Differential effects of light quality, provided by different grass neighbours, on the growth and morphology of Trifolium repens L. (white clover)

The ability to respond in a specific manner to different light conditions i mposed by different species of grass is a major factor contributing to whit e clover persistence in pastures. Caps in a pasture provide light with a hi gher red:far-red ratio (R:FR) and higher photosynthetic photon flux density (PPFD) than the Light filtered through neighbours. White clover (Trifolium repens L.) was grown under different light conditions in ways that tried t o simulate as closely as possible some of the light conditions experienced in a natural field situation, being partially shaded and receiving light re flected from neighbouring grasses. The objective was to determine specifica lly if the mere presence of neighbouring grasses could influence the growth and morphology of white clover individuals without physically contacting t hem, and thereby send a signal of impending competition. In the first exper iment, white clover was subjected to shading cast from three different gras s species. There were differences in both the quantity and quality of light received under the various grass canopies. The canopies reduced overall gr owth and branching of clones, while increasing the length of and biomass al location to petioles. Lolium perenne L. canopy shade had different effects compared to Holcus lanatus L, or Dactylis glomerata L., but between the lat ter two species, no differences were detected. In the second experiment, li ght reflected from grass neighbours was provided simultaneously with direct light There was a strong increase in FR and a resulting decrease in the R: FR due to neighbouring D. glomerata, but few consistent effects on white cl over growth and morphology; there was evidence of phototropic movement by t he leaves. We show that plants must experience partial shading, and not jus t reflected light, in order to alter their morphology in response to the pr esence of different species of grass neighbours.