Effect of urban expansion on arbuscular mycorrhizal fungal mediation of landscape tree growth

Field and glasshouse pot studies were conducted to determine effects of urban expansion on arbuscular mycorrhizal fungal (AMF) populations and AMF impact on landscape tree growth. Soil and root segments were collected and evaluated for root colonization by AMF of trees at remnant Sonoran Desert sites and nearby, formerly desert, drip-irrigated residential landscape sites in the Phoenix, Arizona, USA, metropolitan area. Native desert trees had greater colonization by AMF than residential landscape trees, and AMF species composition differed at the two site types. A glasshouse pot experiment using AMF inocula from the desert or residential sites was used to evaluate AMF effects on growth and carbon fluxes of three landscape trees in 12-L (3-gal) polyethylene containers relative to non-AMF controls. Growth and P nutrition of Acacia smallii and Fraxinus uhdei were increased by AMF colonization. Acacia carbon assimilation was increased by AMF root colonization. Soil respiration by Acacia and Fraxinus tree roots was decreased by AMF root colonization. Growth and carbon fluxes of Parkinsonia microphylla were not affected by AMF. We conclude that AMF might significantly increase landscape tree carbon storage potential depending on tree species, AMF population characteristics, soil water availability, and improved P uptake.