organic matter

soil fungi

Heterobasidion

Oidiodendron

Trichoderma

Microbiology

Scots pine and birch were planted in soils left fallow for 3, 6, or 15 years after arable cropping. We investigated the effects of Scots pine sawdust amendment, applied a year before planting, on the abundance and diversity of culturable soil fungi 4, 14, and 16 years after treatment. The treatment was intended to increase populations of fungi antagonistic to Heterobasidion and soil suppressiveness to tree root pathogens. Effects of treatment on fungal abundance were inconsistent; general or local, seasonal or continuous decreases or increases, often significant, were observed. There were, however, significant and continuous increases in frequency of antagonistic Clonostachys + Trichoderma and the mycorrhizal fungus Oidiodendron in treated soils compared with the control in all three fallow areas. Local and seasonal decreases in frequency of Penicillium + Talaromyces, Pseudogymnoascus, and entomopathogenic and nematophagous species were observed in treated soils. Abundance of fungi was moderately and negatively correlated with soil pH (R² = -0.61, P<0.0001). Abundance of Clonostachys + Trichoderma was moderately and positively correlated with mean annual temperature and positively correlated with total annual rainfall. Fresh sawdust, even applied undecomposed and without added mineral N (to aid microbial decomposition and plant growth), may be beneficial in sandy soil.