Maximum Rate Of Photosynthesis Research Articles

Characterization of a heat-tolerant Chlorella sp. GD mutant with enhanced photosynthetic CO2 fixation efficiency and its implication as lactic acid fermentation feedstock

BackgroundFermentative production of lactic acid from algae-based carbohydrates devoid of lignin has attracted great attention for its potential as a suitable alternative substrate compared to lignocellulosic biomass.ResultsA Chlorella sp. GD mutant with enhanced thermo-tolerance was obtained by mutagenesis using N-methyl-N′-nitro-N-nitrosoguanidine to overcome outdoor high-temperature inhibition and it was used as a feedstock for fermentative lactic acid production. The indoor experiments showed that biomass, reducing sugar content, photosynthetic O2 evolution rate, photosystem II activity (Fv/Fm and Fv′/Fm′), and chlorophyll content increased as temperature, light intensity, and CO2 concentration increased. The mutant showed similar DIC affinity and initial slope of photosynthetic light response curve (α) as that of the wild type but had higher dissolved inorganic carbon (DIC) utilization capacity and maximum photosynthesis rate (Pmax). Moreover, the PSII activity (Fv′/Fm′) in the mutant remained normal without acclimation process after being transferred to photobioreactor. This suggests that efficient utilization of incident high light and enhanced carbon fixation with its subsequent flux to carbohydrates accumulation in the mutant contributes to higher sugar and biomass productivity under enriched CO2 condition. The mutant was cultured outdoors in a photobioreactor with 6% CO2 aeration in hot summer season in southern Taiwan. The harvested biomass was subjected to separate hydrolysis and fermentation (SHF) for lactic acid production with carbohydrate concentration equivalent to 20 g/L glucose using the lactic acid-producing bacterium Lactobacillus plantarum 23. The conversion rate and yield of lactic acid were 80% and 0.43 g/g Chlorella biomass, respectively.ConclusionsThese results demonstrated that the thermo-tolerant Chlorella mutant with high photosynthetic efficiency and biomass productivity under hot outdoor condition is an efficient fermentative feedstock for large-scale lactic acid production.

Melanisation in the old forest lichen Lobaria pulmonaria reduces the efficiency of photosynthesis

Abstract The old forest lichen Lobaria pulmonaria synthesizes melanic pigments when exposed to ultraviolet light and high solar radiation. Here, we tested the effect of melanisation on photosynthetic efficiency. Melanisation effectively reduces high-light stress in lichen photobionts, as the photobionts of melanised thalli are healthy, based on chlorophyll contents and maximum rates of photosynthesis. However, the quantum yields of both photosynthetic CO2 uptake and O2 evolution were more than 40 percent lower in melanised thalli compared with control thalli. While chlorophyll fluorescence measurements suggested that melanised and pale thalli had similar apparent electron transport rates, this result was probably an artefact caused by screening reducing the light reaching the photobionts. Melanic thalli also had a higher chlorophyll a/b ratio and more xanthophyll cycle pigments, suggesting that the photosynthetic apparatus had adapted to high light. In conclusion, while protecting photobionts from high light, melanisation clearly reduced photosynthetic efficiency. Melanised thalli will be significantly disadvantaged if light levels return to lower values, more typical for those habitats in which this shade adapted lichen is most abundant.

A mutant of Chlamydomonas without LHCSR maintains high rates of photosynthesis, but has reduced cell division rates in sinusoidal light conditions.

The LHCSR protein belongs to the light harvesting complex family of pigment-binding proteins found in oxygenic photoautotrophs. Previous studies have shown that this complex is required for the rapid induction and relaxation of excess light energy dissipation in a wide range of eukaryotic algae and moss. The ability of cells to rapidly regulate light harvesting between this dissipation state and one favoring photochemistry is believed to be important for reducing oxidative stress and maintaining high photosynthetic efficiency in a rapidly changing light environment. We found that a mutant of Chlamydomonas reinhardtii lacking LHCSR, npq4lhcsr1, displays minimal photoinhibition of photosystem II and minimal inhibition of short term oxygen evolution when grown in constant excess light compared to a wild type strain. We also investigated the impact of no LHCSR during growth in a sinusoidal light regime, which mimics daily changes in photosynthetically active radiation. The absence of LHCSR correlated with a slight reduction in the quantum efficiency of photosystem II and a stimulation of the maximal rates of photosynthesis compared to wild type. However, there was no reduction in carbon accumulation during the day. Another novel finding was that npq4lhcsr1 cultures underwent fewer divisions at night, reducing the overall growth rate compared to the wild type. Our results show that the rapid regulation of light harvesting mediated by LHCSR is required for high growth rates, but it is not required for efficient carbon accumulation during the day in a sinusoidal light environment. This finding has direct implications for engineering strategies directed at increasing photosynthetic productivity in mass cultures.

