Light Response Of Photosynthesis Research Articles

Nitrogen and Light Responses of Cotton Photosynthesis and Implications for Crop Growth

Leaf nitrogen content and light intensity affect leaf photosynthesis. Responses of cotton (Gossypium hirsutum L.) leaf photosynthesis to nitrogen and light were developed and used in a framework that scales from leaf photosynthesis to canopy radiation use efficiency (RUE). This was then used to explore the impact of nitrogen and light dynamics on RUE of cotton canopies. Photosynthetic rate and nitrogen concentration of leaves (specific leaf nitrogen, SLN) were measured from two field experiments in which the rate of nitrogen application was varied. The overall shape of the relationship between photosynthesis and SLN of individual leaves was consistent with that for other species, being described by an exponential rise to a maximum of 32.49 ± 1.08 μmol CO2 m−2 s−1 Incorporating the influence of age improved the relationship, showing an impact of leaf age independent of SLN. The photosynthesis relationship developed should be appropriate for use in simulating cotton crops. The approach used to scale from leaf photosynthesis to canopy RUE was effective in capturing the variation in the RUE of cotton as observed in three field experiments. There appeared to be little impact of the ontogenetic changes in light extinction coefficient and vertical gradients of SLN within the canopy on the variation in RUE. For crop simulation purposes, this simplifies the process of modulating RUE in growth models.

Nitrogen and Light Responses of Cotton Photosynthesis and Implications for Crop Growth

Leaf nitrogen content and light intensity affect leaf photosynthesis. Responses of cotton (Gossypium hirsutum L.) leaf photosynthesis to nitrogen and light were developed and used in a framework that scales from leaf photosynthesis to canopy radiation use efficiency (RUE). This was then used to explore the impact of nitrogen and light dynamics on RUE of cotton canopies. Photosynthetic rate and nitrogen concentration of leaves (specific leaf nitrogen, SLN) were measured from two field experiments in which the rate of nitrogen application was varied. The overall shape of the relationship between photosynthesis and SLN of individual leaves was consistent with that for other species, being described by an exponential rise to a maximum of 32.49 ± 1.08 μmol CO2 m−2 s−1 Incorporating the influence of age improved the relationship, showing an impact of leaf age independent of SLN. The photosynthesis relationship developed should be appropriate for use in simulating cotton crops. The approach used to scale from leaf photosynthesis to canopy RUE was effective in capturing the variation in the RUE of cotton as observed in three field experiments. There appeared to be little impact of the ontogenetic changes in light extinction coefficient and vertical gradients of SLN within the canopy on the variation in RUE. For crop simulation purposes, this simplifies the process of modulating RUE in growth models.

Ａｌａｓｋａ州Ｂａｒｒｏｗの湛水ツンドラにおける２０００年度植物生育期間のＣＯ２フラックスの季節変化とＣＯ２収支

The CO2 flux of a wet sedge tundra ecosystem in the Arctic, at Barrow, Alaska, was measured applying an eddy correlation method. The seasonal change of CO2 uptake by the vegetation and the net CO2 budget through the growing period were examined for the 2000 growing season. Tundra CO2 budget analysis model(TCBM) was applied to examine the vegetation responses to the environmental variables. Photosynthesis of the vegetation was well parameterized as functions of measured solar radiation, Rsd and air temperature, Ta, and ecosystem respiration was determined as a function of soil temperature at 0.01 m depth, Ts. Estimated CO2 flux by TCBM with measured Rsd and Ta was verified by comparison with observed CO2 flux, and then was used for gap-filling of data missing or eliminated data during the quality control. Parameters of TCBM functions were in accordance with previous studies; temperature dependence of the ecosystem respiration Q10 was 2.6, peak levels of photosynthesis-light response curve ranged 0.12-2.43gCO2m-2h-1 with optimum air temperature of 0.5-14.0°C, with high levels in late July, and the initial slope of the curve ranged 0.002-0.067 gCO2 W-1h-1. Daily CO2 flux was almost 0gCO2 m-2d-1 while the snow covered the ground. Then that changed to a source of up to 1.6gCO2m-2d-1 for about a week after snowmelt. After mid June, CO2 flux was a sink until mid September; those levels showed clear seasonal trends with a maximum of −17.8gCO2 m-2d-1 occurring on August 2. The Tundra ecosystem at Barrow accumulated −335gCO2 m-2 during 122 days of growing season in 2000. Photosynthesis and ecosystem respiration calculated by TCBM were −490gCO2 m-2 and 156 gCO2m-2, respectively. The larger photosynthesis and lower respiration were brought about because of the high water level condition, with standing water completely submerging the base of the wet sedge tundra. These conditions provided high photosynthetic activity and less gases-exchange between rhizosphere and atmosphere.

