics. Clones DN-17, DN-2, DN-182, DN-14274, 328-162, and NM6 exhibited high emergence and survival rates, and DN-17, DN-14274, DN-182 and NE-222 had a short growing period. Other clones (306-45, 195-522, 184-411 and 328-162) had a long growing period and may be more suitable in southern China. Clones DN-2, DN-182, and 195-522, had the highest productivity and the best potential as biomass producers. Clones DN-14274, DN-17, DN-182, NE-222, and DTAC-7 allocated more belowground biomass than the other clones during the first growing season, indicating that they might be better adapted to arid regions such as those in northern China. Clones 195-522, 184-411, DTAC-7, NE-222, R-270 and 306-45 had a higher capacity for CO 2 assimilation. Clones NE-222, 306-45, DTAC-7, 195-522, R-270, 15-29, and DN-17 had a higher photosynthetic potential and could potentially adapt to a wide range of environmental conditions. Clones 195-522, 184-411, 328-162, DN-182, and NM6 had higher water-use efficiency than the others, suggesting that they would utilize soil water more effectively, especially in the dry season and in arid regions. Clones R-270, DN-14274, 15-29, DN-2, and DTAC-7 had higher transpiration rates, indicating that they would require frequent irrigation in the dry season and in arid regions to ensure normal survival and growth.

Are the fluorescence parameters of German chamomile leaves the first indicators of the anthodia yield in drought conditions?

7-day soil drought followed by 7-day rehydration was applied to potted German chamomile (Chamomilla recutita) plants at the beginning of their generative stage. Plants of a wild type (WT), plus two diploid (2n) and two tetraploid (4n) genotypes were studied, in order to examine the alterations in chlorophyll (Chl) and carotenoids (Car) contents, and chlorophyll fluorescence (CF) parameters during water shortage and rehydration. The fresh mass of the anthodia after the recovery was also studied.WT plants adjust better to water stress than modern breeding genotypes, because drought resulted in the low fall in leaf water content of WT, the lowest decrease in the fresh mass of its anthodia (a 41% decrease from the control), and the most elastic response of the photosynthetic apparatus. 4n C11/2 strain plants suffered from the highest reduction in anthodia yield (87%), and had the lowest constitutive pigment contents. It was also the only genotype which revealed nontypical alterations in various CF parameters obtained on a dark- and light-adapted leaf. During drought, a big increase was noticed in minimal, maximal, and variable fluorescence of PSII reaction centres in the dark- adapted (F0, Fm and Fv, respectively), and in the light-adapted state (F0', Fm' and Fv'). It was accompanied by the biggest decline in linear electron transport rate (ETR), quantum efficiency of PSII electron transport (ΦPSII) and photochemical quenching coefficient (qP). These alterations were prolonged to the stage when the normal leaf water content was retained. On the contrary, C6/2 strain plants had the highest constitutive Chl and Car contents, which additionally increased after rehydration, similarly to the values of F0, Fm and Fv, which reflects the high photosynthetic potential of this genotype. It was accompanied by the relatively high yield of its anthodia after drought. Considering the drop in the yield triggered by drought, it seems to be the only parameter which may be linked with the ploidy level.Although the yield formation of chamomile strains cannot simply be estimated by CF assay, this technique may serve as an additional tool in the selection of plants to drought. The following circumstances should be submitted; namely: measurement at the proper developmental stage of plants, in different water regimes, and an analysis of various CF parameters. The increase in F0 and F0', and the reduction in ETR, Fv'/Fm', ΦPSII and qP values in response to water deficit should be an indicator of the impairment of the photosynthetic apparatus through drought.

Leaf-level responses to light in two co-occurring Quercus (Quercus ilex and Quercus suber): leaf structure, chemical composition and photosynthesis

