Colonization of growing media by saprophytic fungi - importance of carbon and nitrogen fractions

E. Meinken, D. Lohr, C. Wöck
In recent years the colonization of growing media by saprophytic fungi is of increasing concern. Due to poor appearance and possible harmful effects on plants and humans, risk of fungal colonization should be covered by quality assurance. One key factor for risk assessment might be a characterization of biodegradability of organic constituents, but common measurements of nitrogen or carbon provide little information about organic matter quality. Aim of the research was to explore (1) the intensity of fungal colonization for a range of growing media and (2) the suitability of hydrolysable carbon and nitrogen fractions for characterizing organic matter and to assess the risk of fungal colonization. Intensity of fungal colonization of 87 samples (lightly, moderately and strongly decomposed peat, green waste and bark compost, coir pith, wood fibre and various mixtures) was investigated. Limed and fertilized samples were inoculated with mycelium of Peziza ostracoderma and incubated for twelve days. Subsequently, content of ergosterol as indicator of fungal biomass was analysed. Concurrent samples were digested in 0.005 and 1 M HCl. In the digestion solution carbon was measured by ICP-OES and nitrogen by photometry after an UV-assisted oxidation. Total organic carbon (TOC) and total organic nitrogen (TON) were analysed by combustion methods. In contrast to fractions of hydrolysable nitrogen fractions, both fractions of hydrolysable carbon are suitable for characterizing degree of decomposition: first of all of the different types of peat, but also of all other materials. Also hydrolysable carbon shows a high positive correlation to fungal biomass. For total organic carbon significant negative correlations were found if peats were considered separately, but not if all materials were pooled. Results indicate that hydrolysable carbon could be used to assess risk of fungal colonization.
Meinken, E., Lohr, D. and Wöck, C. 2017. Colonization of growing media by saprophytic fungi - importance of carbon and nitrogen fractions. Acta Hort. (ISHS) 1168:325-332
Peziza ostracoderma, acid hydrolysis, organic matter quality, ergosterol

Acta Horticulturae