Controls Regulating Biological Nitrogen Fixation in Longleaf Pine (Pinus palustris) Ecosystems: The Role of Fire and Military Training
RC-2328
Objective
The process of biological di‐nitrogen (N2) fixation is the primary pathway for nitrogen (N) to be introduced to land ecosystems. N2 fixation is mediated by a suite of soil‐dwelling microorganisms that collectively offer a recovery mechanism for ecosystems undergoing disturbance. Longleaf pine (Pinus palustris) forests dominate several military installations of the southeastern United States and are ecosystems where N2 fixation is suspected to be crucial for recovery from disturbances. These ecosystems are inherently poor in N, and a previous SERDP study (RC-1114D) documented that human disturbance (e.g., fire and military training) can cause them to be even more N‐poor. N2 fixation is the primary control replenishing these losses of N (see SERDP RC‐1462), yet we have little specific knowledge about the process of N2 fixation in these ecosystems. The primary objective of this project is to fill this knowledge gap by investigating the importance of biological N2 fixation in longleaf pine ecosystems influenced by military training and land management. Specific objectives are to: (1) reduce uncertainties about the process of N2 fixation, including the role of different taxonomic groups of N2‐fixers and soil nutrients in regulating the input of N to ecosystems, and (2) quantify the importance of N2 fixation at the landscape level and determine if these N inputs are sufficient to counteract the loss of N through fire, leaching, and volatilization.
Technical Approach
This project will examine the process of N2 fixation with particular attention to the impact of fire and military activity. A 2-year and a 4-year fire‐return interval as well as a 2-year interval on forests where fire has historically been suppressed will be implemented. Through a series of field‐based measurements, researchers will quantify the abundance and activity of N2 fixing organisms (herbaceous legumes, biological soil crusts, and free‐living bacteria) across a network of sites at Fort Benning and Eglin Air Force Base. With manipulative experiments in the field and laboratory (e.g., nutrient additions and stable isotope tracers), researchers will examine how soil nutrients including N, phosphorus (P), and molybdenum (Mo) regulate N2 fixation both directly and indirectly through effects with land management. Finally, N2 fixation will be placed within the broader context of the N cycle by rigorously quantifying pools and fluxes of N. This approach will enable researchers to determine if a threshold exists among fire‐return intervals, where N2 fixation is insufficient to replenish N losses and allow for longleaf pine ecosystems to recover from disturbance.
Benefits
This research will offer critical new knowledge about the regulatory controls of N2 fixation in longleaf pine ecosystems. The work builds directly on previous research in tropical ecosystems where researchers have developed a new conceptual framework for how N, P, and Mo interact to regulate N2 fixation. Results of the current research will provide practical knowledge for the management of longleaf pine ecosystems on military installations of the southeastern United States. In particular, this research will help inform the development of effective management strategies (e.g., managing military training impacts and fire regimes) that would utilize N2‐fixing organisms as vectors of N inputs and offer a natural solution for ecosystem rehabilitation. (Anticipated Project Completion - 2018)
Symposium & Workshop
FY 2013 New Start Project Selections
Points of Contact
Principal Investigator
Dr. Nina Wurzburger
University of Georgia
Phone: 706-542-5109
Fax: 706-542-4819
Program Manager
Resource Conservation and Climate Change
SERDP and ESTCP
Document Types
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