Importance of the green color,absorption gradient,and spectral absorption of chloroplasts for the radiative energy balance of leaves

Terrestrial green plants absorb photosynthetically active radiation (PAR; 400–700 nm) but do not absorb photons evenly across the PAR waveband. The spectral absorbance of photosystems and chloroplasts is lowest for green light, which occurs within the highest irradiance waveband of direct solar radiation. We demonstrate a close relationship between this phenomenon and the safe and efficient utilization of direct solar radiation in simple biophysiological models. The effects of spectral absorptance on the photon and irradiance absorption processes are evaluated using the spectra of direct and diffuse solar radiation. The radiation absorption of a leaf arises as a consequence of the absorption of chloroplasts. The photon absorption of chloroplasts is strongly dependent on the distribution of pigment concentrations and their absorbance spectra. While chloroplast movements in response to light are important mechanisms controlling PAR absorption, they are not effective for green light because chloroplasts have the lowest spectral absorptance in the waveband. With the development of palisade tissue, the incident photons per total palisade cell surface area and the absorbed photons per chloroplast decrease. The spectral absorbance of carotenoids is effective in eliminating shortwave PAR (<520 nm), which contains much of the surplus energy that is not used for photosynthesis and is dissipated as heat. The PAR absorptance of a whole leaf shows no substantial difference based on the spectra of direct or diffuse solar radiation. However, most of the near infrared radiation is unabsorbed and heat stress is greatly reduced. The incident solar radiation is too strong to be utilized for photosynthesis under the current CO₂ concentration in the terrestrial environment. Therefore, the photon absorption of a whole leaf is efficiently regulated by photosynthetic pigments with low spectral absorptance in the highest irradiance waveband and through a combination of pigment density distribution and leaf anatomical structures.     

The short- and long-term response of <Emphasis Type="Italic">Scrippsiella trochoidea</Emphasis> (Pyrrophyta) to solar ultraviolet radiation

To assess the short- and long-term impacts of UV radiation (UVR, 280–400 nm) on the microalga Scrippsiella trochoidea, we exposed cells to three different radiation treatments (PAB: 280–700 nm, PA: 320–700 nm, and P: 400–700 nm). A significant decrease in the photochemical efficiency (Φ_PSII) at high irradiance (100% of incident solar radiation, 216.0 W m⁻²) was observed. Photoinhibition was reduced from 62.7 to 10.9% when the cells were placed in 12% solar radiation (26.1 W m⁻²). In long-term experiments (11 days) using batch cultures, cell densities during the first 5 days were decreased under treaments P, PA, and PAB, reflecting a change in the irradiance experienced in the laboratory to that of incident solar irradiance. Thereafter, specific growth rates increased and UV-induced photoinhibition decreased, indicating acclimation to solar UV. Cells were found to exhibit both higher ratios of repair to UV-related damage, shorter period for recovery and increased concentrations of UV-absorbing compounds (UV_abc), whose maximum absorption was found to be at 336 nm. Our data indicate that S. trochoidea is sensitive to ultraviolet radiation, but was able to acclimate relatively rapidly (ca. 6 days) by synthesizing UV_abc and by increasing the rates of repair processes of D1 protein in PSII.     

Leaf anatomy during leaf development of photoautotrophically <Emphasis Type="Italic">in vitro</Emphasis>-grown tobacco plants as affected by growth irradiance

Tobacco (Nicotiana tabacum L.) plants were cultured in vitro photoautotrophically at three levels of irradiance (PAR 400–700 nm): low (LI, 60 μmol m⁻² s⁻¹), middle (MI, 180 μmol m⁻² s⁻¹) and high (HI, 270 μmol m⁻² s⁻¹). Anatomy of the fourth leaf from bottom was followed during leaf development. In HI and MI plants, leaf area expansion started earlier as compared to LI plants, and both HI and MI plants developed some adaptations of sun species: leaves were thicker with higher proportion of palisade parenchyma to spongy parenchyma tissue. Furthermore, in HI and MI plants palisade and spongy parenchyma cells were larger and relative abundance of chloroplasts in parenchyma cells measured as chloroplasts cross-sectional area in the cell was lower than in LI plants. During leaf growth, chloroplasts crosssectional area in both palisade and spongy parenchyma cells in all treatments considerably decreased and finally it occupied only about 5 to 8 % of the cell cross-sectional area. Thus, leaf anatomy of photoautotrophically in vitro cultured plants showed a similar response to growth irradiance as in vivo grown plants, however, the formation of chloroplasts and therefore of photosynthetic apparatus was strongly impaired.     

