Potential Ecosystem Services of Free-Living, Nitrogen-Fixing Bacteria in Land Reclamation.

Industrial fertilizer production requires high fossil fuel inputs and accounts for one-third of all energy consumed in agriculture. Increased use of biologically fixed N₂ could help reduce global energy demands. In a collaboration between the University of the Philippines at Baguio and The Pennsylvania State University, ecosystem services provided by free-living, N₂-fixing soil bacteria are being assessed for use in mineland reclamation. The amount of N₂ fixed by free-living soil bacteria has been estimated to range from 0.1-25 kg N per ha per year, but few studies involving direct measurements of atmospheric N₂ uptake have been conducted. Cyanobacteria are a group of free-living, N₂-fixing, photosynthetic soil bacteria that grow naturally in thin films on soil surfaces. Although cyanobacteria are used extensively as renewable N sources in rice production in the Philippines, they have received little consideration for use in land reclamation. Research at Penn State on reclamation of mine spoil materials demonstrated that acidic, Fe-rich surface materials had C and N contents similar to native topsoils. We hypothesized that N in mine materials had been derived from the activity of free-living bacteria, notably acid-tolerant cyanobacteria or acidithiobacilli. A suite of primers for nifH genes was applied to community DNA extracts to detect the presence of N₂-fixing populations, and the most consistent results were obtained with the primers of Poly et al. (2001). These primers are currently being applied to community DNA from naturally occurring cyanobacterial crusts. Work is underway to sequence nifH gene products and conduct real-time PCR estimation of nifH gene copies. This work paves the way to investigate application of cyanobacteria to minelands in the Philippines as a means to enrich soils with fixed N, protect newly forming soils from erosion, and condition soils for seed germination.