A sorghum (Sorghum bicolor) mutant with altered carbon isotope ratio.

Recent efforts to engineer C4 photosynthetic traits into C3 plants such as rice demand an understanding of the genetic elements that enable C4 plants to outperform C3 plants. As a part of the C4 Rice Consortium’s efforts to identify genes needed to support C4 photosynthesis, EMS mutagenized sorghum populations were generated and screened to identify genes that cause a loss of C4 function. Stable carbon isotope ratio (δ13C) of leaf dry matter has been used to distinguishspecies with C3 and C4 photosynthetic pathways. Here, we report the identification of a sorghum (Sorghum bicolor) mutant with a low δ13C characteristic. A mutant (named Mut33) with a pale phenotype and stunted growth was identified from an EMS treated sorghum M2 population. The stable carbon isotope analysis of the mutants showed a decrease of 13C uptake capacity. The noise of random mutation was reduced by crossing the mutant and its wildtype (WT). The back-cross (BC1F1) progenies were like the WT parent in terms of 13C values and plant phenotypes. All the BC1F2 plants with low δ13C died before they produced their 6th leaf. Gas exchange measurements of the low δ13C sorghum mutants showed a higher CO2 compensation point (25.24 μmol CO2.mol-1air) and the maximum rate of photosynthesis was less than 5μmol.m-2.s-1. To identify the genetic determinant of this trait, four DNA pools were isolated; two each from normal and low δ13C BC1F2 mutant plants. These were sequenced using an Illumina platform. Comparison of allele frequency of the single nucleotide polymorphisms (SNPs) between the pools with contrasting phenotype showed that a locus in Chromosome 10 between 57,941,104 and 59,985,708 bps had an allele frequency of 1. There were 211 mutations and 37 genes in the locus, out of which mutations in 9 genes showed non-synonymous changes. This finding is expected to contribute to future research on the identification of the causal factor differentiating C4 from C3 species that can be used in the transformation of C3 to C4 plants.

Modeling forest carbon cycle using long‐term carbon stock field measurement in the Delaware River Basin

AbstractProcess‐based models are a powerful approach to test our understanding of biogeochemical processes, to extrapolate ground survey data from limited plots to the landscape scale, and to simulate the effects of climate change, nitrogen deposition, elevated atmospheric CO2, increasing natural disturbances, and land‐use change on ecological processes. However, in most studies, the models are calibrated using ground measurements from only a few sites, though they may be extrapolated to much larger areas. Estimation accuracy can be improved if the models are parameterized using long‐term carbon (C) stock data from multiple sites representative of the simulated region. In this study, forest biomass C stocks measured in 61 forested plots located in three research sites in the Delaware River Basin (DRB) were used to modify the PnET‐CN model in three ways: (1) Field‐measured mortality rates in each forest type were used to parameterize the wood turnover rate; (2) a numerical approach was used to calibrate the relationship between foliage N and maximum photosynthesis rate; and (3) stand age was incorporated into the model as an input variable, which determines the year of the last disturbance. The results showed that these model modifications improved model performance in capturing the spatial variation of forest C dynamics in the DRB forests. The spatial distribution of forest C pools and fluxes in the three sites was mapped using the modified model. The modified model was also used in experimental scenarios, which predicted that 39% of forest C sequestered over the past decade could be attributed to the combined effects of elevated CO2 and N deposition. This study demonstrated an effective method for using long‐term biometric measurements of forest biomass C stocks to constrain and improve a process‐based ecosystem model at a regional scale. Further research should target improving model parameters that are sensitive to the spatial variation of forest C dynamics.

