Exploring a community of saline soil microorganisms: Who, where, and when

The abundance, distribution, and diversity of the soil microbial community from a seawater-irrigated, halophyte agroecosystem was examined. The abundance and trophic composition of decomposers responded to the biochemical composition of residue from three salt-tolerant plants, Salicornia bigelovii, Suaeda sp., and Batis maritima. Decomposers were also influenced by the decomposition environment as it interacted with residue resource quality. The microbial community responded to the availability of residues and the planting density of the halophyte Salicornia bigelovii (Chenopodiaceae) in a season-long study at a research farm in Sonora, Mexico. Soil microbial biomass, activity and efficiency, as well as nematode abundance and trophic composition, generally increased in association with soil-incorporated halophyte residues. However, soil moisture and salinity, which decreased with depth, may also have been influential. Microbial biomass and activity responded to plant density only after plants entered senescence. This result suggested that live-root exudations were not available to the microbial community possibly due to competition with plant roots for available nutrient resources. An increase in the abundance of plant-feeding, but not bacterial- or fungal-feeding, nematodes was associated with the presence of S. bigelovii. The functional diversity of a microbial community from an agronomic halophyte system was compared to natural and constructed halophyte salt marsh communities. Functional diversity of the microbial community at the agronomic sites was intermediate compared to the other sites; e.g., higher than the constructed marsh but lower than the natural salt marshes. Relationships among the study communities determined by microbial functional diversity reflected both habitat and geographical influences.