High-frequency optical measurements in shallow Lake Taihu, China: determining the relationships between hydrodynamic processes and inherent optical properties

In order to determine the effect of wind-induced waves (influenced by wind velocity and direction) on the dynamics of optical properties in shallow lakes, we determined the short-term variability of the inherent optical properties (IOPs) in Meiliang Bay, Lake Taihu, China, by examining high-frequency data collected between 8 and 21 September 2010 from meteorology and optical sensors. The absorption and beam attenuation coefficients under strong winds were significantly higher than those under weak and moderate winds (t test, P < 0.001). Significant correlations were found between absorption, scattering, beam attenuation, and wind speed, showing that the hydrodynamic process was an important factor that influenced the instantaneous IOPs of the water. However, the different wind directions have a different effect degree on the IOPs. Western wind is the most important driven wind direction of this site. In addition, significant correlations were found between b _p(440), c _p+g(440), b _p(677), c _p+g(677), b _p(440), and turbidity under each wind direction (P < 0.001). Exponential and hyperbolic exponent models of the absorption and beam attenuation coefficients were fitted, and linear models between a _p+g(677), c _p+g(677), and turbidity were developed. Thus, in shallow lakes such as Lake Taihu, using real-time high-frequency monitoring of the turbidity to deduce the water IOPs could be an efficient and practical approach. Our study will be helpful in monitoring the IOPs and in improving the accuracy of bio-optical models to estimate water quality parameters in Lake Taihu.     

Photosynthesis of two Arctic macroalgae under different ambient radiation levels and their sensitivity to enhanced UV radiation

The change in optimal quantum efficiency (F _v/F _m) of the Arctic species Laminaria saccharina and Palmaria palmata was investigated in a long-term experiment in situ under different radiation levels during the summer of 1997 in the Kongsfjord (Ny-Ålesund, Spitsbergen, Norway, 78°55.5′N, 11°56.0′E). Whole plants were incubated in an open box system made of UV-transparent Perspex and exposed to solar radiation (λ>295?nm), solar radiation excluding UVB (λ?>?320?nm) and solar radiation excluding UVA?+ UVB (λ?>?400?nm). Increasing radiation levels were simulated by transplantation of the pre-adapted algae from their growth depth at 2?m to a water depth of 1?m. Sensitivity to artificially increased UV radiation was determined by exposure of algae from the three treatments to 6?h of strong UV radiation. P. palmata was relatively insensitive to increasing UV radiation and recovered very fast and almost completely in 2?h. Even plants pre-cultured in ambient radiation levels excluding UVA?+?UVB or UVB only showed no photoinhibition after exposure to extra UV radiation in the laboratory. L. saccharina was, in comparison to P. palmata, more sensitive and showed photoinhibition under solar radiation and solar minus UVB radiation after transplantation from 2 to 1?m water depth. However, after 3?weeks at 1?m depth, F _v/F _m of L. saccharina was equal in all treatments and restored to the original values at the start of the experiment. Sensitivity to extra UV radiation in the laboratory increased in time, although recovery was also fast and occurred within 20?h.     