We studied morphological, biochemical and physiological leaf acclimation to incident Photon-Photosynthetic-Flux-Density (PPFD) in Quercus ilex (holm oak) and Quercus suber (cork oak) at Mediterranean evergreen oak woodlands of southern Portugal. Specific leaf area (SLA) decreased exponentially with increasing PPFD in both species. Q. ilex had lower SLA values than Q. suber. Leaf nitrogen, cellulose and lignin concentration (leaf area-based) scaled positively with PPFD. Maximum rate of carboxylation (Vcmax), capacity for maximum photosynthetic electron transport (Jmax), rate of triose-P utilization (VTPU) and the rate of nonphotorespiratory light respiration (Rd) were also positively correlated with PPFD in both Quercus species, when expressed in leaf area but not on leaf mass basis. Q suber showed to have higher photosynthetic potential (Vcmax, J max m and V TPU m ) and a higher nitrogen efficient nitrogen use than Q.ilex. Leaf chlorophyll concentration increased with decreasing PPFD, improving apparent quantum use efficiency (Φ) in both Quercus species. We concluded that, in Q.ilex and Q.suber, leaf structural plasticity is a stronger determinant for leaf acclimation to PPFD than biochemical and physiological plasticity.

Increased activity of ATP-sulfurylase and increased contents of cysteine and glutathione reduce high cadmium-induced oxidative stress in mustard cultivar with high photosynthetic potential

Cadmium is known to reduce photosynthesis and overall growth of plants. Plants adopt several mechanisms of Cd detoxification, such as accumulation of sulfur-rich compounds, like glutathione (GSH) and its precursor cysteine. The accumulation of GSH is regulated by the activity of ATP-sulfurylase, a rate-limiting enzyme in sulfur assimilation. The carbon of Cys is provided through photosynthesis. Thus, a plant with the higher photosynthetic potential and ATP-sulfurylase activity may have the higher contents of Cys and GSH and therefore may provide for a greater tolerance to Cd stress. Mustard (Brassica juncea L. Czern and Coss.) cvs. Varuna (high photosynthetic potential) and RH30 (low photosynthetic potential) were subjected to 0 and 200 mg Cd/kg soil, and the activity of ATP-sulfurylase, the contents of Cys and GSH, oxidative stress, and activities of antioxidant enzymes were studied. Under 200 mg Cd/kg soil, cv. Varuna showed an increased ATP-sulfurylase activity, the higher contents of Cys and GSH, and the net photosynthetic rate than cv. RH30. In contrast, the activity of superoxide dismutase, the contents of thiobarbituric acid-reactive substances, and H2O2, and electrolyte leakage were found to be greater in cv. RH30 showing an increased oxidative stress than cv. Varuna. However, the activities of ascorbate peroxidase and glutathione reductase were greater in cv. Varuna than cv. RH30. The results show that a greater ATP-sulfurylase activity, an enhanced production of Cys and GSH, and an efficient antioxidant enzyme system in the high photosynthetic mustard cv. Varuna helped to the reduce the oxidative stress maintaing high photosynthesis.

Interannual variability of photosynthesis across Africa and its attribution

Africa is thought to be a large source of interannual variability in the global carbon cycle, only vaguely attributed to climate fluctuations. This study uses a biophysical model, Simple Biosphere, to examine in detail what specific factors, physiological (acute stress from low soil water, temperature, or low humidity) and biophysical (low vegetation radiation use), are responsible for spatiotemporal patterns of photosynthesis across the African continent during the period 1982–2003. Acute soil water stress emerges as the primary factor driving interannual variability of photosynthesis for most of Africa. Southern savannas and woodlands are a particular hot spot of interannual variability in photosynthesis, owing to high rainfall variability and photosynthetic potential but intermediate annual rainfall. Surprisingly low interannual variability of photosynthesis in much of the Sudano‐Sahelian zone derives from relatively low vegetation cover, pronounced humidity stress, and somewhat lower rainfall variability, whereas perennially wet conditions diminish interannual variability in photosynthesis across much of the Congo Basin and coastal West Africa. Though not of focus here, the coefficient of variation in photosynthesis is notably high in drylands and desert margins (i.e., Sahel, Greater Horn, Namib, and Kalahari) having implications for supply of food and fiber. These findings emphasize that when considering impacts of climate change and land surface feedbacks to the atmosphere, it is important to recognize how vegetation, climate, and soil characteristics may conspire to filter or dampen ecosystem responses to hydroclimatic variability.

