Abstract
This study investigated the influence of elevated CO2 on three perennial weed species (Achillea millefolium, Leontodon autumnalis and Rumex acetosa) and seven annual species (Chenopodium album, Matricaria matricarioides, Poa annua, Polygoniini persicaria, Senecio vulgaris, Spergula arvensis and Stellaria media). The study was carried out during the period 3 May to 5 August in ten field chamber units of 9 m2 in a cool (12.6°C) maritime climate under long days (15.8–18.1 h day‐1) on the south‐west coast of Norway (59° N, 6° E). Dry weights of the seven annual species were not significantly affected by the CO2 concentration. Of the three perennial species, L. autumnalis increased in dry weight by 27% and A. millefolium by 19% at elevated compared with ambient CO2 concentration. Plant height increased by 8% in L. autumnalis and decreased by 12 and 10% in M. matricarioides and P. annua respectively. Leaf size increased by 32% and specific leaf area decreased by 23% in P. persicaria at elevated CO2, while the other species were unaffected. The results are discussed in relation to competition between species and the influence of climate on the CO2 responses.
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