Leaf photosynthetic characteristics and net primary production of the polar willow (Salix polaris) in a high arctic polar semi-desert, Ny-Ålesund, Svalbard

Photosynthetic characteristics and their leaf-age dependence were examined to estimate ecophysiological effects on net primary production (NPP) of a polar willow (Salix polaris), a dominant dwarf shrub species in a polar semi-desert area of Ny-Ålesund, Svalbard. Leaves of S. polaris emerged just after snowmelt in early July in 2000; flowers were initiated within 1 week, and fruits in late July. Light-saturated rate of photosynthesis and stomatal conductance to water vapor increased rapidly to their maximum values within 1 week after leaf emergence and then decreased gradually. Depending on the leaf age, photosynthetic rates saturated at photosynthetically active photon flux density (PPFD) of 200–400 µmol·m–2·s–1, which is the light level usually available in the natural habitat. Optimum leaf temperature of photosynthesis ranged from 10 to 18°C, while air temperature in the habitat ranged from 8 to 20°C. These light and temperature responses of photosynthesis of S. polaris would be suitable for efficient carbon gain in the natural habitat characterized by highly variable light and temperature conditions. Using the photosynthetic and respiratory characteristics, biomass distribution, and meteorological data, NPP of S. polaris in the current year was estimated to be 26.1 g C·m–2. A model simulation of rising temperature conditions predicted a reduction of NPP because of a large increase in respiration. It was suggested that temperature condition and leaf phenological aspects strongly influence the carbon fixation by plants in the high arctic area studied.Key words: arctic semi-desert, climate change, net ecosystem production (NEP), net primary production (NPP), Salix polaris, photosynthesis.

Depth-acclimation of photosynthesis, morphology and demography of Posidonia oceanica and Cymodocea nodosa in the Spanish Mediterranean Sea

Depth-related changes in population structure, biomass partitioning and photosynthesis were studied in populations of Cymodocea nodosa and Posidonia oceanica on the NE Spanish coast. The population structure of both species changed much more with depth than leaf morphology and physiology. Leaf biomass declined 5- to 7-fold along the depth gradient reducing self-shading within the canopy, whereas the leaf area per unit leaf biomass and the photosynthesis-light response varied less than 1.5-fold among depths. Moreover, C. nodosa developed a greater proportion of leaves relative to rhizomes and roots at greater depths, thereby promoting the balance between photosyn- thesis and respiration in the shoots. C. nodosa, being a potentially fast-growing species compared to P. oceanica, had higher maximum photosynthetic and respiration rates as well as light compensation points for photosynthesis. Photosynthetic efficiency at low light, however, was almost the same for the 2 species as suggested by the relatively small differences in mass-specific light absorption. Only C. nodosa acclimated physiologically to depth as light-use efficiency increased, and light compensation point declined significantly from shallow to deep water. P. oceanica, however, possessed low respira- tion rates and slightly lower light compensation points values than C. nodosa throughout the depth range. Shoot mortality and recruitment rates were unaffected by rooting depth. C. nodosa stand experienced fast shoot turnover compared to P. oceanica, and shoot longevity of the former species decreased significantly with depth, suggesting higher risk of patch mortality at the depth limit. In contrast, P. oceanica shoot longevity was highest at great depths. Overall, these species differences in leaf metabolism and shoot dynamics suggest that C. nodosa responds faster to changing light con- ditions, whereas P. oceanica is able to survive longer at low irradiance due to low growth and respi- ratory maintenance rates.

