Question: The use of plant traits to predict weed impact is a long-standing goal in weed ecology. In particular, trait plasticity, i.e. the variability of a trait response to environmental change, is widely considered to contribute to weed success. However, the generality of the role of trait plasticity in determining weed impacts has never been systematically tested.
Methods and location: We tested the hypothesis that high-impact environmental weeds have greater plasticity in growth responses to nutrient availability than low-impact species. In a glasshouse experiment, we supplied a complete nutrient solution at five different concentrations to seedlings of 24 species of high- and low-impact environmental weeds from south east Queensland, Australia.
Results: Almost all species showed plasticity in biomass accumulation in response to the nutrient treatments, but plasticity in biomass accumulation did not differ between related high- and low-impact species. There was no evidence of nutrient-related plasticity in root:shoot allocation. Seedling survival was greater at higher nutrient concentrations, and also differed greatly between families. Survival among low-impact species was marginally (p = 0.0610) lower than among high-impact species.
Conclusion: We conclude that the impact of environmental weeds in south east Queensland cannot be predicted from nutrient-related plasticity in seedling growth. The effects of nutrients on seedling survival warrant further research.