Photosynthetic property and primary production of phytoplankton in sublittoral sand bank area in the Seto Inland Sea, Japan

We investigated the photosynthesis–light intensity (P–I) relationships of phytoplankton collected from a sublittoral sand bank in the Seto Inland Sea, Japan, under different temperature conditions. In spite of low chlorophyll a concentration (<3 mg m−3), phytoplankton had considerably high photosynthetic potential (>10 mg C (mg chl a)−1 h−1) in the study area. Based on the P–I relationships, we conducted numerical simulation of areal primary production using published data on water temperature, chlorophyll a concentration, and irradiance. The areal primary production ranged between 159 and 187 g C m−2 year−1. This production was within the range of typical values reported previously in deeper areas of the Seto Inland Sea. The productivity in the sand bank area was discussed in relation to water current, allochthonous resource input, and fisheries.

Nocturnal respiration of lichens in their natural habitat is not affected by preceding diurnal net photosynthesis

Dark respiration (DR) of lichens is reported to be higher in species with a high photosynthetic potential (suggesting a metabolic maintenance cost effect) and also, often in laboratory studies, transiently after photosynthesis (suggesting a substrate-driven effect). We investigated the occurrence of the latter, the effect of diurnal net photosynthesis (NP) on subsequent nocturnal DR, under natural temperate climate conditions in the chlorolichens Lecanora muralis and Cladonia convoluta and the cyanolichen Collema cristatum. Data sets totalling 15 months, 106 and 113 days, respectively, were obtained from automatic cuvettes that continually measured CO2 exchange and ambient conditions at 30 min intervals. For each 24 h period (sunrise to following sunrise), several measures of NP and DR were extracted, including maximal and mean rates and daily sums. No statistically significant correlations between the various measures of DR and preceding NP were found for L. muralis, only one weak correlation for Co. cristatum (the means of DR and NP) and three for Cl. convoluta (sums and means of DR and NP). It is proposed that even these significant correlations are actually a result of embedded codependencies between NP, DR and thallus water content. Overall it is concluded that no substrate-driven dependency of DR on preceding NP under natural conditions could be recognised. The periods of desiccation that often occur between the NP and following DR as well as the wide range of combinations of conditions would certainly contribute to this lack of relationship.

Ecohydrological impacts of woody‐plant encroachment: seasonal patterns of water and carbon dioxide exchange within a semiarid riparian environment

AbstractAcross many dryland regions, historically grass‐dominated ecosystems have been encroached upon by woody‐plant species. In this paper, we compare ecosystem water and carbon dioxide (CO2) fluxes over a grassland, a grassland–shrubland mosaic, and a fully developed woodland to evaluate potential consequences of woody‐plant encroachment on important ecosystem processes. All three sites were located in the riparian corridor of a river in the southwest US. As such, plants in these ecosystems may have access to moisture at the capillary fringe of the near‐surface water table. Using fluxes measured by eddy covariance in 2003 we found that ecosystem evapotranspiration (ET) and net ecosystem exchange of carbon dioxide (NEE) increased with increasing woody‐plant dominance. Growing season ET totals were 407, 450, and 639 mm in the grassland, shrubland, and woodland, respectively, and in excess of precipitation by 227, 265, and 473 mm. This excess was derived from groundwater, especially during the extremely dry premonsoon period when this was the only source of moisture available to plants. Access to groundwater by the deep‐rooted woody plants apparently decouples ecosystem ET from gross ecosystem production (GEP) with respect to precipitation. Compared with grasses, the woody plants were better able to use the stable groundwater source and had an increased net CO2 gain during the dry periods. This enhanced plant activity resulted in substantial accumulation of leaf litter on the soil surface that, during rainy periods, may lead to high microbial respiration rates that offset these photosynthetic fluxes. March–December (primary growing season) totals of NEE were −63, −212, and −233 g C m−2 in the grassland, shrubland, and woodland, respectively. Thus, there was a greater disparity between ecosystem water use and the strength of the CO2 sink as woody plants increased across the encroachment gradient. Despite a higher density of woody plants and a greater plant productivity in the woodland than in the shrubland, the woodland produced a larger respiration response to rainfall that largely offset its higher photosynthetic potential. These data suggest that the capacity for woody plants to exploit water resources in riparian areas results in enhanced carbon sequestration at the expense of increased groundwater use under current climate conditions, but the potential does not scale specifically as a function of woody‐plant abundance. These results highlight the important roles of water sources and ecosystem structure on the control of water and carbon balances in dryland areas.