MICROALGAL LIGHT-HARVESTING IN EXTREME LOW-LIGHT ENVIRONMENTS IN MCMURDO SOUND, ANTARCTICA1

Microalgal pigment composition, photosynthetic characteristics, single-cell absorption efficiency (Qa_(λ)) spectra, and fluorescence-excitation (FE) spectra were determined for platelet ice and benthic communities underlying fast ice in Mc Murdo Sound, Antarctica, during austral spring 1988. Measurements of spectral irradiance (E_(λ)) and photosynthetically active radiation (PAR) as well as samples for particulate absorption measurements were taken directly under the congelation ice, within the platelet layer, as profiles vertically through the water column, and at the benihic surface. Light attenuation by.sea ice, algal pigments, and particulates reduced PAR reaching the platelet ice layer to 3%(9–33 fimol photons m-²-^?s-¹) of surface values and narrowed its spectral distribution to a band between 400 and 580 nm. Attenuation by the water column further reduced PAR reaching the sea floor (28–m depth) to 0.05% of surface levels (< 1 μmol photons m-² s-¹), with a spectral distribution dominated by 470–580–nm wavelengths. The photoadaptive index (I) for platelet ice algae (5.9–12.6 μmol photons m-^2.s-¹) was similar to ambient PAR, indicating that algae had acclimated to their light environment (i.e. the algae were light-replete). Maximum Qa_(λ) at the blue absorption peak (440 nm) was 0.63, and enhanced absorption was observed from 460–500 nm and was consistent with observed high cellular chlorophyll (chi) c:chl a and fucoxanthin: chl a molar ratios (0.4 and 1.2, respectively). Benthic algae were light-limited despite the maintenance of very low I_k values (4–11 μmol photons.m-^2.s-¹). Extremely high fucoxanthin: chi a ratios (1.6) in benthic algae produced enhanced green light absorption, resulting in a high degree of complementation between algal absorption and ambient spectral irradiance. Qa_(λ) values for benthic algae were maximal (0.9) between 400 and 510 nm but remained >0.35 even at absorption minima. Strong spectral flattening, a characteristic of intense pigment packaging, was also apparent in the Qa_(λ) spectra for benthic algae. FE and Qa_(λ) spectra were similar in shape for platelet ice algae, indicating that the efficiency at which absorbed energy was transferred to photosystem II (PSII) was independent of wavelength. Fluorescence emission by benthic algae was greatest for the 500–560–nm excitation wavelengths, suggesting that most energy absorbed by accessory pigments was transferred to PSII. These results suggest that under ice algae employ complementary pigmentation and maximize absorption efficiency as adaptive strategies to low-light stress. Regulating the distribution of absorbed energy between PSI and PSII may be an adaptive response to the restricted spectral distribution of irradiance.     

DIEL PATTERNS IN LIGHT ABSORPTION AND ABSORPTION EFFICIENCY FACTORS OF ISOCHRYSIS GALBANA (PRYMNESIOPHYCEAE)1

The chl a specific absorption coefficients [a* (λ), m²·mg chl a ^{? 1}] were examined in chemostat culture of the Prymnesiophyceae Isochrysis galbana (Parke) under a 12:12‐h light:dark cycle at low light (75 μmol photons·m ^{? 2}·s ^{? 1}) and high light (500 μmol photons· m ^{? 2}·s ^{? 1}) conditions. Other associated measurements such as pigment composition, cell density, and diameter as the measure of cell size were also made at the two light regimes every 2 h for 2 days to confirm the periodicity. A distinct diel variability was observed for the a* (λ) with maxima near dawn and minima near dusk. The magnitude of diel variation in a* (440) was 15% at low light and 22% at high light. Pronounced diel patterns were observed for cell size with minima near dawn and maxima near dusk. The magnitude of diel variation in cell size was 9.3% at low light and 21% at high light. The absorption efficiency factors [Q _a (440)] were determined by reconstruction using intracellular concentrations of pigments and cell size. The Q _a (440) also showed a distinct diel variability, with minima near dawn and maxima near dusk. The diel variation in a* (λ) and Q _a (λ) was primarily caused by changes in cell size due to growth, although there was some influence from diel variations in the intracellular pigment concentrations. The results presented here indicated that diel variation in a* (λ) was an important component of the optical characterization of phytoplankton.     

Phytantriol-Based In Situ Liquid Crystals with Long-Term Release for Intra-articular Administration

The purpose of this study was to develop an injectable in situ liquid crystal formulation for intra-articular (IA) administration, and in situ forming a viscous liquid crystalline gel with long-term release of sinomenine hydrochloride (SMH) upon water absorption. The pseudo-ternary phase diagram of phytantriol (PT)-ethanol (ET)-water was constructed, and isotropic solutions were chosen for further optimization. The physicochemical properties of isotropic solutions were evaluated, and the phase structures of liquid crystalline gels formed by isotropic solutions in excess water were confirmed by crossed polarized light microscopy (CPLM) and small-angle X-ray scattering (SAXS). In vitro drug release studies were conducted by using a dialysis membrane diffusion method. The optimal in situ cubic liquid crystal (ISV₂) (PT/ET/water, 64:16:20, w/w/w) loaded with 6 mg/g of SMH showed a suitable pH, showed to be injectable, and formed a cubic liquid crystalline gel in situ with minimum water absorption within the shortest time. The optimal ISV₂ was able to sustain the drug release for 6 days. An in situ hexagonal liquid crystal (ISH₂) system was prepared by addition of 5% vitamin E acetate (VitEA) into PT in the optimal ISV₂ system to improve the sustained release of SMH. This ISH₂ (PT/VitEA/ET/water, 60.8:3.2:16:20, w/w/w/w) was an injectable isotropic solution with a suitable pH range. The developed ISH₂ was found to be able to sustain the drug release for more than 10 days and was suitable for IA injection for the treatment of rheumatoid arthritis (RA).KEY WORDS: in situ cubic liquid crystal, in situ hexagonal liquid crystal, phytantriol, sinomenine hydrochloride, sustained drug release     

