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181.
Abstract The chemical compositions of a number of halophytes from salt marshes on Ynys Môn (Anglesey), Wales, and of some related mesophytes and sand dune plants have been determined. Analyses of the inorganic ions broadly confirmed the existence of a characteristic chemical composition of many monoco-tyledonous salt-marsh plants in that they contain high levels of potassium and relatively low levels of sodium. In contrast to most dicotyledonous halophytes, especially members of the Chenopodiacease, the monocots restrict the entry of inorganic ions and use high levels of soluble sugars to maintain an adequate solute potential. Low calcium levels were not found to be a feature of these plants, as was previously reported. The large amounts of sugars found in the monocotyle-donous plants suggested that they must be located mainly in the vacuoles, in contrast to glycinebetaine which is thought to accumulate principally in the cytoplasm of the salt accumulating Chenopodiaceae. The monocotyledonous halophytes which accumulate proline differ from the normal monocotyledonous physiotype in the accumulation of larger quantities of sodium. Triglochin maritima is one species of this type, and Puccinellia maritima a less extreme example. Spartina spp. accumulating glycinebetaine and β-dimethyl-sulphoniopropionate also have unusually high inorganic ion contents for monocots. Several salt marsh plants contained large quantities of amino acids other than proline. As with ionic composition, the nature of the organic solutes broadly followed taxonomic lines. The usefulness of the physiotype concept is discussed. 相似文献
182.
B. A. OSBORNE 《Plant, cell & environment》1994,17(2):143-152
Photon requirements for O2-evolution in red (λ=680nm) light (Фr) were measured for six C3 species, one C3-like, C3–C4 intermediate species, and three C4 species, including examples of NADP-malic enzyme and PEP-carboxykinase C4 sub-groups. Variation in Фr within the C3 species was small with a mean value of 7.96 ±0.12 mol photon mol−1 O2, whereas the mean value for the C4 species was 12.27± 1.53 mol photon mol−1 O2, with the lowest value, 9.24 ±0.13 mol photon mol−1 O2, for the PEP-carboxykinase C4 species Spartina townsendii. The C3–C4 intermediate species Panicum milioides had a value of 9.05 ±0.29 mol photon mol−1 O2, approximately 1 mol photon mol−1 O2 greater than the C3 species. The possibility that this extra cost is due to PEP-carboxylase-dependent recycling of CO2 is discussed. No correlation was found between Фr and chlorophyll content or leaf absorptance. Based on white (ФW) and red light measurements of the photon requirement, values in red light were approximately 20% higher than white-light estimates. These results are discussed with reference to accepted mechanisms of energy transduction in thylakoid membranes (Z-scheme), expected inefficiencies and losses during light-harvesting and electron transport reactions, and the influence of respiratory processes. 相似文献
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白沙蒿粘液瘦果萌发中聚糖内切水解酶的活动特性
黄振英4* Daphne J.OSBORNE 2 相似文献
187.
Invertebrate diet of the Houbara Bustard Chlamydotis [undulata] macqueenii in Abu Dhabi from calibrated faecal analysis 总被引:1,自引:0,他引:1
The ecology of the Houbara Bustard Chlamydotis [undulata] macqueenii is poorly known and populations are declining due to hunting and habitat loss. As wintering populations in Abu Dhabi may be limited by habitat and food, we studied the diet using calibrated faecal analysis. Prey were categorized into 16 groups and fed to captive birds under controlled conditions. We calculated the recovery rates of prey following digestion and identified consistent fragments for each group. Wild Houbara Bustard faeces were collected and examined for key fragments, and initial prey intake was calibrated. Plant remains were identified and their contribution was estimated. Fewer than 28% faeces contained >50% plant material by volume and only 12% contained 95% or more. Numerically, the most important prey were: ants (64%), large nocturnal tenebrionids (14.5%), small climbing tenebrionids (12%) and diurnal tenebrionids. However, the Tenebrionidae contributed 97% of the animal biomass. The relative proportions of prey in the diet were similar to relative abundance as assessed by pitfall trapping. Estimates of the energetic value of the prey suggested that on average Houbara Bustards must consume around 670 desert invertebrates/day to meet energy needs. The effort required to catch these prey may vary at least ten-fold seasonally. On average plants could provide a further 6.4–14% energy but more work is needed on this. Whether Houbara Bustards wintering in Abu Dhabi are prey-limited depends on prey densities and renewal rates which remain unknown. 相似文献
188.
The representation of root processes in models addressing the responses of
vegetation to global change 总被引:5,自引:0,他引:5
The representation of root activity in models is here confined to considerations of applications assessing the impacts of changes in climate or atmospheric [CO2 ]. Approaches to modelling roots can be classified into four major types: models in which roots are not considered, models in which there is an interplay between only selected above-ground and below-ground processes, models in which growth allocation to all parts of the plants depends on the availability and matching of the capture of external resources, and models with explicit treatments of root growth, architecture and resource capture. All models seem effective in describing the major root activities of water and nutrient uptake, because these processes are highly correlated, particularly at large scales and with slow or equilibrium dynamics. Allocation models can be effective in providing a deeper, perhaps contrary, understanding of the dynamic underpinning to observations made only above ground. The complex and explicit treatment of roots can be achieved only in small-scale highly studied systems because of the requirements for many initialized variables to run the models. 相似文献
189.
JENNIFER CUNNIFF COLIN P. OSBORNE BRAD S. RIPLEY† MICHAEL CHARLES‡ GLYNIS JONES‡ 《Global Change Biology》2008,14(3):576-587
The synchronous origin of agriculture in at least four independent climatic regions at the end of the last glacial period (c10 kyr bp ) points to a global limitation for crop domestication. One hypothesis proposes that a rapid carbon dioxide (CO2) increase from 18 Pa to ~27 Pa during deglaciation caused significant increases in the growth rates of wild crop progenitors, thereby removing a productivity barrier to their successful domestication. However, early C4 crops present a challenge to this hypothesis, because they were among the first domesticates, but have a carbon‐concentrating mechanism that offsets the limitation of photosynthesis by CO2. We investigated the CO2‐limitation hypothesis using the wild progenitors of five C4 founder crops from four independent centres of domestication. Plants were grown in controlled environment chambers at glacial (18 Pa), postglacial (28 Pa) and current ambient (38 Pa) CO2 levels, and photosynthesis, transpiration and biomass were measured. An increase in CO2 from glacial to postglacial levels caused a significant gain in vegetative biomass of up to 40%, but the equivalent rise in CO2 from postglacial to modern levels generally had no effect on biomass. Investigation into the underlying mechanisms showed C4 photosynthesis to be limited more by glacial than postglacial CO2 levels, matching theoretical expectations. Moreover, the increase in CO2 from glacial to postglacial levels caused a reduction in the transpiration rate via decreases in stomatal conductance of ~35%. In combination, these physiological changes conferred a large improvement in water‐use efficiency at the postglacial CO2 partial pressure compared with the glacial level. Our data, therefore, provide experimental support for the CO2‐limitation hypothesis, suggesting that these key physiological changes could have greatly enhanced the productivity of wild crop progenitors after deglaciation. 相似文献
190.