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131.
The effect of food supplementation on the reproductive success of Black-billed Magpies Pica pica 总被引:1,自引:0,他引:1
The effect of supplementary food on the reproductive success of Black-billed Magpies Pica pica was studied in an urban habitat in the city of Edmonton, Alberta, Canada. We provided supplementary food (pelleted dog food) regularly from August 1986 to June 1988 in a feeder situated outside all known magpie territories. Magpies using the supplementary food showed (i) an advancement of 7 days in the initiation of laying, (ii) no increase in clutch-size, (iii) higher survival of nest contents (eggs and young) during a spring snow storm, (iv) an increase in rate of nestling weight gain, and (v) an increase in fledging success. Supplementary food did not prompt the fed pairs to select nest sites nearer the feeder in 1988 than in 1987. The feeder did not affect the breeding density because the nearest neighbour distances of fed magpies did not differ from unfed magpies in either year, nor did they differ between the two years for either fed or unfed magpies. This study provided evidence that magpies frequently renest even if their initial nests fail after the eggs hatch—a practice that has been reported to be absent or rare in other studies. Although brood reduction was equally frequent in the nests of food-supplemented and control pairs, the actual number of nestlings disappearing from the former (1.56 per nest) was significantly smaller than that from the latter (2.60 per nest), suggesting that the availability of food plays a major role in magpie reproductive success. 相似文献
132.
Inhibition of Nitrate Assimilation in Roots in the Presence of Ammonium: The Moderating Influence of Potassium 总被引:11,自引:1,他引:10
RUFTY THOMAS W. Jr; JACKSON WILLIAM A.; RAPER C. DAVID Jr. 《Journal of experimental botany》1982,33(6):1122-1137
Experiments were conducted to investigate the effect of concentrationof NH4+ in nutrient solution on root assimilation of NO3and to determine whether the NH4+NO3 interaction wasmodified in the presence of K+. Dark-grown, detopped corn seedlings(cv. Pioneer 3369A) were exposed for 8 h to 0.15 mM Ca(NO3)2and varying concentrations of (NH4)2SO4 in the absence or presenceof 0.15 mM K2SO4. The accelerated phase of NO3 uptakeappeared most sensitive to restriction by additions of 0.15mM (NH4)2SO4. In the absence of K+, the restriction increasedonly slightly even when solution (NH4)2SO4, was increased from0.15 mM to 12.5 mM which was accompanied by an increase of NH4+in the tissue from about 7.0 to 35 µmol g1 fr.wt. of root. Increasing concentrations of solution NH4+ progressivelyinhibited net K+ uptake. At the highest solution NH4+ concentrations,there was an initial net efflux of K+ and no net influx occurredduring the treatment period. The severity of the NH4)SO4 restrictionof NO3 uptake was moderated considerably in the presenceof K+ as long as a net influx of K+ occurred. However, net influxof K+ was not associated with alteration of NH4+ uptake, assimilation,or accumulation in the root tissue. The lack of correlationbetween the severity of restriction of NO3 uptake andendogenous NHJ suggested the restriction resulted from an effectexerted by exogenous NH4+ which tended to saturate at lowersolution NHJ concentrations or by inhibitory factors generatedduring assimilation of NH4+. Several mechanisms were postulatedto account for the moderating influence of K+. In all experiments,root NO3 reduction was restricted by the presence ofambient NH4+. The quantitative decreases in reduction tendedto be less than decreases in NO3 uptake and therefore,could result from inhibition solely of uptake with subsequentlimitation in availability of substrate for the reduction process,but the possibility of a direct effect on reduction could notbe excluded. 相似文献
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A comparison was made of energy metabolism of nodulated N2 fixing plants and non-nodulated NO3-fed plants of Lupinus albus L. Growth, N-increment, root respiration (O2 uptake and CO2 production) and the contribution of a SHAM-sensitive oxidative pathway (the alternative pathway) in root respiration were measured. Both growth rate and the rate of N-increment were the same in both series of plants. The rate of root respiration, both O2 uptake and CO2 production, and the activity of the SHAM-sensitive pathway were higher in NO3-fed plants than in N2 fixing plants. The rate of ATP production in oxidative phosphorylation was computed also to be higher in NO3-fed plants. It is concluded that both carbohydrate costings and ATP costings for synthesis + maintenance of root material were lower in N2 fixing than in NO3-fed plants. The respiratory quotient of root respiration was 1.6 in N2-fixing plants and 1.4 in NO3-fed plants. These values were slightly higher than the values calculated on the basis of CO2 output due to N-assimilation and the experimental values of O2 uptake, but showed the same trend: highest in N2 fixing plants. Root respiration of NO3-fed plants showed a diurnal pattern (both O2 uptake, CO2 production and the activity of the SHAM-sensitive pathway), whilst no diurnal variation in root respiration was found in N2 fixing plants. However, C2H2 reduction did show a diurnal rhythm, which is suggested to be related to the diurnal variation in transpiration. Addition of NO3 to N2 fixing plants increased the rate of root respiration and the activity of the alternative pathway. This treatment did not decrease C2H2 reduction and H2 evolution within 4 days. Withdrawal of NO3-supply from NO3-fed plants decreased the rate of root respiration but had no effect on the relative activity of the alternative pathway. It is suggested that the higher rate of root respiration and the higher activity of the SHAM-sensitive pathway in NO3-fed plants is due to a larger supply of carbohydrates to the roots, partly due to a better photosynthetic performance of the shoots and partly due to a higher capacity of the roots to attract carbohydrates. 相似文献
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Serial dilutions: Error effects and optimal designs 总被引:1,自引:0,他引:1
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