PARENT SESSION
Oral Session #59: Soil Ecology: Microbial and Invertebrate.
Presiding: M. Rillig
Wednesday, August 7. 8:00 AM to 11:30 AM. Palo Verde Room, Radisson.

Distribution and abundance of Frankia and three actinorhizal host species (Shepherdia canadensis, Alnus incana ssp. rugosa, and Myrica gale) over a dune- swale primary successional gradient in east-central Wisconsin.

Zimpfer, Jeff^*,2, McCray Batzli, Janet¹, Dawson, Jeffrey³, Huguet, Valerie⁴, Smyth, Charles³, Fernandez, Maria⁴, ² Department of Biological Sceinces, Las Vegas, NV¹ College of Natural Science, East Lansing, MI³ Natural Resources & Environmental Science, Urbana, IL⁴ Laboratoire d'Ecologie Microbienne, Lyon 1, France

ABSTRACT- Distribution and abundance of the diazotrophic, root microsymbiont, Frankia, are described relative to the presence of the hosts Shepherdia canadensis, Myrica gale, and Alnus incana ssp. rugosa in two sites along Lake Michigan to identify patterns of symbiont: colonization, and ecological specificity relative to the host, edaphic and topographic characteristics. At the successional site, infective Frankia was detected in 82% of the 120 sampling plots, stratified over three ridge-swale communities of increasing age, while only 14% of the plots supported actinorhizal host plant species. Frankia appeared to colonize the site prior to the establishment of plant host species. The presence of Frankia was not correlated with specific host plant presence, nor was Frankia found in submerged soils (water depth >21cm). However, if one strain was present we were likely to find the other two strains as well. Shepherdia-infective-Frankia increased in abundance earlier in succession than either Alnus- or Myrica-infective-Frankia, which corresponds to the presence of S. canadensis at an earlier stage in succession than the other two actinorhizal species. Shepherdia-infective-Frankia were found to be ecologically and genetically different than those that infect A. incana rugosa and M. gale based on rrs gene polymorphism. In a second site, where all three actinorhizal species were found growing sympatrically, Shepherdia and Alnus infective Frankia were detected in high abundance (56.4 and 5.7 I.U. Frankia cm^-3 soil, respectively) compared to Myrica infective Frankia (0.21 I.U. Frankia cm^-3 soil). Populations of Myrica infective Frankia at this second site appear to be genetically distinct and different from the Frankia populations examined along the successional gradient. Our results suggest that the Frankia populations analyzed in this study are not only host specific but specific to particular environmental conditions found in different seres and sampling locations.

KEY WORDS: Frankia , actinorhizal , ridge-swale community, colonization