Abiotic and Biotic Factors Shaping Plant-Microbe Interactions

Symbioses between plants and soil microbes can shape plant traits and performance, population dynamics, community composition, and ecosystem function. However, the context-dependency of plant-microbe interactions remains an underexplored frontier of scientific understanding. Given that the biotic and abiotic contexts of ecological communities is rapidly shifting due to anthropogenic change, understanding the factors that shape plant-microbe interactions will allow us to make more accurate predictions of ecological interactions both presently and in the future. Here, we explore plant-microbe interactions across three different contexts—herbivory, ecological succession, and a water availability gradient. In each of these contexts we demonstrate of the importance of context dependency in shaping the outcomes of plant-microbe interactions. For example, in Chapter II, we found evidence that a multiple species mixture of mycorrhizal fungi in soils can facilitate aboveground herbivory, but only in the context of previous herbivory. The interaction between aboveground herbivory experiences and belowground microbial symbioses yielded entirely different directional outcomes for herbivore performance. In Chapter III, we explored whether soil microbes from three distinct ecological communities across a successional gradient differentially influenced plant defense strategies against herbivores. We found evidence that soil microbes from mid and late successional habitats increased plant capacity to reduce herbivore damage (resistance) but did not influence plant capacity to regrow after damage (tolerance). In Chapter IV, we pivot to assess an important abiotic context of plant-microbe interactions: water availability. We demonstrated through direct experimentation that the positive effect of mycorrhizae on plant performance increased as water availability increased. To our knowledge, is the first strong evidence that indicates the importance of mycorrhizae in facilitating the host plant’s ability to improve growth when provided ample water or even flooding conditions. In exploring the context-dependency of plant-microbe interactions, we gathered strong evidence that the biotic and abiotic environment shapes the outcomes of plant-microbes interactions ranging from negative (facilitation of aboveground herbivores) to positive (improved resistance against herbivores; increased biomass production in high water conditions). Taken together, this works emphasizes the need to incorporate variability in abiotic and biotic conditions into our understanding of ecological relationships between interacting species.