The Features of Production Processes in the Lakes of the Valaam Archipelago

The paper reports the characteristics of primary production and destruction processes in small lakes of the Valaam archipelago. The study was carried out on 11 small lakes where the natural regime of functioning is preserved. Studied lakes have different origins, morphometric and hydrochemical parameters. Investigated lakes were characterized by high concentrations of nutrients, especially in the bottom layers. Structure of phytoplankton community differed between lakes. In total, 306 species of phytoplankton had been found in the lakes of the Valaam archipelago. The highest species richness was registered for green algae, diatoms, euglenids and cyanoprokaryota. The lakes of the Valaam archipelago differed in species composition, ratio of taxonomic groups, phytoplankton abundance and biomass. Abundance of phytoplankton and biomass varied from 0.1 to 676.6 million cells/l and from 0.1 to 105.2 mg/ l, accordingly. A wide range of photosynthetic rate (from 0.0 to 4.3 mgO2/ l day and destruction (from 0.0 to 4.2 mgO2/l day) had been shown for all studied lakes. High values of the maximum primary production (Amax) were typical for Igumenskoe, Leschevoe, Krestovoe and Vitalevskoe Lakes, low values were recorded in lakes Simnyahovskoe, Antonievskoe and Nikonovskoe. Mean values Amax (1.14 ± 0.08 mgO2/l day) and maximum destruction Rmax (1.19 ± 0.07 mgO2/l day) were high in all the lakes. In most cases (90%), the maximum photosynthesis rate was registered in the water layer from a surface down to a lower border of the Secchi depth. Data on chlorophyll α content in small lakes of the Valaam archipelago are provided for the first time. It was shown that most of the lakes are mesotrophic with signs of eutrophia (TSI 50–68).

Extracting phytoplankton physiological traits from batch and chemostat culture data

AbstractAs the role of phytoplankton diversity in ocean biogeochemistry becomes widely recognized, the description of plankton in ocean ecological models is becoming more sophisticated. This means that a growing number of plankton physiological traits need to be determined for various species and under various growth conditions. We investigate how these traits can be estimated efficiently from common batch culture and chemostat experiments. We use the Metropolis algorithm, a random‐walk Monte Carlo method, to estimate phytoplankton parameter values, along with the uncertainties in these values. First, we fit plankton physiological models to high‐resolution batch culture and chemostat data sets to obtain parameter sets that are as accurate as possible. Then, we subsample these data sets and assess to which extent the accuracy is sacrificed when fewer measurements are taken. Two measurement points within the exponential growth stage of the batch culture data set are sufficient to constrain the maximum protein synthesis rate, the maximum photosynthesis rate, and the chlorophyll‐to‐nitrogen ratio. Two measurements during the stationary phase of the batch culture experiment are then enough to constrain the parameters related to carbon excretion and the photoacclimation time. From the chemostat experiment, only four measured points are needed to constrain the parameters connected with the internal reserve dynamics of phytoplankton. Thus, we demonstrate that traits related to key biogeochemical and physiological processes can be determined with only a few batch culture and chemostat measurements, as long as the measurement points are selected appropriately.

Effect of CO2 enrichment on phytoplankton photosynthesis in the North Atlantic sub-tropical gyre

The effects of changes in CO2 concentration in seawater on phytoplankton community structure and photosynthesis were studied in the North Atlantic sub-tropical gyre. Three shipboard incubations were conducted for 48h at ∼760ppm CO2 and control (360ppm CO2) from 49°N to 7°N during October and November 2010. Elevated CO2 caused a decrease in pH to ∼7.94 compared to ∼8.27 in the control. During one experiment, the biomass of nano- and picoeukaryotes increased under CO2 enrichment, but primary production decreased relative to the control. In two of the experiments the biomass was dominated by dinoflagellates, and there was a significant increase in the maximum photosynthetic rate (PmB) and light-limited slope of photosynthesis (αB) at CO2 concentrations of 760ppm relative to the controls. 77K emission spectroscopy showed that the higher photosynthetic rates measured under CO2 enrichment increased the connection of reversible photosystem antennae, which resulted in an increase in light harvesting efficiency and carbon fixation.