Stomatal control of transpiration in the canopy of a clonal Eucalyptus grandis plantation

 Predawn leaf water potential, stomatal conductance and microclimatic variables were measured on 13 sampling days from November 1995 through August 1996 to determine how environmental and physiological factors affect water use at the canopy scale in a plantation of mature clonal Eucalyptus grandis Hill ex-Maiden hybrids in the State of Espirito Santo, Brazil. The simple ”big leaf” Penman-Monteith model was used to estimate canopy transpiration. During the study period the predawn leaf water potential varied from –0.4 to –1.3 MPa, with the minimum values observed in the winter months (June and August 1996), while the average estimated values for canopy conductance and canopy transpiration fell from 17.3 to 5.8 mm s^–1 and from 0.54 to 0.18 mm h^–1, respectively. On the basis of all measurements, the average value of the decoupling coefficient was 0.25. During continuous soil water shortage a proportional reduction was observed in predawn leaf water potential and in daily maximum values of stomatal conductance, canopy transpiration and decoupling coefficient. The results showed that water vapour exchange in this canopy is strongly dominated by the regional vapour pressure deficit and that canopy transpiration is controlled mainly by stomatal conductance. On a seasonal basis, stomatal conductance and canopy transpiration were mainly related to predawn leaf water potential and, thus, to soil moisture and rainfall. Good results were obtained with a multiplicative empirical model that uses values of photosynthetically active radiation, vapour pressure deficit and predawn leaf water potential to estimate stomatal conductance. Received: 10 June 1998 / Accepted: 20 July 1998     

Evaluation of the different levels of variability in the underwater light field of a shallow estuary

The underwater light climate of a shallow estuary located at the southern coast of the Baltic Sea has been investigated, with special emphasis on the spectral irradiance composition and on short-term irradiance fluctuations caused by vertical mixing and wave focussing. The inherent optical properties of the water body were dominated by phytoplankton pigment absorption in the long-wavelength range and by coloured, dissolved organic matter (cDOM) absorption in the wavelength range <500 nm, including ultraviolet-A (UV-A) and ultraviolet-B radiation (UV-B). Pronounced particulate scattering combined with the absorption values to give very high attenuation coefficients, especially for the shorter wavelengths of UV-B radiation. Photosynthetically active radiation (PAR) was found to be reduced to 1% of the surface value within 0.8 m in the inner, hypertrophic end of the estuary and within 1.9 m in the outer, eutrophic parts of this system, with corresponding 1% penetration depths for UV-B of 0.13 and 0.31 m. During late winter and early spring, the period when reduced atmospheric ozone concentrations and enhanced UV-B have been reported over northern Europe, the irradiance levels in the water column were greatly reduced, due to strong attenuation by ice cover and overlying snow. cDOM concentration of the water was also found to remain at a high level during these periods, and indeed throughout the year, thus reducing the exposure of organisms to UV-R and PAR still further. A complex irradiance regime was found in this system, with irregular and high amplitude fluctuations caused by wind-induced vertical mixing and wave focussing being superimposed upon the solar-angle-dependent seasonal and daily cycles. The methods used to quantify the short-term fluctuations are described, and their relevance to phytoplankton physiology is discussed. The wave-focussing effect is unique to the aquatic environment, and measurements showed that average subsurface irradiances could be increased by up to 5 times for periods lasting for <1 s. The highest irradiances recorded during wave-focussing events reached over 9,000 μmol photons m^–2 s^–1. Received in revised form: 7 April 2000 Electronic Publication     

