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1.
E. Walter Helbling M. Eugenia Farías M. Verónica Fernández Zenoff Virginia E. Villafañe 《Hydrobiologia》2006,559(1):123-134
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. 相似文献
2.
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 (ΦPSII) 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, UVabc and ratio of repair to damage rates of D1 protein were detected). A significant decrease in the photochemical efficiency
(ΦPSII) 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. 相似文献
3.
Evaluation of the different levels of variability in the underwater light field of a shallow estuary 总被引:18,自引:0,他引:18
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 相似文献
4.
This study focuses on the impact of natural levels of UVBR (ultraviolet-B radiation: 280 to 315 nm) on bacterio- and phytoplankton
(<10 mm) from the Gulf of Aqaba, Red Sea. Incident biologically effective doses (BEDs) and attenuation of biologically effective
radiation in the water column were measured using a DNA biodosimeter. UVBR-induced DNA damage was measured as cyclobutane
pyrimidine dimers (CPDs), using an antibody directed to CPDs followed by chemiluminescent detection. Depth profiles of DNA
damage were determined in two plankton size fractions (0.2 to 0.8 mm and 0.8 to 10 mm) collected down to 50 m depth. Furthermore,
accumulation and removal of CPDs were monitored in surface plankton samples during several daily cycles. Small plankton (plankton
<10 mm) composition was determined by flow cytometry. The plankton community in the Gulf of Aqaba was dominated by nonphototrophic
bacteria and the free-living prochlorophyte Prochlorococcus spp. (<0.8 mm). In general, no DNA damage could be detected in
dosimeter DNA below 15 m. In contrast, DNA damage (up to 124 CPD Mnucl-1) could be detected in all bacterio- and phytoplankton
samples. DNA damage accumulated throughout the day, indicating that plankton in the Gulf of Aqaba undergo UVBR stress via
CPD induction. Although the numbers of CPDs decreased during darkness, both size fractions showed some residual DNA damage
at the end of the night. This suggests that dark repair processes did not remove all CPDs, or that part of the plankton community
was incapable of repair at all. CPD levels in the two size fractions showed no significant differences in situ. During full
solar radiation exposures (samples incubated in bags), more CPDs were detected in the smaller (0.2 to 0.8 mm) size fraction
as compared to the larger (0.8 to 10 mm) size fraction. In these experiments, initial plankton composition was significantly
different from the field samples. This implies that a shift in the population structure or irradiance conditions can lead
to a significant change in UVBR sensitivity. In conclusion, the results show that the picoplankton-dominated phyto- and bacterioplankton
communities in the clear surface waters from the Gulf of Aqaba undergo UVBR stress. Repair pathways are not sufficient to
eliminate damage during or after UVBR exposure hours, suggesting photomortality as a potential loss parameter of the plankton
community. 相似文献
5.
The detrimental effect of solar radiation on the survival of conidia of the entomopathogenic fungusPaecilomyces fumoroseus was studied by monitoring germinability and ability to form colonies (CFU) of conidia irradiated at two temperatures, 25 and 35 °C, harmless to shaded conidia. There was no apparent effect when spores were exposed to a high level of artificial radiation (0.66 W m–2 UVB). However, at a lower level of irradiance (0.33 W m–2), effects of radiation occurred more quickly at 35 °C than at 25 °C. Under natural solar radiation, the rate of decrease in germinability or viability was doubled at 35 °C as compared to 25 °C, indicating an interaction between temperature and radiation effects under natural conditions. This interaction was not detected in indoor experiments, indicating that the spectral distribution of UV radiation has to be taken in account as well as its irradiance when studying its effects.Abbreviations CFU
Colony Forming Units
- UTC
Universal Time Coordinates
- UVB
Ultra Violet B radiation (280–320 nm) 相似文献
6.