The spectral distribution and attenuation of underwater irradiance in Tasmanian inland waters

SUMMARY. 1. Measurements were made of the attenuation and spectral distribution of downwelling and upwelling photosynthetically-available radiation (PAR) in all the principal types of natural waters found in Tasmania. 2. Most lakes in the State are clear and non-turbid, with water itself and the low concentrations of gilvin being the principal determinants of the green underwater light climate. Many others are deeply coloured by dissolved and colloidal organic material (gilvin, gelbstoff) which rapidly attenuates short wavelengths, specifying a shallow, predominantly red euphotic zone. 3. A spectrophotometric measure of colour, the absorption coefficient at 440 nm, is statistically related to measurements on the platinum scale with good precision. 4. Few Tasmanian lakes are turbid but in those that are the underwater light climate is almost identical to that of non-turbid, humic lakes. 5. Reflectance, R, varied with depth but not in the asymptotic way previously encountered. A linear relationship existed between the scattering coefficient, b, and nephelometric turbidity, but not at the approximate 1:1 ratio reported elsewhere. 6. Most Tasmanian lakes are oligotrophic or dystrophic and phytoplankton rarely influenced the underwater light field. 7. Seasonal variation in optical character is not great in natural lakes and their optical properties and light fields can be used typologically. 8. Simple and multiple regression analysis showed that Secchi depth was a poor predictor of euphotic depth but the optical properties and the underwater light field of inaccessible lakes could be reasonably predicted from laboratory measurements made on small water samples, using regressions developed for a wide range of lake types and by reference to the quantaradiometric scans of lakes with comparable optical properties. 9. An optical classification of Tasmanian lakes made by cluster analysis agreed reasonably well with one based on edaphic, vegetational and chemical criteria.     

Subsurface irradiance reflectance spectra of inland waters differing in morphometry and hydrology

A database has been established for relating subsurface irradiance reflectance, i.e. water ‘colour’, to the optical properties and water quality parameters of more than 120 Dutch inland water bodies. The concentrations of total chlorophyll-a (TChl-a = chlorophyll-a plus phaeopigment), total suspended matter and the Secchi-disc depth varied between 0.6 and 468 mg m^-3, 0.8 and 98 g m^-3, and 0.15 and 5.50 m, respectively. The water bodies represented very different water types based on morphometry and hydrology. The depth ranged from 0.4 to 40 m, and the surface area from 0.25 ha (fens in the moorland Peel) to 1200 km² (Lake IJsselmeer). The mean specific phytoplankton absorption coefficient at 676 nm was 0.013 ± 0.003 m² (mg TChl-a)^-1. The absorption by tripton and dissolved humic substances at 440 nm varied between 0.1 and 16.4 m^-1, and 0.1 and 65.5 m^-1, respectively. By using the spectral position and magnitude of the subsurface irradiance reflectance peak alone, it was possible to distinguish groups of water bodies according to a classical typology based on morphometry and hydrology. This revised version was published online in July 2006 with corrections to the Cover Date.     