Photosynthesis and water-use characteristics in Indian mangroves

Photosynthesis and water efflux were measured in different PAR and stomatal conductance in members of Avicenniaceae and Rhizophoraceae. Trend of leaf temperature with irradiance and its effect on photosynthesis were also estimated. In most of the studied species, photosynthesis and stomatal conductance followed similar trends with increase in irradiance. The rate of net photosynthesis and stomatal conductance were higher in members of Avicenniaceae than in Rhizophoraceae. In Avicenniaceae, the optimum PAR for maximum photosynthesis ranged between 1340–1685 (μmol m^-2s^-1, which was also higher than that of Rhizophoraceae (840-1557 μmol m^-2s^-1). Almost in all the studied taxa, transpiration and stomatal conductance followed similar trends and reached the maximal peaks at the same PAR value. The range of breakeven leaf temperature was almost the same in both the families (34-36°C in Avicenniaceae and 33.5-36.3°C in Rhizophoraceae), beyond which assimilation rate declined.     

Effects of solar ultraviolet radiation on photochemical efficiency of <Emphasis Type="Italic">Chaetoceros curvisetus</Emphasis> (Bacillariophyceae)

To assess the short- and long-term impacts of Ultraviolet radiation (UVR, 280–400 nm) on the red tide alga Chaetoceros curvisetus, we exposed cells to three different solar radiation treatments–PAB:280–700 nm, PA:320–700 nm, and P:400–700 nm under 20°C incubated temperature. Short-term exposures were investigated: the photochemical efficiency (Φ_PSII) versus irradiance curves under six levels of solar radiation by covering the incubators with a variable number of neutral density screens (the irradiance thus varied from 100 to 3%) lasting 1 h, and long-term exposures were designed to assess how the cells acclimate to solar radiation (the growth, UV_abc and ratio of repair to damage rates of D1 protein were detected). A significant decrease in the photochemical efficiency (Φ_PSII) at high irradiance (100% of incident solar radiation, 261.6 Wm⁻²) was observed in short-term exposure (1 h). UVR-induced photoinhibition was reduced to 7% in 3% solar radiation (4.08 Wm⁻²), compared with 66% in 100% solar radiation (261.6 Wm⁻²). In long-term experiments (11 days) using batch cultures, cell densities during the first 6 days were relatively constant for treatment P, and decreased slightly under PA and PAB treaments, reflecting a change in the irradiance experienced in the laboratory to that of incident solar irradiance. Thereafter, cell density increased and UV-induced photoinhibition decreased with the following days, indicating acclimation to solar UV. At the end of experiment, cells were found to exhibit both higher ratios of repair to UV-related damage and increased concentrations of UV-absorbing compounds, whose maximum absorption was found to be at 329 nm. Our data indicate that C. curvisetus is sensitive to ultraviolet radiation, but was able to acclimate relatively rapidly (ca. 6 days) by synthesizing UV-absorbing compounds and by increasing the rates of repair processes of D1 protein in PSII.     

The effects of propagation environment and foliar area on the rooting physiology of Cordia alliodora (Ruiz & Pavon) Oken cuttings

 The effects of propagation microclimate and foliar area on the rooting of Cordia alliodora (Ruiz & Pavon) Oken cuttings were investigated using non-mist propagators with and without shade. Photosynthetic rates (P _n ), stomatal conductance (g _s ) and chlorophyll fluorescence ratio (Fv/Fm) of the cuttings were assessed during propagation. Pronounced differences in microclimate were recorded between treatments, with lower temperatures and vapour pressure deficit (VPD) under shade. During the first 8 days after insertion, P _n varied between 2.21 and 4.96 and 0.47 – 2.54 μmol CO₂ m^{–  2}s^{–  1} in the shaded and unshaded propagators, respectively. In the unshaded propagator, Fv/Fm decreased to a minimum of 0.72 2 days after insertion, recovering thereafter. In two separate rooting experiments, rooting percentage was reduced by high irradiance in the 20 and 30 cm² leaf area treatments, but not in the 10 cm² treatment. P _n decreased with an increase in leaf area in both shaded and unshaded propagators. Fv/Fm also declined with increasing leaf area in the high irradiance treatment. PAR and P _n were positively correlated under shade (r ² = 0.51) but negatively correlated in the unshaded treatment (r ² = 0.49); maximum P _n values were recorded at a PAR of 400 μmol m^{–  2} s^{–  1}. No significant differences in g _s were found between treatments, values ranging between 130 and 194 mmol H₂O m^{–  2} s^{–  1}. Positive correlations were found between rooting percentage and mean Fv/Fm. These results indicate that rooting of C. alliodora cuttings is related to photosynthetic activity during propagation, which is itself influenced both by propagator microclimate and cutting leaf area. Received: 7 May 1996 / Accepted: 17 December 1996     