The role of ammonium in photoprotection against high irradiance in the red alga Grateloupia lanceola
Combined and/or interactive effects of inorganic nitrogen (as ammonium) and irradiance on the accumulation of nitrogenous compounds, like UV-absorbing mycosporine-like amino acids (MAAs), chlorophyll a and phycobiliproteins, were examined in the red alga Grateloupia lanceola (J. Agardh) J. Agardh in a high irradiance laboratory exposure and a subsequent recovery period under low light. Also, photosynthetic activity as in vivo chlorophyll fluorescence of photosystem II, i.e. optimum quantum yield (Fv/Fm), electron transport rate (ETR) and quantum efficiency, were examined. Photosynthetic activity, phycobiliproteins and internal nitrogen content declined during the 3-day PAR (photosynthetically active radiation; 600 μmol s−1 m−2) and PAR + UVR (ultraviolet radiation; UVB 280–315 nm 0.8 W m−2, UVA 315–400 nm 16 W m−2) exposure. Ammonium supplied in the culture medium (0, 100 and 300 μM NH4Cl) modified the responses of the alga to high irradiance exposures in a concentration dependent manner, mainly with respect to recovery, as the highest recovery during a 10-day low light period was produced under elevated concentration of ammonium (300 μM). The recovery of photosynthetic activity and phycobiliproteins was enhanced in the algae previously incubated under PAR + UVR as compared to exposure to only PAR, suggesting a beneficial effect of UVR on recovery or photoprotective processes under enriched nitrogen conditions. However, the content of MAAs did not follow the same pattern and thus it could not be concluded as the cause of observed enhanced recovery. 相似文献
7.
Long-term records of solar UV radiation reaching the Earth’s surface are scarce. Radiative transfer calculations and statistical
models are two options used to reconstruct decadal changes in solar UV radiation from long-term records of measured atmospheric
parameters that contain information on the effect of clouds, atmospheric aerosols and ground albedo on UV radiation. Based
on earlier studies, where the long-term variation of daily solar UV irradiation was derived from measured global and diffuse
irradiation as well as atmospheric ozone by a non-linear regression method [Feister et al. (2002) Photochem Photobiol 76:281–293], we present another approach for the reconstruction of time series of solar UV radiation.
An artificial neural network (ANN) was trained with measurements of solar UV irradiation taken at the Meteorological Observatory
in Potsdam, Germany, as well as measured parameters with long-term records such as global and diffuse radiation, sunshine
duration, horizontal visibility and column ozone. This study is focussed on the reconstruction of daily broad-band UV-B (280–315 nm),
UV-A (315–400 nm) and erythemal UV irradiation (ER). Due to the rapid changes in cloudiness at mid-latitude sites, solar UV
irradiance exhibits appreciable short-term variability. One of the main advantages of the statistical method is that it uses
doses of highly variable input parameters calculated from individual spot measurements taken at short time intervals, which
thus do represent the short-term variability of solar irradiance. 相似文献
8.
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 (ΦPSII) 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 (UVabc), 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 UVabc and by increasing the rates of repair processes of D1 protein in PSII. 相似文献
9.
SUMMARY 1. We tested the influence of ultraviolet radiation (UVR) and shallow stratification on phytoplankton and bacterioplankton from the surface and the base of the mixed layer in two boreal lakes in north-western Ontario, Canada.
2. We measured phytoplankton biomass and production, bacterioplankton production and plankton respiration after transplantation under three solar radiation treatments: ambient radiation (Photosynthetically active radiation (PAR) + ultraviolet-A (UVA) + ultraviolet-B (UVB)), minus UVB (PAR + UVA) and PAR only. We repeated this experiment on three occasions in each lake during the summer.
3. Solar stress (measured as reduced growth and photoinhibition) was generally only found in the 'base phytoplankton' (i.e. originating from the base of the mixed layer). No inhibition of photosynthesis by UVB exposure was found in near-surface phytoplankton. On the other hand, production of near-surface bacterioplankton was reduced following a 4-h UVR exposure but had increased after a 48-h exposure to both UVA and UVB compared with the PAR only treatment.
4. Negative effects of UVR on phytoplankton and bacterioplankton were not ubiquitous. We emphasise the importance of conducting experiments repeatedly, particularly those which test the effects of UVR on different community assemblages from different lakes. 相似文献
2. We measured phytoplankton biomass and production, bacterioplankton production and plankton respiration after transplantation under three solar radiation treatments: ambient radiation (Photosynthetically active radiation (PAR) + ultraviolet-A (UVA) + ultraviolet-B (UVB)), minus UVB (PAR + UVA) and PAR only. We repeated this experiment on three occasions in each lake during the summer.
