Submitted to: Weed Science
Publication Type: Peer reviewed journal
Publication Acceptance Date: 7/1/2003
Publication Date: 11/1/2003
Citation: Ziska, L.H. 2003. Evaluation of yield loss in field-grown sorghum from a c3 and c4 weed as a function of increasing atmospheric carbon dioxide. Weed Science. 51:914-918. Interpretive Summary: Since the start of the industrial revolution, humans have poured a lot of carbon dioxide (CO2) in the atmosphere. In addition to being the principle greenhouse gas, CO2 is also the source of carbon for photosynthesis, and giving plants more CO2 makes them grow more. However, not all plants are "good", some plants are undesirable. We call these plants weeds. In farmers fields both desirable (crops) and undesirable plants (weeds) grow together. In this experiment, I set out to address a simple question: "As CO2 increases, will weeds respond more or will crops respond more?" This study showed that weeds responded more, and as a consequence crop losses associated with weedy competition increased in response to rising atmospheric carbon dioxide. This information is of obvious interest to growers, extension agents and companies which manufacture herbicides.
Technical Abstract: Dwarf sorghum (cv, "Martin") was grown at ambient and at elevated levels of atmospheric carbon dioxide (250 ppm above ambient) with and without the presence of a C3 weed (Velvetleaf) and a C4 weed (redroot pigweed), in order to quantify the potential impact of rising atmospheric carbon dioxide concentration [CO2] on weed/crop interactions and potential crop loss. In a weed-free environment, elevated [CO2] resulted in increased leaf weight and leaf area of sorghum, but no significant effect on seed yield or total above ground biomass relative to the ambient CO2 condition. At ambient [CO2] the presence of velvetleaf had no significant effect on either sorghum yield or biomass; however, at elevated CO2, yield and biomass losses were significant, (-16 and -14%, respectively relative to the elevated, weed-free control). The additional loss in sorghum yield and biomass was associated with a significant (~3x) increase in velvetleaf biomass in response to elevated [CO2]. The presence of pigweed at ambient CO2 resulted in significant losses in total above ground biomass but not seed yield of sorghum. However, at elevated levels of [CO2], significant losses in both sorghum yield and biomass were observed for the sorghum/pigweed comparison. The increase in [CO2] was associated with a slight (+25%), but non-significant increase in pigweed biomass. These results demonstrate a greater yield loss in a widely grown C4 crop from weedy competition at projected, elevated levels of CO2, and suggests the need to include weed/crop interactions in future projections of crop productivity in response to increased atmospheric CO2.