| The red:far-red ratio (R:FR) of solar radiation is modified from that of ambient by absorption of red (R) and reflection and transmission of far-red (FR) radiation within plant canopies and it is capable of modulating a suite of architectural plaid responses described as the shade avoidance syndrome. However, both the expression and ecological significance of shade avoidance has been inconsistently expressed in perennial grasses. A series of four field experiments were conducted in an experimental garden to resolve these inconsistencies and to more effectively wale the responses of perennial grasses to the R:FR from individual plants to canopies and communities.; Shade avoidance in Schizachyrium scoparium was inconsistently expressed in plants of different ages and phenological stages was not affected by photon fluence rate or son volume, indicating that resource availability did not modulate shade avoidance. Ramet initiation in six dominant C 4 perennial grasses, two from three distinct communities along a productivity gradient, was reduced only in the shortgrass Buchloe dactyloides, indicating that these perennial grasses may be less responsive to low R:FR or that they nay require more specific conditions to respond. Ramet number plant-1 in two perennial grasses known to express contrasting shade avoidance responses was lower when grown with a low diffuse R:FR compared to ambient, bid not when a low diffuse R:FR was coupled with deep shade suggesting that diffuse and direct R:FR may function as primary and secondary signals to modulate shaft avoidance in perennial grasses. However, in deep shaft, juvenile ramet initiation was lower in diffuse+direct low R:FR compared to diffuse+shade low R:FR in Paspalum dilatatum, but not in S. scoparium, indicating the occurrence of substantial interspecific variation. Evaluation of the diffuse R:FR In short, mid, and tallgrass canopies indicated that it was closely related to canopy attenuation of photon fluence rate, as has been demonstrated for the attenuation of direct radiation. Consequently, the unique effects of direct and diffuse R:FR in canopies of varying densities and recognition of considerable interspecific variation in response to low R:FR reconcile many of the inconsistent expressions of shade avoidance in perennial grasses. |
