REGULAR ARTICLE Arbuscular mycorrhizas and their role in plant growth, nitrogen interception and soil gas efflux in an organic production system T. R. Cavagnaro & F. H. Barrios-Masias & L. E. Jackson Received: 3 April 2011 /Accepted: 3 October 2011 /Published online: 5 November 2011 # Springer Science+Business Media B.V. 2011 Abstract Background and aims Roots and mycorrhizas play an important role in not only plant nutrient acquisition, but also ecosystem nutrient cycling. Methods 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 lyco- persicum 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 15 N-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 (CO 2 and 14+15 N 2 O and 15 N 2 O) emissions, relative to root free soils, were also studied. Results 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 15 N 2 O emissions from soils at 23 h after labeling, compared to the root-free treatment, arbuscular mycorrhizal fungi (AMF) had little effect on N 2 O emissions. In contrast soil CO 2 emissions were higher in plots containing mycorrhizal root systems, where root biomass was also greater. Conclusions Taken together, these data indicate that roots and AMF have an important role to play in plant nutrient acquisition and ecosystem N cycling. Keywords Arbuscular mycorrhizas . Carbon dioxide . Nitrogen . Nitrous oxide . Nutrient cycling . Plant nutrition . Tomato mutant Introduction Biotic processes such as symbioses can improve agricultural sustainability with less reliance on non- renewable inputs such as synthetic fertilizers (Cardoso and Kuyper 2006). Arbuscular mycorrhizas (AM) are symbiotic associations formed between plant roots and a specialized group of soil fungi that can enhance plant nutrient acquisition (Smith and Read 2008). Although usually considered important primarily for P uptake, arbuscular mycorrhizal fungi (AMF) can also increase plant acquisition of N, Zn, Fe, Cu and Plant Soil (2012) 353:181–194 DOI 10.1007/s11104-011-1021-6 Responsible Editor: Angela Hodge. T. R. Cavagnaro (*) School of Biological Sciences, Monash University, Clayton, Victoria 3800, Australia e-mail: timothy.cavagnaro@monash.edu T. R. Cavagnaro Australian Centre for Biodiversity, Monash University, Clayton, Victoria 3800, Australia F. H. Barrios-Masias : L. E. Jackson Department of Land, Air and Water Resources, University of California Davis, One Shields Avenue, Davis, CA 95616-8627, USA