Constraining the Distribution of Photosynthetic Parameters in the Global Ocean

Global and regional ocean primary production estimates are highly dependent on assumptions concerning the photosynthetic potential of the resident phytoplankton communities. Little is known, however, about global patterns in the distribution of photosynthetic potential and their causes. Here, we review existing literature reporting photosynthetic characteristics of natural populations. From this, we formulate hypotheses regarding abiotic and biotic factors of potential importance in determining photosynthetic performance. These hypotheses are then tested using data we have compiled from nearly all major ocean basins on the maximum rate of photosynthesis, PBmax, and the slope of the photosynthesis vs. light curve, αB (both parameters normalised to chlorophyll) as well as standard environmental variables, size fractioned chlorophyll, taxonomic data (to group), size and biovolume data for pico-, nano-, and micro-phytoplankton. In terms of abiotic variables, depth of sampling, temperature and nutrient availability all can be related to photosynthetic parameters. The most important biotic variable influencing photosynthetic performance was found to be community size distribution and the small component (i.e. the proportion of the phytoplankton community passing through a 10 µm filter) is shown to have both higher PBmax and αB than the larger phytoplankton component. A simple model was used to derive best fit values for PBmax (1.53/2.50 µgC l-1 h-1) and αB (0.025/0.040) for the large/small groups in the subset of the data where taxonomic data were available (both surface and sub-surface samples) using fractioned chlorophyll data and bulk community photosynthetic parameters. Non-metric multidimensional scaling (NMDS) was used to relate the distribution of photosynthetic parameters and dominant (by biovolume) phytoplankton groups. High PBmax was recorded in communities dominated by dinoflagellates, small flagellates and, in warmer waters, picoeukaryotes and Synecococcus. Diatom dominated communities exhibited lower PBmax and were associated with high inorganic nutrients and colder temperatures. That photosynthetic parameters appear closely related to community size distributions and taxonomic group provides some hope for improving the parameterization of photosynthetic performance in global ocean primary production estimates as both of these parameters can be made from remotely sensed optical characteristics of surface waters.

Growth and physiology of Hopea odorata planted within gaps in an acacia plantation acting as a nurse crop

Background: Mixtures of tropical acacia nurse crops and understorey native species have been established to aid forest restoration in Vietnam, but with partial success. Knowledge of physiological mechanisms underlying competitive interactions remains limited.Aims: To examine growth and physiological responses of Hopea odorata, a shade-tolerant dipterocarp, established within an Acacia hybrid (Acacia mangium × Acacia auriculiformis) nurse-crop plantation.Methods: H. odorata seedlings were planted within three 22-m diameter gaps in a 3-year-old Acacia hybrid plantation in Central Vietnam. Growth and physiology responses to an environmental gradient in gaps were examined over 2 years.Results: Growth rate and maximum rates of photosynthesis and stomatal conductance of H. odorata saplings increased significantly with increases in relative daily incident photosynthetically active radiation from 24% at the gap perimeter (GP) to 61% at the gap centre. Leaf N, P, and chlorophyll concentration were unaffected by position in the gap. At the end of dry season, there were significant reductions in leaf water potential for saplings close to the GP suggesting interspecific competition for water.Conclusions: Despite naturally regenerating in shade, the strong ability of H. odorata to acclimate to high light environments suggests that its re-establishment on degraded sites, using Acacia hybrid as a nurse crop should be possible, provided that competition for light and water are managed.

Impaired Stomatal Control Is Associated with Reduced Photosynthetic Physiology in Crop Species Grown at Elevated [CO2

