Rhizosphere microbial community structure in relation to root location and plant iron nutritional status - PubMed (original) (raw)

Rhizosphere microbial community structure in relation to root location and plant iron nutritional status

C H Yang et al. Appl Environ Microbiol. 2000 Jan.

Abstract

Root exudate composition and quantity vary in relation to plant nutritional status, but the impact of the differences on rhizosphere microbial communities is not known. To examine this question, we performed an experiment with barley (Hordeum vulgare) plants under iron-limiting and iron-sufficient growth conditions. Plants were grown in an iron-limiting soil in root box microcosms. One-half of the plants were treated with foliar iron every day to inhibit phytosiderophore production and to alter root exudate composition. After 30 days, the bacterial communities associated with different root zones, including the primary root tips, nonelongating secondary root tips, sites of lateral root emergence, and older roots distal from the tip, were characterized by using 16S ribosomal DNA (rDNA) fingerprints generated by PCR-denaturing gradient gel electrophoresis (DGGE). Our results showed that the microbial communities associated with the different root locations produced many common 16S rDNA bands but that the communities could be distinguished by using correspondence analysis. Approximately 40% of the variation between communities could be attributed to plant iron nutritional status. A sequence analysis of clones generated from a single 16S rDNA band obtained at all of the root locations revealed that there were taxonomically different species in the same band, suggesting that the resolving power of DGGE for characterization of community structure at the species level is limited. Our results suggest that the bacterial communities in the rhizosphere are substantially different in different root zones and that a rhizosphere community may be altered by changes in root exudate composition caused by changes in plant iron nutritional status.

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Figures

FIG. 1

(A) Microbial community 16S rDNA fingerprints of bacteria from different locations on iron-stressed (+ Iron) and iron-sufficient (− Iron) barley roots as determined by PCR-DGGE. (B) Line image profiles generated by image analysis. The arrows indicate a common band determined to be plastid DNA (top arrow) and a second predominant band (bottom arrow) that was cloned and sequenced for all root locations. Lanes: 1 and 5, old roots; 2 and 6, sites of lateral root emergence; 3 and 7, nongrowing root tips; 4 and 8, elongating new root tip.

FIG. 2

Ordination diagram of microbial communities associated with different root locations on iron-stressed and nonstressed barley plants generated by correspondence analysis of 16S rDNA profiles for individual root segments and adhering rhizosphere soil. Symbols: ▴ and ▵, new root tips; ⧫ and ◊, old root tips; ● and ○, lateral emergence sites; ■ and □, old roots; open symbols, iron-sufficient plants; solid symbols, iron-deficient plants.

FIG. 3

Line graph profiles of 16S rDNA band patterns resulting from DGGE of microbial communities associated with iron-stressed (− Fe) and nonstressed (+ Fe) barley root tips. Each profile shown was generated from root tips of replicate plants in different containers. The profiles reveal the very consistent community structure associated with this root zone and the impact of iron stress on community species composition.

FIG. 4

Canonical correspondence analysis, showing the relative similarities of microbial communities associated with specific barley root locations as affected by plant iron nutritional status. Iron is included as a covariable on the x axis. (A) New root tips. (B) Secondary, nongrowing root tips. (C) Sites of lateral root emergence. (D) Older roots axes distal from root tips. Symbols: ▴, individual 16S rDNA bands ordinated with respect to plant iron nutritional status; ○, centroids representing 16S rDNA from communities associated with iron-sufficient plants; ●, centroids representing 16S rDNA samples from iron-deficient plants.

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Rhizosphere microbial community structure in relation to root location and plant iron nutritional status - PubMed (original) (raw)