SEASONAL CHANGES OF PHOTOSYNTHETIC CHARACTERISTICS IN 12 TREE SPECIES INTRODUCED ONTO OIL SHALE WASTE

Background and Aims Phytoremediation is an important method for restoring bare soil or slag; however, the physiological traits of plants used for revegetation are poorly known, even though such traits are important to successful remediation. This study was carried out on oil shale waste in Maoming City, Guangdong Province to screen for tree species with high photosynthetic potential, appraise the ability of these plants to acclimatize to oil shale waste, and provide valuable information for ecological restoration of similar waste sites. Methods Diurnal variation of photosynthesis was measured for 12 tree species in summer and winter, using portable photosynthetic equipment (LI-6400, LI-COR, Inc., USA). Other parameters such as transpiration, stomatal conductance, relative humidity, etc. were measured simultaneously, and water use efficiency (WUE) was calculated as net photosynthesis divided by transpiration. Key Results There were large seasonal differences in all parameters, with values of net photosynthesis, transpiration, and stomatal conductance higher in summer than winter (60.9%, 77.7% and 85.7%, respectively), but WUE higher in winter than in summer (26.8%-77.2%). Diurnal variation of net photosynthesis also exhibited seasonal differences. Many tree species exhibited a bimodal peak in summer and a unimodal peak in winter; however, Cinnamomum camphora was unimodal in both seasons; Terminalia bellirica, Tristania confertam, and Tectona grandis were bimodal in both seasons; and Syzygium cumini was bimodal in winter and unimodal in summer. Trees with higher mean net photosynthetic rate in both winter and in summer should be more useful for phytoremediation than species with high net photosynthetic rate in only one season. Accordingly, net photosynthetic rate, which synthesizes all parameters examined, should be considered the most important parameter to appraise the ability of plants to acclimatize. Conclusions According to mean net photosynthetic rates in both winter and summer, the sequence of photosynthesis efficiency of the 12 tree species tested was: Acacia auriculiformis, Terminalia bellirica, Cassia siamea, Gmelina arborea, Tectona grandis, Tristania conferta, Cinnamomum camphora, Ormosia pinnata, Ilex rotunda, Syzygium cumini, Peltophorum ptetocarpum and Pterygota alata.

Microstructure of microphytobenthic biofilm and its spatio-temporal dynamics in an intertidal mudflat (Aiguillon Bay, France)

The spatio-temporal dynamics of the microphytobenthic biofilm was analysed at microscale over a complete day-time emersion period in an intertidal mudflat. The structures of the biofilm were monitored by analysing the variability of the epipelic diatom cover in the horizontal dimension and the kinetics of biomass dispersion in the vertical dimension. Colonisation of the sediment surface by diatoms was rapid (within 15 min); 75% of the biomass contained in the top 1 mm was concentrated in the upper 200 µm, but the cover never reached 100%. This biomass had a higher chlorophyll a/pheopigment ratio than deeper in the sediment, suggesting a better phys- iological state and a higher photosynthetic potential. The dynamics of the biomass in the upper 200 µm turned out to be independent of that deeper in the sediment, supporting the concept of an independent surface compartment, mainly responsible for primary production. In the second part of emersion, the horizontal dispersion of the microphytobenthic biofilm was concomitant with the onset of downward migration. The process was slow, showing that the diatoms were not phased in their downward movement. The migration process appeared to be asymmetrical: rapid upward migration and biofilm formation versus slow downward movement and dispersion of the biofilm. To take into account these structural characteristics of the biofilm and to simulate its dynamics, we developed a new mathematical model that provides simulations consistent with our observations. We have also shown for the first time that the constitution of the biofilm at the sediment surface (0 to 200 µm) is connected to an increase of biomass in the top 1 cm.

