Effects of sediment anoxia and light on turion germination and early growth of Potamogeton crispus

Potamogeton crispus is a cosmopolitan aquatic species and is widely used as a pioneer species for vegetation restoration of eutrophic lakes. However, many restoration projects applying P. crispus turions have not been successful. Earlier studies focused on effects of light and temperature on turion germination. The purpose of this study was to determine whether sediment anoxia and light interactively affected the turion germination and early growth of P. crispus. Anoxic conditions in the experiment were produced by adding sucrose to the sediment. The germination rate of the turions was 68-73% lower in the highly anoxic condition treatment than in the control. Medium light intensity (10% of natural light at the water surface) was more favorable for germination under slightly anoxic conditions than either low or high light intensity. The growth of newly-formed sprouts was also significantly inhibited by sediment anoxia. Photosynthesis and shoot biomass were reduced under sediment anoxia, whereas total chlorophyll content, root biomass, and soluble protein content were highest in the low anoxic condition treatment. Medium light improved net photosynthesis and biomass production of the sprouts. We conclude that turion germination and sprout growth can be significantly inhibited by sediment anoxia. Medium light intensity may alleviate this inhibition by anoxia, but light has little effect when sediment anoxia is severe. For the purposes of vegetation restoration, more attention should be paid to the role of sediment anoxia, and it is necessary to improve sediment and light conditions for turion germination and early growth of P. crispus in eutrophic lakes. These results will contribute to a more complete understanding of turion germination dynamics of P. crispus and will be useful for future restoration programs.

Responses of dark respiration in the light to desiccation and temperature in the intertidal macroalga, Ulva lactuca (Chorophyta) during emersion

Dark respiration (nonphotorespiratory mitochondrial CO2 release) in the light (R-L) of the intertidal macroalga Ulva lactuca (Chorophyta) during emersion was investigated with respect to its response to variations in temperature and desiccation. R-L was estimated by CO2 gas-exchange analysis using the Kok effect method, whereas dark respiration in darkness (R-D) was determined from CO2 release at zero light. Rates of R, were significantly and consistently lower than those of R-D in emersed U. lactuca across all the temperature and desiccation levels measured. This demonstrated that dark respiration was partially depressed in the light, with the percentage inhibition ranging from 32 to 62%. Desiccation exerted a negative effect on R-L and R-D at a high temperature, 33 degrees C, whereas it had much less effect on respiration at low and moderate temperatures, 23 and 28 degrees C. In general, R-L and R-D increased with increasing temperature in U. lactuca during all stages of emersion but responded less positively to temperature change with increasing desiccation. Additionally, the Q(10) value (i.e. the proportional increase of respiration for each 10 degrees C rise in temperature) for R-L calculated over the temperature range of 23 to 33 degrees C was significantly higher than that for R-D in U. lactuca during the initial stages of emersion. Respiratory carbon loss as a percentage of gross photosynthetic carbon gain increased with increasing temperature and/or desiccation but was significantly reduced when estimated using R-L rather than R-D. It is suggested that measurements of R-L and how it changes in a variable environment are as important as estimates of R-D and photosynthesis in determining simultaneous balance between photosynthetic carbon uptake and respiratory carbon loss and in modeling the net daily carbon gain for an intertidal macroalga.

Effects of solar UV radiation on germination of conchospores and morphogenesis of sporelings in Porphyra haitanensis (Rhodophyta)

The effects of ultraviolet radiation (UVR 280-400 nm) on the germination of Porphyra haitanensis conchospores and on the growth and morphogenesis of the subsequent sporelings were investigated by culturing the released conchospores under natural sunlight from 29 September to 6 October 2005. Germination increased with time and was faster when UV-B was excluded using cut-off filters. There were significant negative effects of UV-B radiation on growth and cell division of sporelings, with decreases up to 18% for thallus length, between 6 and 18% for thallus width, up to 29% for thallus area, and between 6 and 14% for cell size as compared to PAR-controls. UV-A had a significant positive effect on morphogenesis, enhancing the formation of sporelings with cells dividing transversely; on the other hand, UV-B delayed the formation of such sporelings. We also tested the effects of solar UVR on the growth of P. haitanensis juveniles and found no significant effects. Our results indicate that UV-A has an important role in the germination and morphogenesis of the species, but on the other hand, sporelings of P. haitanensis are more sensitive to UV-B radiation than juveniles.

