IN INOCULANTS Nodulaid - 17th International Nitrogen Fixation ...

17 th International Congress on Nitrogen Fixation
Fremantle, Western Australia
27 November – 1 December 2011
Session Details: Wednesday 30 November 2011
Concurrent Session 15 – Quantification of N-Fixation
1600 – 1740
Authors: Xinhua He 1, 2, 3, 4 , Christa Critchley 4 , Caroline Bledsoe 5
1, 2 State Centre of Excellence for Ecohydrology, Centre for Ecosystem Management,
1 School of Natural Resources, Edith Cowan University, Joondalup, WA 6207, Australia
2 School of Plant Biology, University of Western Australia, Crawley, WA 6009, Australia
3 Key Laboratory of Crop Nutrition and Fertilization, Institute of Agricultural Resources
and Regional Planning, Chinese Academy of Agricultural Sciences, Beijing 100081,
China
4 School of Agriculture & Food Sciences, University of Queensland, Brisbane, QLD 4072
Australia
5 Department of Land, Air and Water Resources, University of California, Davis, CA
95616 USA
Presentation Title: Reciprocal two-way n ( 15 NH4 or 15 NO3) transfer between non-N2-fixer Eucalyptus
maculata and Frankia N2-fixer Casuarina cunninghamiana
Presentation Time: 1620 – 1640
Nitrogen (N) movement or transfer from one plant to another could have important implications for nutrient
cycling and eco-physiological significance in terrestrial and agricultural ecosystems. In controlled pots with or
without Frankia inoculation to Casuarina, two-way N transfers through an ectomycorrhizal fungus Pisolithus sp.
were examined by excluding root contact and supplying 15 NH4 + or 15 NO3 � to 5 or 11-month-old Eucalyptus
maculata or Casuarina cunninghamiana pairs grown in 2-chambered-pots separated by 37 µm nylon screens.
With either Eucalyptus or Casuarina as the N-donor, the three pairs were non-nodulated nonmycorrhizal/nonmycorrhizal,
non-nodulated mycorrhizas/mycorrhizal and nodulated mycorrhizal/mycorrhizal.
Using an environmental scanning electron microscope, living mycorrhizal hyphae were observed to interconnect
Eucalyptus and Casuarina. Results showed that N2-fixation supplied ~35% of the N in Casuarina and was
enhanced by mycorrhization, which was 67% in Eucalyptus and 36% in Casuarina. Biomass, N and 15 N contents
were lowest in the non-mycorrhizal and greatest in the nodulated/mycorrhizal plants. Nitrogen transfer was
enhanced by nodulation and/or mycorrhization, and greater when N was supplied as 15 NH4 + than 15 NO3 � .
Nitrogen transfer from either 15 N-source was lowest in the non-mycorrhizal treatment and greatest in the
nodulated mycorrhizal treatment, and also was greater to Casuarina than to Eucalyptus and where NH4 + than
NO3 � supplied. Irrespective of the 15 N-source and of whether Casuarina or Eucalyptus was the N sink, net N
transfer was low and similar in non-nodulated treatments, but was much greater when Casuarina was the N sink
in the nodulated mycorrhizal treatment. High-N-demand by Casuarina resulted in greater net N transfer from the
less N-demand Eucalyptus. Net N transfer from a non-N2-fixing to an N2-fixing plant may reflect the very high N
demand of N2-fixing species. Our research may provide insights into our understanding of complex interactions
among plants, Frankia, mycorrhizal fungi, and soil resources in both terrestrial and agricultural ecosystems.
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2011