Aims Weed communities in rape fields have changed with occurrence of extreme weather events and global warming. Our objective was to investigate the effects of different regimes of temperature change on rape (Brassica napus ‘Qinyou-10’) and eight companion weeds, i.e. Descurainia sophia, Euphorbia helioscopia, Avena fatua, Polypogon fugax, Veronica didyma, Alopecurus aequalis, Chenopodium glaucum and Amaranthus retroflexus, to help with predicting the succession of companion weed communities under extreme temperatures.
Methods Seed germination, seedling growth and several physiological properties were investigated under five temperature treatments (10 °C/5 °C, 18 °C /10 °C, 25 °C /20 °C, 35 °C /30 °C and 40 °C /35 °C) (day/night) controlled by a climate-control growth chamber. Physiological properties tested included contents of malondialdehyde (MDA), soluble sugar and soluble protein, and activities of superoxide dismutase (SOD) and peroxidase (POD).
Important findings There were significant differences among the weed species in response to temperature change. The optimal temperatures for seed germination in Alopecurus aequalis, Chenopodium glaucum and Amaranthus retroflexus were high; for instance, the highest seed germination rate (91%) occurred at temperature of 40 °C /35 °C in Amaranthus retroflexus. In contrast, seed germination in Descurainia sophia, Euphorbia helioscopia, Avena fatua, Polypogon fugax and Veronica didyma required a much lower optimal temperature (i.e. 10–18 °C). At the highest treatment temperature (40 °C /35 °C), Amaranthus retroflexus seedlings grew vigorously, and their MDA contents were much lower than under low temperature treatment of 10 °C /5 °C. Moreover, the concentrations of soluble sugar and soluble protein and the activities of SOD and POD in Amaranthus retroflexus seedlings all increased with temperature, indicating the strong ability of this weed species in adapting to high temperature stress. Chenopodium glaucum had the similar responses as Amaranthus retroflexus in those properties to changes in temperature. Therefore, these two weeds should be paid more attention with the increasingly intensified global warming. Contrarily, at the lowest treatment temperature of 10 °C/5 °C, seed germination reached 100%, and the seedlings exhibited high soluble sugar and soluble protein concentrations as well as high SOD and POD activities in Avena fatua. Descurainia sophia had the similar responses as Avena fatua. Therefore, we should take additional measures to prevent malignant growth of Avena fatua and Descurainia sophia in cold years. Rape (‘Qinyou-10’) had stable and high seed germination rate, and grew well as seedlings, indicating that it better adapted to temperature changes compared to the eight companion weeds. We deduced ‘Qinyou-10’ is a rape species that can adapt well to temperature changes.