Showing papers on "Shading published in 1974"

The effects of shading and defoliation on nodulation and nitrogen fixation by white clover

Abstract: In a glasshouse experiment, single plants of ten-weeks old white clover (Trifolium repens L.) were subjected to two levels of shading and two levels of defoliation. Nodulation and nitrogen fixation parameters were measured at six sequential harvest over four weeks. Changes in nodule number and hence nodule dry weight per plant were due to nodule decay, sloughing off and non-production and were closely related to losses in root dry weight. Severe defoliation caused degradation of leghaemoglobin, an effect which was seen in less than three days from treatment. It led also to a temporary but marked decrease in the nitrogen fixation capacity of the nodules as measured by the acetylene reduction assay. Recovery of normal activity by the nitrogenase system took about ten days. The effects of shading and defoliation on the pattern of nodulation have been described briefly.

Studies on the productivity of tropical pasture plants. V.* Effect of shading on growth, photosynthesis and respiration in two grasses and two legumes

Abstract: Two grasses and two legumes were grown at three illuminances: one grass and one legume in a growth cabinet (100, 50 and 34% relative illuminance) and one of each in a glasshouse (100, 30 and 10% relative illuminance). The response to shading was investigated by using classical growth analysis techniques, and the photosynthesis-respiration balance obtained by Watson and Hayashi's method. Shading caused a reduction in the proportion of root and a corresponding increase in the proportion of leaf, and an increase in the shoot/root ratio in all species except green panic. The relative growth rates of grasses (which were only clearly superior at the highest illuminance) were affected more by shading than were those of legumes, and the greater shading effect resulted from a greater decrease in net assimilation rate, and to a lesser extent, from a smaller compensatory increase in leaf area ratio in the grasses than in the legumes. The greater sensitivity of net assimilation rate of grasses to shading arose from a stronger dependence of the photosynthetic rate on illuminance. The significance of these findings for pasture production is discussed. Both tiller and runner production were dependent upon the total amount of radiant energy received by the plant, and in the growth cabinet, at least, were independent of its intensity, duration and sequence. ______________________ *Part IV, Aust. J. Agric. Res., 25: 415 (1974).

High resolution shading correction.

Abstract: Quantitative cytology requires accurate representation of a specimen's optical densities. As the requirements for measurement precision increase, instrument-induced errors become increasingly more difficult to reduce to the point at which their effect on experimental data is insignificant compared to the measured parameters. Shading induces a significant amount of amplitude ambiguity to data obtained from a scanning system. A method of shading correction on single pixels is introduced as a new way to reduce some errors that currently plague scanning systems.

Effects of shading of the leaf sheath on the growth and development of the tiller stems of kentucky bluegrass

Abstract: Two separate greenhouse experiments were conducted to measure the effects of shading of the leaf sheath on the growth and development of tiller stems of cultivars of Kentucky bluegrass (Poa pratensis L.). In the first experiment, four cultivars were grown as single plants and the initial stem was shielded, allowing the tip of the leaf blade to protrude slightly but retaining the sheath in darkness. As growth of the tiller proceeded, further shields were added in a similar fashion for a growth period of 234 days. The second experiment was similarly conducted but included nine cultivars representing a wide range of latitudinal origin. They were grown for a period of 188 days. All shielded stems were much longer than the unshaded stems and developed into long aerial rhizomes with vegetative rhizome-type buds with cataphylls, indicating the morphogenic effect of light on the leaf sheath and the apparent insensitivity of the leaf blade in this reaction. The growth of the stem and buds of the cultivars Windsor,...