Arbuscular mycorrhizas and their role in plant growth, nitrogen interception and soil gas efflux in an organic production system

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 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 (CO ₂ and ¹⁴⁺¹⁵N ₂O and ¹⁵N ₂O) 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 ¹⁵N ₂O emissions from soils at 23 h after labeling, compared to the root-free treatment, arbuscular mycorrhizal fungi (AMF) had little effect on N ₂O 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.