THE INFLUENCE OF THE RADIATION ENVIRONMENT AROUND THE NODE ON MORPHOGENESIS AND GROWTH OF WHITE CLOVER (TRIFOLIUM-REPENS)

The growth of clonally propagated clover plants (Trifolium repens) in the glasshouse was compared with their growth under canopies of Tropaeolum peregonium with or without supplementation from red light emitting diodes (LEDs) directed at the youngest node bearing a fully expanded leaf. The T. peregonium was grown over a net support so that its roots did not meet those of the clover. A similar experiment was set up in a permanent grassland using canopy shade from various grass species (Holcus lanatus, Lolium perenne and Agrostis stolonifera) with and without supplementation. The LEDs increased the ratio of red to far red radiation (R/FR) received by the treated node with no apparent increase in photosynthetically active radiation (PAR) during the day. The morphogenetic effects of canopy shading (notably fewer branched nodes and less well-developed branches) were largely removed by supplementation so that the supplemented plants came to resemble those grown in full daylight, particularly in the glasshouse experiments. The results highlight the importance of the radiation environment at the base of the canopy in the morphogenetic responses of plants to putative competition, and the data are consistent with the hypothesis that responses are communicated acropetally along the stolon.