Photoadaptation in marine phytoplankton : changes in spectral absorption and excitation of chlorophyll a fluorescence

The optical properties of marine phytoplankton were examined by measuring the absorption spectra and fluorescence excitation spectra of chlorophyll a for natural marine particles collected on glass fiber filters. Samples were collected at different depths from stations in temperate waters of the Southern California Bight and in polar waters of the Scotia and Ross Seas. At all stations, phytoplankton fluorescence excitation and absorption spectra changed systematically with depth and vertical stability of the water columns. In samples from deeper waters, both absorption and chlorophyll a fluorescence excitation spectra showed enhancement in the blue-to-green portion of the spectrum (470-560 nm) relative to that at 440 nm. Since similar changes in absorption and excitation were induced by incubating sea water samples at different light intensities, the changes in optical properties can be attributed to photoadaptation of the phytoplankton. The data indicate that in the natural populations studied, shade adaptation caused increases in the concentration of photosynthetic accessory pigments relative to chlorophyll a. These changes in cellular pigment composition were detectable within less than 1 day. Comparisons of absorption spectra with fluorescence excitation spectra indicate an apparent increase in the efficiency of sensitization of chlorophyll a fluorescence in the blue and green spectral regions for low light populations.     

Optical characterization of coastal lagoons in Tunisia: Ecological assessment to underpin conservation

Ghar El Melh is a shallow lagoon (average depth of 0.8 m) that has undergone a eutrophication process due to growing human pressures. To obtain a global frame of the ecosystem functioning, an optical and an ecological classification were used in parallel. Downwelling and upwelling spectral irradiances were measured in situ in 22 sampling stations across the water body; then Apparent Optical Properties (AOPs), namely reflectance R(λ) and vertical attenuation coefficient K_d(λ) were calculated for each wavelength of visible spectrum, furnishing typical spectra from turbid waters, rich in dissolved and suspended matter. From water samples of the same stations the concentrations of OASs (Optically Active Substances), i.e. Chromophoric Dissolved Organic Matter (CDOM), Non-Algal Particulate (NAP) and Phytoplankton, were assessed. The use of an optical classification for water bodies rich in TSM and CDOM, integrating AOPs and OASs, highlighted a great spatial heterogeneity, well overlapping with hydrology and human impacts patterns. A modified version of the Ecological Evaluation Index (EEI), considering the macrophyte distribution (based on a visual assessment of macrophyte coverage, without quantitative sampling) was then used, highlighting an intermediate ecological condition, despite high water turbidities. The integrated use of both systems thus furnished a complete characterization, rapidly detecting the most impacted sectors and the possible primary causes. The method might be applied as a monitoring procedure in other Mediterranean coastal lagoons, with the aim to adopt a common conservation strategy for these important transitional water bodies.     

Herb and conifer roots show similar high sensitivity to water deficit

Root systems play a major role in supplying the canopy with water, enabling photosynthesis and growth. Yet, much of the dynamic response of root hydraulics and its influence on gas exchange during soil drying and recovery remains uncertain. We examined the decline and recovery of the whole root hydraulic conductance (Kr) and canopy diffusive conductance (g_c) during exposure to moderate water stress in two species with contrasting root systems: Tanacetum cinerariifolium (herbaceous Asteraceae) and Callitris rhomboidea (woody conifer). Optical dendrometers were used to record stem water potential at high temporal resolution and enabled non-invasive measurements of Kr calculated from the rapid relaxation kinetics of water potential in hydrating roots. We observed parallel declines in Kr and g_c to <20% of unstressed levels during the early stages of water stress in both species. The recovery of Kr after rewatering differed between species. T. cinerariifolium recovered quickly, with 60% of Kr recovered within 2 h, while C. rhomboidea was much slower to return to its original Kr. Recovery of g_c followed a similar trend to Kr in both species, with C. rhomboidea slower to recover. Our findings suggest that the pronounced sensitivity of Kr to drought is a common feature among different plant species, but recovery may vary depending on root type and water stress severity. Kr dynamics are proposed to modulate g_c response during and following drought.

Root hydraulic conductance shows a similar high sensitivity to soil water deficit in herbaceous and woody roots and may control canopy diffusive conductance during drought and following recovery.     

