Rising CO 2 can alter fodder–weed interactions and suppression of Parthenium hysterophorus

Summary Three C 4 grass ( Setaria incrassata , Astrebla squarrosa and Bothriochloa decipiens ) and one C 3 legume ( Clitoria ternatea ) suppressive fodder species, were re‐evaluated against the growth of the C 3 Parthenium hysterophorus under an ambient (390 μmol mol −1 ) and an elevated atmospheric CO 2 concentration (550 μmol mol −1 ). Under the elevated atmospheric CO 2 , shoot dry biomass and suppression index ( SI ) value of the C 4 S. incrassata were both reduced by 32% and 0.7 respectively, while those for A. squarrosa were reduced by 23% and 0.3. In contrast and under the same elevated atmospheric CO 2 concentration, the shoot dry biomass and SI of the C 4 B .  decipiens were increased by 8% and 0.1 respectively, while those for the C 3 C. ternatea were increased by 38% and 0.8. Our results suggest that C 3 fodder plants along with certain C 4 species could be utilised for the effective management of P .  hysterophorus under the future elevated atmospheric CO 2 conditions. However, this system needs more fodder species to be investigated. Our results suggest that rising CO 2 per se may alter the efficacy of suppressive fodder management of an invasive C 3 species, P .  hysterophorus .