ISSN:0022-3646    

DOI:10.1111/j.0022-3646.1994.00161.x

出版商:Blackwell Science Inc    

年代:1994

数据来源: WILEY

摘要:

ABSTRACTThe comparative ecophysiology of nine culture isolates of the eulittoral red algaBostrychia radicans(Montagne) Montague collected at sites from seven states along the east coast of the U.S.A. was investigated. The growth response in relation to different salinity and light conditions as well as photosynthesis‐irradiance curves were studied. In addition, the effect of salt treatment on the content of the isomeric polyolsd‐sorbitol andd‐dulcitol was also studied. All isolates grew between salinities of 5.3 and 70 ppt but with quite different optima and maxima. The isolates were all adapted to low light levels, i.e. growth was already recorded at 2.5 μmol photons·m−2·s−1, and growth rates peaked between 40 and 60 μmol photons·m−2·s‐1. These low‐light requirements were also reflected by the photosynthesis‐irradiance curves: all plants had low light compensation points (2.5–9.7 μmol photons ·m−2·−1) and low photon fluence rates for initial saturation of photosynthesis (38.1–84.7 μmol photons·m−2·s−1, indicating that these isolates are “shade‐adapted.” Isolates from Florida and Georgia synthesized and accumulated both the osmolytesd‐sorbitol andd‐dulcitol in increasing salinities, whereas onlyd‐sorbitol was present in plants from North Carolina north to Connecticut.d‐sorbitol was always strongly involved in osmotic acclimation. In various isolates from the same location in South Carolina, both polyol patterns were found, i.e.d‐sorbitol plusd‐dulcitol andd‐sorbitol only. All data indicate thatB. radicansexhibits a broad salinity tolerance and a low‐light preference, which explain the successful colonization of this alga on various intertidal and shaded substrates. The data also clearly indicate intraspecific differences among the nine isolates, which is

ISSN:0022-3646    

DOI:10.1111/j.0022-3646.1994.00174.x

出版商:Blackwell Science Inc    

年代:1994

数据来源: WILEY

摘要:

ABSTRACTExperiments on a marine diatom,Thalassiosira pseudonana(Hustedt) clone 3H, demonstrate that under moderate photon flux densities (75 μmol quanta·m−2·s−1) of visible light the inhibition of photosynthesis by supplemental ultraviolet (UV) radiation (UV‐B: 280–320 nm) is well described as a hyperbolic function of UV‐B irradiance for time scales of 0.5–4 h. Results are consistent with predictions of a recently developed model of photosynthesis under the influence of UV and visible irradiance. Although net destruction of chlorophyll occurs during a 4‐h exposure to UV‐B, and the effect is a function of exposure, the principal effect of UV‐B is a decrease in chlorophyll‐specific photosynthetic rate. The dependence of photoinhibition on dosage rate, rather than cumulative dose, and the hyperbolic shape of the relationship are consistent with net photoinhibition being an equilibrium between damage and repair. The ratio of damage to repair is estimated by a mathematical analysis of the inhibition of photosynthesis during exposures to UV‐B. A nitrate‐limited culture was much more sensitive to UV‐B than were the nutrient‐replete cultures, but the kinetics of photoinhibition were similar. The analysis suggests that the nutrient‐limited culture was more sensitive than the nutrient‐replete cultures because repair or turnover of critical proteins associated with photosynthesis is inhibited. An inhibitor of chloroplast protein synthesis was used to suppress repair processes. Photoinhibition by UV‐B was enhanced, and inhibition was a function of cumulative dose, as would be expected if damage were not countered by repair. The fundamental importance of repair processes should be considered in the design of field experiments and models of UV‐B effects in the environment, especially in the context of vertical mixing. Repair processes must also be considered whenever biolog

ISSN:0022-3646    

DOI:10.1111/j.0022-3646.1994.00183.x

出版商:Blackwell Science Inc    

年代:1994

数据来源: WILEY

摘要:

