Climate models predict that future average temperatures in the northeastern USA will increase by 2.9-5.3°C by the end of this century, accompanied by a 12%-30% increase in winter precipitation and a 0-15% increase in summer precipitation. To examine how two congeneric invasive weeds, Carduus nutans and C. acanthoides, respond to these potential climate changes, we conducted a two-cohort climate manipulation experiment in Pennsylvania. We achieved a 1.5°C average daily temperature increase by using Open Top Chambers (OTCs), and a 30% increase in winter precipitation and a 15% increase in summer precipitation by using passive precipitation collectors.
Results/Conclusions
Our results show that both species advanced their phenology (bolting, flowering, and seed setting) and grew significantly taller (an increase of 12 cm for both species) in warmer conditions. However, while C. nutans responded to warming in terms of increased fall seedling emergence (an increase of 30%), enhanced early rosette growth (an increase of 8%), higher winter survival (an increase of 8%), and larger flower head production (an increase of 44%), C. acanthoides showed no response except for a lower fall seedling emergence (a decrease of 23%). Water effect was not significant except that winter precipitation addition delayed bolting in C. acanthoides. No significant interaction between warming and water addition was observed in our results. Given the positive response of C. nutans, its spread is likely to be accelerated in the future. Our work suggests that differences in species life history traits may lead to divergent responses to climate change, which should be considered in future management of biological invasions.
