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Effective Quantum Yield (effective + quantum_yield)
Selected AbstractsPhotophysiology of Surface Phytoplankton Communities in a Transect from the Mouth of the Peene-Strom to the Arkona Sea (Baltic)INTERNATIONAL REVIEW OF HYDROBIOLOGY, Issue 5 2003Anna Maria Müller Abstract The potential of surface phytoplankton to withstand photostress was investigated in August 1998 along a transect from the mouth of the Peene-Strom (Pomeranian Bight) to the open Arkona Sea (Baltic). Photosynthetic efficiency, algal class composition and pigment pattern were determined. Algae were photoinhibited by artificial illumination and the kinetics of recovery were recorded. Under photoinhibitory treatment, algae from the estuary showed a low effective quantum yield but a high potential to recover their maximum photosynthetic efficiency. Contrary to this, the relatively high effective quantum yield of open sea algae under photoinhibitory treatment is accompanied by a low final recovery of maximum photosynthetic efficiency. These phenomena are discussed with respect to nutrient supply, algal class composition and to different strategies of algae to react to light stress. Literature data of summer primary productivity of open sea and coastal algae are compared with our data on electron transport rates. This revealed a low influence of photoinhibitory effects on productivity. [source] Melting out of sea ice causes greater photosynthetic stress in algae than freezing in,JOURNAL OF PHYCOLOGY, Issue 5 2007Peter J. Ralph Sea ice is the dominant feature of polar oceans and contains significant quantities of microalgae. When sea ice forms and melts, the microalgal cells within the ice matrix are exposed to altered salinity and irradiance conditions, and subsequently, their photosynthetic apparatuses become stressed. To simulate the effect of ice formation and melting, samples of sea-ice algae from Cape Hallett (Antarctica) were exposed to altered salinity conditions and incubated under different levels of irradiance. The physiological condition of their photosynthetic apparatuses was monitored using fast and slow fluorescence-induction kinetics. Sea-ice algae exhibited the least photosynthetic stress when maintained in 35, and 51, salinity, whereas 16, 21, and 65, treatments resulted in significant photosynthetic stress. The greatest photosynthetic impact appeared on PSII, resulting in substantial closure of PSII reaction centers when exposed to extreme salinity treatments. Salinity stress to sea-ice algae was light dependent, such that incubated samples only suffered photosynthetic damage when irradiance was applied. Analysis of fast-induction curves showed reductions in J, I, and P transients (or steps) associated with combined salinity and irradiance stress. This stress manifests itself in the limited capacity for the reduction of the primary electron receptor, QA, and the plastoquinone pool, which ultimately inhibited effective quantum yield of PSII and electron transport rate. These results suggest that sea-ice algae undergo greater photosynthetic stress during the process of melting into the hyposaline meltwater lens at the ice edge during summer than do microalgae cells during their incorporation into the ice matrix during the process of freezing. [source] PHOTOSYNTHETIC INSENSITIVITY OF THE TERRESTRIAL CYANOBACTERIUM NOSTOC FLAGELLIFORME TO SOLAR UV RADIATION WHILE REHYDRATED OR DESICCATED,JOURNAL OF PHYCOLOGY, Issue 4 2007Kunshan Gao Photosynthetic performance of the terrestrial cyanobacterium Nostoc flagelliforme (M. J. Berkeley et M. A. Curtis) Bornet et Flahault during rehydration and desiccation has been previously characterized, but little is known about the effects of solar UV radiation (280,400 nm) on this species. We investigated the photochemical activity during rehydration and subsequent desiccation while exposing the filamentous colonies to different solar radiation treatments. Photochemical activity could be reactivated by rehydration under full-spectrum solar radiation, the species being insensitive to both ultraviolet-A radiation (UVAR; 315,400 nm) and ultraviolet-B radiation (UVBR). When the rehydrated colonies were exposed for desiccation, the effective PSII photochemical yield was inhibited by visible radiation (PAR) at the initial stage of water loss, then increased with further decrease in water content, and reached its highest value at the water content of 10%,30%. However, no significant difference was observed among the radiation treatments except for the moment when they were desiccated to critical water content of about 2%,3%. At such a critical water content, significant reduction by UVBR of the effective quantum yield was observed in the colonies that were previously rehydrated under indoor light [without ultraviolet radiation (UVR)], but not in those reactivated under scattered or direct solar radiation (with UVR), indicating that preexposure to UVR during rehydration led to higher resistance to UVR during desiccation. The photosynthetic CO2 uptake by the desiccated colonies was enhanced by elevation of CO2 but was not affected by both UVAR and UVBR. It increased with enhanced desiccation to reach the maximal values at water content of 40%,50%. The UV-absorbing compounds and the colony sheath were suggested to play an important role in screening harmful UVR. [source] Research note: Salinity tolerance of Arctic kelps from SpitsbergenPHYCOLOGICAL RESEARCH, Issue 4 2007Ulf Karsten SUMMARY The effect of hypo- and hypersaline treatments on the effective quantum yield of photosystem II was comparatively studied with a pulse amplitude modulated fluorometer (PAM) in the brown algal species Alaria esculenta, Fucus distichus, Laminaria digitata, Laminaria solidungula, Saccharina latissima (formerly Laminaria saccharina) and Saccorhiza dermatodea collected in the Arctic Kongsfjorden (Spitsbergen). While the euryhaline F. distichus was not affected at all by salinities ranging from 5 to 60 psu, A. esculenta, S. latissima and L. solidungula exhibited under hyposaline conditions strong loss of pigments (bleaching) or even high mortality reflecting stenohaline features. In contrast to the latter species, L. digitata and S. dermatodea survived all salinities, but showed reduced photosynthetic