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71.
The effects of root feeding by larvae of Sitona hispidulus (F.) (a common weevil pest of white clover) on the rate of transfer of nitrogen between plants of white clover (Trifolium repens L.) and perennial ryegrass (Lolium perenne L.) were investigated using a nutrient slant board technique. Clover plants, labelled with 15N were grown adjacent to ryegrass plants and were either infested with Sitona larvae or not infested. Ryegrass plants associated with the infested clover plants had a significantly higher dry matter yield and nitrogen content (75% and 74% respectively) than the uninvested plants, after 33 days exposure to insect herbivory. It was concluded that root feeding insects could play an important role in the cycling of nitrogen in grass/clover swards. 相似文献
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MOORE DH LASFARGUES EY MURRAY MR HAAGENSEN CD POLLARD EC 《The Journal of biophysical and biochemical cytology》1959,5(1):85-92
Biophysical procedures have been used to determine the size and structure of the biologically active agent responsible for the transmission, through milk, of mouse mammary adenocarcinoma. Filtration of milk from RIII high-breast-cancer mice through gradocol membranes with decreasing pore sizes indicated that a minimum of activity passed through intermediate pore sizes (100 to 160 mmicro). Filtrates through smaller pores were significantly active. Milk treated with small doses of deuteron irradiation produced more tumors than the control, unirradiated milk; larger doses indicated a particle size much less than 100 mmicro. Free diffusion experiments indicated that the activity was associated with particles of two different sizes. Altogether the data denoted the presence of a large agent about 100 mmicro in diameter and a small agent 20 to 30 mmicro in diameter or possibly smaller. Furthermore, the presence in the milk of an inhibitor 40 to 60 mmicro is indicated by the results of all three approaches. The complex nature of the milk agent disclosed by the physical measurements agrees with the picture of one of the structures revealed by electron microscopy as well as with seemingly conflicting measurements reported in the literature. The large agent defined by these indirect methods corresponds to the whole particle seen in the electron microscope and the small agent corresponds to its internal core or nucleoid. It is suggested that the nucleoid is essentially a nucleic acid which may, in the absence of the "inhibitor," retain its activity after being stripped of its outer membrane or sac. 相似文献
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Changes in Growth and Quality Characteristics of Lucerne (Medicago sativa L.) in Response to Sulphur Dioxide Exposure under Field Conditions 总被引:2,自引:0,他引:2
The effects of SO2 on some growth and quality characteristicsof lucerne (Medicago sativa L.) were investigated by exposingplants to mean SO2 concentrations of 215, 78 or 2.8 µgm3 in open-top chambers for 166 d. Plants exposed to215 µg m3 had significantly lower shoot and rootweights compared with plants exposed to 78 µg m3,but not compared with control plants. Exposure to 215 or 78µg m 3 increased the plant shoot: root ratio, buthad no effect on leaf area. During the middle of the fumigationperiod, relative growth rate and net assimilation rate werehighest in plants exposed to 215 fig m, but these later fellbelow control values, and plants exposed to 78 µg m3had the highest relative growth rate and net assimilation rate.As the duration of exposure increased, an initial SO2-inducedstimulation of growth may have developed to toxicity at thehighest SO2 exposure. Exposure to SO2 depressed L-ascorbic acid concentrations inleaves, had no effect on foliar protein or starch concentrations,and increased the specific energy of shoots and plant sulphurconcentrations. The effect of SO2 on L-ascorbic acid concentrationsmay suggest a mechanism for reduced freezing tolerance of plantsafter exposure to SO2. Key words: SO2, Medicago sativa L., Growth 相似文献
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PEPTIDES OF THE HYPOTHALAMUS 总被引:1,自引:1,他引:0
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Double sampling to assess the accuracy of ground‐based surveys of tree hollows in eucalypt woodlands
Ground‐based surveys of tree hollows often give poor estimates of hollow abundance in forests. Woodlands have shorter trees and a more open structure than forests, which may make hollows easier to detect. Therefore, one would expect ground‐based surveys of tree hollows to be more accurate in woodlands than in forests. We compared hollow counts from ground‐based and climbing surveys (double sampling) for four species of Eucalyptus trees in woodlands of central‐western New South Wales, Australia: E. camaldulensis Dehnh, E. melliodora A. Cunn. ex Schauer, E. microcarpa Maiden and E. populnea F. Muell. ssp. bimbil L.A.S. Johnson & K.D. Hill and E. melliodora A. Cunn. ex Schauer. Overall, 83% of hollow‐bearing trees and 93% of trees without hollows were correctly classified by ground‐based surveys. Mean difference in hollow counts of ground‐based surveys to climbed surveys was 1.7 hollows ± 0.2 SE (all species combined) with 91% of ground‐based hollow counts being within five of the actual number of hollows. The error in ground‐based counts of hollows in E. microcarpa was larger than for the other three species. Errors in all species resulted from both overestimation and underestimation of hollow abundance by ground‐based surveys. A larger error was associated with the detection of hollows located in branches compared with hollows located in the main trunk(s). Total number of hollows in the tree (based on climbing surveys), crown area or maximum trunk diameter were significant predictors of ground‐based survey accuracy. Overall, the accuracy associated with ground surveys was relatively high and generally error rates were lower than those published for forests. 相似文献