EAGER: Investigating changes to forest soil microorganism communities due to the interactive effects of increasing soil P and pH

Forests cover 30% of the Earth’s surface. They support a large portion of the earth’s living organisms and play an important role in the global cycling of carbon and water. While often being directly affected by humans via activities like logging, they are also often indirectly threatened by human activities such as those that result in acid rain and high nutrient deposition.

The resulting changes in soil nutrients from these indirect activities can fundamentally alter the soil microorganism community which in turn can have consequences for forest composition and processes. For example, soil microorganisms like bacteria and fungi can drive plant growth, and particular root-associated fungi can favor some plant species over others.

This experimental study will evaluate how soil microbial composition and abundance change with soil acidification and with changes in phosphorus in a forested landscape and how root-associated microbes change as the canopy tree species change. The results of this experimental study can be used to predict how forests will respond to changes in soil nutrient availability associated with human influences.

In addition to the traditional training of graduate and undergraduate students, this project benefits the broader scientific community and society in several ways. It will engage teachers and school administrators to improve STEM education for students in sixth grade in the Dayton Regional STEM School by developing programs to highlight microbial biology and soil fungi and their important roles and associations.

It will also provide training to private woodlot owners and professional foresters about soil fertility and forest management.

Previous work in a variety of systems has shown that soil acidity is important for shaping soil microorganism communities with potential consequences for plant composition. Soil and root-associated microbial responses to acidity are likely facilitated through changes in soil P. Despite this important linkage between pH and P, experimental manipulations of both pH and P in forest ecosystems are relatively rare and instead studies tend to take advantage of existing gradients in nutrient availability.

This lack of factorial manipulation of pH and P limits the ability to tease apart mechanisms driving the responses of microorganisms to alterations in pH versus other nutrients . To fully understand how changing P alters the soil microorganism community,studies that manipulate soil P directly versus indirectly by changing soil pH are needed. The proposed research utilizes a unique, 12-year forest fertilization experiment that has increased soil pH and P availability independently and together, through the addition of lime and/or phosphate fertilizer.

The main objective of this proposal is to determine if altered soil P availability drives changes in taxonomic and functional composition of microorganism communities. The proposed work seeks to disentangle biotic and abiotic drivers of these microbial communities and to identify whether particular phyla or key dominant strains of the microorganism community are driving changes.

In doing so, outcomes from the research proposed will contribute to understanding microbial contributions to changing nutrient cycles and provide a critical step towards a predictive understanding of how soil P availability can alter forest community composition with consequences for future carbon storage.

This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.