There has been a rapid increase in atmospheric CO₂ concentration, from pre-industrial values of 280 ppm to more than 400 ppm currently, and this is expected to double by the end of the 21^st century. Studies have shown that plants grown at elevated CO₂ concentrations have increased growth rates and invest more in carbon-based defences. This has important implications for the management of invasive alien plants, especially using biological control which is mostly dependent on herbivorous insects. The aim of this study was to investigate the effects of elevated atmospheric CO₂ on the biological control of four invasive aquatic weeds (Azolla filiculoides, Salvinia molesta, Pistia stratiotes and Myriophyllum aquaticum). These species are currently under successful control by their respective biological control agents (Stenopelmus rufinasus, Cyrtobagous salviniae, Neohydronomus affinis, and Lysathia sp.) in South Africa. The plant species were grown in a two factorial design experiment, where atmospheric CO₂ concentrations were set at ambient (400 ppm) or elevated (800 ppm), and plants were either subjected to or not subjected to herbivory by their target biological control agents. There was an overall increase in biomass production and C:N across all species at elevated CO₂, both in the absence and presence of biological control, although C:N of M. aquaticum and biomass of A. filiculoides with herbivory were not constant with this trend. Insect feeding damage was reduced by elevated CO₂, except for S. molesta. Thus, we can expect that plants will respond differently to CO₂ increase, but the general trend suggests that these species will become more challenging to manage through biological control in future.

目前已在大气CO的快速增加₂浓度，从为280ppm的工业革命前的值，以目前大于400ppm，这是预期到21的端部增加一倍^ST世纪。研究表明，以较高的CO ₂浓度生长的植物具有更高的生长速率，并在碳基防御方面投入了更多的资金。这对外来入侵植物的管理具有重要意义，特别是使用主要依赖食草昆虫的生物防治。这项研究的目的是调查大气中CO ₂浓度升高对四种入侵水生杂草（Azolla filiculoides，Salvinia molesta，Pistia stratiotes和水生的Myriophyllum aquaticum）。这些物种目前在南非受到其各自的生物防治剂（Snonopelmus rufinasus，Cyrtobagous salviniae，Neohydronomus affinis和Lysathia sp。）的成功控制。通过两因素设计实验来种植植物，其中将大气中的CO ₂浓度设置为环境（400 ppm）或升高（800 ppm），并且使植物接受或不接受其目标生物防治剂进行的除草。在不存在和存在生物防治的情况下，尽管没有水生分枝藻的C：N和水生生物的C：N，但在没有生物控制的情况下，CO ₂升高时所有物种的生物量生产和C：N总体增加。具有草食性的丝线虫在这种趋势中不是恒定的。除葡萄球菌外，CO ₂浓度升高降低了昆虫的摄食危害。因此，我们可以预期植物对CO _2的增加会有不同的反应，但是总体趋势表明，这些物种在未来通过生物控制的管理上将更具挑战性。