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SIMPSON RR 《Texas reports on biology and medicine》1952,10(3):660-673
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The macroinvertebrate fauna of an acid-stressed headwater stream system in the Adirondack Mountains, New York 总被引:1,自引:0,他引:1
SUMMARY.
- 1 The Silver Run system in the Adirondack Mountains of New York includes three first-order streams with very different pH regimes: one moderately acidic (pH 5.8-7.2), the others much more so (pH generally 4.4-5.0)
- 2 The less acidic (acidophilic) site yielded a relatively diverse, well balanced fauna, with at least 10% each of midges, mayflies, stoneflies and elmid beetles. Ephemerella funcralis (Ephemeroptera) and Oulimnius latiusculus (Coleoptera) were dominant in this community. They appear to be among the most acid-tolerant species of their respective families and may become abundant under moderately acidic conditions. Their absence or low abundance in the more acidic tributaries of the Silver Run system suggests that they arc eliminated as acidification intensifies, These species therefore may he useful indicators of advancing acidification.
- 3 The more acidic (acidobiontic) communities contained fewer Hum half as many taxa as the acidophilic communities, contained few elmid beetles or mayflies, and were heavily dominated In stoneflies. Leuctra feiruinea and Isopecrla sp. were dominant, comprising.56-86% of the individuals. Other common constituents included black flies (Simuliumn gouldingi and S. venustum) and the caddisfly Rhyacvphila fuscula.
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ABSTRACT. The detailed behavioural mechanisms underlying an instance of compensation for changes in dietary nutrients are described for the first time in an insect. Nymphs of Locusta migratoria L. were given one of four artificial diets on the third day of the fifth instar, and their feeding patterns recorded in detail for 12 h. The diets represented combinations of two protein and two digestible carbohydrate levels (28% and 14% dry weight) presented in an otherwise complete nutrient mix. At the nutrient levels used, locusts regulated their intake of food with respect to protein but not digestible carbohydrate in the diet. They ate more of the lower protein diets by eating the same sized meals more frequently than insects fed on the higher protein diets. Compensation was not complete over the 12 h observation period: insects on the lower-protein diets ingested and absorbed 72% as much nitrogen as those insects fed on the higher-protein diets. Possible physiological mechanisms underlying the behavioural mechanisms are discussed. 相似文献
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Effects of Drought on Partitioning of Nitrogen in Two Wheat Varieties Differing in Drought-tolerance 总被引:2,自引:0,他引:2
NICOLAS MARC E.; SIMPSON RICHARD J.; LAMBERS HANS; DALLING MICHAEL J. 《Annals of botany》1985,55(5):743-754
A model was constructed to describe the translocation and partitioningof nitrogen on the seventh day after anthesis for well-wateredand droughted plants of two wheat varieties (Triticum aestivumL. cv. Warigal and Condor). The glasshouse-grown plants weredetillered so that a simplified model could be derived for themain stem. A 9-d drought treatment was imposed just after anthesisand this coincided with the period of endosperm cell divisionin the grains. Warigal, which had a higher grain yield thanCondor under drought, absorbed up to 15-times more nitrogenand translocated 1.5-fold more nitrogen to the shoot via thexylem. In both varieties, nitrogen redistributed from vegetativeorgans accounted for more than 60 per cent in control and 70per cent in droughted plants of the nitrogen needed for eargrowth. The net loss of nitrogen increased by 4-3 per cent inthe leaves, but decreased by 60 per cent in the stem under drought.Stem and roots appeared to play an important role in the nitrogeneconomy of droughted plants: less nitrogen was translocateddirectly to the grains from the senescing leaves and 4060per cent more nitrogen was translocated to the roots. Nearlyall the nitrogen reaching the roots in the phloem was reloadedinto the xylem stream and translocated back to the shoot. Thetransfer of nitrogen through the stem was reduced under droughtand this resulted in a constant C:N ratio of the grains whichmay be important in the regulation of endosperm cell division. Triticum aestivum L., wheat, drought, nitrogen, senescence, translocation 相似文献
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Changes in nitrogenase activity (C2H2 reduction and H2 production),nodulated root respiration and the efficiency of nitrogenasefunctioning were measured in response to progressive dehydrationof nodules on intact well-watered plants of subterranean clover(Trifolium subterraneum L.) cv. Seaton Park. The nodulated rootsof vegetative plants grown to the 14-leaf stage were incubatedin a gas exchange system through which a continuous dry airstreamwas passed over an 8 d period. The root tips were immersed inan N-free nutrient solution during this time so that water andion uptake was unimpeded. The decline in nodulated root respirationresulting from nodule drying was associated with a continualreduction in respiration coupled to nitrogenase activity. Asnodule water potential (nod) decreased, the proportion of totalnodulated root respiration which was nitrogenase-linked declinedfrom 50% (day 1) to 33% (day 8). This was accompanied by a 79%reduction in specific nitrogenase activity (from 3.79 to 0.81umol C2H4 g1 nodule dry weight min1). Nodule dehydrationalso induced a decline in hydrogen (H2) production in air. Therelative decline in hydrogen production exceeded that of acetylenereduction activity and this resulted in an increase in the relativeefficiency of nitrogenase functioning. However, the carbon costof nitrogenase activity progressively increased above 2.0 molCO2 respired per mol C2H4 reduced as rood decreased below 0.4to 0.5 MPa. Consecutive measurements of the rates ofhydrogen evolution, 15N2 fixation and acetylene reduction activityon intact unstressed plants resulted in a C2H4/N2 conversionfactor of 4.08 and an electron balance of 1.08. These resultsindicated that the pre-decline rate of acetylene reduction activitymeasured in a flow-through system provided a valid measure ofthe total electron flux through nitrogenase. Key words: Subterranean clover, dehydration, efficiency, nitrogenase activity 相似文献
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Fructan exohydrolase from grasses 总被引:8,自引:6,他引:2
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Ouabain-insensitive salt and water movements in duck red cells. II. Norepinephrine stimulation of sodium plus potassium cotransport 总被引:11,自引:9,他引:2 下载免费PDF全文
Catecholamines induce net salt and water movements in duck red cells incubated in isotonic solutions. The rate of this response is approximately three times greater than a comparable effect observed in 400 mosmol hypertonic solutions in the absence of hormone (W.F. Schmidt and T. J. McManus. 1977 a.J. Gen. Physiol. 70:59-79. Otherwise, these two systems share a great many similarities. In both cases, net water and salt movements have a marked dependence on external cation concentrations, are sensitive to furosemide and insensitive to ouabain, and allow the substitution of rubidium for external potassium. In the presence of ouabain, but the absence of external potassium (or rubidium), a furosemide-sensitive net extrusion of sodium against a large electrochemical gradient can be demonstrated. When norepinephrine-treated cells are incubated with ouabain and sufficient external sodium, the furosemide-sensitive, unidirectional influxes of both sodium and rubidium are half- maximally saturated at similar rubidium concentrations; with saturating external rubidium, the same fluxes are half-maximal at comparable levels of external sodium. In the absence of sodium, a catecholamine-stimulated, furosemide-sensitive influx of rubidium persists. In the absence of rubidium, a similar but smaller component of sodium influx can be seen. We interpret these results in terms of a cotransport model for sodium plus potassium which is activated by hypertonicity or norepinephrine. When either ion is absent from the incubation medium, the system promotes an exchange-diffusion type of movement of the co-ion into the cells. In the absence of external potassium, net movement of potassium out of the cell leads to a coupled extrusion of sodium against its electrochemical gradient. 相似文献