ABSTRACTA circadian rhythm in growth was detected by computer‐aided image analysis in 3–4‐cm‐long, juvenile sporophytes of the kelp speciesPterygophora CaliforniaRupr. and in sevenLaminariaspp. InP. californica, the free‐running rhythm occurred in continuous white fluorescent light, had a period of 26 h at 10°or 15°C, and persisted for at least 2 weeks in white or blue light. The rhythm became insignificant in continuous green or red light after 3 cycles. Synchronization by white light‐dark regimes, e.g. by 16 h light per day, resulted in an entrained period of 24 h and in a shift of the circadian growth minimum into the middle of the light phase. A morning growth peak represented the decreasing portion of the circadian growth curve, and an evening peak the increasing portion. The circadian growth peak was not visible during the dark phase, because growth rate decreased immediately after the onset of darkness. At night, some growth still occurred at 16 or 12 h light per day, whereas growth stopped completely at 8 h light per day, as in continuous darkness. During 11 days of darkness, the thallus area became reduced by 3.5%, but growth rate recovered in subsequent light–dark cycles, and the circadian growth rhythm reappeared in subsequent c

ISSN:0022-3646    

DOI:10.1111/j.0022-3646.1994.00193.x

出版商:Blackwell Science Inc    

年代:1994

数据来源: WILEY

摘要:

ABSTRACTThe importance of annual recruitment to the structure of adult stands ofSargassumwas determined for a mixed speciesSargassumbed at Rottnest Island, Western Australia. The morphologically similar speciesSargassum spinuligerumSonder,S. distichumSonder, andS. podacanthumSonder grew together in the shallow subtidal (6 m). Positive species determinations were only possible when thalli were reproductive, so recruits, bases, and vegetative annuals for all species were grouped together. Densities of recruits, perennial bases, vegetative annuals, and reproductive annuals were determined at monthly intervals from 20 randomly placed 0.25‐m−2quadrats. Recruitment and mortality for recruits and adults were further determined at three monthly intervals from6‐×‐1‐m−2permanent quadrats.The density of adults varied little with season (between 32 and 58 m−2). Growth of annuals was initiated in April, thalli became reproductive by late August–early September, and senescence occurred in December–January. Density of recruits was highly variable (1.6–210 individuals‐m−2) and peaked seasonally during late summer (January–February) and then declined rapidly.Adults showed a complete turnover of thalli in the bed over 25–27 months. Adult mortality was compensated by annual recruitment from propagules (43%) and vegetative regeneration from fragments of holdfasts left on the reef (57%). A seasonal pattern in survivorship was observed for adults that grew from recruits with higher initial numbers and lower mortalities for August and November cohorts. Little seasonally was observed in survivorship of adults that grew vegetatively from remnant crusts. Although initial cohort sizes were smaller for adults grown from recruits than from remnant crusts, mortality was lower, resulting in similar contributions to adult density from both recruits and remnant crusts.Recruitment from propagules and vegetative regeneration played an important role in buffering the adult stand from high rates of mortality and reducing seasonal variation in adult density and contributed to the persistence and seasonal structure ofSarg

ISSN:0022-3646    

DOI:10.1111/j.0022-3646.1994.00200.x

出版商:Blackwell Science Inc    

年代:1994

数据来源: WILEY

摘要:

ABSTRACTThe Greater Yellowstone Area ecosystem experienced major wildfires in 1988, resulting in a substantial number of catchments being burned. We studied diatom assemblage structure at 14 sites over 5 years in catchments ranging from 0 to over 90% burned. Coefficients of variation for selected physical measures provided a good assessment of the degree of disturbance experienced by the various sites and correlated highly with percentage of catchment burned. Principal components analysis quantitatively estimated the degree of temporal change in diatom assemblages at a site. The more extensively burned catchments showed the greatest amount of structural change in diatom taxa among years.Navicula permitisHust. andNitzschia inconspicuaGrun. were predominant in the heavily disturbed systems, whereasAchnanthes minutissimaKuetz.,A. lanceolata(Breb.) Grun.,Rhoicosphenia curvata(Kuetz.) Grun.exRabh., andDiatoma hiemalevar.mesodon(Ehr.) Grun. were common in less disturbed streams. The results demonstrate that recovery trajectories of lotic diatom assemblages following major landscape‐scale disturbances are a function of disturbance intensity resulting from differences in catchment characteristic

ISSN:0022-3646    

DOI:10.1111/j.0022-3646.1994.00209.x

出版商:Blackwell Science Inc    

年代:1994

数据来源: WILEY

摘要:

