The strength and magnitude of the effects of climate warming on ecosystem processes such as carbon cycling remain uncertain. Microbes, in particular, soil fungi are central to these processes due to their roles as decomposers of soil organic matter and as determinants of plant diversity. Yet despite their importance, we lack a clear understanding of the long-term response of soil fungal communities to warming. Toward this goal, we assessed changes in the diversity and composition of soil fungi found in organic and mineral soil horizons following 5-20 years of soil warming. We hypothesized that functional groups such as symbionts, saprotrophs and pathogens would vary in their sensitivities to long-term warming. Soils were assayed for fungi from two replicated soil warming experiments at the Harvard Forest (Petersham, MA, USA) which had experienced 5°C above ambient soil temperatures for 5 and 20 years at the time of sampling. We assessed fungal diversity and composition by sequencing barcoded samples of the ITS1 region of rDNA using Illumina technology and analyzing the data using the QIIME bioinformatics platform.
Results/Conclusions
The effect of warming on fungal community structure was dynamic through time with pronounced differences in the responses among mycorrhizal, saprotrophic and pathogenic fungi. Overall, there was an initial decline in the richness and abundance of mycorrhizal and saprotrophic fungi with warming as compared to control plots, while pathogenic fungi remained invariant. In organic soils, the abundance of mycorrhizal fungi declined with chronic warming, whereas an increase in mycorrhizal fungal abundance was found in mineral soils exposed for the same duration of warming. Similarly, there was an initial overall decrease in the abundance of saprotrophic and pathogenic fungi assayed from mineral soils as compared to control plots. In contrast, organic soils exposed to 20 years of warming had an increase in the abundance of yeasts and wood decomposers compared to control plots, although under similar warming conditions, there was a decline in the richness and overall abundance of plant pathogenic fungi. Here we show that complex shifts in soil fungal communities occur following long-term soil warming and are likely due to differences in the dissipation of carbon among the soil horizons.