Effects of Prescribed Fire on Physiology and Growth of Acer rubrum and Quercus spp. Seedlings in an Oak-Pine Forest on the Cumberland Plateau, KY

GILBERT, N. L. (Department of Biology, University of Kentucky, Lexington, KY, 40546), S. L. JOHNSON (Department of Biology, Middle Tennessee State University, Mufreesboro, TN, 37132) S. K. GLEESON (Department of Biology, University of Kentucky, Lexington, KY, 40546), B. A. BLANKENSHIP AND M. A. ARTHUR (Department of Forestry, University of Kentucky, Lexington, KY, 40546). Effects of prescribed fire on physiology and growth of Acer rubrum and Quercus spp. seedlings in an oak-pine forest on the Cumberland Plateau, KY. J. Torrey Bot. Soc. 130: 253-264. 2003.-Poor survival of oak regeneration has been attributed to fire suppression and the physiological limitations imposed by the increasing dominance of competitors, especially red maple (Acer rubrum L.). We examined the physiological responses of red maple, chestnut oak (Quercus prinus L.) and scarlet oak (Q. coccinea Muenchh.) seedlings following a prescribed fire in an upland oak-pine forest in eastern Kentucky. Immediately following fire, seedlings on burned sites had significantly greater foliar concentrations of N, P, K, and Mg than seedlings on unburned sites; this effect of treatment diminished over the first growing season. Seedlings on burned sites also demonstrated significantly higher photosynthetic potential and had greater relative growth rates of diameter and height through the second and third growing seasons postfire. Among species, chestnut oak consistently had the greatest foliar concentrations of all nutrients, with red maple being intermediate and scarlet oak the lowest. Both oaks had significantly greater maximum photosynthesis than red maple, but there were no significant differences among species for diameter or height relative growth rates. Treatment by species interactions indicated that red maple seedlings were significantly taller than oaks on the burned site, while there were no differences in height among species on the unburned site. Although a single fire improved the performance of all species, our results suggest no improvement in the status of oak regeneration based on post-fire seedling physiology and growth.

Leaf-trait Variation of Tundra Plants along a Climatic Gradient: An Integration of Responses in Evergreen and Deciduous Species

To understand response patterns of leaf traits in tundra plants against decreasing annual season length comprehensively, a graphic model based on carbon balance theory was presented. The model predicted that leaves with very short life-span and high nitrogen concentration (Nmass) or leaves with very long life-span and small Nmass will be dominate under the conditions of a short growing season. To test this prediction, leaf life-span and other leaf traits of 26 tundra species were compared among four sites selected along a gradient of climatic harshness: a subalpine site at Abisko in northern Sweden, two nearby mid-alpine sites at Latnjajaure with early and late snowmelt, and a site at Ny-Ålesund (Svalbard) in the High Arctic. In herbaceous and deciduous shrub species, leaf life-span and/ or leaf mass per unit area (LMA) tended to decrease, and leaf Nmass tended to increase along the climatic gradient with decreasing growing season and lower temperatures. In evergreen shrub species, both leaf life-span and leaf Nmass tended to increase under harsh conditions, but the response pattern of LMA was less clear. Deciduous species produced short-lived leaves with a low construction cost and probably high photosynthetic potential, whereas evergreen species produced long-lived leaves. The contrastive patterns of leaf-trait variation between the deciduous and evergreen plants observed in this study were concordant with the prediction of the model.

Leaf-Trait Variation of Tundra Plants along a Climatic Gradient: An Integration of Responses in Evergreen and Deciduous Species

To understand response patterns of leaf traits in tundra plants against decreasing annual season length comprehensively, a graphic model based on carbon balance theory was presented. The model predicted that leaves with very short life-span and high nitrogen concentration (Nmass) or leaves with very long life-span and small Nmass will be dominate under the conditions of a short growing season. To test this prediction, leaf life-span and other leaf traits of 26 tundra species were compared among four sites selected along a gradient of climatic harshness: a subalpine site at Abisko in northern Sweden, two nearby mid-alpine sites at Latnjajaure with early and late snowmelt, and a site at Ny-Ålesund (Svalbard) in the High Arctic. In herbaceous and deciduous shrub species, leaf life-span and/ or leaf mass per unit area (LMA) tended to decrease, and leaf Nmass tended to increase along the climatic gradient with decreasing growing season and lower temperatures. In evergreen shrub species, both leaf life-span and leaf Nmass tended to increase under harsh conditions, but the response pattern of LMA was less clear. Deciduous species produced short-lived leaves with a low construction cost and probably high photosynthetic potential, whereas evergreen species produced long-lived leaves. The contrastive patterns of leaf-trait variation between the deciduous and evergreen plants observed in this study were concordant with the prediction of the model.