Relative importance of microhabitat, plant form and photosynthetic physiology to carbon gain in two alpine herbs

Abstract1. The effects of microhabitat and plant form on sunlight interception, leaf temperatures, frost occurrence and photosynthesis were evaluated for Caltha leptosepala DC and Erythronium grandiflorum Pursh. Both plants are perennials that commonly emerge from alpine snowbanks where the combination of cool temperatures and strong sunlight is among the most extreme for vascular plants.2. Caltha leptosepala occurred in microsites where colder air accumulates, and has larger, less inclined and more densely clustered leaves compared to E. grandiflorum (which has two steeply inclined leaves).3. These differences in microsite and plant form led to leaf temperatures below 0 °C on 70% of nights during the summer growth season in C. leptosepala, compared to only 38% in E. grandiflorum. Leaves of C. leptosepala warmed more slowly on mornings following frosts compared to E. grandiflorum, due to less aerodynamic coupling between leaf and air temperature, and also a 45% smaller ratio of sunlit to total leaf area due to mutual shading among leaves.4. As a result, night frost did not affect subsequent CO2 assimilation (A) in E. grandiflorum, while frostless nights and warmer mornings led to 35% greater A in C. leptosepala in the early morning.5. There were no appreciable differences in the temperature and light response of photosynthesis between the two species. The apparent quantum yield of A declined only ≈8% in both species following frost and exposure to strong sunlight, indicating little adjustment of photosynthetic physiology.6. Greater daily carbon gain probably occurs for E. grandiflorum because of its plant form and microclimate, rather than differences in photosynthetic physiology.

Vertical gradients in photosynthetic light response within an old-growth Douglas-fir and western hemlock canopy.

We examined needle-level light response of photosynthesis across a vertical light gradient within 45-55-m-tall western hemlock (Tsuga heterophylla (Raf.) Sarg.) and Douglas-fir (Pseudotsuga menziesii (Mirb.) Franco) trees growing in a 400-500-year-old mixed species stand. We determined: (1) whether light-saturated photosynthetic rates, light compensation points, and respiration rates varied from the upper to the lower canopy, and (2) if light-saturated photosynthetic rates, light compensation points, and respiration rates varied between Douglas-fir and western hemlock. Over a 25-m gradient from the canopy top to the lower canopy, mean light-saturated photosynthetic rates, light compensation points, and respiration rates declined in overstory Douglas-fir and western hemlock needles, paralleling a 65% decline in the mean daily photosynthetic photon flux density (PPFD). At the canopy top, increasing light-saturated photosynthetic rates relative to lower canopy needles increased carbon uptake at high PPFD. In the lower canopy, reduced respiration rates relative to upper canopy needles increased carbon uptake at low PPFD by reducing the light compensation point. At all canopy positions, western hemlock had lower mean light-saturated photosynthetic rates, light compensation points and respiration rates than Douglas-fir. As a result, western hemlock had higher net photosynthetic rates at low PPFD, but lower net photosynthetic rates at high PPFD compared with Douglas-fir.

PLANT CARBON–NUTRIENT INTERACTIONS CONTROL CO2EXCHANGE IN ALASKAN WET SEDGE TUNDRA ECOSYSTEMS

We explored the long-term (8-yr) effects of separate field manipulations of temperature and nutrient availability on carbon balance in wet sedge tundra near the Arctic Long Term Ecological Research (LTER) site at Toolik Lake, Alaska. Our goals were (1) to assess the relative importance of chronic warming (with field greenhouses) and increased N and P availability (by fertilization) in controlling gross ecosystem photosynthesis, ecosystem respiration (plant plus heterotrophic respiration), and ultimately ecosystem C balance; and (2) to attempt to partition ecosystem responses to these treatments between plant and soil contributions. We present results of the effects of these manipulations on whole-system CO2 exchange over seasonal and diel cycles, and on nonrhizosphere soil microbial respiration using in situ soil incubations. Wet sedge control plots were, at best, a weak sink for carbon even during the peak growing season. Chronic nutrient additions of N + P shifted wet sedge carbon balance to a strong sink throughout the growing season; nutrient availability regulated seasonal and diel CO2 exchanges in these two wet sedge ecosystems. The N + P plots had significantly higher photosynthesis and ecosystem respiration in spite of the unanticipated effect of ∼30% reduction in thaw depth in these plots, apparently due to a twofold increase in litter accumulation insulating the soil surface and/or possible shading from greater plant cover in these plots. These results highlighted the prevailing importance of nutrient–carbon interactions in controlling ecosystem processes and ecosystem C balance in arctic tundra. In contrast, warming had only subtle effects on CO2 exchanges. Increased temperatures in the warmed plots had little effect on instantaneous rates of photosynthesis or respiration. After eight years of chronic warming with an average 5.6°C higher air temperature over the growing season and a 40–200% increase in net N mineralization rate, it was surprising that warming did not have more profound effects on CO2 exchange and plant cover. If there were an effect of warming, increased temperatures might cause early canopy development and lengthen the growing season, rather than directly affect instantaneous rates of photosynthesis. Based on photosynthesis–light response curves developed from the early- and late-season diel measurements, we demonstrated that the main effect of warming was to accelerate the development of the canopy early in the season. By midseason, however, there were no significant differences in C exchange between warmed and control plots. Perhaps the most important and novel result emerging from this study is the prevailing importance of plant C exchange, not soil processes, in driving ecosystem C fluxes. First, nonrhizosphere soil microbial respiration as estimated CO2 flux from in situ soil incubations was a small fraction of whole-system respiration and did not vary among treatments. This suggests that anaerobic conditions or some other factor may limit soil microbial respiration more than do temperature or nutrients. Second, plant respiration contributed most (90%) of the ecosystem respiration in fertilized plots. This unanticipated and large contribution from plant respiration highlights the critical importance of understanding the response of plant respiration to global environmental change in these wet sedge ecosystems.

