The field of plant-soil feedbacks has focused mostly on the impacts of biotic interactions on community assembly. There have been comparatively few studies on how plant-soil feedbacks shift in response to varying abiotic conditions. Studies of small groups of mycorrhizae have demonstrated shifts from mycorrhizal mutualism to parasitism in response to fertilization, suggesting that mycorrhizae deliver a greater benefit to plants with decreasing soil nutrients. However, studies that investigate whether such effects can change the direction or magnitude of plant-soil feedbacks are lacking. Furthermore, most plant-soil feedback studies have either treated the soil microbial community as a “black box” or used profiling techniques with relatively limited power. Here, I combine a factorial growth experiment with high-throughput ITS sequencing to tie patterns of fungal community composition to the growth of bur oaks in 20 field-collected soils. Field soils were sampled from within 1 meter of adult bur oak, red oak, shagbark hickory and red maple trees and from an adjoining old field, with four replicate soils taken from each origin.
Results/Conclusions
Preliminary data indicate that under nutrient excess, sterilization of soils had a positive or neutral effect on seedling growth, demonstrating a generally net negative effect of soil microbes. Under nutrient limitation, the effect of sterilization became less positive in some soils and even became negative in the field soil. This pattern is consistent with the hypothesis that mycorrhizae deliver a greater benefit to plants when nutrients are limiting. Further analyses on a soon-to-be complete dataset will reveal whether these effects are great enough to change the direction of plant-soil feedbacks. Results from ITS sequencing and subsequent bioinformatic guild assignment will demonstrate the degree to which fungal pathogens and mutualists are host-specific and consequently, the relative contribution of pathogenicity and mutualism to feedback patterns.