Row orientation effect on UV-B,UV-A and PAR solar irradiation components in vineyards at Tuscany,Italy

Besides playing an essential role in plant photosynthesis, solar radiation is also involved in many other important biological processes. In particular, it has been demonstrated that ultraviolet (UV) solar radiation plays a relevant role in grapevines (Vitis vinifera) in the production of certain important chemical compounds directly responsible for yield and wine quality. Moreover, the exposure to UV-B radiation (280–320 nm) can affect plant–disease interaction by influencing the behaviour of both pathogen and host. The main objective of this research was to characterise the solar radiative regime of a vineyard, in terms of photosynthetically active radiation (PAR) and UV components. In this analysis, solar spectral UV irradiance components, broadband UV (280–400 nm), spectral UV-B and UV-A (320–400 nm), the biological effective UVBE, as well as the PAR (400–700 nm) component, were all considered. The diurnal patterns of these quantities and the UV-B/PAR and UV-B/UV-A ratios were analysed to investigate the effect of row orientation of the vineyard in combination with solar azimuth and elevation angles. The distribution of PAR and UV irradiance at various heights of the vertical sides of the rows was also studied. The results showed that the highest portion of plants received higher levels of daily radiation, especially the UV-B component. Row orientation of the vines had a pronounced effect on the global PAR received by the two sides of the rows and, to a lesser extent, UV-A and UV-B. When only the diffused component was considered, this geometrical effect was greatly attenuated. UV-B/PAR and UV-A/PAR ratios were also affected, with potential consequences on physiological processes. Because of the high diffusive capacity of the UV-B radiation, the UV-B/PAR ratio was significantly lower on the plant portions exposed to full sunlight than on those in the shade.     

Net primary productivity estimation and its relationship with tree diversity for tropical dry deciduous forests of central India

Present study aims at estimation and validation of net primary productivity (NPP) using production efficiency model (PEM), and its possible relationship with tree diversity. The PEM estimates NPP, based on light use efficiency (LUE) and intercepted photosynthetically active radiation (IPAR). Weighted average LUE varied between 0.02 gC/μmol/m² of PAR (Mixed forest (miscellaneous)) to 0.08 gC/μmol/m² of PAR (Acacia forest), in growing phase (GP), and 0.0008 gC/μmol/m² of PAR (Boswellia mixed forest) to 0.023 gC/μmol/m² of PAR (Acacia forest) during the senescent phase (SP). The average weighted LUE for tropical dry and Moist deciduous forest (MDF) in GP were 0.05 gC/μmol/m² of PAR and 0.03 gC/μmol/m² of PAR, respectively. The average IPAR for different forest types was 2079.58 μmol/m²/s during GP and 1510.58 μmol/m²/s during SP. The PEM based NPP varied between 0.58–275.78 gC/m²/year during GP and 0.43–74.34 gC/m²/year during SP. The PEM based NPP and conventional (ground based) NPP were related with R ² of 0.55. The tree diversity and NPP relationship was observed with R ² of 0.55 at the level of both plot and forest types.     

