Potential changes in weed competitiveness in an agroecological system with elevated temperatures

Increases in temperature due to global climate changes could significantly impact weed competitiveness and crop–weed interactions. Factors contributing to the responsiveness of a plant species to increasing temperature include the inherent genetic limitations of the species and the ability to acquire water and nutritional resources. The purpose of this study was to examine the temperature responses of selected species from a model agronomic system in the Southeastern U.S.: soybean (Glycine max), sicklepod (Senna obtusifolia) and prickly sida (Sida spinosa). We also determined temperature effects on mycorrhizal colonization and development of the soybean N2-fixation system, two below-ground associations critical for resource acquisition. The species were grown at 42/37 (day/night), 36/31, 32/27, 28/23, or 23/18 °C for 30 days in a field soil with naturally low fertility. Growth of the weed species was maximized at a higher temperature than that for soybean, 36/31 °C versus 32/27 °C, probably reflecting different geographical origins. At the optimal temperature, weeds had higher root:shoot mass ratios (1.3–1.5 versus 0.9) than soybean, and greater mycorrhizal colonization. In soybean, nodule weights, numbers, and total nitrogenase activity were highest at the growth temperature optimum but decreased considerably at higher temperatures. The results collectively indicate that increases in aerial temperatures above ∼32 °C would enhance weed competitiveness. Increased interference with soybean growth and yields should be expected.