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1.
A psychrotrophic toxin-producing strain of Aeromonas hydrophila grew well in a range of food slurries (scallop, prawn, fish, chicken liver paté, liverwurst, chicken luncheon slice and commercial baby food preparations) held at refrigeration temperatures. In most foods, excluding the baby food preparations, exotoxins were produced at levels comparable with production in bacteriological broth without apparent food spoilage (all but prawn and fish). Addition of ultra-heat treated (UHT) milk to toxin-containing broth culture supernatants markedly decreased or removed haemolytic and cytotoxic activities, explaining low levels of toxins found in milk in a previous study. Baby food preparations did not inactivate exotoxins under similar conditions suggesting production of toxins rather than their inactivation was inhibited in these foods. 相似文献
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Royd Vinya Yadvinder Malhi Joshua B. Fisher Nick Brown Timothy J. Brodribb Luiz E. Aragao 《Oecologia》2013,173(3):711-720
Although precipitation plays a central role in structuring Africa’s miombo woodlands, remarkably little is known about plant-water relations in this seasonally dry tropical forest. Therefore, in this study, we investigated xylem vulnerability to cavitation for nine principal tree species of miombo woodlands, which differ in habitat preference and leaf phenology. We measured cavitation vulnerability (Ψ50), stem-area specific hydraulic conductivity (K S), leaf specific conductivity (K L), seasonal variation in predawn water potential (ΨPD) and xylem anatomical properties [mean vessel diameter, mean hydraulic diameter, mean hydraulic diameter accounting for 95 % flow, and maximum vessel length (V L)]. Results show that tree species with a narrow habitat range (mesic specialists) were more vulnerable to cavitation than species with a wide habitat range (generalists). Ψ50 for mesic specialists ranged between ?1.5 and ?2.2 MPa and that for generalists between ?2.5 and ?3.6 MPa. While mesic specialists exhibited the lowest seasonal variation in ΨPD, generalists displayed significant seasonal variations in ΨPD suggesting that the two miombo habitat groups differ in their rooting depth. We observed a strong trade-off between K S and Ψ50 suggesting that tree hydraulic architecture is one of the decisive factors setting ecological boundaries for principal miombo species. While vessel diameters correlated weakly (P > 0.05) with Ψ50, V L was positively and significantly correlated with Ψ50. ΨPD was significantly correlated with Ψ50 further reinforcing the conclusion that tree hydraulic architecture plays a significant role in species’ habitat preference in miombo woodlands. 相似文献
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Angiosperm and conifer tree species respond differently when exposed to elevated CO2, with angiosperms found to dynamically reduce water loss while conifers appear insensitive. Such distinct responses are likely to affect competition between these tree groups as atmospheric CO2 concentration rises. Seeking the mechanism behind this globally important phenomenon we targeted the Ca2+-dependent signalling pathway, a mediator of stomatal closure in response to elevated CO2, as a possible explanation for the differentiation of stomatal behaviours. Sampling across the diversity of vascular plants including lycophytes, ferns, gymnosperms and angiosperms we show that only angiosperms possess the stomatal behaviour and prerequisite genetic coding, linked to Ca2+-dependent stomatal signalling. We conclude that the evolution of Ca2+-dependent stomatal signalling gives angiosperms adaptive benefits in terms of highly efficient water use, but that stomatal sensitivity to high CO2 may penalise angiosperm productivity relative to other plant groups in the current era of soaring atmospheric CO2. 相似文献
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The photosynthetic drought physiology of a diverse group of southern hemisphere conifer species is correlated with minimum seasonal rainfall 总被引:5,自引:0,他引:5
1. The instantaneous and integrated leaf gas exchange of 13 species of southern hemisphere conifers grown under identical glasshouse conditions were examined to determine whether there was any correlation between the characteristics of water use at the leaf level and environmental water availability.
2. In the conifer species examined, the minimum ratio of internal to ambient CO2 measured in leaves during artificially imposed drought [( c i / c a )min ] was strongly correlated with the minimum rainfall observed within the natural range of each species. This suggests that the distributions of these species are constrained by the drought tolerance of their photosynthetic apparatus.
3. A good correlation was found between the ratio of internal to ambient CO2 measured in leaves under optimal conditions ( c i / c a )max and leaf δ13 C (and hence inferred ∫[ c i / c a ]). Neither of these, however, correlated with the environmental parameters considered most likely to be limiting species distribution, i.e. precipitation and altitude.