Photosynthetic Response of Carrots to Varying Irradiances

Response to irradiance of leaf net photosynthetic rates (P _N) of four carrot cultivars: Cascade, Caro Choice (CC), Oranza, and Red Core Chantenay (RCC) were examined in a controlled environment. Gas exchange measurements were conducted at photosynthetic active radiation (PAR) from 100 to 1 000 μmol m⁻² s⁻¹ at 20 °C and 350 μmol (CO₂) mol⁻¹(air). The values of P _N were fitted to a rectangular hyperbolic nonlinear regression model. P _N for all cultivars increased similarly with increasing PAR but Cascade and Oranza generally had higher P _N than CC. None of the cultivars reached saturation at 1 000 μmol m⁻² s⁻¹. The predicted P _N at saturation (P _Nmax) for Cascade, CC, Oranza, and RCC were 19.78, 16.40, 19.79, and 18.11 μmol (CO₂) m⁻² s⁻¹, respectively. The compensation irradiance (I _c) occurred at 54 μmol m⁻² s⁻¹ for Cascade, 36 μmol m⁻² s⁻¹ for CC, 45 μmol m⁻² s⁻¹ for Oranza, and 25 μmol m⁻² s⁻¹ for RCC. The quantum yield among the cultivars ranged between 0.057–0.033 mol(CO₂) mol⁻¹(PAR) and did not differ. Dark respiration varied from 2.66 μmol m⁻² s⁻¹ for Cascade to 0.85 μmol m⁻² s⁻¹ for RCC. As P _N increased with PAR, intercellular CO₂ decreased in a non-linear manner. Increasing PAR increased stomatal conductance and transpiration rate to a peak between 600 and 800 μmol m⁻² s⁻¹ followed by a steep decline resulting in sharp increases in water use efficiency. This revised version was published online in August 2006 with corrections to the Cover Date.     

Developmental phase-dependent photosynthetic responses to ultraviolet-B radiation: damage, defence, and adaptation of primary leaves of wheat seedlings

Alterations in photosynthetic capacity of primary leaves of wheat seedlings in response to ultraviolet-B (UV-B; 280–320 nm; 60 μmol m⁻² s⁻¹) exposure alone and in combination with photosynthetically active radiation (PAR; 400–800 nm; 200 μmol m⁻² s⁻¹) during different phases of leaf growth and development were assessed. UV-B exposure resulted in a phase-dependent differential loss in photosynthetic pigments, photochemical potential, photosystem 2 (PS2) quantum yield, and in vivo O₂ evolution. UV-B exposure induced maximum damage to the photosynthetic apparatus during senescence phase of development. The damages were partially alleviated when UV-B exposure was accompanied by PAR. UV-B induced an enhancement in accumulation of flavonoids during all phases of development while it caused a decline in anthocyanin content during senescence. The differential changes in these parameters demonstrated the adaptation ability of leaves to UV-B stress during all phases of development and the ability was modified in UV-B+ PAR exposed samples.     

Morpho-anatomical and physiological leaf traits of two alpine herbs, Podophyllum hexandrum and Rheum emodi in the Western Himalaya under different irradiances

Morpho-anatomical leaf traits and photosynthetic activity of two alpine herbs, Podophyllum hexandrum (shade-tolerant) and Rheum emodi (light-requiring), were studied under field (PAR>2 000 μmol m⁻² s⁻¹) and greenhouse (PAR 500 μmol m⁻² s⁻¹) conditions. Mesophyll thickness, surface area of mesophyll cells facing intercellular spaces (S_mes), surface area of chloroplasts facing intercellular spaces (S_c), intercellular spaces of mesophyll cells (porosity), photon-saturated rate of photosynthesis per unit leaf area (P _Nmax), and ribulose-1,5-bisphosphate carboxylase/oxygenase activity decreased in the greenhouse with respect to the field and the decreases were significantly higher in R. emodi than in P. hexandrum. P. hexandrum had lower intercellular CO₂ concentration than R. emodi under both irradiances. The differences in acclimation of the two alpine herbs to low irradiance were due to their highly unlikely changes in leaf morphology, anatomy, and P _Nmax which indicated that the difference in radiant energy requirement related to leaf acclimation had greater impact under low than high irradiance.     