Redescription of Trypanosoma ophiocephali Chen 1964 (Kinetoplastida : Trypanosomatina : Trypanosomatidae) and first record from the blood of dark sleeper (Odontobutis obscura Temminck and Schlegel) in China

During the parasite fauna investigation within 2004 and 2005, the freshwater fish trypanosomes were isolated from the blood of dark sleeper (Odontobutis obscura Temminck and Schlegel) and snakehead fish (Ophiocephalus argus Cantor) from Niushan Lake, Hubei Province, China. Blood trypomastigotes were used for light microscopy investigations. The detailed descriptions of three morphological groups of the genus Trypanosoma: Trypanosoma sp. I and Trypanosoma sp. II found in blood of O. obscura, and Trypanosoma sp. III found in blood of O. argus were provided. Morphological features and host species show Trypanosoma sp. III belong to Trypanosoma ophiocephali Chen 1964, an incompletely described species. Infection with trypanosomes of O. obscura was recorded for the first time. According to the size and appearance, the trypanosomes in O. obscura were also tentatively identified as T. ophiocephali Chen 1964.

A new method to reduce the dark current of GaN based Schottky barrier ultraviolet photodetector

A new method to reduce the dark current of GaN based Schottky barrier ultraviolet photodetector is proposed. In comparision with conventional i-CaN/n(+)-GaN structure, an additional thin p-GaN cap layer is introduced on the i-GaN(n(-)-GaN) in the new structure. The simulation results showed that the additional layer makes the dark current to decrease in the photodetector due to the increase of the Schottky barrier height. The effects of thickness and carrier concentration of p-GaN layer on the dark current of the photodetector were also studied. It is suggested that the dark current of the new structure device could be better reduced by employing p-GaN with higher carrier concentration as the cap layer.

Excitonic bright-to-dark transition induced by spin-orbit coupling

The center-of-mass motion of quasi-two-dimensional excitons with spin-orbit coupling is calculated within the framework of effective mass theory. The results indicate that the spin-orbit coupling will induce a controllable bright-to-dark transition in a quasi-two-dimensional exciton system. This procedure can work as a way to increase the lifetime of excitons. (c) 2008 American Institute of Physics.

Kinetic spectra of light-adaptation dark-adaptation and M-intermediate of BR-D96N

BR-D96N is a kind of genetically site-specific mutants of bacteriorhodopsin (BR) with obvious photochromic effect. Compared to the wild type BR, the lifetime of M state of BR-D96N is prolonged to several minutes so that the photochromic kinetics and the intermediates formation can be studied by the conventional spectra analysis. In the experiment, the absorption spectra of the sample at different time after light illumination are measured with spectrophotometer. By fitting and analyzing the variation of the spectra, we suppose that there are three main states in the, photochromic process, i.e., B state (light-adapted state), M state and D state (dark-adapted state). The absorption spectra of the B state, M state and D state are extracted from the experimental data based on this three-state model and the spectra at various time are fitted with the least-square method. So, the variations of population percentages of the M state, B state and D state are obtained and the M state and B state lifetimes are estimated. In another way, from the measurement of the absorption dynamics at 407 and 568 nm, the M state and B state lifetimes are also obtained by two exponential data fitting, which give coincident results with those of the spectra analysis. (C) 2003 Elsevier Science B.V. All rights reserved.

Steady-state bright-dark vector spatial solitons in biased photorefractive-photovoltaic crystals

We show that bright-dark vector solitons are possible in biased photorefractive-photovoltaic crystals under steady-state conditions, which result from both the bulk photovoltaic effect and the spatially nonuniform screening of the external bias field. The analytical solutions of these vector solitons can be obtained in the case of \sigma\ much less than 1, where sigma is the parameter controlling the intensities of the two optical beams. In the limit of -1 < sigma much less than 1, these vector solitons can also be determined by use of simple numerical integration procedures. When the bulk photovoltaic effect is neglectable, these vector solitons are bright-dark vector screening solitons studied previously in the \sigma\ much less than 1 regime, and predict bright-dark vector screening solitons in the -1 < sigma less than or equal to 1 regime. When the external bias field is absent, these vector solitons predict bright-dark vector photovoltaic solitons in closed and open circuits. (C) 2002 Elsevier Science B.V. All rights reserved.