Shifts in the microbial community in rhizosphere and non-rhizosphere soils during the growth of Agrostis stolonifera

Abstract

An investigation was conducted into the use of phospholipid fatty acid (PLFA) profiles to follow temporal shifts in microbial community structure. A laminar pot was designed to allow the harvest of an intact layer of rhizosphere soil 0–2 mm from plant roots without the removal of the root material itself. Agrostis stolonifera plants were grown under controlled conditions in environmental chambers for 70, 90, 120 and 160 days. A subset of pots was fertilised with N/P/K after 100 days. Over the 90 days between the first and last harvests microbial biomass declined by 20%. At 70 days respiration was approximately 50% higher in the rhizosphere compared to the bulk soil. This difference had declined to <10% by the end of the experiment. PLFA analysis showed significant changes in microbial community structure with time. In particular, the unsaturated fatty acids commonly found in Gram-negative bacteria and fungi increased with age. Principal component analysis (PCA) of fatty acid data showed: separation of bulk and rhizosphere soils from 90 days onwards, and; fertiliser addition and rhizosphere development produced similar shifts in community structure.