COMPARATIVE PHOTOSYNTHESIS OF TWO SPECIES OF INTERTIDAL EPIPHYTIC MACROALGAE ON MANGROVE ROOTS DURING SUBMERSION AND EMERSION

Photosynthesis and dark respiration rates were measured in water and in air, and the capacity to recover photosynthetic activity from emersion stress was examined for two species of intertidal, epiphytic macroalgae—Bostrychia calliptera (Montagne) Montagne and Caloglossa leprieurii (Montagne) J. Agardh—collected on prop roots of the red mangrove Rhizophora mangle L. in Buenaventura Bay, Pacific coast of Colombia. In both species, net photosynthetic rates were significantly higher under submersed conditions. Maximum photosynthetic rates (Pmax) in water and in air were highest in B. calliptera, 126 ± 4 versus 52 ± 9 μmol O2·mg chl a−1·h−1, respectively. In C. leprieurii, Pmax of submerged plants in water and in air were 98 ± 9 versus 30 ± 11 μmol O2·mg chla−1·h−1. The photoinhibition model of Platt et al. (1980) was used to fit the experimental data in both water and air for both species. Photoinhibition occurred at irradiance as low as 200 μmol·m−2·s−1. The photosynthesis–light response curves demonstrated an adaptation to shaded habitats for both species, as light compensation points in water and air for both species were below 17 ± 5 μmol·m−2·s−1. The rate of dehydration was significantly lower in thalli of B. calliptera compared to C. leprieurii. An increase of photosynthetic activity in B. calliptera was evident between 5% and 15% water loss, but rates decreased thereafter with declining water content. In C. leprieurii, desiccation negatively influenced photosynthetic rates that significantly decreased linearly with declining water content. In B. calliptera, net photosynthesis reached zero only at a water content between 29% and 35%, whereas in C. leprieurii no net photosynthesis occurred in plants containing less than about 50% of their relative water content. Resubmerged plants ofB. calliptera exhibited 100% photosynthetic recovery after 45 min, whereas C. leprieurii recovered 100% at about 120 min. On the basis of the comparison of rates of light‐saturated net photosynthesis for B. calliptera in air versus in water, aerial photosynthetic activity ranged from 35% to 42% of that in water, whereas the emersed photosynthetic capacity of C. leprieurii ranged from 24% to 29% of that in water. Using tidal predictions and the emersed photosynthetic rates, a carbon balance model was constructed for both species over a single daylight period. The calculations indicated that emersed photosynthesis increased average daily carbon production of B. calliptera by 17% and C. leprieuri by 12%. The physiological responses to desiccation stress and the photosynthetic recovery capacities between species correlated with, and may determine, their vertical distribution in the mangrove habitats of Buenaventura Bay.

