Does resource availability modulate shade avoidance responses to the ratioof red to far-red irradiation? An assessment of radiation quantity and soil volume

We conducted two experiments to investigate the expression of shade avoidan ce in response to low ratios of red to far-red irradiation (R:FR) in the C- 4 perennial grass Schizachyrium scoparium at two levels of above-ground (ph otosynthetic photon flux density (PFD) 400-700 nm) and below-ground (soil v olume) resource availability and in plants of two ages. Young plants showed greater sheath and ramet height in response to low R:FR and old plants sho wed reduced ramet initiation in experiments one and two, respectively, but both responses were not expressed simultaneously in either group. Growth of all ramet variables, including ramet initiation, was suppressed in small a s opposed to large soil volumes. By contrast, architectural variables, but not ramet initiation, were greater for plants grown in low as opposed to am bient PFD. However, expression of shade avoidance to low R:FR was not signi ficantly affected by either level of PFD or soil volume. We must conclude t hat the levels of resource availability provided do not modulate shade avoi dance in this perennial grass. These results demonstrate that S. scoparium is capable of expressing shade avoidance in response to low R:FR, but incon sistent juvenile ramet initiation and architectural responses in plants of different ages and phenological stages of development indicate that the sha de avoidance response might not be expressed consistently throughout the li fe of plants.