Microorganisms persist at record depths in the subseafloor of the Canterbury Basin

The subsurface realm is colonized by microbial communities to depths of >1000 meters below the seafloor (m.b.sf.), but little is known about overall diversity and microbial distribution patterns at the most profound depths. Here we show that not only Bacteria and Archaea but also Eukarya occur at record depths in the subseafloor of the Canterbury Basin. Shifts in microbial community composition along a core of nearly 2 km reflect vertical taxa zonation influenced by sediment depth. Representatives of some microbial taxa were also cultivated using methods mimicking in situ conditions. These results suggest that diverse microorganisms persist down to 1922 m.b.sf. in the seafloor of the Canterbury Basin and extend the previously known depth limits of microbial evidence (i) from 159 to 1740 m.b.sf. for Eukarya and (ii) from 518 to 1922 m.b.sf. for Bacteria.     

Subsurface chlorophyll maximum (SCM) location and extension in the water column as governed by a density interface in the strongly stratified Kattegat estuary

The aims of the study were to analyse the relations between the physics of a water column and the location of the subsurface chlorophyll maximum (SCM) peaks in a strongly stratified estuary. Could extension and depth location of the SCM be explained by the physical conditions in terms of water column stratification and density interface? Questions were addressed by obtaining data on water column density (CTD), chlorophyll a (Chl a), nutrients, (F _v/F _m), σ_PSII and K _d(PAR) at 15 positions along a 575 km transect in the Kattegat estuary. Results showed that the estuary was strongly stratified with mixed surface and bottom layers intercepted by a layer where density increased with depth. The SCM occurred only in this density interface, and widths of SCM and density interface were highly correlated. The surface waters were nearly depleted of inorganic nitrogen, phosphate and silicate though with significant higher concentrations in the waters below the interface. The Chl a concentration was comparatively higher in the SCM peak as well as maximum quantum efficiency (F _v/F _m) and functional cross sectional area (σ_PSII). The SCM was maintained at very low light levels and by a diapycnal nitrogen flux, with a stratified water column and nutrient depleted surface waters as predecessors. It was concluded that the depth location and vertical extension of the SCM in the estuary were closely linked to the physical structure of the water column in terms of density interface and stratification.     

Chemiluminescence in the reaction of cytochrome c with hydrogen peroxide

(1) Aqueous solutions of 1–10 μM ferricytochrome c treated with 100 μM–100 mM H₂O₂ at pH 8.0 emit chemiluminescence with quantum yield $\text{Ф ? 10}{}^{\mathrm{?9}}$ and absolute maximum intensity $\text{I}{}_{\mathrm{<mtext>max</mtext>}}\text{? 10}{}^5\text{hv/}\text{s}$ per cm³ (λ = 440), and exhibit exponential decay with a rate constant of 0.15 s^?1. (2) The emission spectrum of the chemiluminescence covers the range 380–620 nm with the maximum at 460 ± 10 nm. (3) Neither cytochrome c nor haemin fluoresce in the spectral region of the chemiluminescence. In the reaction course with H₂O₂, a weak fluorescence in the region 400–620 nm with λ_max = 465–510 nm (λ_exc 315–430 nm) gradually arises. This originates from tryptophan oxidation products of the formylkynurenine type or from imidazole derivatives, respectively. (4) Frozen solutions (77 K) of cytochrome c exhibit phosphorescence typical of tryptophan (λ_exc = 280 nm, λ_em = 450 nm). During the peroxidation, an additional phosphorescence gradually appears in the range 480–620 nm with λ_max = 530 nm (λ_exc = 340 nm). This originates from oxidative degradation products of tryptophan. (5) There are no red bands in the chemiluminescence spectra of cytochrome c or haemin. This result suggests that singlet molecular oxygen $\text{O}{}_2\text{(}{}^1\text{Δ}{}_{\mathrm{<mtext>g</mtext>}}\text{)}$ is not involved in either peroxidation or chemiluminescence. (6) The haem Fe³⁺ group and H₂O₂ appear to be crucial for the chemiluminescence. It is suggested that the generation of electronically excited, light-emitting states is coupled to the production of conformational out-of-equilibrium states of peroxy-Fe-protoporphyrin IX compounds.     

