A superweed in the making: adaptations of Parthenium hysterophorus to a changing climate. A review

Parthenium weed (Parthenium hysterophorus L.) is a globally invasive plant with significant negative impacts on the environment, agriculture, economy, and health. This invasion problem is likely to be exacerbated by climate change. Elevated atmospheric carbon dioxide concentration ([CO₂]), high ambient temperatures, heatwaves, and droughts will facilitate the establishment, range expansion, and interference potential of this invasive species while making its management more difficult. Here, for the first time, we review the potential impact of climate change elements on parthenium weed biology and management at regional and global levels. We establish that (1) parthenium weed plants morphologically and physiologically adapt to sustain or promote their growth, fecundity, competitive ability, and allelopathic effect under most climate change scenarios; (2) climate change elements can reduce the relative vigor of neighboring plants, especially C4 grasses, in competition with parthenium weed, providing this invasive species a competitive edge; (3) elevated [CO₂] has the most pronounced positive effect on parthenium weed performance compared to other climate change elements; (4) the efficacy of a widely used herbicide, glyphosate, may be reduced on parthenium weed grown under elevated [CO₂]; (5) mixed effects have been reported for biological control agents, with some losing ground, while others are maintaining or improving their efficacy; and (6) a greater risk of spread and range expansion under sustained climate change will pose greater challenges for management in natural and managed ecosystems. There has been a disturbing transition of this weed from noncropped landscapes to agroecosystems in response to recent climatic and land use changes. All evidence presented in this review suggests that the situation will be greatly aggravated if drastic management interventions are not implemented. Therefore, the research, policy, and outreach focus must be revisited and revamped considering the impacts of climate change to develop pragmatic solutions to combat this “superweed”.