Development of microbial communities associated with tobacco root systems

Abstract

Comparisons were made between patterns of microbial community development associated with tobacco root systems in nonautoclaved and autoclaved soils. Patterns of root system colonization by fluorescent Pseudomonas spp, actinomycetes and other bacteria did not differ between the two soils. Fungal community diversity, measured in terms of number and densities of taxa present, was greater in association with rhizospheres and root surfaces of tobacco grown in nonautoclaved soil than in autoclaved soil. Diversity within the rhizosphere and at root surfaces increased more slowly over time in autoclaved soil than in nonautoclaved soil. At all sampling dates fungal colonization of surfaces of first-order roots was more extensive in nonautoclaved soil than in autoclaved soil. As measured by Lloyd's index of mean crowding, average densities of hyphae in colonized regions of root surfaces were greater in nonautoclaved soil than in autoclaved soil at 7 and 28 days of plant growth. Colonized regions along root surfaces were more patchy or aggregated within autoclaved soil than in nonautoclaved soil as determined from values of Lloyd's index of patchiness. Measurements describing root surface colonization remained fairly constant over time because samples at each date were taken from tissues of similar physiological age.