Leaf surface roughness influences colonization success of aquatic hyphomycete conidia

Aquatic hyphomycetes are primary colonizers and decomposers of deciduous leaves decaying in streams. Conidial attachment to new substrata is a crucial first step in their life cycle, and the dominant spore morphologies – multiradiate or sigmoid – are assumed to have been shaped by convergent evolution to increase the probability of attachment to a substratum. Another factor influencing attachment success is roughness of the leaf's surface. In SEM preparations, we estimated the three roughness parameters Ra, Rz and Rq of upper and lower surfaces of linden (Tilia cordata), maple (Acer rubrum) and elm (Ulmus americana) leaves. Generally, roughness values were highest with linden and lowest with maple leaves, but the greatest roughness was measured on the lower surface of elm. In 48 h, target leaf disks captured approx. 20 % of the conidia released from stream-exposed inoculum disks in microcosms. Capture rates of the six surfaces correlated significantly with all three roughness parameters. Estimated R2 was around 0.4, indicating surface factors other than roughness influenced conidial attachment. The sigmoid conidia of Anguillospora filiformis were captured at a greater rate than the tetraradiate conidia of Articulospora tetracladia and Clavariopsis aquatica.