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排序方式: 共有772条查询结果,搜索用时 31 毫秒
1.
A winter bloom dominated by Pseudo-nitzschia calliantha Lundholm, Moestrup et Hasle (Bacillariophyceae), a potential domoic acid producer, is reported for the first time in the Aegean Sea, Greece, in a semi-enclosed embayment (Kalloni Gulf) surrounded by agricultural land and drained by intermittent rivers. Abundances of this species in the inner part of the Gulf during February were extremely high (max 1.1 × 107 cells l−1). The species Alexandrium insuetum Balech (Dinophyceae) was also found in considerable cell numbers (max 1.4 × 105 cells l−1) during the bloom and reached up to 40% of the total biovolume. This study demonstrates an evident cause and effect relationship between nutrient inflows originating from agricultural activities in the watershed and the development of a potential HAB. The massive bloom formation was observed soon after an episodic rainfall event during the fertilizer application period (December to February). A bloom was also observed the following year, but it was less pronounced due to the fact that rainfalls were more evenly spaced in time and were of moderate intensity. 相似文献
2.
The effects of ultraviolet-B radiation on loblolly pine. I. Growth, photosynthesis and pigment production in greenhouse-grown seedlings 总被引:5,自引:0,他引:5
One-year old loblolly pine ( Pinus taeda L.) seedlings were grown in an unshaded greenhouse for 7 months under 4 levels of ultraviolet-B (UV-B) radiation simulating stratospheric ozone reductions of 16, 25 and 40% and included a control with no UV-B radiation. Periodic measurements were made of growth and gas exchange characteristics and needle chlorophyll and UV-B-absorbing-compound concentrations. The effectiveness of UV-B radiation on seedling growth and physiology varied with the UV-B irradiance level. Seedlings receiving the lowest supplemental UV-B irradiance showed reductions in growth and photosynthetic capacity after only 1 month of irradiation. These reductions persisted and resulted in lower biomass production, while no increases in UV-B-absorbing compounds in needles were observed. Seedlings receiving UV-B radiation which simulated a 25% stratospheric ozone reduction showed an increase in UV-B-absorbing-compound concentrations after 6 months, which paralleled a recovery in photosynthesis and growth after an initial decrease in these characteristics. The seedlings grown at the highest UV-B irradiance (40% stratospheric ozone reduction) showed a more rapid increase in the concentration of UV-B-absorbing compounds and no effects of UV-B radiation on growth or photosynthetic capacity until after 4 months at this irradiance. Changes in photosynthetic capacity were probably the result of direct effects on light-dependent processes, since no effects were observed on either needle chlorophyll concentrations or stomatal conductance. Further studies are necessary to determine whether these responses persist and accumulate over subsequent years. 相似文献
3.
Yuichi Takeuchi Megumi Akizuki Hideyuki Shimizu Noriaki Kondo Kiyoshi Sugahara 《Physiologia plantarum》1989,76(3):425-430
Cucumber ( Cucumis sativus L. cv. Natsusairaku 3) seedlings were grown in a growth cabinet under UV-B (290–320 nm) irradiation (equivalent to the UV-B radiation normally incident at Tokyo, 36°N latitude, during clear sky conditions in mid-april on a weighted daily fluence basis) and a UV-B-free control condition. UV-B irradiation inhibited the growth of the cotyledons, i.e. the increase in area, and increase in fresh and dry weights of the cotyledons. The greatest inhibition rate was observed in the increase in area, causing a significant increase in specific leaf weight (the ratio of weight to area). UV-B irradiation had no significant effect on DNA and RNA contents in the cotyledons, but decreased protein content slightly. In contrast, the irradiation reduced the amounts of organic acids and soluble sugars, indicating that primary carbon metabolism was very sensitive to UV-B radiation. UV-B irradiation lowered the photosynthetic activity in the cotyledons without any effect on chlorophyll content and respiratory activity. These results indicate that UV-B radiation at the ambient level may act as a physiological stress in some UV-sensitive plants. 相似文献
4.
Seasonal changes in the pigments, carbohydrates and growth of red spruce as affected by ozone 总被引:9,自引:7,他引:2
R. G. ALSCHER R. G. AMUNDSON J. R. CUMMNG S. FELLOWS J. FINCHER G. RUBIN P. VAN LEUKEN L. H. WEINSTEIN 《The New phytologist》1989,113(2):211-223
Two-year-old red spruce seedlings were exposed to various levels ot ozone, from 0.4 to 3 times ambient levels, in open-top chambers in Ithaca, NY, USA. Exposures, which varied with changes in day length, commenced on May 30, 1987 and continued until December 14, 1987. Seedling biomass, carbohydrate contents, pigment contents, and rate of electron transport were assessed twice monthly during the fumigation period. Orthogonal quadratic or cubic polynomials were used to model the response through time each variable measured. A one-way analysis of variance model was fitted to every regression coefficient in each polynomial model to test for ozone effects on seasonal physiological patterns. Ozone did not influence growth, foliar pigment content, foliar starch content, root carbohydrate content, or rate of electron transport. The seasonal change of needle raffinose content differed between exposed to low (0.4 ×, 1×) and high (2×, 3×) ozone levels. There was also a trend towards reduced total soluble sugar content foliage during late autumn in higher ozone treatments. 相似文献
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7.
