Empirical studies show that adult trees alter the microbial community within their local soil to create negative density-dependence (NDD) and positive density-dependence (PDD) effects. This process is known as plant-soil feedback (PSF). Community-wide patterns in tree-species relative abundance correlate with the strength of NDD in plants. Likewise, the presence of mutualistic nutrient-fixing fungi can create PDD, mediating tree community structure. However, we still cannot reconcile variation in the strength of net PSF effects across species and (potentially) across latitudes. For example, some species consistently exhibit stronger negative feedbacks than others, such as rare plant species and their co-occurring common counterparts.
A key challenge to understanding how soil microbiomes affect overall diversity and relative species abundance within plant communities is to correctly identify the causes and consequences of interspecific variation in the strength of net PSF. Specifically, why do some plant species exhibit stronger negative PSF than others, and how does this variation affect plant community structure and diversity?
To test this question, the investigators present a spatially explicit simulation representing a dynamic and flexible distribution of microbes. This model identifies possible ecologically realistic conditions for seedlings which result in stable biodiversity of plant communities, while simultaneously maintaining interspecific variation among common and rare species.
Results/Conclusions
As we continue to develop next-gen sequencing technologies, we improve the resolution with which we can examine the ecological processes underlying the observed natural world. This work presents one previously unconsidered insight – representing a possible mechanism contributing to the maintenance of stable biodiversity over thousands of years. The findings from the model clearly show that plant-soil feedback strength – as calculated by relative survival of seedlings – is the strongest predictor of diversity maintenance. Removing the pressures of pathogens and mutualist microbes living in the soil decreases feedback strength, and consequently reduces overall diversity within the simulation. Although we recognize the one-dimensional circular array is a simplification of a complex forest, the model clearly demonstrates the significance of density-dependence maintaining microbial pressures, both positive (mututalists) and negative (pathogens).