Functional metabolic diversity of the bacterial community in undisturbed resource island soils in the southern Sonoran Desert

Resource islands (RIs), a natural revegetation phenomenon in arid lands, consist of a single nurse tree or few large shrubs and numerous understory nurslings. We analyzed 18 individual mesquite RIs for plant diversity and richness, area, trunk diameter (reflecting age), soil characteristics, physiological functionality of microbial populations, and interactions among these variables. Nursing Capacity reflected the availability of habitat and was positively correlated to plant richness, but not to plant diversity. No relationship between plant diversity and bacterial diversity was found. The structure of the bacterial communities of RIs differed from the bacterial communities of bare areas, which showed greater richness and diversity compared with those of RIs. The Nursing Capacity of the RIs was related to plant richness and accompanied by variations in soil properties. A high correlation was found by substrate utilization analysis between metabolic parameters of bacteria and diversity and richness of plants in the RIs. RI bacterial communities were more metabolically active and could degrade different carbon sources than bare area communities. RI bacterial communities contained species with greater capability to metabolize diverse carbon substrates in soil with more organic matter. Bacteria from low, medium, and high plant diversity areas were cultured and found to belong to four bacterial families. This study demonstrates that numerous parameters interact, but not every parameter significantly affected bacterial activity in the RI.