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Barley, ryegrass, and fodder radish were grown in flowing nutrientsolutions at four potassium concentrations, [Ke+], from 0.05to 4 mg I1. During the first 2 weeks after germinationthe response to [Ke+] (fodder radish > barley > ryegrass)depended on the potential relative growth rate, the ratio ofroot surface area to plant weight, and on the K+ flux into theroots. Subsequently, there was no effect of [Ke+] on growthrate within the range tested. The K+ flux decreased from 423? 1012 mol cm2 s1 in the first 2 weeksafter germination, when it was concentration-dependent, to 25? 1012 mol cm2 s1 after 45 weeks,when it became independent of [Ke+] down to 0.05 mg 11.The results explain the importance of high [Ke+] and rapid rootgrowth during the first 2 weeks after seed germination. 相似文献
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The typical multi‐host life cycle of many parasites, although conferring several advantages, presents the parasites with a highly hazardous transmission route. As a consequence, parasites have evolved various adaptations increasing their chances of transmission between the different hosts of the life cycle. Some trematode species like the opecoelid Coitocaecum parvum have adopted a more drastic alternative strategy whereby the definitive host is facultatively dropped from the cycle, resulting in a shorter, hence easier to complete, life cycle. Like other species capable of abbreviating their life cycle, C. parvum does so through progenetic development within its intermediate host. Laboratory‐reared C. parvum can modulate their developmental strategy inside the second intermediate host according to current transmission opportunities, though this ability is not apparent in natural C. parvum populations. Here we show that this difference is likely due to the time C. parvum individuals spend in their intermediate hosts in the natural environment. Although transmission opportunities, i.e. chemical cues of the presence of definitive hosts, promoted the adoption of a truncated life cycle in the early stages of infection, individuals that remained in their amphipod host for a relatively long time had a similar probability of adopting progenesis and the abbreviated cycle, regardless of the presence or absence of chemical cues from the predator definitive host. These results support the developmental time hypothesis which states that parasites capable of facultative life cycle abbreviation should eventually adopt progenesis regardless of transmission opportunities, and provide further evidence of the adaptive plasticity of parasite transmission strategies. 相似文献
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The Uptake of Nitrate by Lolium perenne from Flowing Nutrient Solution: I. EFFECT OF CONCENTRATION 总被引:1,自引:0,他引:1
Experiments with simulated swards of perennial ryegrass (Loliumperenne L.) show the relationship between concentration in flowing nutrient solution, nitrate uptake,plant growth, and the chemical composition of roots and shoots.Rates of uptake exceeding 1 g N m2 d1 were maintainedat concentrations in solution down to 002 mg N l1. Short-term studies confirmed that at such lowconcentrations the plants were able to maintain rates of uptakeof about 85% of maximum. Between 02 and 200 mg N l1the concentration of in solution had little effect on rate of uptake or plant growth. With at 1000 and 2000 mg N l1 there was a marked reductionin weight of the shoots and, more particularly, in the lengthand tensile strength of the roots. There were several significanttrends in mineral composition of the plants (notably in S, Ca,Mg) which were apparently correlated with increasing concentrationof in solution. 相似文献
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COLETTE L. HEALD MICHAEL J. WILKINSON† RUSSELL K. MONSON†‡ CLEMENT A. ALO§ GUILING WANG§ ALEX GUENTHER¶ 《Global Change Biology》2009,15(5):1127-1140
We explore the potential role of atmospheric carbon dioxide (CO2) on isoprene emissions using a global coupled land–atmosphere model [Community Atmospheric Model–Community Land Model (CAM–CLM)] for recent (year 2000, 365 ppm CO2) and future (year 2100, 717 ppm CO2) conditions. We incorporate an empirical model of observed isoprene emissions response to both ambient CO2 concentrations in the long‐term growth environment and short‐term changes in intercellular CO2 concentrations into the MEGAN biogenic emission model embedded within the CLM. Accounting for CO2 inhibition has little impact on predictions of present‐day global isoprene emission (increase from 508 to 523 Tg C yr?1). However, the large increases in future isoprene emissions typically predicted in models, which are due to a projected warmer climate, are entirely offset by including the CO2 effects. Projected global isoprene emissions in 2100 drop from 696 to 479 Tg C yr?1 when this effect is included, maintaining future isoprene sources at levels similar to present day. The isoprene emission response to CO2 is dominated by the long‐term growth environment effect, with modulations of 10% or less due to the variability in intercellular CO2 concentration. As a result, perturbations to isoprene emissions associated with changes in ambient CO2 are largely aseasonal, with little diurnal variability. Future isoprene emissions increase by more than a factor of two in 2100 (to 1242 Tg C yr?1) when projected changes in vegetation distribution and leaf area density are included. Changing land cover and the role of nutrient limitation on CO2 fertilization therefore remain the largest source of uncertainty in isoprene emission prediction. Although future projections suggest a compensatory balance between the effects of temperature and CO2 on isoprene emission, the enhancement of isoprene emission due to lower ambient CO2 concentrations did not compensate for the effect of cooler temperatures over the last 400 thousand years of the geologic record (including the Last Glacial Maximum). 相似文献
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A revision of the genus Halectinosoma (Harpacticoida: Ectinosomatidae): a reappraisal of H. sarsi (Boeck) and related species 总被引:1,自引:0,他引:1
Ectinosomatid material was examined from extensive collections around the British Isles and from several additional world localities and museum collections, permitting a revision of the genus Halectinosoma. This paper describes 12 morphologically similar species and erects five new species. H. sarsi (Boeck) is regarded as species incertae sedis, while H. sarsi sensu Sars (1904) is redescribed as H. pseudosarsi sp. nov.; H. sarsi sensu T. & A. Scott (1894) is synonymized with H. canaliculatum (Por). H. propinquum is regarded as a junior subjective synonym of H. chrystalli (T. Scott). H. clavatum (Sars) is resurrected, having previously been regarded as a synonym of H. brunneum (Brady). A key for the identification of females belonging to this group of species is provided. 相似文献
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MIKE L. GRANT ERIC J. CLEMENT fls 《Botanical journal of the Linnean Society. Linnean Society of London》2004,146(4):447-451
Arguments in favour of using Nothofagus alpina (Poepp. & Endl.) Oerst. (Fagaceae) rather than N. procera Oerst. or N. nervosa (Phil.) Krasser as the correct name for rauli are presented. We also refute suggestions that N. alpina is based on hybrid material. The hybrid of N. alpina with N. obliqua (Mirb.) Blume is formally described as N . × dodecaphleps Mike L. Grant & E. J. Clement and a key to the deciduous taxa of Nothofagus is provided. © 2004 The Linnean Society of London, Botanical Journal of the Linnean Society , 2004, 146 , 447–451. 相似文献
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