Background/Question/Methods
We assessed the influence of litter chemistry on fungal community composition through early stages of decomposition. Specifically, we hypothesized that the abundance of a given fungal group on decomposing litter would be related to the chemical composition of that litter as well as the substrate preferences of the fungal group. To test our hypothesis, we decomposed litter of two plant species, Picea mariana (black spruce) and Populus tremuloides (quaking aspen), in otherwise-unmanipulated areas of an Alaskan boreal forest. We collected litter samples after 9, 10, 12, and 24 months of incubation. We PCR-amplified fungal 18S rDNA from the litter and created 13,067 clones. Genetic identities of clones were determined by using oligonucleotide fingerprinting of rRNA genes (OFRG). OFRG is an rRNA gene profiling method that sorts genes into taxonomic groups with a high degree of resolution, and has a large capacity for sample processing. We then merged our sequence database with that of a complementary database that characterized substrate response profiles of fungal taxa from the same sampling location.
Results/Conclusions
We identified 116 fungal taxa that were each represented by five or more clones. For these taxa, fungal community composition varied significantly among sampling times (P < 0.001) and between litter types (P < 0.001). Moreover, there was a significant interaction between sampling time and litter type (P < 0.001); fungal succession progressed differently between black spruce versus aspen litter. Taxa tended to be negatively related to one another overall (P = 0.037). In particular, fungal taxa tended to segregate among sampling times. For example, Dermateaceae and Leucosporidium groups were most abundant at early-succession; Cystofilobasidiales and Sistotrema oblongisporum at mid-succession; and Sarcosomataceae and Rhytismataceae at late-succession. The taxa that peaked in early- and mid-succession also tended to respond positively to arginine (an amino acid). In addition, S. oblongisporum responded negatively to tannin-protein additions. Shannon diversity shifted differently over time depending on litter type (P < 0.001). Specifically, diversity progressively decreased in spruce litter, but increased in aspen litter. Forthcoming chemical analyses will enable us to test whether variations in chemical content between litter types and among sampling times are linked to the documented variations in fungal community composition.