PARENT SESSION
Poster Session #63: Late Breaking and Newsworthy Papers.
Friday, August 9. Presentation from 8:00 AM to 9:30 AM. Exhibit Hall B & C, TCC
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Two-way nitrogen transfer between Eucalyptus and Casuarina linked by a common ectomycorrhizal network.
HE, XINHUA*,1,2,3, NG, HOCK2, STEWART, GEORGE2,4, CRITCHLEY, CHRISTA2, 1 University of California at Davis, Davis, CA2 University of Queensland, Brisbane, AUSTRALIA3 currently at UC Davis4 currently at University of Western Australia, Perth, AUSTRALIA
ABSTRACT- Plant roots in natural communities are often linked by common mycorrhizal networks (CMNs) that are pathways for nutrient transfer between plants. One-way N-transfers between mycorrhizal plants have been reported, but not two-way transfers. In mixed Australian native Casuarina and Eucalyptus communities, both mycorrhization and nitrogen cycling are extensive. We asked two questions: Does two-way N-transfer occur between the non-leguminous actinorhizal N2-fixer Casuarina and the non-N2-fixer Eucalyptus? Is N-transfer affected by mycorrhization and/or N2-fixation? By excluding root contact (37 micron mesh) and water movement (high water holding crystals), we observed bi-directional N-transfers (15NH4+ or 15NO3-) between Eucalyptus maculata/Casuarina cunninghamiana pairs of seedlings, linked by a CMN with the fungus Pisolithus tinctorius. We demonstrated that N2-fixing capacity is not a prerequisite for N-transfer, but may affect the intensity of this two-way mycorrhiza-mediated N-transfer. If Casuarina was not nodulated, N-transfer to Casuarina or to Eucalyptus was similar. If Casuarina was nodulated, more N (4-10 times) was transferred than in non-nodulated mycorrhizal pairs, whether Casuarina or Eucalyptus was the N-donor. Surprisingly, Eucalyptus (non-N2-fixer) donated 2-4 times more N to Casuarina (N2-fixer) than the reverse. Growth of Casuarina was significantly increased by interspecific N-transfer relative to Eucalyptus. We postulate a myco-centric N-transfer mechanism to account for these differences. The magnitude of mycorrhiza-mediated N-transfer and N movement may be determined by dynamic four-way interactions among plant roots, mycorrhizal fungi, N2-fixing bacteria, and soil N resource availability.
KEY WORDS: Common mycorrhizal networks, two-way N-transfer, Eucalyptus , Casuarina