Invasive species management cost billions of dollars annually so understanding how environmental factors affect invasive species expansion is essential for effective management, especially in the context of accelerating anthropogenic environmental changes. Although a large body of studies has focused on what favorable environmental conditions would promote biological invasions, a more comprehensive and mechanistic understanding of how invasive species respond to unfavorable/stressful conditions is still developing. Grass invasion has been problematic across the globe; in particular, C4 grass invaders, with its high drought tolerance, adaptations to high temperatures, and high water use efficiency, could become more problematic. Here, we conducted a rigorous microcosm experiment, with an invasive species that is considered one of the most damaging in the world, cogongrass (Imperata cylindrica), to explore how cogongrass responds to both water and nutrient stress. Specifically, we measured the effects of water and nutrient stresses on both current generation and rhizome production to assess the effects of the legacy stresses. We further integrated the results of the microcosm study with a species distribution model to (1) corroborate greenhouse results with field observations and (2) validate the robustness of our results at sub-continental scales.
Results/Conclusions
Both the microcosm experiment and species distribution model agreed that cogongrass was sensitive to water stress but not nutrient stress. Cogongrass rhizome storage was not affected by environmental stress, but rather produced similar tissue quality (foliage and rhizomes nutrient contents) to compensate for reduced biomass production, especially under the low water conditions, indicating its cross-generational strategies to cope with stresses. Lastly, new vegetative growth of cogongrass was inhibited by the prior water stress. Contrary to conventional wisdom that nutrient enrichment could facilitate biological invasions, this study highlighted the possibility that water stress may have a stronger effect on some aggressive invaders. Therefore, an important implication of this study on biological conservation is that field managers might take advantage of the negative effect of global drought on some invasive species to increase the efficiency of their controlling efforts because invasive species may become more vulnerable under drought effect.