Microbial and arbuscular mycorrhizal fungi diversity along altitudinal gradient in South American Puna grassland

LUGO MA; MENOYO E; ESTÉVEZ MC; FERRERO M; SIÑERIZ F

San Francisco

Congreso; XI International Congreso of Mycology.; 2005

Arbuscular mycorrhizal fungi (AMF) are main component of the microbial soil community and its diversity is associated with plant community structure and functioning. They are highly effective at capture and translocation of soil nutrients as phosphorus from soil to the plant. AMF interactions with bacteria have synergistic beneficial effect on plant growth, but little is known about these interactions in pot and crop systems. Puna is a South American stressed biogeographic region with unique features. Rhizospheric soil samples were taken along altitudinal gradient and bacterial and fungal biodiversity associated was analyze using PCR-DGGE and morphological methods, respectively. Methods Five sample sites were placed along an altitudinal gradient between 3320 and 3870 masl) in the Puna mountain grassland. Rhizospheric soil samples were collected from each 6 grass species as host, in each site. The AMF spores were extracted from soil by wet sieving and sucrose centrifugation and their diversity (density and richness) was quantified at 500X magnification under dissecting microscope using the gridline methods. The genomic DNA extracted directly from soils samples and from total bacteria grown over R2A medium plates was used as target in PCR reactions, using universal primer for Bacteria 341fGC/ 518r. Fragments of 16S rRNA gene were subsequent run on denaturing gradient gel electrophoresis (DGGE) on a 6% polyacrylamide gel containing 30% and 70% denaturing gradient. Results A wide range of phosphorus concentration (between 0.56 and 14.32 ppm) could be sampled at each species and altitude. Bacterial counts ranged between 1.3 x 102  and 5.5 x 105 CFU g-1 of soil. The number of DGGE bands per lane ranged between 4 and 12. Only one band is common to all sites. Predominant (defined by intensity and frequency of appearance) DGGE bands were excised and re-amplified for later sequencing. AMF spores diversity and spores species richness were low, only 5 glomalean species were found. The highest spore density value was 296 spores/100 ml of wet soil. Conclusions The increase of P concentration affected negatively to AMF root colonization and plant growth. The AMF spores diversity diminishing with higher P soil level. Richness of bands in DGGE gels seem to be related to P concentration present at soil.