Effects of global environmental changes on weeds.

Abstract The global environment is projected to change significantly by the end of the 21st century, mainly as a result of intensifying human activities. Important environmental changes include rising carbon dioxide (CO 2 ) in the atmosphere, higher global average temperatures and altered precipitation patterns. As we strive to feed the rapidly increasing human population, it is of socioeconomic and ecological significance to understand the effects of environmental changes on the serious weeds that cause significant crop losses. This paper reviews the responses of 12 of the world's most serious agricultural weeds in response to global environmental changes. The weeds include species of a variety of growth forms as well as C 3 and C 4 photosynthetic pathways. In addition, we used meta-analytical techniques to synthesize the effects of elevated CO 2 on total biomass production for six of the most studied weeds. Our review found non-uniform biomass and reproductive responses to global changes among weeds. Consequently, the injuriousness of weeds to crops is likely to increase in some weeds, e.g., Chenopodium album , but decrease in others, e.g., Sorghum halepense . Because many of these agricultural weeds are also found in non-agricultural habitats, their differential responses to global changes will bear implications on community structure and species interactions in future natural ecosystems.