The effects of shade on growth, development, and resource allocation patterns of three species of foxtail (Setaria)

Three weedy foxtail species, Setaria glauca (L.) Beauv., S. verticillata (L.) Beauv., and S. viridis (L.) Beauv. occur in southwestern Ontario. Plants of the three species were grown in pure stands in the open and under one, two, or three layers of cheesecloth which transmitted 71, 40, and 19% of incident insolation, respectively. Six harvests were taken between July and September in which height, tiller number, dry weight of component parts, and leaf area were determined for randomly selected plants of each species. In unshaded conditions, S. verticillata was the tallest species and had the greatest total dry weight per plant. However, this species was the most adversely affected by shade, with significant reductions in tiller number, biomass production, and reproductive effort with increasing shade. Setaria viridis and S. verticillata exhibited a relative increase in allocation to leaves with increasing shade while S. glauca had a relative increase to stems, indicating different strategies in response to shade. The apparent lower tolerance of shade in S. verticillata may help to explain the comparative rarity of this species in southwestern Ontario.