Light response curves for Gelidium sesquipedale from different depths, determined by two methods: O2 evolution and chlorophyll fluorescence

Photosynthesis-light response curves of Gelidium sesquipedale from the west coast of Portugal (Cape Espichel) were determined at four different depths, 3, 10, 15 and 22 m. Data acquisition using chlorophyll a fluorescence methodology and oxygen electrode measurements were compared. Response curves were determined over an increasing range of irradiance values (I), from darkness to 900 μmol photon m-2 s-1 PAR. In general, light response curves obtained for G. sesquipedale showed a similar pattern whether determined by the chlorophyll fluorescence method or by oxygen evolution. The photosynthetic capacity of G. sesquipedale decreased with depth, as expected, revealing a ‘sun’ and ‘shade’ acclimation pattern, between shallow and deeper waters.

Temperate rainforest lichens in New Zealand: Light response of photosynthesis

The photosynthetic response to photosynthetically active photon flux density (PPFD) was measured in the field for nine New Zealand rain forest lichen species spanning environments from the deep shade within the forest through the forest margin to outside, open ground sites. Light compensation (PPFDcomp) and light saturation (PPFDsat) were much higher for the species of the open sites (over 50 and 500 μmol/m2.s, respectively). Lichens at forest margin or within the forest had PPFDsat of 64.3-29, and 61–162, μmol/m2.s, respectively, but showed no apparent adaptive trends for these parameters. PPFD response of photosynthesis was measured at several thallus water contents (WC) for one species, Pseudocyphellaria coronata, which showed severe depression of photosynthesis at high WC because of increased diffusion resistances, at all PPFD above compensation. PPFDsat was also depressed but not dark respiration, PPFDcomp, or quantum efficiency. Green algal and cyanobacterial lichens showed no relationship between nitrogen and chlorophyll contents but green algal species were always ≤0.7% nitrogen. A third group, cephalodiate (nitrogen fixing) lichens, had nitrogen contents of 1.5–4.4% dry weight with a clear, positive relationship with chlorophyll content. Chlorophyll and nitrogen contents both increased at more shaded sites within the forest. It is suggested that the possession of cephalodia providing a nitrogen source is advantageous within these evergreen forests by allowing a greater contribution to be made to photosynthetic machinery. The PPFDsat of forest lichens seems to be too high for the prevailing PPFD environment and the lichens would rarely be able to photosynthesise at optimal PPFD. It is suggested that this is a protection against transient high light in sunflecks.

Patterns of genotypic variation and phenotypic plasticity of light response in two tropical Piper (Piperaceae) species

Patterns of phenotypic plasticity and genotypic variation in light response of growth and photosynthesis were examined in two species of rain forest shrub that differ in ecological distribution within the forest. We further examined correlations among photosynthetic and growth traits. We hypothesized that the pioneer species, Piper sancti-felicis, would display greater phenotypic plasticity than the shade-tolerant species, Piper arieianum. We further proposed that, in both species, genotypic effects would be more apparent in growth-related traits than photosynthetic traits due to more concentrated selection pressure on gas-exchange traits. P. sancti-felicis did not demonstrate greater phenotypic plasticity of light response. Although many of the traits measured had significant genotype effects, neither species showed any significant effects of genotype on light response of photosynthesis, suggesting little genetic variation for this trait within populations. A principal components analysis clearly illustrated both species and light effects, with the treatments dividing neatly along the axis of the first principal component and the species separating along the second principal component axis. Results indicated general similarities between the species in their trait correlation structure and level of integration among traits, but characteristic differences were observed in the patterns of change between low and high light. Both species had more correlations than expected within groups of growth-related or photosynthetic traits; strong correlations of traits between these two groups were underrepresented. The similar pattern of genetic variation and phenotypic integration observed in these two congeners may be due more to their close phylogenetic relation than to their ecological distributions.

The ratio UV-B/photosynthetically active radiation (PAR) determines the sensitivity of rye to increased UV-B radiation

To evaluate the effect of different naturally occurring irradiation conditions on the sensitivity of rye ( Secale cereale L.) to increased UV-B levels, plants were grown under eight different light treatments. In the control series (at ambient levels of UV-B), UV-B and visible light were decreased in parallel, resulting in four different total irradiation treatments with the same UV-B/photosynthetically active radiation (PAR) ratios. A second series with a 30% increase in UV-B irradiation at each PAR level was used to investigate the effect of UV-B under the varying total irradiance levels. The different total irradiance levels resulted in significant differences in total dry weight, specific leaf weight, photosynthesis-light response and pigment concentrations. A 30% increase in UV-B resulted in equal reductions in total dry weight (from 20.0 to 28.6%) and effective photosynthesis for all light levels. The accumulation of protective pigments in the leaves was stimulated by PAR and even more by UV-B, except at the highest UV-B irradiation, where a small decrease was noted. These results indicate that rye plants are able to adapt to changes in the natural light environment as long as the ratio UV-B/PAR is constant.