Physiological control of stomatal conductance (Gs) permits plants to balance CO2-uptake for photosynthesis (PN) against water-loss, so optimizing water use efficiency (WUE). An increase in the atmospheric concentration of carbon dioxide ([CO2]) will result in a stimulation of PN and reduction of Gs in many plants, enhancing carbon gain while reducing water-loss. It has also been hypothesized that the increase in WUE associated with lower Gs at elevated [CO2] would reduce the negative impacts of drought on many crops. Despite the large number of CO2-enrichment studies to date, there is relatively little information regarding the effect of elevated [CO2] on stomatal control. Five crop species with active physiological stomatal behavior were grown at ambient (400 ppm) and elevated (2000 ppm) [CO2]. We investigated the relationship between stomatal function, stomatal size, and photosynthetic capacity in the five species, and then assessed the mechanistic effect of elevated [CO2] on photosynthetic physiology, stomatal sensitivity to [CO2] and the effectiveness of stomatal closure to darkness. We observed positive relationships between the speed of stomatal response and the maximum rates of PN and Gs sustained by the plants; indicative of close co-ordination of stomatal behavior and PN. In contrast to previous studies we did not observe a negative relationship between speed of stomatal response and stomatal size. The sensitivity of stomata to [CO2] declined with the ribulose-1,5-bisphosphate limited rate of PN at elevated [CO2]. The effectiveness of stomatal closure was also impaired at high [CO2]. Growth at elevated [CO2] did not affect the performance of photosystem II indicating that high [CO2] had not induced damage to the photosynthetic physiology, and suggesting that photosynthetic control of Gs is either directly impaired at high [CO2], sensing/signaling of environmental change is disrupted or elevated [CO2] causes some physical effect that constrains stomatal opening/closing. This study indicates that while elevated [CO2] may improve the WUE of crops under normal growth conditions, impaired stomatal control may increase the vulnerability of plants to water deficit and high temperatures.

The influence of light habitat on the physiology, biomass allocation, and fecundity of the invasive shrub Amur honeysuckle (Lonicera maackii, Caprifoliaceae)1

Many exotic invasive plants exhibit plasticity in form and function across a range of environmental conditions, optimizing available resources in a manner that frequently outcompetes native organisms. The invasive shrub Lonicera maackii is one of the most prominent invasive plant species in the Midwestern United States. The objectives of this research were to investigate the morphological and physiological plasticity of this invasive shrub across light environments, and to study allometric parameters that will help estimate the aboveground biomass of L. maackii of all size classes. Shrubs were selected from open, forest edge, and understory habitats. Photosynthetic responses to light and leaf nitrogen content were measured throughout the growing season in 2003 and shrubs were harvested in October 2003. The maximum photosynthetic assimilation rates for open grown shrubs were more than double the values measured in the edge and understory. Maximum photosynthesis rates were strongly correlated with leaf nitrogen content, yet the photosynthetic nitrogen use efficiency was uniform across habitats. Open-grown shrubs had the highest values of total and partitioned biomass, although shrubs from all locations showed a proportional distribution to leaf, branch, trunk, and fruit. Although reproductive shrubs can produce copious amounts of fruits and seed in high light environments, fruit production still occurred in forest interior environments and is a direct source of seeds in the understory. Results suggest that because L. maackii exhibits physiological and morphological plasticity coupled with prolific fecundity (even in the understory), this species can persist in all habitats.

Effect of environmental and biotic factors on net ecosystem CO2 exchange over a coastal wetland in the Yellow River Delta.

Using the eddy covariance technique, we measured the net ecosystem CO2 exchange (NEE) and its environmental and biotic factors over a coastal wetland in the Yellow River Delta to investigate the diurnal and seasonal variation in NEE and quantify the effect of environmental and biotic factors on NEE. The results showed that the diurnal change of NEE showed a distinct U-shaped curve during the growing season, but not with substantial variation in its amplitude during the non-growing season. During the growing season, the wetland acted as a significant net sink for CO2, while it became carbon source during the non-growing season. On the scale of a whole year, the wetland functioned as a strong carbon sink of -247 g C·m-2. Daytime NEE was mainly dominated by photosynthetically active radiation (PAR). Apparent quantum yield (α) and daytime respiration of ecosystem (Reco,d) reached maximum in August, while maximum photosynthesis rate (Amax) reached its maximum in July. Nighttime NEE had an exponential relationship with air temperature (Ta). The mean value of temperature sensibility coefficient (Q10) was 2.5, and it was positively related to soil water content (SWC). During the non-growing season, NEE was negatively correlated with net radiation (Rn), but not with other environmental factors significantly. However, during the growing season NEE was significantly correlated with Rn, Ta, soil temperature at 10 cm depth (Ts 10) and leaf area index (LAI), but not with aboveground biomass (AGB). Stepwise multiple regression analysis indicated that Rn and LAI explained 52% of the variation in NEE during the growing season.

