Aspects of the microbiology and oxidation of wicken fen soil

Abstract

Microbial populations of three different layers of undrained sedge peat in Wicken Fen and of the surface layer of an adjacent cultivated garden soil developed from the peat were examined. The surface layer (0–7.5 cm) of the undrained peat had a rhizosphere population of Gram-negative bacteria, including Pseudomonas, Enterobacter and Serratia, as well as a large Bacillus population; fungi, actinomycetes and pleomorphic bacteria were less important; anaerobes constituted 9 per cent of the total bacterial populations; and protozoan populations were low, a feature attributed in part to the presence of high Serratia populations. The subsurface layer of the sedge peat, at a depth of 7.5–15 cm, had a smaller Gram-negative population; spore-forming and pleomorphic bacteria, and actinomycetes were relatively more important; and there was a slightly larger protozoan population. The deep layer (sampled at 1 m) had a reduced population. Bacillus spores forming 44 per cent of the total bacterial populations, and anaerobes 25 per cent; and the protozoan fauna was small. The surface layer (0–7.5 cm) of the garden soil had a more diverse microflora; algae, actinomycetes and moulds were more numerous; the bacteria showed lower counts than were found in the upper peat layers (0–7.5 and 7.5–15 cm) and only 2 per cent were anaerobes; spores formed only 5 per cent of the count, but vegetative Bacillus cells formed the major part of the bacterial flora. Gramnegative and pleomorphic bacteria being of less importance; and the garden soil had the richest and most active protozoan fauna. Attempts to isolate nitrogen-fixing Clostridium proved negative, but strains of Bacillus polymyxa capable of growing in a nitrogen-free medium were isolated from all the layers and appeared to constitute the principal nitrogen-fixing population of these layers, at least under anaerobic conditions. Respiratory measurements showed a very low rate of carbon dioxide production, generally depressed by anaerobic conditions. Only the upper undrained peat layers showed a marked response to added glucose. From 14C dating of the peat profile down to the underlying clay, and from measurement of boron concentrations, it appeared that there might have been a delay of some hundreds of years between the marine invasion and commencement of peat formation some 4000 years ago; and that peat formation proceeded more rapidly during the first 2000 years of this period than in the last 2000 years. Fire and erosion, rather than microbial oxidation, appear to have been primarily responsible for the loss of the peat during the last two centuries. The microbial oxidation of peat declines with increasing age of the carbon.