The combined effects of ultraviolet-B (UV-B, 280–320 nm) radiation and water stress were investigated on the water relations of greenhouse grown soybean [ Glycine max (L.) Merr. cv. Essex]. On a weighted (Caldwell 1971), total daily dose basis, plants received either 0 or 3 000 effective J m2 UV-BBE supplied by filtered FS-40 sunlamps. The latter dose simulated the solar UV-B radiation anticipated at College Park, Maryland, U.S.A. (39°N latitude) in the event that the global stratospheric ozone column is reduced by 25%. Plants were either well-watered or preconditioned by drought stress cycles. Diurnal measurements of water potential and stomatal conductance were made on the youngest fully expanded leaf. Various internal water relations parameters were determined for detached leaves. Plants were monitored before, during and after water stress. There were no significant differences in leaf water potential or stomatal conductance between treatments before plants were preconditioned to water stress. However, drought stress resulted in significantly lower midday and afternoon leaf water potentials and lower leaf conductances as compared to well-watered plants. UV-B radiation had no additional effect on leaf water potential; however, UV did result in lower leaf conductances in plants preconditioned to water stress. Turgid weight:dry weight ratio, elastic modulus, bound water and relative water content were unaffected by UV-B radiation. Osmotic potentials at full and zero turgor were significantly lower in the drought stressed treatments as compared to well-watered plants. 相似文献
8.
Alan H. Teramura Mark C. Perry John Lydon Marla S. McIntosh Edwin G. Summers 《Physiologia plantarum》1984,60(4):484-492
Soybean { Glycine max (L.) Merr. ev. Essex} was grown from seed in a greenhouse under ultraviolet-B (UV-B, 280–320 nm) radiation supplied by filtered FS-40 sunlamps. On a weighted, total daily dose basis these plants received either 0 (control) or 2875 effective J m−2 day−1 UV-BBE . When weighted with the generalized plant action spectrum (Caldwell 1971), this simulated the solar ultraviolet-B irradiance expected to occur at College Park, Maryland, USA (39°N) in the event the global stratospheric ozone column is reduced by 23%. The effects of ultraviolet radiation on the photosynthetic recovery from water stress were measured with an infrared gas analyzer. These effects were examined in plants which were either well-watered or previously preconditioned to water stress, during two distinct phenological stages of development. During the early stages of soybean growth, enhanced levels of UV-B reduced net photosynthesis by 25%, and water stress also reduced photosynthesis to nearly the same extent (by 20%). The combination of these two stresses resulted in smaller biomass than that produced by plants exposed to either stress independently. Photosynthesis in older, larger plants was much more sensitive to water stress and was reduced by as much as 50–60% in non-preconditioned plants. Although non-irradiated, non-preconditioned (control) plants recovered to only within 60% of their prestressed value, preconditioned plants recovered to within 70–80% during the 3 day recovery period. Both water stress and UV-B radiation affected non-stomatal conductance, while stomatal conductance was primarily affected by water stress. 相似文献
9.
Jacqueline Jollès Ellen M. Prager Emad S. Alnemri Pierre Jollès Ibrahim M. Ibrahimi Allan C. Wilson 《Journal of molecular evolution》1990,30(4):370-382
Summary Complete amino acid sequences are presented for lysozymesc from camel and goat stomachs and compared to sequences of other lysozymesc. Tree analysis suggests that the rate of amino acid replacement went up as soon as lysozyme was recruited for the stomach function in early ruminants. The two lysozymes from goat stomach are the products of a gene duplication that probably took place before the divergence of cow, goat, and deer about 25 million years ago. Partial sequences of three lysozymes from goat tears indicated that (a) the goat tear family of lysozymes may have diverged from the stomach lysozyme family by an ancient duplication and (b) later duplications are probably responsible for the multiple forms of tear and milk lysozymes in ruminants. 相似文献
10.
EDU and ozone protection: Foliar glycerolipids and steryl lipids in snapbean exposed to O3 总被引:1,自引:0,他引:1
Effects of the antiozonant EDU, N-[2-(2-oxo-1-imidazolidinyl) ethyl]-N'-phenylurea, on the content and composition of foliar lipids in snapbean ( Phaseolus vulgaris L. cv. Bush Blue Lake 290) before and after a single, acute ozone (O3 ) exposure were assessed. Pretreatment with EDU conferred protection against O3 -induced necrosis and losses of glycerolipids and chlorophyll. Systemic treatment of snapbean plants with EDU did not significantly alter membrane lipids in the first trifoliate leaf. Leaves of untreated controls had lost ca 50% of both galacto- (GL) and phospholipids (PL) by the end of a 3 h exposure to 0.4 μl l−1 O3 . A decline in the ratio of mono- to di-galactosyldiacylglycerol (MGDG/DGDG) was associated with the loss of GL, and a decline in the ratio of linoleic to linolenic acid (18:2/18:3) was associated with the loss of PL in untreated controls. EDU-treated plants showed no significant loss of foliar GL and PL. The MGDG/DGDG ratio declined only slightly, and the 18:2/18:3 ratio in PL increased during O3 exposure of EDU-treated seedlings. The level of total membrane sterols, including free sterols (FS), acylated steryl glycosides (ASG) and steryl glycosides (SG), did not change during O3 exposure of either treated or untreated plants. However, in the controls the proportions of ASG and SG increased at the expense of FS, and the ratio of stigmasterol/sitolsterol increased in FS and SG. In EDU-treated plants, a relatively small increase in SG was offset by a decrease in FS, and there was no change in the stigmasterol/sitosterol ratio in ASG, SG or FS. The results indicate that EDU may confer tolerance to O3 through induction of enzyme systems involved in the elimination of activated oxygen species and free radicals. 相似文献