Studies on microfungi from litter and soil in relation to the ecology of lignin decomposition

Abstract

The studies reported here on microfungi from litter and soil involved:

1) The behaviour of microfungi in pure culture towards lignin related-phenolic acids. 2) The chemistry and microbiology of Scots Pine litter in relation to lignin decomposition. 3) The decomposition of ferulic acid by mixed populations of microorganisms.

Ferulic acid incorporated into agar could be inhibitory or stimulatory to the spore germination and germ hyphal growth of microfungi depending upon its concentration and the fungal species. Within a certain concentration range, the total growth potential of some Angiosperm leaf saprophytes was depressed relative to control whereas there was an increase in the case of conifer needle litter saprophytes and some common soil fungi. Other phenolic acids produced similar patterns of results but the differential effects were generally less marked.

The ability of litter and soil microfungi to utilise ferulic acid as a sole carbon source was defined from the decomposition of the substrate after inoculating culture solution with spores. The pattern in the ability to decompose ferulic acid was not related to the effects of this compound on germination on agar or in the liquid medium.

Dothichiza pityophila and Fusicoccum bacillare were isolated as the principal primary saprophytes of Scots Pine needle litter while the widespread primary saprophytes of Angiosperm leaf litters, including Aureobasidium pullulans were absent, confirming and reinforcing the results of previous European work. The use of Infra-red spectroscopy of finely divided, but unextracted, Pine needles and humus to follow the course of the decomposition of the litter permitted an evaluation of the role of soil-inhabiting fungi in this process.

Burial of litter needles in a deciduous woodland soil or in a field soil led to colonisation by several soil fungi not characteristic of Pine litter, notably Gliocladium roseum and an Actinomycete of genus Nocardia. These two species were able to colonise the needle interior in the presence of needle saprophytes surviving in buried needles whereas Trichoderma viride remained restricted to the needle surface by prior- colonisation.

Finally, experiments are described in which Pine needle and soil material from the burial experiments and samples of two other soils of contrasting ligninolytic characteristics were used as inoculum for the decomposition of ferulic acid, the results of these experiments relating to known microbiological and chemical properties of the soils.

The importance of phenolic acids released during lignin decomposition in the fungal colonisation of substrates in litter and soil is discussed, and some conclusions are made regarding the validity of phenolic acids as 'lignin model compounds'.