Charcoal effects on soil solution chemistry and growth of Koeleria macrantha in the ponderosa pine/Douglas-fir ecosystem

We conducted laboratory and greenhouse experiments to determine whether charcoal derived from the ponderosa pine/Douglas-fir ecosystem may influence soil solution chemistry and growth of Koeleria macrantha, a perennial grass that thrives after fire. In our first experiment, we incubated forest soils with a factorial combination of Douglas-fir wood charcoal generated at 350°C and extracts of Arctostaphylos uva-ursi with and without the addition of glycine as a labile N source. These results showed that charcoal increased N mineralization and nitrification when glycine was added, but reduced N mineralization and nitrification without the addition of glycine. Charcoal significantly reduced the solution concentration of soluble phenols from litter extracts, but may have contributed bioavailable C to the soil that resulted in N immobilization in the no-glycine trial. In our second experiment, we grew K. macrantha in soil amended with charcoal made at 350°C from ponderosa pine and Douglas-fir bark. Growth of K. macrantha was significantly diminished by both of these charcoal types relative to the control. In our third experiment, we grew K. macrantha in soil amended with six concentrations (0, 0.5, 1, 2, 5, and 10%) of charcoal collected from a wildfire. The data showed increasing growth of K. macrantha with charcoal addition, suggesting some fundamental differences between laboratory-generated charcoal and wildfire-produced charcoal. Furthermore, they suggest a need for a better understanding of how temperature and substrate influence the chemical properties of charcoal.