Leaf δ13C in Pinus resinosa trees and understory plants: variation associated with light and CO2 gradients

 Our objective was to evaluate the relative importance of gradients in light intensity and the isotopic composition of atmospheric CO₂ for variation in leaf carbon isotope ratios within a Pinus resinosa forest. In addition, we measured photosynthetic gas exchange and leaf carbon isotope ratios on four understory species (Dryopteris carthusiana, Epipactus helleborine, Hieracium floribundum, Rhamnus frangula), in order to estimate the consequence of the variation in the understory light microclimate for carbon gain in these plants. During midday, CO₂ concentration was relatively constant at vertical positions ranging from 15 m to 3 m above ground. Only at positions below 3 m was CO₂ concentration significantly elevated above that measured at 15 m. Based on the strong linear relationship between changes in CO₂ concentration and δ¹³C values for air samples collected during a diurnal cycle, we calculated the expected vertical profile for the carbon isotope ratio of atmospheric CO₂ within the forest. These calculations indicated that leaves at 3 m height and above were exposed to CO₂ of approximately the same isotopic composition during daylight periods. There was no significant difference between the daily mean δ¹³C values at 15 m (–7.77‰) and 3 m (–7.89‰), but atmospheric CO₂ was significantly depleted in ¹³C closer to the ground surface, with daily average δ¹³C values of –8.85‰ at 5 cm above ground. The light intensity gradient in the forest was substantial, with average photosynthetically active radiation (PAR) on the forest floor approximately 6% of that received at the top of the canopy. In contrast, there were only minor changes in air temperature, and so it is likely that the leaf-air vapour pressure difference was relatively constant from the top of the canopy to the forest floor. For red pine and elm tree samples, there was a significant correlation between leaf δ¹³C value and the height at which the leaf sample was collected. Leaf tissue sampled near the forest floor, on average, had lower δ¹³C values than samples collected near the top of the canopy. We suggest that the average light intensity gradient through the canopy was the major factor influencing vertical changes in tree leaf δ¹³C values. In addition, there was a wide range of variation (greater than 4‰) among the four understory plant species for average leaf δ¹³C values. Measurements of leaf gas exchange, under natural light conditions and with supplemental light, were used to estimate the influence of the light microclimate on the observed variation in leaf carbon isotope ratios in the understory plants. Our data suggest that one species, Epipactus helleborine, gained a substantial fraction of carbon during sunflecks. Received: 21 March 1996 / Accepted: 13 August 1996     

Light climate and energy flow in the seagrass canopy of Amphibolis griffithii (J.M. Black) den Hartog

 Absorption of light and radiation use efficiency (RUE) were measured in a dense stand of the seagrass Amphibolis griffithii in Warnbro Sound, a temperate marine embayment in southern Western Australia. Total light intercepted by the canopy was measured and compared with dry weight leaf production, under both summer and winter conditions. RUE was found to be higher in winter (1.56 g MJ^–1) than summer (1.01 g MJ^–1). These values are very similar to values measured for annual crop plants and emphasise the value of applying theory developed for terrestrial crop plants to seagrasses. Canopy extinction coefficients were 0.93 m^–1 in winter and 0.44 m^–1 in summer. There were large differences in hours above saturating irradiance (H _sat) between the top (H_sat = 5 h 14 min) and base (18 min) of the canopy in winter. Energy flows in A. griffithii suggest that this species is highly susceptible to short-term perturbations in incident irradience during the winter period as the energy stored within the rhizomes is small relative to daily respiratory demands. Received: 5 October 1995 / Accepted: 14 August 1996     

Compensatory effects of elevated CO<Subscript>2</Subscript> concentration on the inhibitory effects of high temperature and irradiance on photosynthetic gas exchange in carrots