The Impact of the Optical Properties and Respiration of Algal Cells with Truncated Antennae on Biomass Production Under Simulated Outdoor Conditions

Background: Previous studies have shown the positive effect of genetically induced antenna truncation on the photosynthetic performance of mutant strains (tla). From the increase of maximum photosynthesis rates per unit chlorophyll under saturating irradiance, it has been concluded that photobioreactors with tla mutants could be operated at higher cell numbers and should show increased biomass production under high irradiance. Objective: The potential of three wild type (WT) strains and one tla mutant of Chlamydomonas reinhardtii to adjust cellular Chlorophyll content (Chlcell) in response to different light conditions and its consequences for the cell physiology was investigated. Results: Under high growth irradiance, some WT strains can achieve a comparable level of antenna reduction as observed in the tla mutant. Respiration and maximum photosynthesis rate showed an inverse correlation with Chlcell independently of whether antenna size reduction was achieved by light adaptation or by genetic transformation. Thus, under diurnal light conditions increased respiratory losses compensate for increased photosynthesis rates and exert negative impact on biomass production. The reduction of Chlcell inevitably resulted in an increase of the absorption efficiency of Chl. This implies that cell number and transparency in a bioreactor cannot be increased to a similar extent as expected from Chlcell reduction. Conclusion: Under natural light conditions, the negative impact of increased respiration and absorptivity of antenna truncated cells has to be taken into account to judge the biomass production potential of antenna truncated alga strains. A further reduction of antenna size beyond the current degree could even decrease biomass productivity. Alternative approaches to increase biomass productivity of photobioreactors are suggested. Keywords: antenna truncation, tla mutants, biomass production, Chlamydomonas reinhardtii Keywords: antenna truncation, tla mutants, biomass production, Chlamydomonas reinhardtii.

Effects of temperature on growth and photosynthesis in the seedling stage of the sheath blight-resistant rice genotype 32R

The 32R rice genotype is resistant to sheath blight disease (ShB), with a high-yield potential. We examined effects of temperature on the plant responses of 32R in comparison with those of the ShB-susceptible rice genotype (29S) and Nipponbare (Nb, a Japonica standard cultivar). The seedlings at the 4th leaf stage of rice genotypes were exposed to 14/14, 19/14, 25/20, 31/26, 37/32 and 37/37 °C (day/night) for 5, 10 and 15 days. The dry weight, leaf area, photosynthesis, contents of ribulose 1,5-bisphosphate carboxylase/oxygenase (Rubisco) and chlorophyll contents were examined. The dry weight showed lower in 32R than in 29S and Nb at a low temperature, and total dry weight correlated strongly with root dry weight and leaf area. The relative growth rate (RGR) correlated strongly with the net assimilation rate (NAR). Rubisco, chlorophyll contents and the photosynthetic rates were limited at a low temperature and showed lower in 32R than in 29S and Nb. The strong correlations between Rubisco and the rates of maximum photosynthesis and initial slope were found in 32R, but not found in 29S and Nb. In addition, RGR and NAR of 32R correlated positively with Rubisco. These suggest that 32R contains traits of cold-sensitive genotypes that are related to limiting Rubisco at a low temperature, thus diminishing photosynthesis and limiting plant growth. Differences of growth among 32R, 29S and Nb were discussed in the relation of genotypes.

The Dual Role of the Plastid Terminal Oxidase PTOX: Between a Protective and a Pro-oxidant Function.

The Dual Role of the Plastid Terminal Oxidase PTOX: Between a Protective and a Pro-oxidant Function.

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.

Effects of Soil Water Potential and Nitrogen Fertilization on Characteristics of Photosynthesis and Chlorophyll Fluorescence Induction in Schisandra chinensis Baillon

