Arbuscular mycorrhizas and their role in plant growth, nitrogen interception and soil gas efflux in an organic production system
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Background and aims
Roots and mycorrhizas play an important role in not only plant nutrient acquisition, but also ecosystem nutrient cycling.
A field experiment was undertaken in which the role of arbuscular mycorrhizas (AM) in the growth and nutrient acquisition of tomato plants was investigated. A mycorrhiza defective mutant of tomato (Solanum lycopersicum L.) (named rmc) and its mycorrhizal wild type progenitor (named 76R) were used to control for the formation of AM. The role of roots and AM in soil N cycling was studied by injecting a 15N-labelled nitrate solution into surface soil at different distances from the 76R and rmc genotypes of tomato, or in plant free soil. The impacts of mycorrhizal and non-mycorrhizal root systems on soil greenhouse gas (CO2 and 14+15N2O and 15N2O) emissions, relative to root free soils, were also studied.
The formation of AM significantly enhanced plant growth and nutrient acquisition, including interception of recently applied NO 3 − . Whereas roots caused a small but significant decrease in 15N2O emissions from soils at 23 h after labeling, compared to the root-free treatment, arbuscular mycorrhizal fungi (AMF) had little effect on N2O emissions. In contrast soil CO2 emissions were higher in plots containing mycorrhizal root systems, where root biomass was also greater.
Taken together, these data indicate that roots and AMF have an important role to play in plant nutrient acquisition and ecosystem N cycling.
KeywordsArbuscular mycorrhizas Carbon dioxide Nitrogen Nitrous oxide Nutrient cycling Plant nutrition Tomato mutant
This work would not have possible without the ongoing support of our farmer cooperators Jim and Deborah Durst. We wish to thank Professor Sally E. Smith (University of Adelaide) and Dr Susan J. Barker (University of Western Australia), for allowing us to use the rmc tomato mutant/wild-type system. Thanks also to the various members of the Jackson lab for their excellent technical assistance and valuable discussions. We thank Professors Kate M. Scow and Dennis E. Rolston for valuable discussions and Ms Dianne Louie for advice on gas sampling and analysis. This research was funded by the California Department of Food and Agriculture Specialty Crops Program (SA6674) and the United States Department of Agriculture National Research Initiative Soils and Soil Biology Program (2004–03329). TRC also acknowledges the Monash Research Accelerator program for supporting travel to Davis to complete this manuscript. We also thank two anonymous reviewers of this manuscript for their valuable comments.
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