Document: THO-3-29-15

Contrasting shade avoidance responses in two perennial grasses: A comparative field investigation in simulated sparse and dense canopies.

MONACO, T.A.* and D.D.BRISKE

Texas A&M University, College Station, Texas, U.S.A ¹

Abstract:
We designed an experiment with containerized plants grown outdoors to investigate the expression of shade avoidance in simulated sparse and dense canopies by two perennial grasses known to express contrasting responses to low red:far-red ratios (R:FR). Plants were grown in canopy microenvironments designed to lower R:FR by reflection of diffuse FR from neighbors and by direct attenuation of R by acetate filters located above plants. Two specific hypotheses were tested: (1) Paspalum dilatatum will express greater shade avoidance than Schizachyrium scoparium to the low in both sparse and dense canopies, and (2) low R:FR will produce greater expressions of shade avoidance in sparse than in dense canopies in both species. Plants of both species expressed significant shade avoidance to diffuse R:FR in sparse canopies including lower ramet number plant ^-1. However, neither species expressed shade avoidance to direct R:FR in dense canopies, with the exception of juvenile ramet initiation for P. dilatatum. Significant differences in blade length, juvenile ramet initiation, and juvenile ramet and plant shoot mass between species confirmed the occurrence of interspecific variation to low R:FR. Consequently, neither hypotheses was rejected. Variable species responses to the R:FR over a range of canopy densities suggests that specific attributes of the radiation signal or associated variables within the canopy microenvironment may be involved in modulating species responses to low R:FR under field conditions.

Keywords: grassland ecology, proximal signal, ramet demography, ramet regulation, R:FR, shade avoidance syndrome

This abstract is being presented at: 10:30 AM in session:
Poster Session #1: Light Relations.