3. Solar stress (measured as reduced growth and photoinhibition) was generally only found in the 'base phytoplankton' (i.e. originating from the base of the mixed layer). No inhibition of photosynthesis by UVB exposure was found in near-surface phytoplankton. On the other hand, production of near-surface bacterioplankton was reduced following a 4-h UVR exposure but had increased after a 48-h exposure to both UVA and UVB compared with the PAR only treatment.
4. Negative effects of UVR on phytoplankton and bacterioplankton were not ubiquitous. We emphasise the importance of conducting experiments repeatedly, particularly those which test the effects of UVR on different community assemblages from different lakes. 相似文献
10.
Impacts of solar radiation, humic substances and nutrients on phytoplankton abundance at different depths were investigated in a temperate dimictic lake, Lake Solumsjö. Penetration of solar radiation profiles at different depths, represented as light attenuation coefficient (K
d) were examined. Water sampling and downward irradiance of photosynthetically active radiation (PAR), ultraviolet-A (UV-A, 320–400 nm) and ultraviolet-B (UV-B, 280–320 nm) radiation were performed once a week and at three different times of the day (08.00, 12.00 and 16.00 hrs, local time) between September 13 and November 1, 1999. During the period of investigation, solar radiation above the water surface declined from 474 to 94 mol m–2 s–1 for PAR, from 1380 to 3.57 W m–2 for UV-A and from 13.1 to 0.026 W m–2 for UV-B, respectively. The attenuation coefficient (K
d) for UV-B radiation ranged from 3.7 to 31 m–1 and UV-B radiation could not be detected at depths greater than 0.25 m. Humic substances measured at 440 nm ranged from 35.5 to 57.7 Pt mg l–1. Mean values of biomass, estimated from chlorophyll a, in the whole water column (0–10 m) varied between 2.3 and 5.6 g l–1 and a diel fluctuation was observed. During stratified conditions, high levels of iron (1.36 mg l–1) and manganese (4.32 mg l–1) were recorded in the hypolimnion, suggesting that the thermocline played a major role in the vertical distribution of phytoplankton communities in Lake Solumsjö. The high levels of iron and manganese stimulated the growth of Trachelomonas volvocinopsis in the hypolimnion at a depth of 10 m. Negative impacts of UV-B radiation on phytoplankton in lake Solumsjö are reduced due to the high levels of humic substances and the high degree of solar zenith angle at the latitude studied. 相似文献
11.
The spectral distribution of biologically active solar radiation at Miami,Florida, USA 总被引:3,自引:0,他引:3
The spectral distribution of solar radiation was studied under different sky conditions during a 15-month period in Miami, Florida (USA), and over a latitudinal gradient at solar maximum. Spectroradiometric scans were characterized for total irradiance (300–3000 nm) and the relative energetic and photon contributions of the following wavelength regions: UV-B (300–320 nm); UV-A (320–400 nm); B (400–500 nm); PAR (400–700 nm); R (600–700 nm); and FR (728–732 nm). Notable results include: (i) significantly higher UV-A energy fluxes than currently in use for laboratory experiments involving the biological effects of this band-width (values ranged from 33.6 to 55.4 W/m2 in Miami over the year); (ii) marked diurnal shifts in B:R and R:FR, with elevated R:FR values in early morning: (iii) a strong correlation between R:FR and atmospheric water content; and (iv) unusually high PAR values under direct sunlight with cloudy skies (2484 mol/2 per s). 相似文献
12.
