Effects of expected climatic conditions on performance of native and invasive prairie grasses

Background/Question/Methods

Biological invasion by non-native plants is a major cause of native ecosystem loss.  It has been widely suggested that climate change will increase the success of biological invaders, yet studies that combine these global changes are limited. Climate change may directly increase success of non-natives as these species often possess traits that are favored by increasing climates, or indirectly through impacts on native vegetation or alterations in native soil communities, including symbiotic arbuscular mycorrhizal (AM) fungi.  In our study, we assess the effect of climate warming and soil drought on vegetative biomass production, flowering, and soil microbial communities of native and invasive grasses. Our experiment, a full-factorial design, examined two caespitose warm-season grasses (native [Schizachyrium scoparium] and invasive [Bothriochloa ischaemum]) x two temperatures (ambient; ambient+5C) x four soil water treatments (100% field capacity [FC]; 75% FC; 50% FC; 25% FC); 32 treatment combinations x 6 replicates = 96 pots. A follow-up study, modeled from the experiment previously described, was performed using an invasive C₃ prairie grass (Bromus inermis), and a paired native counterpart (Pascopyrum smithii). Plant vegetative and reproductive biomass was assessed at senescence, roots were subsampled for mycorrhizal colonization, and soil was sampled for microbial community analyses.

Results/Conclusions

Our preliminary data indicate invasive C₄ grasses produced as much as 400% greater vegetative and reproductive biomass across all treatments, compared to their paired native species. Furthermore, increased temperature and soil moisture treatments showed no effect on reproductive biomass of invasive grasses, compared to ambient treatments, while drought treatments reduced reproductive biomass in native species. Mycorrhizal percent root colonization was significantly greater in the invasive grass, B. ischaemum, as compared to the native grass, S. scoparium. However, these patterns were not observed in the C₃ invasive species, as the native and invasive C₃ grasses performed similarly across all climatic treatments.  These results suggest C₃ invasive grasses may not possess the drought tolerance of invasive C₄ grasses. Given the overall goal of this research is to help bridge the gap in our understanding of above- and belowground alterations of functionally similar native and invasive grass species under current climate change scenarios, our results suggest C₄ grasses may pose a greater threat to native grasslands under predicted global climate change.