activities at the lowest and highest salt treatments and hence, can be characterized as stenohaline-euryhaline organisms. The data are discussed in terms of vertical zonation (eulittoral versus sublittoral habitat), in terms of interactive effects with other abiotic factors such as temperature and in terms of the species-specific acclimation potential. [source] Ethylene insensitivity impedes a subset of responses to phosphorus deficiency in tomato and petuniaPLANT CELL & ENVIRONMENT, Issue 12 2008HYE-JI KIM ABSTRACT The role of ethylene in growth and developmental responses to low phosphorus stress was evaluated using ethylene-insensitive ,Never-ripe' (Nr) tomato and etr1 petunia plants. Low phosphorus increased adventitious root formation in ,Pearson' (wild-type) tomato plants, but not in Nr, supporting a role for ethylene in adventitious root development and showing that ethylene is important for this aspect of phosphorus response. Low phosphorus reduced ethylene production by adventitious roots of both genotypes, suggesting that ethylene perception , not production , regulates carbon allocation to adventitious roots at the expense of other roots under low phosphorus stress. With the exception of its effect on adventitious rooting, Nr had positive effects on growth and biomass accumulation in tomato whereas etr1 tended to have negative effects on petunia. This was particularly evident during the recovery from transplanting, when the effective quantum yield of photosystem II of etr1 petunia grown with low phosphorus was significantly lower than ,Mitchell Diploid', suggesting that etr1 petunia plants may undergo more severe post-transplant stress at low phosphorus availability. Our results demonstrate that ethylene mediates adventitious root formation in response to phosphorus stress and plays an important role for quick recovery of plants exposed to multiple environmental stresses, i.e. transplanting and low phosphorus. [source] DNA damage and photosynthesis in Antarctic and Arctic Sanionia uncinata (Hedw.) Loeske under ambient and enhanced levels of UV-B radiationPLANT CELL & ENVIRONMENT, Issue 12 2002D. LUD Abstract The response of the bipolar moss Sanionia uncinata (Hedw.) Loeske to ambient and enhanced UV-B radiation was investigated at an Antarctic (Léonie Island, 67°35, S, 68°20, W) and an Arctic (Ny-Alesund, 78°55, N, 11°56, E) site, which differed in ambient UV-B radiation (UV-BR: 280,320 nm) levels. The UV-BR effects on DNA damage and photosynthesis were investigated in two types of outdoor experiments. First of all, sections of turf of S. uncinata were collected in an Arctic and Antarctic field site and exposed outdoors to ambient and enhanced UV-BR for 2 d using UV-B Mini-lamps. During these experiments, chlorophyll a fluorescence, chlorophyll concentration and cyclobutyl pyrimidine dimer (CPD) formation were measured. Secondly, at the Antarctic site, a long-term filter experiment was conducted to study the effect of ambient UV-BR on growth and biomass production. Additionally, sections of moss turf collected at both the Antarctic and the Arctic site were exposed to UV-BR in a growth chamber to study induction and repair of CPDs under controlled conditions. At the Antarctic site, a summer midday maximum of 2·1 W m,2 of UV-BR did not significantly affect effective quantum yield (,F/Fm,) and the ratio of variable to maximal fluorescence (Fv/Fm). The same was found for samples of S. uncinata exposed at the Arctic site, where summer midday maxima of UV-BR were about 50% lower than at the Antarctic site. Exposure to natural UV-BR in summer did not increase CPD values significantly at both sites. Although the photosynthetic activity remained largely unaffected by UV-B enhancement, DNA damage clearly increased as a result of UV-B enhancement at both sites. However, DNA damage induced during the day by UV-B enhancement was repaired overnight at both sites. Results from the long-term filter experiment at the Antarctic site indicated that branching of S. uncinata was reduced by reduction of ambient summer levels of UV-BR, whereas biomass production was not affected. Exposure of specimens collected from both sites to UV-BR in a growth chamber indicated that Antarctic and Arctic S. uncinata did not differ in UV-BR-induced DNA damage. It was concluded that S. uncinata from both the Antarctic and the Arctic site is well adapted to ambient levels of UV-BR. [source] Evaluation of instant light-response curves of chlorophyll fluorescence parameters obtained with a portable chlorophyll fluorometer on site in the fieldPLANT CELL & ENVIRONMENT, Issue 12 2000U. Rascher ABSTRACT Miniaturized pulse-amplitude modulated photosynthesis yield analysers are primarily designed for measuring effective quantum yield (,F/Fm,) of photosystem II under momentary ambient light conditions in the field. Although this provides important ecophysiological information, it is often necessary to learn more about the potential intrinsic capacities of leaves by measuring light-response curves. Thus, instruments provide light-curve programmes, where light intensities are increased in short intervals and instant light-response curves are recorded within a few minutes. This method can be criticized because photosynthesis will most likely not be in steady state. This technical report shows that with the appropriate precautions instant light curves can nevertheless provide reliable information about cardinal points of photosynthesis. First, the geometry of the light source of the instrument in relation to the quantum sensor must be considered and quantum sensor readings must be corrected. Second, the measurements of the light-response curves must be compared with readings of effective quantum yield of photosystem II under ambient light conditions where photosynthesis is in steady state. This may show that in the critical range of the light curves either both measurements perfectly coincide or are offset against each other by a constant value (examples are given here). In the first case results of light curves can be taken at face values, and in the second case a simple correction can be applied. With these precautions and careful interpretations instant light-response curves can be an enormous advantage in ecophysiological field work. [source] | ||||||||||