MYCORRHIZAL DIVERSITY AND EFFECTS ON BRITTLEBUSH IN A SONORAN DESERT URBAN ECOSYSTEM

In this study, the functioning of AM fungi in brittlebush (Encelia
farinosa A. Gray ex Torr.) grown at an urban site and a desert site are
compared. E. farinosa is a native, desert shrub commonly found in the Sonoran
Desert surrounding Phoenix and used as an ornamental shrub in residential and
commercial sites in the Phoenix metropolitan area. Because this shrub is common
in urban and desert areas, it can be used to compare AM fungal colonization
levels between these areas. In addition, the impact of AM fungi on E. farinosa growth and
reproductive output was studied by attempting to manipulate the levels of AM
fungal colonization using the fungicide
methyl-1-(butyl-carbamoyl)-2-benzimidazole (benomyl). This fungicide has been
shown to suppress colonization of roots by AM fungi with little phytotoxicity or
effect on soil nutrients (Fitter and Nichols 1988; Hartnett and Wilson 2002).
Hartnett and Wilson (2002) stated that the best method available to assess the
roles and functions of AM fungi in natural communities is through the use of
fungicides such as benomyl. Treatment with benomyl should allow for comparisons
between plants that have typical levels of mycorrhizal colonization and those
with lower, suppressed levels of colonization. The impact of AM fungi on the productivity of brittlebush plants
was examined at an urban and desert site. Fungal colonization was greater at the
desert site but biomass and reproductive output was higher at the urban site.
When mycorrhizal colonization was suppressed, plants had greater vegetative
growth, but there was no effect on reproductive output. .