Effects of drying and freezing autumn leaves on leaching and colonization by aquatic hyphomycetes

SUMMARY 1. Drying or freezing autumn‐shed leaves of Betula papyrifera, Ulmus americana and Acer saccharum increased the leaching of soluble substances. The difference between fresh and treated leaves was most pronounced in birch. 2. Dried and frozen leaves supported more species of aquatic hyphomycetes during early decay, and conidium production from these fungi was higher. 3. Anguillospora filiformis was the most prolific spore producer on most samples. It declined in later stages of decay, when Articulospora tetradadia became more common. Crucella subtilis , an unspecialized parasite of aquatic hyphomycetes, was quite common in many samples. 4. In the autumn of 1990, 50% of elm and maple leaves, and 30% of birch leaves were shed before the air temperature dropped below 0°C; 10% (elm, maple) to 30% (birch) experienced more than one freezing period before being shed. 5. Water‐soluble extracts from leaves inhibited radial growth of four fungal species. Maple extracts generally had the greatest inhibitory effect, followed by birch and elm.