Localization of Casuarina-infective Frankia near Casuarina cunninghamiana trees in Jamaica

Soil sampled along a 100-m linear series of plots extending from the stems of three Casuarina cunninghamiana Mig. trees was bioassayed to estimate the number of infective units (IU) of the symbiotic diazotroph Frankia per gra m of soil using native Myrica cerifera L. and exotic C. cunninghamiana as F rankia traps. Casuarina-infective Frankia was detected only in soils within 20 m of Casuarina host trees. Myrica-infective Frankia was found in all of the plots assayed even though none of the native M. cerifera occurred on o r near the site. Polymerase chain reaction - restriction fragment length po lymorphism characterization of nodule microsymbiont DNA from both host spec ies indicates that Casuarina were nodulated by a different group of Frankia than thr groups nodulating Myrica. The Casuarina-infective Frankia is in t he same taxonomic group as most other Casuarina-infective Frankia found whe re Casuarina trees were introduced outside of Australia. Soil collected nea r the C, cunninghamiana,tn trees had higher total N, NO3, organic matter, P , Mg, K, Ca, pH, and cation exchange capacity. Homogenates of C, cunningham iana leaves and stems increased the number of IUs of Frankia CjI82 001 when inoculated and incubated for 3 months in an artificial soil. Thus, it seem s that C. cunninghamiana is able to alter soil chemical properties and poss ibly favor its specific microsymbiont in soil.