Effects of pH on the comparative culturability of fungi and bacteria from acidic and less acidic forest soils

Abstract

Under aerobic conditions, the culturable microbial population of acidic forest soils was more tolerant to acidic cultivation conditions than was the culturable microbial population of less acidic soils. The number of culturable bacteria decreased sharply under acidic cultivation conditions, while the number of culturable fungi remained relatively constant over the pH range 2.2-6.5. The ratios of culturable bacteria to culturable fungi were greater than one at pH 6.5; in contrast, the bacteria-to-fungi ratios were less than one at pH 2 . 2 4 . At pHs approximating those of the soils examined, culturable fungi predominated the culturable microbial community in acidic soils. However, relative to the populations resolved, acidic forest soils displayed a more acid tolerant bacterial population than did less acidic forest soils. The culturable fungal population contained both filamentous and yeast morphologies. An acid-tolerant fungal isolate that grew at pH 1 was identified as a subspecies of Penicillium frequentans, and an acid-tolerant yeast that grew at pH 2 was identified as the yeast stage of the basidjomycetes Ustilago maydis.

Effects of Pseudomonas fluorescens F113 on Ecological Functions in the Pea Rhizosphere Are Dependent on pH

“…The total bacterial and yeast populations were significantly greater pH 6.4 than the two lower pH's, whereas the fungal populations increased when the pH was both reduced to 4.4 or increased to 6.4. This is a logical progression as fungi prefer more acidic and bacteria less acidic conditions and reflects previous results where the number of culturable bacteria decreased sharply under acid cultivation conditions whilst the number of culturable fungi remained relatively constant over a pH range of 2.2-6.5 [17].…”

Clostridium akagii sp. nov. and Clostridium acidisoli sp. nov.: acid-tolerant, N2-fixing clostridia isolated from acidic forest soil and litter.

“…Anoxic microsites exist within soils (Smith, 1980 ;Sexstone et al, 1985) and needle litter (van der Lee et al, 1999), and the spontaneous capacity of acidic soils to produce CO # under anoxic conditions is approxi- C. H. Kuhner and others mately one-third of that under oxic conditions (Matthies et al, 1997). A number of anaerobic processes including methanogenesis (Williams & Crawford, 1984 ;Goodwin & Zeikus, 1987 ;Crill et al, 1988), denitrification (Shirey & Sexstone, 1989 ;Blo$ sl & Conrad, 1992 ;Nielsen et al, 1994) and sulfate reduction (Wieder et al, 1990) have been demonstrated to occur in acidic soils.…”

Forest floor properties across sharp compositional boundaries separating trembling aspen and jack pine stands in the southern boreal forest

“…Given that fungi are more acid tolerant and can metabolize substrates of lower chemical quality (i.e. more recalcitrant to decomposition) than bacteria (Högberg et al 2007;Matthies et al 1997), we should observe bacteriabased food webs under aspen, and fungi-based foodwebs under jack pine. Bacteria generally grow faster and are more nutrient rich than fungi (Wardle 2002), hence we expect higher nutrient and energy cycling rates under aspen.…”