Dynamic model of phytoplankton growth and acclimation:responses of the balanced growth rate and the chlorophyll a:carbon ratio to light, nutrient-limitation and temperature

MEPS Marine Ecology Progress Series Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections MEPS 148:187-200 (1997) - doi:10.3354/meps148187 Dynamic model of phytoplankton growth and acclimation: responses of the balanced growth rate and the chlorophyll a:carbon ratio to light, nutrient-limitation and temperature Geider RJ, MacIntyre HL, Kana TM Acclimation of the photosynthetic apparatus to changes of irradiance, temperature and nutrient availability, involving regulation of the chlorophyll a:carbon ratio (theta), is a universal feature of all phytoplankton studied to date. We derive a dynamic regulatory model that predicts the dependencies of theta and growth rate (mu) on irradiance, daylength, temperature and nutrient availability. The model requires specification of 4 parameters to describe the light-dependencies of theta and mu under nutrient-saturating conditions at constant temperature. These are the maximum value of theta (theta m), the initial slope of the chl a-specific photosynthesis-light response curve (alphachl), the maximum carbon-specific photosynthesis rate (PmC) and the cost of biosynthesis (zeta). The influences of temperature and nutrient availability are accommodated through their effects on PmC. The temperature dependence is described by the slope of an Arrhenius plot and the nutrient dependence is described through the half saturation constant (KN) of the Monod equation. Fidelity of the model results to empirical studies suggests that microalgal cells adjust theta in response to an imbalance between the rate of light absorption and the energy demands for photosynthesis and biosynthesis. Chlorophyll a · Chlorosis · Nutrient-limitation · Light · Temperature · Photoadaptation · Photoacclimation · Phytoplankton Full text in pdf format PreviousNextExport citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 148. Publication date: February 27, 1997 Print ISSN:0171-8630; Online ISSN:1616-1599 Copyright © 1997 Inter-Research.

Genotypic Variation in Light and Temperature Response of Photosynthesis in Nothofagus solandri Var. cliffortioides and N. menziesii

Responses of photosynthesis to light and temperature were studied in two Nothofagus species native to New Zealand: N. solandri var. cliffortioides (Hook. f.) Poole and N. menziesii (Hook. f.) Oerst.. Measurements of leaf photosynthesis were made in a controlled environment growth chamber at photosynthetic photon flux density between 0 and 700 μmol m-2 s-1 with temperatures set for 10, 20 and 25�C, on seedlings previously grown in a glasshouse from seed of three different origins. In both species, pronounced intraspecific variation was shown in dark respiration, light compensation point and light-saturated net photosynthesis (Amax). Seedlings of N. solandri showed higher dark respiration and light compensation levels than N. menziesii seedlings, but the two species did not differ in Amax. Change in temperature resulted in significant change in the response of photosynthesis to light in both N. solandri and N. menziesii. The differences between N. solandri and N. menziesii in light response of photosynthesis are discussed in terms of ecosystem dynamics of Nothofagus forests in New Zealand.

Effect of light and temperature on the photosynthetic activity of the cyanobacterium Spirulina platensis

The response of the photosynthetic activity of Spirulina platensis M2 to temperature and light stress was studied. The optimal temperature for photosynthesis was 35°C, while dark respiration was highest at 45 C. At temperature extremes outside those optimal for growth, both respiratory and photosynthetic activity declined. However, the sensitivity of respiration to such extremes was significantly greater than the sensitivity of photosynthesis under the same conditions. Under conditions where respiration was completely inhibited, photosynthetic oxygen evolution was maintained at about 30% of the optimum value. Exposing Spirulina cells to high photon flux densities results in a significant reduction in all the photosynthetic parameters (i.e. initial slope, light-saturated rate and the convexity of the photosynthesis-light response curve). The photoinhibitory stress resulted in much larger decreases in the quantum yield than in the light-saturated rate of photosynthetic oxygen evolution. The extent of photoinhibition was much higher when applied at temperatures over or below the optimum for photosynthesis. The implications of these findings are discussed with respect to the outdoor cultivation of Spirulina.

