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31.
The magnitude of previously reported pH changes at the surfaceof Chara corallina cells has been measured with specially constructedpH electrodes. An experimental system was designed to reducethe dissipation of pH gradients by convection. When cells areilluminated their surfaces become partitioned into alkalineregions (pH 8.59.5) with sharp peaks and acid regions(pH about 5.5) which are more uniform. In the dark these regionsrapidly disappear and the pH of the cell surface becomes uniform(about pH 6.0). With cells initially free of any deposits ofCaCO3, alkaline regions may appear temporarily, and may migratealong the cell surface. The presence of CaCO3 stabilizes theregions. It is proposed that alkalinization results from HCO3uptake, CO2 fixation, and subsequent localized OH- efflux. Alkalinizationis prevented by photosynthetic inhibitors. The nature and magnitude of the HCO3/OH- exchange processis discussed, and the possible role of H+ and OH- fluxes incontrolling the ionic and electrical properties of Characeancells is emphasized. 相似文献
32.
LUCAS BESSIRE 《American anthropologist》2009,111(1):101-103
ABSTRACT This report compares two recent media events centered on the iconography of Amazonian indigenous peoples to highlight the cultural activism of the collaborative video project, Video nas Aldeias. [Keywords: Amazonia, Video nas Aldeias, indigenous media, cultural activism] 相似文献
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MARTYN C. LUCAS DAMIAN H. BUBB MIN-HO JANG KYONG HA JEROME E. G. MASTERS 《Freshwater Biology》2009,54(3):621-634
1. Conservation of freshwater animal populations requires their access to, as well as sufficient availability of, critical habitats, such as those for reproduction. Abundant small-scale barriers may cause extensive fragmentation of freshwater habitat but, by comparison to larger structures their effects are rarely considered by catchment managers. The relationship between the distribution of, and access to, spawning habitat in a regulated river, characterized by abundant small barriers, was examined for river lamprey Lampetra fluviatilis , a threatened migratory fish.
2. Telemetry of adult lamprey in the River Derwent, North East England was used to quantify upriver migration and access to spawning habitat, together with surveys of spawning habitat availability and spawning activity between 2002 and 2007.
3. Access in to the Derwent appeared severely restricted by a tidal barrage, beyond which lamprey migrated rapidly in unobstructed reaches. Of all lamprey tagged in the lower 4 km of river, or ascending the barrage, 64% and 17% passed the first and second weirs respectively, with high flows crucial for this. Although over 98% of lamprey spawning habitat occurred more than 51 km upstream, on average just 1.8% of river lamprey spawners were recorded there.
4. In order to protect or rehabilitate species or species assemblages, greater attention needs to be paid to the relative spatial distribution of low-head barriers and the resultant availability of key habitats within individual catchments. This is particularly important given the renewed emphasis internationally on low-head hydropower solutions as a source of renewable energy, and the rapid growth in numbers of low-head barriers in many catchments. 相似文献
2. Telemetry of adult lamprey in the River Derwent, North East England was used to quantify upriver migration and access to spawning habitat, together with surveys of spawning habitat availability and spawning activity between 2002 and 2007.
3. Access in to the Derwent appeared severely restricted by a tidal barrage, beyond which lamprey migrated rapidly in unobstructed reaches. Of all lamprey tagged in the lower 4 km of river, or ascending the barrage, 64% and 17% passed the first and second weirs respectively, with high flows crucial for this. Although over 98% of lamprey spawning habitat occurred more than 51 km upstream, on average just 1.8% of river lamprey spawners were recorded there.
4. In order to protect or rehabilitate species or species assemblages, greater attention needs to be paid to the relative spatial distribution of low-head barriers and the resultant availability of key habitats within individual catchments. This is particularly important given the renewed emphasis internationally on low-head hydropower solutions as a source of renewable energy, and the rapid growth in numbers of low-head barriers in many catchments. 相似文献
34.
