The hidden potential of saprotrophic fungi in arable soil: Patterns of short-term stimulation by organic amendments

Saprotrophic fungi are abundant in soils of (semi-)natural ecosystems,
where they play a major role in ecosystem functioning. On the contrary,
saprotrophic fungal biomass is remarkably low in intensively managed
soils, and this can have a negative impact on soil functioning.
Nevertheless, arable soils harbour a diverse pool of fungi, which can be
stimulated by organic amendments. Management targeted towards increasing
soil organic matter often coincides with an increase in fungal biomass,
but it can take years before effects are seen. However, a rapid
stimulation of fungal biomass at the start of the growing season could
immediately benefit crop production by improving nutrient availability,
soil structure, and suppression of soil-borne diseases. The objective of
this study is to realize a rapid increase in saprotrophic fungal biomass
with organic amendments. In controlled pot experiments, dried and milled
organic materials of different quality were added to an arable sandy soil.
Ergosterol-based fungal biomass and ITS2-based fungal community structure
were measured over a period of two months. Wood sawdust of deciduous tree
species and paper pulp resulted in a high and lasting increase of fungal
biomass, as opposed to transient effects given by cover crops and other
non-woody plant materials. Little or no stimulation of fungi was seen for
coniferous wood sawdust and agro-industrial by-products. Nitrogen
immobilization induced by sawdust and paper pulp was compensated for by
supplementing mineral nitrogen, which enhanced the stimulation of
saprotrophic fungi. The composition of the stimulated fungi was influenced
by the quality of organic amendments. In particular, deciduous wood
sawdust and paper pulp favoured saprotrophic ascomycete fungi (mainly
Sordariomycetes), with no increment in potential plant-pathogenic fungi.
Overall, our results point to a good perspective to use woody materials as
a sustainable soil improver via stimulation of saprotrophic fungi.