Redwood Reader

Glomalin content of forest soils in relation to fire frequency and landscape position
Melissa A. Knorr A1 A3, R. E. J. Boerner A1, Matthias C. Rillig A2
A1 Department of Evolution, Ecology and Organismal Biology Ohio State University Columbus OH 43210 USA
A2 Microbial Ecology Program, Division of Biological Sciences University of Montana Missoula MT 59812 USA
A3 School of Natural Resources University of New Hampshire Durham NH 03824 USA
Abstract:
Low-intensity, dormant season fires were frequent and widespread in oak-hickory ( Quercus-Carya) forests of eastern North America until widespread fire suppression began in the mid-1900s. To assess how reintroduction of fire into such ecosystems might affect the activity of arbuscular mycorrhizal (AM) fungi and, thereby, predict the long-term responses of plants and soils to fire, we analyzed the content of the immunoreactive fractions of the AM-fungus-specific glycoprotein glomalin in soils taken in 1994 and 2000 from three forested watersheds in southern Ohio, USA. One watershed remained unburned, one was burned annually from 1996–1999 and one was burned twice, in 1996 and 1999. In addition, to account for the strong landscape-scale gradients of microclimate and soil that typify these watersheds, we stratified each watershed-scale treatment area into three microclimatic zones (=landscape positions) using a GIS-based integrated moisture index (IMI). In the unburned control, the concentrations of immunoreactive, easily-extractable glomalin (IREEG) and immunoreactive total glomalin (IRTG) did not change significantly over the 6-year interval between sampling times, either overall or within any of the three IMI classes. IRTG content was greatest in the mesic landscape positions and lowest in the relatively xeric landscape positions, but IREEG did not vary among landscape positions. Neither IREEG nor IRTG contents were affected by fire, nor were there significant interactions between fire and landscape position in glomalin content. Both correlation and regression analyses demonstrated significant linkages between soil glomalin content, the density/diversity of herbaceous plants, and soil N availability. Despite significant effects of fires on soil N availability and root growth, we resolved no effect of fire on AM fungal activity at this spatial scale.
Keywords:
Glomalin, AM fungi, Oak-hickory, Quercus-Carya, Forest, Fire
1: Mycorrhiza. 2003 Aug;13(4):205-10. Epub 2003 Feb 6.

Commentary: This abstract of this study shows us low intensity fires do not disrupt the glomalin scheme with respect to herbaceous plants in oak hickory forests. We note mature forests showed little glomalin change. We see that proportions left alone remained stable over the years, and that total glomalin was highest in the wetter areas and lowest in drier conditions, but easily extractable glomalin was constant across the landscape. The fire affected neiither type, although the herbaceous plants remind us we are only looking at the top several feet of soil.
The upshot is that revegetation after low intensity fire restores the glomalin input maintaining the balance of soil and glue. We know high intensity fires bake the soil into sort of a ceramic material and the revegetation scheme must re-establish conditions in the soil for succeeding species. So we find pioneer species like ceanothus after burns and nitrogen fixers in abundance, some species hosting both types of microbial growth. No mention is made of runoff in this study. The linkages between soil glomalin content, the density/diversity of herbaceous plants, and soil N availability underscore our premise and the finding of no effect from fire on fungal activity extremely useful to land managers using fire regimes to mimic natural processes or reduce fuel loading.
We note Matthias Rillig of the University of Montana and a colleague of Sara Wright, as the glomalin researcher most closely involved with forest soils although, many studies are beginning to occur. Salute!