Total and active soil fungal community profiles were significantly altered by six years of warming but not by grazing

We examined the responses of total and active soil fungal communities to experimental warming, moderate grazing, and their combination. The six years of field experiments were established in a Tibetan alpine meadow. An infrared heating system was used to simulate warming, and the grazing was conducted by a combination of sheep grazing and clipping. Total and active soil fungal community profiles were determined using MiSeq sequencing of internal transcribed spacer (ITS) DNA and RNA, respectively. Fungal abundance and rDNA transcriptional activity were analyzed through real-time PCR. The results showed that the warming significantly changed the community structure of soil fungi, particularly the active populations. Specific changes in fungal community profiles under the warming scenario included an increase in the proportion of Dothideomycetes (a potential oligotrophic class) and a decrease in the proportion of active plant-symbiotic lineages (e.g., Glomerales). FUNGuild-based functional predictions suggested that warming significantly reduced the proportions of arbuscular mycorrhizal and active saprotrophic fungi. We compared our results to those of another investigation performed at the same location, and found that the ITS-FUNGuild approach was even more sensitive than the 18S rDNA-based method with respect to identifying arbuscular mycorrhizal fungal taxa. Additionally, the warming attenuated the interactions among fungal species, reduced the Chao 1 index of active fungal communities, increased the active fungal community dispersion, and tended to suppress the transcription of fungal rDNA. In contrast, no significant effects of grazing and warming-grazing interactions on soil fungal communities were observed. These findings indicate that global warming may weaken the capacity of soil fungi to decompose organic matter and to facilitate plant nutrient absorption, whereas fungi in Tibetan alpine meadow soils are insensitive to moderate grazing.