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 of 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. This study explores the possibility to realize such a rapid increase of 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 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 at a good perspective to use woody materials as sustainable soil improver via stimulation of saprotrophic fungi.

腐生真菌（saprotrophic fungi）广泛存在于（半）自然生态系统的土壤中，在生态系统功能运转中扮演核心角色。与之形成鲜明对比的是，集约化管理农田土壤中的腐生真菌生物量显著偏低，这会对土壤生态功能造成负面影响。尽管如此，耕地土壤仍保有多样的真菌类群，可通过施加有机改良剂得到有效刺激。以提升土壤有机质含量为目标的农田管理措施，通常会伴随真菌生物量的提升，但该效应的显现往往需要数年周期。然而，若能在生长季初期快速提升腐生真菌生物量，则可通过改善养分有效性、优化土壤结构以及抑制土传病害，直接为作物生产带来增益。本研究旨在探索通过有机改良剂实现腐生真菌生物量快速提升的可行性。在受控盆栽试验中，研究人员将不同品质的干燥粉碎有机物料添加至耕地砂质土中，并在为期两个月的试验周期内，测定了基于麦角固醇（ergosterol）的真菌生物量，以及基于内转录间隔区2（ITS2）的真菌群落结构。结果显示，落叶树种木屑与纸浆可使真菌生物量出现高水平且持久的提升，而覆盖作物及其他非木质植物物料仅能带来短暂的刺激效应。针叶树木屑与农工业副产物则几乎未对真菌群落产生显著刺激效果。木屑与纸浆引发的氮固持效应，可通过补充矿质氮得到抵消，此举还能进一步增强腐生真菌的增殖效果。受刺激的真菌群落组成受有机物料品质的调控：其中落叶树种木屑与纸浆尤其有利于腐生子囊菌（主要为粪壳菌纲Sordariomycetes）的增殖，且不会增加潜在植物病原真菌的丰度。总体而言，本研究结果表明，通过木质物料刺激腐生真菌以将其作为可持续土壤改良剂，具备良好的应用前景。