Nurturing vegetation on building envelopes provides an innovative and eco-friendly alternative to urban greening especially in compact cities. Whereas the thermal and other benefits of green roofs have been studied intensively, green walls have received scanty attention. This study evaluates the thermodynamic transmission process of the vertical greenery ecosystem. We designed a field experiment to monitor solar radiation and weather conditions, and developed a thermodynamics transmission model to simulate heat flux and temperature variations. The model was calibrated, tested, and proved to be highly efficient. The results show that seasonal global and direct solar radiation drops to minimum in winter in January and February, and reaches maximum in summer in July and August (1168 W m−2 for global solar radiation and 889 W m−2 for direct solar radiation). Diffuse solar radiation attains maximum in summer (586 W m−2) with moderate rainfall in July and August, and minimum in winter with no rainfall in January and February. Radiation transmission of the green wall strongly correlates with canopy transmittance and reflectance (R2 = 0.83). Thermal shielding effectiveness varies with orientation, with the south wall achieving a higher coefficient (0.31) than the north wall. The south wall has lower heat flux absorbance and heat flux loss than the north wall. The south wall can transfer much more heat flux through the vertical greenery ecosystem due to more intensive canopy evapotranspiration effect. The model matches the transmission properties of green wall radiation, and the model simulation fits empirical transmission results. 相似文献
13.
Effects of UVB radiation on freshwater autotrophic and heterotrophic picoplankton in a subalpine lake 总被引:1,自引:0,他引:1
The effects of UVB radiation on the activity of heterotrophic (HPP) and
autotrophic (APP) picoplankton (0.2-2 m) and
of autotrophic assemblages >2 m has been measured and
compared. Under natural UVB irradiance in a large, deep, oligotrophic
subalpine lake (Lago Maggiore, 4555N) with mean dissolved organic carbon
(DOC) concentrations of 1 mg Cl-1, the
microorganisms of the two size fractions were not significantly
photoinhibited in their autotrophic and heterotrophic activities. The
vertical attenuation coefficient (Kd) for irradiance
at 305 nm ranged from 1.45 to 1.67 during spring and summer. The mixing
layer extended to a greater depth than the layer affected by UVB radiation
(z1% < zmix), thus
enabling the microorganisms living there to photoadapt. As the assimilation
numbers of APP and nanoplankton were higher at 2 m depth than near the
surface, we suspected that the influence of longer wavelength (UVA,
photosynthetically active radiation) could be stronger than UVB in
affecting the photosynthetic efficiency of natural populations. The
artificial increase in UVB irradiance had a higher detrimental effect on
HPP due to their smaller size, less protection and indirect effects through
autotrophic cell inhibition. Picocyanobacteria were percentually more
affected by UVB than nanoplankton during April due to the presence of
diatoms, which are more resistant than other algal groups to solar UVB
irradiance. Furthermore, picocyanobacteria had lower assimilation numbers
with respect to larger phytoplankton in the quartz tubes during
stratification.
相似文献
14.
During a survey from January to March 1998, the occurrence of UV-B radiation (UVBR)- induced DNA damage in Antarctic marine phytoplankton and bacterioplankton was investigated. Sampling was done in Ryder Bay, off the British base Rothera Station, 67°S, 68°W (British Antarctic Survey). Samples were taken regularly during the survey period at fixed depths, after which DNA damage was measured in various plankton size fractions (>10, 2–10, and 0.2–2 μm). Incident solar radiation was measured using spectroradiometry, whereas attenuation of biologically effective UVBR was studied using a DNA dosimeter. A diatom bloom was found in the bay during the research period, judging from microscopic observations and HPLC analyses of taxon-specific pigments. The high phytoplankton biomass likely caused strong attenuation of DNA effective UVBR (Kbd-eff ). Kbd-eff values ranged from 0.83·m − 1 at the peak of the bloom to 0.47·m − 1 at the end of the season. UVBR-mediated DNA damage, as measured by cyclobutane pyrimidine dimer (CPD) abundance, was detected in all plankton size fractions. Highest levels were found in the smallest size fraction, mainly consisting of heterotrophic bacteria. Clear CPD depth profiles were found during mid-summer (January, beginning of February) with surface levels exceeding 100 CPDs per million nucleotides in the bacterioplankton fraction. At that time, melting of the continuously present shelf ice caused strong salinity gradients in the upper meters, thereby stimulating water column stabilization. At the end of February and beginning of March, this phenomenon was less pronounced or absent. At that time, DNA damage was homogeneously distributed over the first 10 m, ranging between 20 and 30 CPDs per million nucleotides for the smallest size fraction. 相似文献
15.
