Microbial communities in rhizosphere soil from sugarcane (Saccharum inter-specific hybrids) and bulk soil were compared at paired field sites with and without a sugarcane cropping history to determine whether monoculture affects soil microbial community composition. Differences were evaluated for culturable microorganisms and functional diversity indicated by community level physiological profiles (CLPP). Qualitative differences in rhizosphere bacterial communities were detected between sites with no sugarcane cropping history (N sub(site)) and sites with a long-term sugarcane cropping history (L sub(site)). More fluorescent pseudomonads were detected in N sub(site) than L sub(site) rhizosphere soil at two of three sites, and Actinobacteria were more numerous in N sub(site) than L sub(site) rhizosphere soil at one site. Fusarial fungi were more numerous in N sub(site) than L sub(site) rhizosphere soils. Bacteria were more numerous in rhizosphere soil compared to bulk soil. Total bacterial, pseudomonad, and Actinobacteria population densities were greater in bulk soil from an N sub(site) compared to an L sub(site). CLPP distinguished bulk from rhizosphere soil at one of two sites and N sub(site) and L sub(site) rhizosphere soils at two of four sites. Site affected CLPP similarity more than cropping history. The results demonstrated that sugarcane monoculture can affect the composition of the microbial community in field soil. The findings have possible implications for reduced yields associated with sugarcane monoculture.
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