Abstract
Exotic invasive plant species can cause biodiversity loss by outcompeting and replacing native species. Herbicides are commonly used to control invasive plants owing to their low cost and high efficiency. However, herbicide use can have unintended effects on co-occurring native plant species by altering the competitive balance. We studied how herbicide application modifies the competition between an invasive and a native species. We examined the effects of applying glyphosate on the mortality, photosynthetic capacity, and growth of Solidago canadensis, an aggressive invasive species, and Imperata cylindrica, a native species that commonly co-occurs with S. canadensis. We also studied how applying glyphosate affected the competition between these species. Various glyphosate concentrations were applied to the two species grown either together or separately. The mortality rate increased while the photosynthetic capacity and growth decreased with increasing glyphosate concentration. Increasing the glyphosate concentration more negatively affected the parameters of I. cylindrica than those of S. canadensis. Plant growth, especially that of I. cylindrica, was more restricted by intraspecific competition than by interspecific competition as the glyphosate concentration increased. Furthermore, the relative competitive potential of the native species decreased with increasing glyphosate concentration. S. canadensis is more tolerant of glyphosate, which enhances its competitive advantage and hinders the proliferation, reintroduction, and success of native plant species. Future studies should focus on developing techniques to mitigate the negative impacts of invasive plant species, for example, via optimizing methods of spraying herbicides.