4. These data suggest that decreasing water availability may have been the major factor responsible for the restriction and extinction of conifers in the southern hemisphere. 相似文献
2. In the conifer species examined, the minimum ratio of internal to ambient CO
3. A good correlation was found between the ratio of internal to ambient CO
4. These data suggest that decreasing water availability may have been the major factor responsible for the restriction and extinction of conifers in the southern hemisphere. 相似文献
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Hydraulic design of leaves: insights from rehydration kinetics 总被引:2,自引:0,他引:2
We examined the leaf hydraulic design in 10 species based on their rehydration kinetics. In all cases, a biphasic response described the temporal pattern of water uptake, with time constants of approximately 30 to 800 s and approximately 800 to 8000 s. The time constants of the fast phase were significantly shorter in the six angiosperms (30 to 110 s) compared with the two single-veined conifer species (>400 s) examined, while the two multi-veined gymnosperm species, Gnetum gnemon and Ginkgo biloba, had time constants for the fast phase of approximately 150 s. Among angiosperm species, the fast phase constituted 50-90% of the total water absorbed, whereas in gymnosperms 70-90% of the water uptake could be assigned to the slow phase. In the four gymnosperms, the relative water uptake corresponding to the fast phase matched to a good degree the relative volume of the venation and bundle sheath extension; whereas in the angiosperm species, the relatively larger water influx during the fast phase was similar in relative volume to the combined venation, bundle sheath extension, epidermis and (in four species) the spongy mesophyll. This suggests a general trend from a design in which the epidermis is weakly connected to the veins (all four gymnosperms), to a design with good hydraulic connection between epidermis and veins that largely bypasses the mesophyll (four of six angiosperms), to a design in which almost the entire leaf appears to function as a single pool. 相似文献
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Although leaf size is one of the most responsive plant traits to environmental change, the functional benefits of large versus small leaves remain unclear. We hypothesized that modification of leaf size within species resulting from differences in irradiance can allow leaves to acclimate to different photosynthetic or evaporative conditions while maintaining an efficient balance between hydraulic supply (vein density) and evaporative demand. To test this, we compared the function and anatomy of leaf hydraulic systems in the leaves of a woody angiosperm (Toona ciliata M. Roem.) grown under high and low irradiance in controlled conditions. Our results confirm that in this species, differential leaf expansion regulates the density of veins and stomata such that leaf hydraulic conductance and stomatal conductance remain proportional. A broader sample of field-grown tree species suggested that differences in leaf venation and stomatal traits induced by sun and shade were not regulated by leaf size in all cases. Our results, however, suggest that leaf size plasticity can provide an efficient way for plants to acclimate hydraulic and stomatal conductances to the contrasting evaporative conditions of sun and shade. 相似文献
9.
Stomatal valves on the leaves of vascular plants not only prevent desiccation but also dynamically regulate water loss to maintain efficient daytime water use. This latter process involves sophisticated active control of stomatal aperture that may be absent from early-branching plant clades. To test this hypothesis, we compare the stomatal response to light intensity in 13 species of ferns and lycophytes with a diverse sample of seed plants to determine whether the capacity to optimise water use is an ancestral or derived feature of stomatal physiology. We found that in seed plants, the ratio of photosynthesis to water use remained high and constant at different light intensities, but fern and lycophyte stomata were incapable of sustaining homeostatic water use efficiency. We conclude that efficient water use in early seed plants provided them with a competitive advantage that contributed to the decline of fern and lycophyte dominated-ecosystems in the late Paleozoic. 相似文献
10.
Stem water transport and freeze-thaw xylem embolism in conifers and angiosperms in a Tasmanian treeline heath 总被引:3,自引:0,他引:3
The effect of freezing on stem xylem hydraulic conductivity and leaf chlorophyll a fluorescence was measured in 12 tree and shrub species from a treeline heath in Tasmania, Australia. Reduction in stem hydraulic conductivity after a single freeze-thaw cycle was minimal in conifers and the vessel-less angiosperm species Tasmannia lanceolata (Winteraceae), whereas mean loss of conductivity in vessel-forming angiosperms fell in the range 17-83%. A positive linear relationship was observed between percentage loss of hydraulic conductivity by freeze-thaw and the average conduit diameter across all 12 species. This supports the hypothesis that large-diameter vascular conduits have a greater likelihood of freeze-thaw cavitation because larger bubbles are produced, which are more likely to expand under tension. Leaf frost tolerances, as measured by a 50% loss of maximum PSII quantum yield, varied from -6 to -13°C, indicating that these species were more frost-sensitive than plants from northern hemisphere temperate forest and treeline communities. There was no evidence of a relationship between frost tolerance of leaves and the resilience of stem water transport to freezing, suggesting that low temperature survival and the resistance of stem water transport to freezing are independently evolving traits. The results of this study bear on the ecological importance of stem freezing in the southern hemisphere treeline zones. 相似文献