Grifoni D Carreras G Zipoli G Sabatini F Dalla Marta A Orlandini S 《International journal of biometeorology》2008,52(8):755-763
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. 相似文献
16.
Heinecke JL Yi J Pereira JC Richter-Addo GB Ford PC 《Journal of inorganic biochemistry》2012,107(1):47-53
Nitrite reduction to nitric oxide by heme proteins is drawing increasing attention as a protective mechanism to hypoxic injury in mammalian physiology. Here we probe the nitrite reductase (NiR) activities of manganese(II)- and cobalt(II)-substituted myoglobins, and compare with data obtained previously for the iron(II) analog wt MbII. Both MnIIMb and CoIIMb displayed NiR activity, and it was shown that the kinetics are first order each in [protein], [nitrite], and [H+], as previously determined for the FeII analog wt MbII. The second order rate constants (k2) at pH 7.4 and T = 25 °C, were 0.0066 and 0.015 M− 1 s− 1 for CoIIMb and MnIIMb, respectively, both orders of magnitude slower than the k2 (6 M− 1 s− 1) for wt MbII. The final reaction products for MnIIMb consisted of a mixture of the nitrosyl MnIIMb(NO) and MnIIIMb, similar to the products from the analogous NiR reaction by wt Mb. In contrast, the products of NiR by CoIIMb were found to be the nitrito complex CoIIIMb(ONO−) plus roughly an equivalent of free NO. The differences can be attributed in part to the stronger coordination of inorganic nitrite to CoIIIMb as reflected in the respective MIIIMb(ONO−) formation constants Knitrite: 2100 M− 1 (CoIII) and <~0.4 M− 1 (MnIII). We also report the formation constants (3.7 and 30 M− 1, respectively) for the nitrite complexes of the mutant metmyoglobins H64V MbIII(NO2−) and H64V/V67R MbIII(ONO−) and a Knitrite revised value (120 M− 1) for the nitrite complex of wt metMb. The respective Knitrite values for the three ferric proteins emphasize the importance of a H-bonding residue, such as His64 in the MbIII distal pocket or the Arg67 in H64V/V67R MbIII, in stabilizing nitrite coordination. Notably, the NiR activities of the corresponding ferrous Mbs follow a similar sequence suggesting that nitrite binding to these centers are analogously affected by the H-bonding residues. 相似文献
17.
Anthropogenic stratospheric ozone depletion causes an increase in UVB radiation impinging on the earth's surface, which is a threat to plants not adapted to higher UVB irradiances. Investigations were carried out among tropical marine macrophytes, Turbinaria turbinata, Sargassum polyceratium var. ovatum, Padina sanctae-crucis, Lobophora variegate, Dictyota spec., Halimeda discoidea, Udotea flabellum, Thalassia testudinum and Syringodium filiforme collected from 0.3 to 26 m depths at the Belizean barrier reef, where ultraviolet radiation (UV)-irradiances are naturally high. Photoinhibition was induced under full solar, UV (UVA + UVB), and UVA only-depleted radiation conditions. Photosynthetic activity during high radiation stress and during recovery in reduced solar radiation was determined in vivo by measuring fluorescence changes using a PAM fluorometer device. Generally, UV caused an additional decrease of photosynthetic performance during high light stress which varies according to species, depth of growth and UV penetration at the site of collection; an observation in concordance with the conventional harmful UV-radiation effects on phototrophs. When solar radiation was reduced by 50%, significant photosynthetic recovery was observed. However, some shallow water species which are adapted to high UV were observed to recover less under treatment with depleted solar UVB radiation. Our result supports earlier reports that UVB causes not only negative effects on photosynthesis, but may also facilitate or induce recovery processes in aquatic macrophytes acclimated to high solar radiation which grow at the upper shoreline. Among the eulittoral macroalgae, e.g. Dictyota spec., P. sanctae-crucis, and H. discoidea and the seagrass T. testudinum, initiation of photosynthetic recovery processes in the presence of low irradiance of short UV-wavelengths may present an ecophysiological advantage compared to macrophytes which initiate photosynthetic recovery process during low light or in the absence of UV. 相似文献
18.
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. 相似文献
19.