We determined the interactive effects of irradiance, elevated CO₂ concentration (EC), and temperature in carrot (Daucus carota var. sativus). Plants of the cv. Red Core Chantenay (RCC) were grown in a controlled environmental plant growth room and exposed to 3 levels of photosynthetically active radiation (PAR) (400, 800, 1 200 μmol m⁻² s⁻¹), 3 leaf chamber temperatures (15, 20, 30 °C), and 2 external CO₂ concentrations (C _a), AC and EC (350 and 750 μmol mol⁻¹, respectively). Rates of net photosynthesis (P _N) and transpiration (E) and stomatal conductance (g _s ) were measured, along with water use efficiency (WUE) and ratio of internal and external CO₂ concentrations (C _i/C _a). P _N revealed an interactive effect between PAR and C _a. As PAR increased so did P _N under both C _a regimes. The g _s showed no interactive effects between the three parameters but had singular effects of temperature and PAR. E was strongly influenced by the combination of PAR and temperature. WUE was interactively affected by all three parameters. Maximum WUE occurred at 15 °C and 1 200 μmol m⁻² s^{− 1} PAR under EC. The C _i /C _a was influenced independently by temperature and C _a. Hence photosynthetic responses are interactively affected by changes in irradiance, external CO₂ concentration, and temperature. EC significantly compensates the inhibitory effects of high temperature and irradiance on P _N and WUE.     

Optical properties and optical constituents of the Faroe Islands shelf and off-shelf waters,North East Atlantic

The study comprises a data set of CTD, optical properties—K ₀(PAR), c _p, a(PAR), b(PAR)—and optical constituents—Chl a, SPM, CDOM—from 72 shelf and off-shelf stations in the Faroe Islands (62°N, 7°W) North East Atlantic, in early spring 2005. Results showed that shelf waters surrounding the islands were cold and low saline, whereas off-shelf waters were warmer (~1°C) and more saline (~0.05) PSU. A pronounced oceanographic front separated the two waters, and diffuse light attenuation K ₀(PAR), beam attenuation c _p, Chl a, absorption a(PAR), and scattering coefficient b(PAR) were all significantly higher on the shelf. Analyses showed that off-shelf light attenuation K ₀(PAR) was governed by Chl a, shown by a high (r ² = 0.64) Chl a–K ₀(PAR) correlation, whereas light attenuation on the shelf was governed by both Chl a, SPM, and CDOM in combination. A Chl a specific diffuse attenuation coefficient K₀^* ( \textPAR ) K_{0}^{*} \left( {\text{PAR}} \right) of 0.056 (m² mg⁻¹ Chl a) and a Chl a specific beam attenuation ( c_\textp^* c_{\text{p}}^{*} ) of 0.27 (m² mg⁻¹ Chl a) coefficients were derived for the off-shelf. It is pointed out that Chl a is the single variable that changes over time as no rivers with high SPM and CDOM enter the shelf area. Data were obtained in early spring, and Chl a concentrations were low ~0.5 mg Chl a m⁻³. Spring bloom Chl a are about 10 mg Chl a m⁻³ and estimations showed that shelf K ₀(PAR) will increase about 5 times and beam attenuation about 10 times. The Faroe Islands shelf–off-shelf waters is a clear example where physical conditions maintain some clear differences in optical properties and optical constituents. The complete data set is enclosed.     

Stress-Induced Changes in Optical Properties,Pigment and Fatty Acid Content of <Emphasis Type="Italic">Nannochloropsis</Emphasis> sp.: Implications for Non-destructive Assay of Total Fatty Acids

In order to develop a practical approach for fast and non-destructive assay of total fatty acid (TFA) and pigments in the biomass of the marine microalga Nannochloropsis sp. changes in TFA, chlorophyll, and carotenoid contents were monitored in parallel with the cell suspension absorbance. The experiments were conducted with the cultures grown under normal (complete nutrient f/2 medium at 75 μmol PAR photons/(m² s)) or stressful (nitrogen-lacking media at 350 μmol PAR photons/(m² s)) conditions. The reliable measurement of the cell suspension absorbance using a spectrophotometer without integrating sphere was achieved by deposition of cells on glass–fiber filters in the chlorophyll content range of 3–13 mg/L. Under stressful conditions, a 30–50% decline in biomass and chlorophyll, retention of carotenoids and a build-up of TFA (15–45 % of dry weight) were recorded. Spectral regions sensitive to widely ranging changes in carotenoid-to-chlorophyll ratio and correlated changes of TFA content were revealed. Employing the tight inter-correlation of stress-induced changes in lipid metabolism and rearrangement of the pigment apparatus, the spectral indices were constructed for non-destructive assessment of carotenoid-to-chlorophyll ratio (range 0.3–0.6; root mean square error (RMSE) = 0.03; r ² = 0.93) as well as TFA content of Nannochloropsis sp. biomass (range 5.0–45%; RMSE = 3.23 %; r ² = 0.89) in the broad band 400–550 nm normalized to that in chlorophyll absorption band (centered at 678 nm). The findings are discussed in the context of real-time monitoring of the TFA accumulation by Nannochloropsis cultures under stressful conditions.     

