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).

Effect of temperature on light utilization efficiency of leaves in C3 legumes and C4 grasses

“…Bull [1] has published similar data for C3 and C4 plants measured at 25-26°C. In addition, the mean relative growth rate of ten C4 grasses was double that of ten C3 legumes at both 20 and 30°C [7] under light limited conditions [8]. This suggests that the C4 grasses were not at a relative disadvantage at the lower temperature.…”

Effect of shading on growth and dinitrogen fixation of kudzu and tropical pasture legumes

“…Greenleaf and centro were not appreciably affected while that of siratro was significantly reduced by shading. The poor growth of siratro under reduced sunlight (Ludlow et al 1974) has also been reported. Although kudzu is mostly cultivated as a cover crop to suppress weeds, improve soil fertility under plantation trees, the response of kudzu to shading has not yet been elucidated.…”

Selection of full-sib families of Panicum maximum Jacq under low light conditions

“…Studies on P. maximum rooting indicate less RDM accumulation with light reduction (Ludlow et al, 1974;Eriksen & Witney, 1981;Jank et al, 2006). In the evaluation of 28 P. maximum genotypes, the decrease in DM in the light intensities of 50% and 70%, compared with full sun, was 41.5% and 70.3%, respectively (Jank et al, 2005).…”