Hermatypic (reef building) corals live in an environment characterized by high ambient levels of photosynthetically active radiation (PAR) and ultraviolet radiation (UVR). Photoadaptive mechanisms have evolved to protect the sensitive cell structures of the host coral and their photosynthetic, endosymbiotic zooxanthellae. Environmental stressors may destabilize the coral-zooxanthellae system resulting in the expulsion of zooxanthellae and/or loss of photosynthetic pigment within zooxanthellae, causing a condition known as bleaching. It is estimated that 1% of the world’s coral population is lost yearly, partly due to bleaching. Despite intensive research efforts, a single unified mechanism cannot explain this phenomenon. Although UVA and UVB cellular damage is well documented, UVC damage is rarely reported due to its almost complete absorption in the stratosphere. A small scale coral propagation system at the University of Maine was accidentally exposed to 15.5 h of UVC radiation (253.7 nm) from a G15T8 germicidal lamp, resulting in a cumulative surface irradiance of 8.39 × 104 J m−2. An experiment was designed to monitor the progression of UVC induced damage. Branch sections from affected scleractinian corals, Acropora yongei and Acropora formosa were submitted to histopathology to provide an historical record of tissue response. The death of gastrodermal cells and necrosis resulted in the release of intracellular zooxanthellae into the gastrovascular canals. Zooxanthellae were also injured as evidenced by pale coloration, increased vacuolization and loss of membrane integrity. The recovery of damaged coral tissue likely proceeds by re-epithelialization and zooxanthellae repopulation of gastrodermal cells by adjacent healthy tissue. 相似文献
20.
Jörg Bendix Brenner Silva Kristin Roos Dietrich Otto Göttlicher Rütger Rollenbeck Thomas Nauß Erwin Beck 《International journal of biometeorology》2010,54(3):283-295
Mountain pastures dominated by the pasture grass Setaria sphacelata in the Andes of southern Ecuador are heavily infested by southern bracken (Pteridium arachnoideum), a major problem for pasture management. Field observations suggest that bracken might outcompete the grass due to its competitive
strength with regard to the absorption of photosynthetically active radiation (PAR). To understand the PAR absorption potential
of both species, the aims of the current paper are to (1) parameterize a radiation scheme of a two-big-leaf model by deriving
structural (LAI, leaf angle parameter) and optical (leaf albedo, transmittance) plant traits for average individuals from
field surveys, (2) to initialize the properly parameterized radiation scheme with realistic global irradiation conditions
of the Rio San Francisco Valley in the Andes of southern Ecuador, and (3) to compare the PAR absorption capabilities of both
species under typical local weather conditions. Field data show that bracken reveals a slightly higher average leaf area index
(LAI) and more horizontally oriented leaves in comparison to Setaria. Spectrometer measurements reveal that bracken and Setaria are characterized by a similar average leaf absorptance. Simulations with the average diurnal course of incoming solar radiation
(1998–2005) and the mean leaf–sun geometry reveal that PAR absorption is fairly equal for both species. However, the comparison
of typical clear and overcast days show that two parameters, (1) the relation of incoming diffuse and direct irradiance, and
(2) the leaf–sun geometry play a major role for PAR absorption in the two-big-leaf approach: Under cloudy sky conditions (mainly
diffuse irradiance), PAR absorption is slightly higher for Setaria while under clear sky conditions (mainly direct irradiance), the average bracken individual is characterized by a higher
PAR absorption potential. (∼74 MJ m−2 year−1). The latter situation which occurs if the maximum daily irradiance exceeds 615 W m−2 is mainly due to the nearly orthogonal incidence of the direct solar beam onto the horizontally oriented frond area which
implies a high amount of direct PAR absorption during the noon maximum of direct irradiance. Such situations of solar irradiance
favoring a higher PAR absorptance of bracken occur in ∼36% of the observation period (1998–2005). By considering the annual
course of PAR irradiance in the San Francisco Valley, the clear advantage of bracken on clear days (36% of all days) is completely
compensated by the slight but more frequent advantage of Setaria under overcast conditions (64% of all days). This means that neither bracken nor Setaria show a distinct advantage in PAR absorption capability under the current climatic conditions of the study area. 相似文献