Impacts on Weeds

Abstract

Weeds compete with crops over nutrients, water, and light and can considerably reduce yields and crop quality. In some cases, weeds can pose human health problems (poisonous plants, allergens) or inhibit harvest. Elevated CO₂, changes in temperature, and precipitation patterns may affect weeds as much as crops. Higher CO₂ will stimulate photosynthesis and growth in C3 weeds and C3 crops and reduce transpiration and increase water-use efficiency in both C3 and C4 weeds and crops. Higher temperatures can possibly offset some of the benefits of elevated CO₂ for both weeds and crops. High temperatures sometimes limit reproductive development, and global warming may decrease reproductive output in such situations despite an increase in CO₂. It is unclear whether this is more likely to occur in C3 than C4 species, but if it were, it could alter weed community compositions and affect crop–weed interactions. This would imply that weed and crops both benefit or lose on the same scale. However, weeds are usually already very competitive due to greater genetic variation and physiological plasticity; otherwise, they would not cause yield losses. Hence, they may gain more advantages from climate change than crops.

In temperate regions, global warming will affect the growth and marginally affect phenology and influence the geographical distribution of weeds. Weed species of tropical and subtropical origins, currently restricted to the southern regions, may expand northward.