Shading Effects on Growth and Partitioning of Plant Biomass in Cogongrass (Imperata cylindrica) from Shaded and Exposed Habitats

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Abstract
The growth responses of cogongrass [Imperata cylindrica (L.) Beauv.] were studied in a controlled-environment greenhouse with a day/night temperature of 29/23 C, under full available light and 56 and 11% of full light. The cogongrass plants were grown from stem and rhizome propagules originating from an interstate highway median, a pecan [Carya illinoensis (Wangenh.) K. Koch] plantation, and a pine (Pinus spp.) forest. After 89 days, the plants from all three populations produced, on average, three times as much total dry weight and leaf area in full available sunlight as in 56% full light and 20 times as much as in 11% full light. The distribution of plant biomass into rhizomes decreased with shading, whereas the distribution into leaves increased. The distribution of leaf biomass as leaf area also increased with shading, with the result that the plants grown in 11% full light had leaf area ratios about 2.5 times greater than those grown in full light. Reductions in dry matter production with shading were due to significant reductions in both net assimilation rate and leaf area duration or total amount of leaf area present. The plants from the shaded and exposed habitats generally did not differ significantly in their responses to shading. Thus, there is little evidence for the presence of sun and shade ecotypes in the populations of cogongrass studied.