Management of soil water and fertilization is known to primarily affect physiological properties and yield in plant. The effect of soil water potential and nitrogen application on characteristics of photosynthesis and chlorophyll fluorescence in Schisandra chinensis Baillon was investigated on a sandy loam soil. Net photosyntheis rate and transpiration rate increased as a photon flux density and was highest at -50kPa of soil water potential. Light compensation point (<TEX>$1.5{\mu}molm^{-1}s^{-1}$</TEX>) and dark respiration (<TEX>$0.13{\mu}molCO_2m^{-1}s^{-1}$</TEX>) was lowest at -50 kPa but maximum photosynthesis rate (<TEX>$13.10{\mu}molCO_2m^{-1}s^{-1}$</TEX>) and net apparent quantum yield (<TEX>$0.083{\mu}molCO_</TEX><TEX>2m^{-1}s^{-1}$</TEX>) was highest at -50 kPa. As results of chlorophyll fluorescence by OJIP analysis, maximum quantum yield (Fv/Fm) of photosystem II (PSII) and PIabs was higher in treatments of -50 kPa and -60 kPa respectively, which reflects the relative reduction state of PSII. But the relative activities per reaction center such as ABS/RC and DIo/RC were low with decreasing soil water potential. Net photosyntheis rate and transpiration rate were highest at treatment of soil testing 1.0 times (<TEX>$92kgha^{-1}$</TEX>). Application of nitrogen resulted in high Fv/Fm, <TEX>$PI_{abs}$</TEX> and low ABS/RC, DIo/RC. This result implies that -50 kPa of soil water potential and nitrogen fertilizer may improve the efficiency of photosynthesis through controlling a photosystem in Schisandra chinensis Baillon.

Photosynthetic Light Responses May Explain Vertical Distribution of Hymenophyllaceae Species in a Temperate Rainforest of Southern Chile.

Some epiphytic Hymenophyllaceae are restricted to lower parts of the host (<60 cm; 10–100 μmol photons m-2 s-1) in a secondary forest of Southern Chile; other species occupy the whole host height (≥10 m; max PPFD >1000 μmol photons m-2 s-1). Our aim was to study the photosynthetic light responses of two Hymenophyllaceae species in relation to their contrasting distribution. We determined light tolerance of Hymenoglossum cruentum and Hymenophyllum dentatum by measuring gas exchange, PSI and PSII light energy partitioning, NPQ components, and pigment contents. H. dentatum showed lower maximum photosynthesis rates (Amax) than H. cruentum, but the former species kept its net rates (An) near Amax across a wide light range. In contrast, in the latter one, An declined at PPFDs >60 μmol photons m-2 s-1. H. cruentum, the shadiest plant, showed higher chlorophyll contents than H. dentatum. Differences in energy partitioning at PSI and PSII were consistent with gas exchange results. H. dentatum exhibited a higher light compensation point of the partitioning of absorbed energy between photochemical Y(PSII) and non-photochemical Y(NPQ) processes. Hence, both species allocated energy mainly toward photochemistry instead of heat dissipation at their light saturation points. Above saturation, H. cruentum had higher heat dissipation than H. dentatum. PSI yield (YPSI) remained higher in H. dentatum than H. cruentum in a wider light range. In both species, the main cause of heat dissipation at PSI was a donor side limitation. An early dynamic photo-inhibition of PSII may have caused an over reduction of the Qa+ pool decreasing the efficiency of electron donation to PSI. In H. dentatum, a slight increase in heat dissipation due to acceptor side limitation of PSI was observed above 300 μmol photons m-2s-1. Differences in photosynthetic responses to light suggest that light tolerance and species plasticity could explain their contrasting vertical distribution.

온도에 따른 단삼의 광합성 특성 및 수확시기가 품질에 미치는 영향

Salvia miltiorrhiza has been used for treating heart and liver disease. In the present study, the influences of temperature on photosynthetical capacity of S. miltiorrhiza under controlled cultivation environment using growth chamber were investigated because of providing information about growth and secondary metabolite synthesis. And effect of harvesting time on growth properties and constituents such as salvianolic acid B, cryptotanshinone, tanshinone I, tanshinone IIA were evaluated. Maximum photosynthesis rate (5.102 μmol CO2/m2/s) and net apparent quantum yield (0.147 μmol CO2/m2/s), stomatal conductance (0.035 mmol/m2/s) and water use efficiency (7.108 μmol CO2/mmol H2O) was highest at 20°C. Results of chlorophyll fluorescence showed that elevated temperature had contributed to reduce a quantum yield and electron flux in photosystem. This result demonstrated that favorable temperature condition was determined at 20°C. Contents of salvianolic acid B, cryptotanshinone, tanshinone I and tanshinone IIA was highest in root sample harvested at 20 March, whereas growth and yield of S. miltiorrhiza had no significant differences with harvesting time. Therefore, this study shows that temperature play an important role in photosynthetic activity and harvesting time have influence upon accumulation of constituents in root of S. miltiorrhiza.