Ecophysiological Studies on Six Species of the Mangrove Red Algal Genus Caloglossa

Several aspects of the ecophysiology were compared in six eulittoral species of the mangrove red algal genus Caloglossa. The growth pattern in relation to different salt and light treatments, photosynthesis-irradiance curves, as well as the influence of salinity on the intracellular D-mannitol concentrations were studied. All Caloglossa isolates can be characterised as halotolerant due to a broad growth response under a range of salinities (5.3-70‰). The D-mannitol content of all isolates increased significantly with hypersaline treatments and decreased significantly with hyposaline treatments. These data indicate the strong involvement of this hexitol in the osmotic acclimation of Caloglossa. The growth-irradiance pattern and the photosynthesis-light response curves demonstrate an adaptation to shaded habitats for all species. All these physiological capabilities allow the successful colonisation of Caloglossa on various intertidal substrates.

The vertical distribution of nitrogen and photosynthetic activity at different plant densities in Carex acutiformis

Shoots of the monocotyledonous perennial Carex acutiformis were grown in open (28 shoots m−2) and dense stands (280 shoots m−2). For fully grown stands the distribution of relative PPFD and leaf nitrogen per unit leaf area over canopy depth was determined. Light response of photosynthesis was measured on leaf segments sampled at various heights in the stands. Relations between parameters of these curves and leaf nitrogen were investigated.

A Model of Leaf Tissue Growth, Acclimation and Senescence

A model for leaf growth, acclimation and senescence is described. The approach is mechanistic and the model, which is carbon-based, has eight state variables: substrate carbon and machinery carbon; primary, secondary and cross-linked cell wall; and two which correspond to parameters of the photosynthesis light response curve—namely, the initial slope and light-saturated photosynthetic rate. The model is used to simulate responses to light and temperature, and predicts quantities such as final leaf area, the time at which the leaf becomes an exporter, senescence time, and the two photosynthetic parameters. The results are in good qualitative agreement with observational responses that have been reported. The model also simulates the effects of changing the light environment of a mature leaf: for instance, it predicts that increasing the light level can increase leaf longevity and vice versa, although, in general, leaves grown continuously in high light have a shorter life than leaves grown continuously in low light.

Regulation of Ribulose-1,5-Bisphosphate Carboxylase Activity in Response to Light Intensity and CO2 in the C3 Annuals Chenopodium album L. and Phaseolus vulgaris L.

The light and CO(2) response of (a) photosynthesis, (b) the activation state and total catalytic efficiency (k(cat)) of ribulose-1,5-bisphosphate carboxylase (rubisco), and (c) the pool sizes of ribulose 1,5-bisphosphate, (RuBP), ATP, and ADP were studied in the C(3) annuals Chenopodium album and Phaseolus vulgaris at 25 degrees C. The initial slope of the photosynthetic CO(2) response curve was dependent on light intensity at reduced light levels only (less than 450 micromoles per square meter per second in C. album and below 200 micromoles per square meter per second in P. vulgaris). Modeled simulations indicated that the initial slope of the CO(2) response of photosynthesis exhibited light dependency when the rate of RuBP regeneration limited photosynthesis, but not when rubisco capacity limited photosynthesis. Measured observations closely matched modeled simulations. The activation state of rubisco was measured at three light intensities in C. album (1750, 550, and 150 micromoles per square meter per second) and at intercellular CO(2) partial pressures (C(1)) between the CO(2) compensation point and 500 microbars. Above a C(1) of 120 microbars, the activation state of rubisco was light dependent. At light intensities of 550 and 1750 micromoles per square meter per second, it was also dependent on C(1), decreasing as the C(1) was elevated above 120 microbars at 550 micromoles per square meter per second and above 300 microbars at 1750 micromoles per square meter per second. The pool size of RuBP was independent of C(1) only under conditions when the activation state of rubisco was dependent on C(1). Otherwise, RuBP pool sizes increased as C(1) was reduced. ATP pools in C. album tended to increase as C(1) was reduced. In P. vulgaris, decreasing C(1) at a subsaturating light intensity of 190 micromoles per square meter per second increased the activation state of rubisco but had little effect on the k(cat). These results support modelled simulations of the rubisco response to light and CO(2), where rubisco is assumed to be down-regulated when photosynthesis is limited by the rate of RuBP regeneration.