Microfungal Populations Associated with the Decomposition of Sugar Maple Leaf Litter

Abstract

Fungi were isolated by dilution plating from green and senescent sugar maple leaves and from decomposing leaf litter sampled at periodic intervals for three consecutive years. Despite quantitative variation, changes in the species composition followed a consistent pattern. Populations from the green and senescent foliage were dominated by a few ubiquitous taxa (e.g., Aureobasidium pullulans, Clad? osporium cladosporioides, and Phoma exigua) that remained abundant for up to eight months after leaf fall. Penicillium spp. (P. frequentans, P. multicolor, P. brevi-compactum and P. implicatum) were typically the first species to appear after abscission, and increased in relative abundance as decay progressed. Other fungi commonly isolated from the mineralized soil horizon (e.g., Acremonium spp., Paecilomyces spp. and Metarrhizium anisopliae) were not isolated until the first summer after abscission. The appearance of this last group of fungi was associated with increased species diversity and may be related to seasonal activity of soil invertebrates in the litter. The impact of seasonal conditions on the species composition ofthe sample populations obtained from the litter was explored. Undecayed leaves, kept in a laboratory freezer, were placed in the woods in the spring and summer. Numbers and kinds of fungi isolated from these leaves as they decayed were then compared to those isolated from litter that began a normal cycle of decay in the fall. Although Aureobasidium pullulans was the most abundant of the initial colonists when the undecayed leaves were placed in the woods in the fall and spring, penicillia dominated when the leaves were put out in the summer. These results suggested that the composition of populations that colonized the litter during at least the first months of exposure was influenced in part by the prevailing seasonal conditions. Thus, popular concepts of fungal succession based on changes in the nutritional composition of the substrate cannot entirely explain the changes in the composition of microfungal populations associated with the decay ofthe leaves.