ABSTRACTThree occurrences of the macroalgaPrasiola fluviatilis(Sommerf.) Aresch. were recorded after the examination of 32 stream segments from the Ellesmere Island National Park Reserve (81°23′ N) in the High Arctic of Canada. The collection sites were small (second‐third order) glacial melt streams characterized by pH 7.3–8.2, specific conductance of 52–159 μS·cm−1, low ion levels, extremely low nutrient levels, and the lack of other prominent macroalgae. These occurrences confirm the reported circumpolar distribution of

ISSN:0022-3646    

DOI:10.1111/j.0022-3646.1994.00217.x

出版商:Blackwell Science Inc    

年代:1994

数据来源: WILEY

摘要:

ABSTRACTNostoc cordubensisProsperi (Cyanophyta, Nostocaceae) is characterized by its mucilaginous colonies. Much of this mucilage is produced by heterocysts. By controlling growth conditions, heterocysts with and without mucilage were obtained. Mucilaginous heterocysts retained nitrogen‐fixing capability at high oxygen concentrations, whereas heterocysts lacking mucilage were unable to fix nitrogen at oxygen concentrations higher than 20%. Comparison of results obtained using tetrazolium salts as indicators of highly reduced zones showed similar result

ISSN:0022-3646    

DOI:10.1111/j.0022-3646.1994.00222.x

出版商:Blackwell Science Inc    

年代:1994

数据来源: WILEY

摘要:

ABSTRACTSessile colonies and motile hormogonia, the two main developmental stages in the life cycle of aNostocstrain isolated from the endocytobiosis withGeosiphon pyriforme(Kützing) F. v. Wettstein, were investigated for their photosynthetic competence. Large‐scale fractionation of the two stages is presented. Photosynthetic parameters were assessed by measurement of chlorophyll fluorescence and oxygen evolution. Hormogonia were as photosynthetically competent as the colonial stage. In addition, hormogonia showed an enhanced capability for nonradiative dissipation of absorbed light energy, a feature that might be important for their function as propagula. Data for the quantum yield of photosystem II of the isolatedNostocstrain were compared to the values determinedin situinG. pyriformeand indicated the possibility of a higher photosynthetic capacity of the endosymbiotic as compared to the isolated cyanobacteri

ISSN:0022-3646    

DOI:10.1111/j.0022-3646.1994.00225.x

出版商:Blackwell Science Inc    

年代:1994

数据来源: WILEY

摘要:

ABSTRACTTwo morphotypes ofEmiliania huxleyi(Lohmann 1902) Hay et al. 1967, types A and B, known to be unequally distributed in the oceans, were grown in dilution cultures at a range of photon flux densities (PFDs) (1.5–155 μmol photons·m−2·s−1) and two temperatures (10° and 15° C). Calcite carbon and organic carbon content of the cells as well as instantaneous growth rate, cell size, chlorophyll fluorescence, and light‐scatter properties clearly depended on growth conditions and differed considerably for the two morphotypes. The ratio between calcite carbon and organic carbon production showed an optimum of 0.65 inE. huxleyitype A cells at PFD=17.5. The ratio increased slightly with a temperature increase from 10° to 15°C but remained<1.0 at both temperatures in light‐limited cells. In contrast, calcite carbon production exceeded organic carbon production (ratio: 1.4–2.2) in phosphate‐deprived cultures.Emiliania huxleyitype B generally showed a higher calcite carbon/organic carbon ratio thanE. huxleyitype A, but the relation with PFD was similar.The content of calcite carbon and organic carbon as well as the instantaneous growth rate, cell size, chlorophyll fluorescence, and light‐scatter properties showed large diel variations that were closely related to the division cycle. Our results show the importance of mapping the structure of any sampled cell population with respect to the phase in the cell division cycle, as this largely determines the outcome of not only “per cell” measurements but also short time (less than 24 h) flux measurements. For instance, dark production of calcite byE. huxleyiwas negatively affected by cell division. Slowly growing (phosphate‐stressed) cultures produced calcite in the light and in the dark. In contrast, rapidly growing cultures at 10°C produced calcite only in the light, whereas in the dark there was a significant loss

ISSN:0022-3646    

DOI:10.1111/j.0022-3646.1994.00230.x

出版商:Blackwell Science Inc    

年代:1994

数据来源: WILEY