Microbial community in the rhizosphere of native plant species growing on reclaimed coal mine soils varying in age

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Abstract
Soil microorganisms in the rhizosphere are important in the revegetation and stabilization of drastically disturbed areas in the semiarid Southwest, as the microbial community is often responsible for the modification of many adverse soil properties. In this study, the soil microbial community was evaluated in the rhizosphere and the nonrhizosphere of two grass species, galleta (Hilaria jamesii,) and alkali sac‐aton (Sporobolus airoides,), and a shrub, fourwing saltbush (Atriplex canescens), growing on a reclaimed coal mine spoil 3 months to 2.25 years after topsoiling and revegetation. Many soil chemical properties and most microbial populations decreased in both soil zones with reclamation age. However, the rhizosphere of galleta and alkali sacaton still had significantly higher levels of soil N, P, organic matter (OM), and microbial populations than did the nonrhizosphere after 2.25 years of plant growth. The rhizosphere of fourwing saltbush had significantly higher EC and SAR values and fungal propagule levels than did the nonrhizosphere. The rhizo‐spheres of the two grass species had significantly higher levels of N, P, OM, and bacterial populations than the rhizosphere of fourwing saltbush. In contrast, the rhizosphere of fourwing saltbush had significantly higher cations and fungal propagule levels than the rhizosphere of the grass species. The diversity of fungal groups generally increased in both soil zones, especially in the nonrhizosphere, with reclamation age. After 2.25 years of plant growth, fungal diversity was lower in the more nutrient‐rich rhizosphere of the three plant species than in the nonrhizosphere soil where there were lower nutrient amounts. Fungal groups changed between soil zones and among and within plant species as the plants aged. Chrysosporium spp. dominated the rhizosphere and nonrhizosphere of all three plant species after 3 months; after 2.25 years Aspergillus spp. dominated the rhizosphere of both grass species, and Penicillium spp. dominated the rhizosphere of fourwing saltbush. Overall, these results showed that each plant species, via its rhizosphere microflora, may contribute differently to revegetation success.