Effects of salinity on photosynthesis,leaf anatomy,ion accumulation and photosynthetic nitrogen use efficiency in five Indian mangroves

Five species of mangroves (Bruguiera gymnorrhiza, Excoecaria agallocha, Heritiera fomes, Phoenix paludosa and Xylocarpus granatum) were investigated with respect to their photosynthesis rate, chlorophyll content, mesophyll conductance, specific leaf area, stomatal conductance and photosynthetic nitrogen use efficiency under saline (15–27 PPT) and non-saline (1.8–2 PPT) conditions. Some inorganic elements were estimated from the leaf samples to compare the concentrations with change in salinity. Elevated assimilation rate coupled with increased chlorophyll content, more mesophyll and stomatal conductance and higher specific leaf area in non-saline condition indicates that these mangroves can grow well even with minimal salinity in soil. In B. gymnorrhiza, E. agallocha and P. paludosa the optimum PAR acquisition for photosynthesis was higher under salt stress, while the maximal rate of assimilation was lower even with minimal salinity. H. fomes and X. granatum followed the opposite trend, where the peak photosynthesis rate was lower under non-saline conditions even at a higher irradiance than in the saline forest. This indicates less affinity of H. fomes and X. granatum to high substrate salinity. Accumulation of Na⁺ increased in plants in saline substrate, while in most of the species, salinity imposed reduction in Ca⁺ and Mg⁺ uptake. Increased K⁺ content can be attributed to high substrate level K⁺ in non-saline soil. Trace amount of salinity induced Cu⁺⁺ detected in leaves of H. fomes may impart some toxic effects. Photosynthetic nitrogen use efficiency increased in non-saline soil that can be attributed to higher photosynthetic peak in most of the species and/or lower nitrogen accumulation in plant samples.     

In situ Responses of Phytoplankton from the Subtropical Lake La Angostura (Tucumán, Argentina) in Relation to Solar Ultraviolet Radiation Exposure and Mixing Conditions

In situ experiments were conducted at various depths in the water column to determine the effects of solar ultraviolet radiation (UVR, 280–400 nm) on photosynthesis of natural phytoplankton assemblages from the subtropical Lake La Angostura (Argentina, 26°45′ S; 65°37° W, 1980 m asl.). Water samples were taken daily and incubated under three radiation treatments: (a) Samples exposed to UVR + Photosynthetic Available Radiation (PAR) – PAB treatment (280–700 nm); (b) Samples exposed to ultraviolet-A radiation (UV-A) + PAR – PA treatment (320–700 nm), and, (c) Samples exposed to PAR only – P treatment (400–700 nm). Additionally, depth profiles were done to determine different physical (i.e., temperature and underwater radiation field) and biological characteristics of the water column – photosynthetic pigments, UV-absorbing compounds, cell concentration, deoxyribonucleic acid (DNA) and cyclobutane pyrimidine dimers (CPDs). The effects of UVR on natural phytoplankton assemblages were significant only in the first 50 cm of the water column, causing a decrease in photosynthetic rates of 36 and 20% due to UV-A and ultraviolet-B radiation (UV-B), respectively; below this depth, however, there were no significant differences between radiation treatments. Concentration of CPDs per mega base of DNA in natural phytoplankton was low, <27 CPDs MB⁻¹ between 0 and 4 m. Data on net DNA damage, together with that on mixing conditions of the water column, suggest that mixing can favour phytoplankton by allowing cells to be transported to depths where active repair can take place. This mechanism to reduce UVR-induced DNA damage would be of great advantage for these assemblages dominated by small cyanobacteria and chlorophytes where UV-absorbing compounds that could act as sunscreens are virtually absent.