LUCAS A. CERNUSAK KLAUS WINTER & BENJAMIN L. TURNER 《Plant, cell & environment》2009,32(10):1441-1455
Water-use efficiency and stable isotope composition were studied in three tropical tree species. Seedlings of Tectona grandis , Swietenia macrophylla and Platymiscium pinnatum were grown at either high or low water supply, and with or without added fertilizer. These three species previously exhibited low, intermediate and high whole-plant water-use efficiency ( TE ) when grown at high water supply in unfertilized soil. Responses of TE to water and nutrient availability varied among species. The TE was calculated as experiment-long dry matter production divided by cumulative water use. Species-specific offsets were observed in relationships between TE and whole-plant 13 C discrimination (Δ13 Cp ). These offsets could be attributed to a breakdown in the relationship between Δ13 Cp and the ratio of intercellular to ambient CO2 partial pressures ( c i / c a ) in P. pinnatum , and to variation among species in the leaf-to-air vapour pressure difference ( v ). Thus, a plot of v · TE against c i / c a showed a general relationship among species. Relationships between δ 18 O of stem dry matter and stomatal conductance ranged from strongly negative for S. macrophylla to no relationship for T. grandis . Results suggest inter-specific variation among tropical tree species in relationships between stable isotope ratios ( δ 13 C and δ 18 O) and the gas exchange processes thought to affect them. 相似文献
35.
C. NOEMI MAZIA ENRIQUE J. CHANETON THOMAS KITZBERGER LUCAS A. GARIBALDI 《Austral ecology》2009,34(4):359-367
Abstract Predators are thought to play a key role in controlling herbivory, thus having positive indirect effects on plants. However, evidence for terrestrial trophic cascades is still fragmentary, perhaps due to variation in top‐down forces created by environmental heterogeneity. We examined the magnitude of predation effects on foliar damage by chewing insects and mean leaf size, by excluding birds from saplings in ‘dry’ and ‘wet’Nothofagus pumilio forests in the northern Patagonian Andes, Argentina. The experiment lasted 2 years encompassing a severe drought during the La Niña phase of a strong El Niño/Southern Oscillation event, which was followed by unusually high background folivory levels. Insect damage was consistently higher in wet than in dry forest saplings. In the drought year (1999), bird exclusion increased folivory rates in both forests but did not affect tree leaf size. In the ensuing season (2000), leaf damage was generally twice as high as in the drought year. As a result, bird exclusion not only increased the extent of folivory but also significantly decreased sapling leaf size. The latter effect was stronger in the wet forest, suggesting compensation of leaf area loss by dry forest saplings. Overall, the magnitude of predator indirect effects depended on the response variable measured. Insectivorous birds were more effective at reducing folivory than at facilitating leaf area growth. Our results indicate that bird‐initiated trophic cascades protect N. pumilio saplings from insect damage even during years with above‐normal herbivory, and also support the view that large‐scale climatic events influence the strength of trophic cascades. 相似文献
36.
THOMAS H. McGOVERN ORRI VÉSTEINSSON ADOLF FRIRIKSSON MIKE CHURCH IAN LAWSON IAN A. SIMPSON ARNI EINARSSON Y DUGMORE GORDON COOK SOPHIA PERDIKARIS KEVIN J. EDWARDS AMANDA M. THOMSON W. PAUL ADDERLEY ANTHONY NEWTON GAVIN LUCAS RAGNAR EDVARDSSON OSCAR ALDRED ELAINE DUNBAR 《American anthropologist》2007,109(1):27-51
Early settlement in the North Atlantic produced complex interactions of culture and nature. The sustained program of interdisciplinary collaboration is intended to focus on ninth- to 13th-century sites and landscapes in the highland interior lake basin of Mývatn in Iceland and to contribute a long-term perspective to larger issues of sustainable resource use, soil erosion, and the historical ecology of global change. 相似文献
37.
Photosynthetic assimilation of exogenous 14CO2 and H14CO3by the aquatic angiosperm Potamogeton lucens L. is reported.Equivalent maximum rates of assimilation (1.5 µmol s1m2) were obtained in the presence of saturating levelsof 14CO2 (1.0 mol m3, pH 5.3) or H14CO3 (1.5 molm3, pH, 9.2). Under subsaturating 14CO2 levels, bothgaseous diffusion and H14CO3 transport were shown tooperate simultaneously, such that maximal photosynthetic rateswere established. An induction lag of approximately 3 min was observed when exogenous14CO2 was assimilated. A longer lag of approximately 12 minwas required, however, before linear assimilation rates wereestablished when H14CO3 acted as the carbon source. The light-activatedH14CO3 transport system was found to be quite labile.A brief (5 min) dark treatment returned the system to the inactivestate. Bicarbonate transport was shown to be competitively inhibitedby CO32ions. The possibility is discussed that this formof inhibition may be common to many HCO3 assimilators. Preliminary polar cation transport studies (from lower to upperleaf surface) indicated an almost exact one to one relationshipbetween the rates of Na+ influx and efflux and H14CO3assimilation. The possible relationship(s) between these transportprocesses and the requirement for electrical neutrality is brieflydiscussed. 相似文献
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