The impact of elevated CO_2 on yield loss from a C_3 and C_4 weed in field-grown soybean

摘要

Soybean (Glycine max) was grown at ambient and enhanced carbon dioxide (CO_2, + 250 #mu#L L~-1 above ambient) with and without the presence of a C3 weed (lambsquarters, Chenopodium album L.) and a C4 weed (redroot pigweed, Amaranthus retroflexus L.), in order to evaluate the impact of rising atmospheric carbon dioxide concentration [CO_2] on crop production losses due to weeds. Weeds of a given species were sown at a density of two per metre of row. A significant reduction in soybean seed yield was observed with either weed species relative to the weed-free control at either [CO_2]. However, for lambsquarters the reduction in soybean seed yield relative to the weed-free condition increased from 28 to 39% as CO_2 increased, with a 65% increase in the average dry weight of lambsquarters at enhanced [CO_2]. Conversely,for pigweed, soybean seed yield losses diminished with increasing [CO_2] from 45 to 30%, with no change in the average dry weight of pigweed. In a weed-free environment, elevated [CO_2] resulted in a significant increase in vegetative dry weight and seed yield at maturity for soybean (33 and 24%, respectively) compared to the ambient CO_2 condition. Interestingly, the presence of either weed negated the ability of soybean to respond either vegetatively or reproductively to enhanced [CO_2]. Results from this experiment suggest: (i) that rising [CO_2] could alter current yield losses associated with competition from weeds; and (ii) that weed control will be crucial in realizing any potential increase in economic yield of agronomic crops such as soybean as atmospheric [CO_2] increases.