Impact of temperature and germination time on the success of a C4 weed in a C3 crop: Amaranthus retroflexus and spring barley

Summary

Elevation in temperatures due to climate change could promote the invasion by C4 weed species of arable fields in the boreal region, which are dominated by C3 crops. The success of Amaranthus retroflexus L. (a C4 weed) in spring barley (a C3 crop) was studied at current and elevated temperatures (3°C difference) in a greenhouse experiment in southern Finland. The competition treatments included no competition and four levels of competition with barley, differing in terms of germination time. The success of A. retroflexus was measured as growth (height and biomass) and seed production (number and biomass). Elevation in temperature enhanced seed production of A. retroflexus, but the impact on growth was minor (only difference in plant height in one treatment). The growth and seed production of A. retroflexus in competition with barley was minimal although the growth of barley decreased with the rise in temperature. The results indicate that climate change could improve growth of a C4 weed such as A. retroflexus, but it is unlikely to succeed in spring barley.