Responses of invasive plants from different families to warming and drought

Climate warming and drought often co-occur to form warm–dry climate patterns. However, systematic comparative studies of the responses of invasive plants from different families to their combined effects remain limited. We conducted a greenhouse experiment to investigate the interactive effects of warm (normal vs. warming) and drought (well-watered vs. drought) conditions on the growth, root traits, and competitive performance of 11 invasive plant species from three families (Amaranthaceae, Poaceae, and Asteraceae) growing in competition with native communities. Our results showed that warming did not significantly increase the total biomass of all invasive species combined but significantly promoted biomass accumulation in Poaceae and Asteraceae. Drought consistently reduced the biomass across all invasive species. Notably, a marginally significant interaction effect of warm and drought conditions on the biomass proportion of Amaranthaceae was detected. Specifically, under normal conditions, drought increased the biomass proportion of Amaranthaceae species, whereas under the warming treatment, drought decreased it. Furthermore, root traits of invasive species exhibited clear family level differentiation. Poaceae adopted an expansion strategy by increasing root length and root surface area under warming treatment, Amaranthaceae exhibited a contraction strategy by reducing root investment under drought treatment, and Asteraceae displayed an efficient strategy with increased specific root length under drought treatment. Except for the biomass proportion of Amaranthaceae, no significant interactive effects were found for most other parameters, indicating that the combined effects of warming and drought were primarily additive. Our results revealed that warm, dry climates influence invasive plants in a taxon-specific manner, with different families employing distinct root trait adjustment strategies in response to environmental stress. These findings highlight the importance of family level comparative studies for predicting invasion dynamics and developing targeted management strategies for future climate scenarios.