9402271 Hirsch This Americas Program award will support Dr. Ann M. Hirsch, University of California, Los Angeles, and Dr. Maria Valdez, Instituto Politecnico Nacional, Mexico, in a research collaboration on nitrogen-fixing symbiosis between Frankia microbe strains and the Casuarina tree (Ironwood). The objective is to find efficient nitrogen-fixing strains that can be used to inoculate Casuarina, an Australian tree introduced in Mexico only 50 years ago. The researchers aim to determine the means by which various isolates found in nodules of the Casuarina tree fix nitrogen, and, particularly, to examine whether the bacteria have alternative nitrogenase genes. Deforestation and the loss of arable lands in tropical and subtropical countries are major global concerns. Numerous efforts to reclaim areas stripped of trees have failed because the fragile tropical soils become depleted in both nitrogen and phosphorous once the trees are removed. The introduction of nitrogen-fixing trees that also establish mycorrhizal relationships is an approach to this problem. This project will enable researchers to identify nitrogen- fixing organisms that are well adapted for nitrogendepleted tropical soils, and is of potential interest to other tropical and subtropical countries having extensively deforested regions with eroded soils. ***