Three-dimensional structure of a Karenia brevis bloom: Observations from gliders,satellites, and field measurements

Autonomous underwater gliders with customized sensors were deployed in October 2011 on the central West Florida Shelf to measure a Karenia brevis bloom, which was captured in satellite imagery since late September 2011. Combined with in situ taxonomy data, satellite measurements, and numerical circulation models, the glider measurements provided information on the three-dimensional structure of the bloom. Temperature, salinity, fluorescence of colored dissolved organic matter (CDOM) and chlorophyll-a, particulate backscattering coefficient, and K. brevis-specific chlorophyll-a concentrations were measured by the gliders over >250 km from the surface to about 30-m water depth on the shallow shelf. At the time of sampling the bloom was characterized by uniform vertical structures, with relatively high chlorophyll-a and CDOM fluorescence, low temperature, and high salinity. Satellite data extracted along the glider tracks demonstrated coherent spatial variations as observed by the gliders. Further, the synoptic satellite observations revealed the bloom evolution during the 7 months between late September 2011 and mid April 2012, and showed the maximum bloom size of ∼3000 km² around 23 November. The combined satellite and in situ data also confirmed that the ratio of satellite-derived fluorescence line height (FLH) to particulate backscattering coefficient at 547 nm (b_bp(547)) could be used as a better index than FLH alone to detect K. brevis blooms. Numerical circulation models further suggested that the bloom could have been initiated offshore and advected onshore via the bottom Ekman layer. The case study here demonstrates the unique value of an integrated coastal ocean observing system in studying harmful algal blooms (HABs).     

Linking dynamics of dissolved organic carbon in a forested lake with environmental factors

Dynamics of dissolved organic carbon concentration (DOC) and capacity toabsorb light (color) are determined by in-lake and external properties andprocesses. In this study, the influence of external factors such as rainfallandsolar radiation on DOC and color dynamics was assessed for a small forestedlake. DOC and absorption coefficients at 440 nm (a₄₄₀)ranged 4-fold from 0.46 to 1.62 mM and from 3.4 to 14.8m^–1, respectively. DOC and a₄₄₀ variedsynchronously, but an important percentage of the variability (26%) ina₄₄₀ was not explained by DOC. The resulting twofold variation inthemolar absorption coefficient of DOC suggested significant seasonal changes inchromophoric content. Both DOC and a₄₄₀ were positive andsignificantly related to cumulative rainfall. Solar radiation, however, onlyappeared to influence a₄₄₀ dynamics. This influence was mediated byphotobleaching. Photobleaching coefficients (k_b) were higher in falland spring relative to the summer. This seasonal variability in k_bvalues was related to monthly rainfall. The influence of photobleaching ona₄₄₀ dynamics was evaluated by comparing the half life ofa₄₄₀ in the water column with water residence time (WRT). For thestudy lake, photobleaching contributed notably to a₄₄₀ dynamicsduring the dry periods when WRT was longer than the a₄₄₀ half life .DOC dynamics, however, were not related to solar radiation becausephotomineralization was considerably slower than photobleaching.     

Structure and siderophore activity of ferric schizokinen

Schizokinen, a citrate-containing dihydroxamate, is a siderophore produced by Bacillus megaterium and Anabaena sp. The involvement of the citrate α-hydroxycarboxylate moiety in iron chelation was investigated by comparing the iron binding behavior of schizokinen with that of acetylschizokinen, a derivative in which the citrate hydroxyl group was modified by acetylation. Ferric schizokinen was found to exhibit an absorption spectrum (λ_max = 460 nm) characteristic of a dihydroxamate below pH 2.5, with an isosbestic shift to a citrate dihydroxamate spectrum (λ_max = 395 nm) above pH 4. Ferric acetylschizokinen also had a dihydroxamate absorption spectrum (λ_max = 465 nm) at low pH. However, its spectral shift (λ_max = 420 nm) and intensity above pH 4 were more typical of a ferric trihydroxamate. The molecular weight and electrophoretic mobility of ferric acetylschizokinen are consistent with a dimeric Fe₂ (acetylschizokinen)₃ structure, whereas ferric schizokinen appears to exist as a monomeric 1:1 complex Despite the differences in molecular weight and α-hydroxycarboxylate coordination, both complexes are effective in promoting iron uptake in Anabaena.     

