COS 61-2 - Spatial dynamics of plant-soil feedbacks in a grassland-shrubland ecotone

Background/Question/Methods

Species must move, adapt, or face decline as environmental conditions exceed their physiological thresholds. Substantial movement in plant range limits requires successful dispersal and establishment away from a high-density population core, and brings novel interactions such as feedbacks with soil microbes. The spatial extent of a plant’s influence sets the boundary at which plants can alter unoccupied space or affect the performance of neighbors via soil microbes, thus affecting their spread relative to the scale of dispersal. However, despite observations on the spatial extent of specificity in plant-microbe associations, knowledge of spatial extent is lacking for the feedback process in any system. We conducted a field plant-soil feedback experiment to answer: What is the spatial extent of influence of host-specific belowground microbes on foundational species fitness in a grassland-shrubland ecotone? In the field, we added seeds of black grama and creosotebush along a gradient of distances from established creosotebush or black grama plants. Seedlings experienced microbial treatments that allowed (i) the full complement of belowground effects (including competition from resident plants), (ii) soil biota only, or (iii) abiotic effects only. We measured seedling emergence and survival to assess how plant-specific effects attenuate with distance during the critical recruitment stage.

Results/Conclusions

We found evidence of species-specific, distance-dependent recruitment during the fall germination period. Black grama seeds showed 87% higher recruitment near black grama resident plants compared to near creosotebush resident plants (Chisq=24.84, df=1, P< 0.0001). In addition, we found that black grama recruitment declined with increasing distance away from a black grama resident plant, whereas they did not show distance-dependence in recruitment near creosotebush resident plants (distance:resident interaction Chisq=5.01, df=1, P=0.03). Microbial treatments had no significant effect on germination, suggesting that the distance-dependent self-facilitation in black grama recruitment is likely driven by abiotic mechanisms. Interestingly, our sensor data show that soil moisture generally increases with distance from a resident black grama plant at the spatial scale (< 1m) at which our experiment is performed, whereas there was no consistent effect of creosoteshrub on soil moisture at distance. In comparison, soil temperature did not significantly vary with distance from resident plant. Our study demonstrates that abiotic plant-soil feedbacks are spatially structured in the field at the spatial scale of < 1m. Future work will combine additional plant vital rates and microbiomics analyses to achieve a holistic understanding of the spatial dynamics of biotic and abiotic plant-soil feedbacks.