The fungal ecology of Sitka spruce stumps
A study of the fungal ecology of Picea sitchensis stumps on mineral soils on first rotation sites in Scotland was carried out to determine fungal colonization, succession and the mechanisms of fungal interaction. Fungal and bacterial colonization of stump and buttress roots of stumps 0, 7, 28 days, 12, 16 and 48/53 months old was assessed. Melanotus proteus was found in all 12 month old stumps; Sistotrema brinkmanni was recorded most frequently in 16 and 48/53 month old stumps. A series of in vitro experiments was carried out to identify interactions occurring between pairs of P. sitchensis fungi on Norkrans agar, P. sitchensis sawdust, root blocks and billets, to determine possible modes of interaction occurring in vivo. Fungi exhibiting antagonism toward Heterobasidion annosum in vitro were noted to determine possible in vivo applications as curative/preventative biological controls against H. annosum. Sitka spruce stumps were highly receptive to H. annosum basidiospore infection up to 24 hours after felling and showed a significant level of receptivity 7 days after felling. M. proteus infection was lower in live stumps, compared to dead or moribund stumps, and was reduced or inhibited in stumps inoculated with Resinicium bicolor sawdust inoculum. In vitro experiments indicated that 5% urea prevented M. proteus basidiospore germination and hyphal growth. Treating stumps or billets with a 20% urea solution, however, had no significant effect on M. proteus colonization. Antifungal metabolites were detectable in 85% of the 25 fungal species tested representing members of the Basidiomycotina, Deuteromycotina and Ascomycotina, when bioassayed with Cladosporium cucumerinum. The production of antifungal metabolites in Sitka spruce stumps by H. annosum, R. bicolor, Stereum sanguinolentum, M. proteus and Hypholoma fasciculare was demonstrated.