Microspectrophotometry of the dioptric apparatus and compound rhabdom of the moth (Manduca sexta) eye

Absorption spectra were obtained by microspectrophotometric (MSP) axial measurements of the compound rhabdom of the night moth Manduca sexta. Difference spectra derived from partial or complete bleaches revealed the evidence of four visual pigments with approximate λ_max at 350, 450, 490, and 530 nm. Upon bleaching with light of the pigment maximum at 21°C, pH 7·4–8·5, each pigment, save the u.v.-sensitive one, formed a photoproduct whose spectral maximum (ca. 370 nm) was indicative of a mixture of free and bound retinal. Rarely, small amounts of an additional photoproduct (λ_max 325–330 nm) formed, which is suggestive of retinol. The u.v.-sensitive pigment, when irradiated with u.v., formed an unknown photoproduct (λ_max 290–300 nm). Bleaching kinetics were of first order. Separate absorption determinations through lens or crystalline cones showed each component of the dioptric apparatus served as a filter effecting a sharp decrease in corneal transmission at 310 nm while being increasingly transparent from near u.v. to red. The survival benefits accruing to a largely nocturnal moth with a presumptive colour vision mechanism are discussed.     

Interactions of Elevated CO2 Concentration and Drought Stress on Photosynthesis in Eucalyptus Cladocalyx F. Muell

Response of net photosynthetic rate (P _N), stomatal conductance (g _s), intercellular CO₂ concentration (c _i), and photosynthetic efficiency (F_v/F_m) of photosystem 2 (PS2) was assessed in Eucalyptus cladocalyx grown for long duration at 800 (C₈₀₀) or 380 (C₃₈₀) µmol mol^-1 CO₂ concentration under sufficient water supply or under water stress. The well-watered plants at C₈₀₀ showed a 2.2 fold enhancement of P _N without any change in g _s. Under both C₈₀₀ and C₃₈₀, water stress decreased P _N and g _s significantly without any substantial reduction of c _i, suggesting that both stomatal and non-stomatal factors regulated P _N. However, the photosynthetic efficiency of PS2 was not altered.     

Root water uptake and profile soil water as affected by vertical root distribution

Water uptake by plant roots is a main process controlling water balance in field profiles and vital for agro-ecosystem management. Based on the sap flow measurements for maize plants (Zea mays L.) in a field under natural wet- and dry-soil conditions, we studied the effect of vertical root distribution on root water uptake and the resulted changes of profile soil water. The observations indicate that depth of the most densely rooted soil layer was more important than the maximum rooting depth for increasing the ability of plants to cope with the shortage of water. Occurrence of the most densely rooted layer at or below 30-cm soil depth was very conducive to maintaining plant water supply under the dry-soil conditions. In the soil layers colonized most densely by roots, daytime effective soil water saturation (S _e) always dropped dramatically due to the high-efficient local water depletion. Restriction of the rooting depth markedly increased the difference of S _e between the individual soil layers particularly under the dry-soil conditions due likely to the physical non-equilibrium of water flow between the layers. This study highlights the importance of root distribution and pattern in regulating soil water use and thereby improving endurance of plants to seasonal droughts for sustainable agricultural productivity.     

Absorption spectra of intermediates of bacteriorhodopsin measured by laser photolysis at room temperatures

Picosecond laser spectroscopic analysis was applied to determine how many intermediates existed in the primary photochemical process of trans-bacteriorhodopsin (light-adapted bacteriorhodopsin) at room temperature (18°C) and to calculate their absorption spectra. Irradiation of bacteriorhodopsin with a laser pulse (wavelength, 532 nm; pulse width, 25 ps) yielded the K intermediate (K) which was produced through a precursor, having an absorption maximum (λ_max) longer than that of K. K was stable during a picosecond time range (50–900 ps). The λ_max was located at 610 nm and the extinction coefficient (?_max) was 0.92-times that of bacteriorhodopsin. The same K intermediate was produced from bacteriorhodopsin even when it was excited with a high-energy pulse by which a saturation effect was induced. A transient difference spectrum measured at 150 ns after the excitation of bacteriorhodopsin was different in shape from that of the K intermediate, suggesting that an intermediate was formed by thermal decay of K. This intermediate, tentatively called the KL intermediate (KL), had a λ_max at 596 nm and an ?_max 0.80-times that of bacteriorhodopsin. KL decayed to the L intermediate (L) with a time constant of 2.2 μs. L has a λ_max at 543 nm and an ?_max 0.66-times that of bacteriorhodopsin.