CANCELLED - A metatranscriptomic analysis of the long-term effects of warming on the Harvard Forest soil microbiome

Background/Question/Methods

: 2020 marked one of the hottest years on record to date, with the average global temperature reaching 1.2 °C above pre-Industrial era (1880) temperatures. Soil microorganisms play major roles in carbon and nutrient cycling, decomposition, and maintaining plant health, among others. Involvement in such processes makes soil microbial communities incredibly insightful for understanding earth’s changing climate. The Harvard Forest Long-Term Ecological Research site in Petersham, MA implements belowground heating cables to warm experimental soils 5°C above the ambient soil temperature. After 15 years of heating, the cables were turned off and the soil was allowed to re-equilibrate to the ambient temperature. Significant changes in soil respiration levels and moisture were observed, leaving the question as to whether the genes expressed by the soil microbial community changed as well. Expression of genes involved in biogeochemical cycling (C, N, S, P, and Fe) and chitin utilization are hypothesized to remain lower as a result of long-term warming. RNA was extracted from both heated and control soils and sequenced for bioinformatic analysis. By comparing microbial gene expression when heated and controlled soils have no temperature difference, to that upon the resumption of heating, the long-term response to elevated soil temperatures can be elucidated.

Results/Conclusions

: Metatranscriptome sequencing from soils collected at the Barre Woods site on Day 0 of the temperature toggle experiments produced a total of 184,499,712 protein coding reads obtained from 28 soil samples. Sequences were assigned to 1,483 taxonomic groups across all domains of life and 6,241 functional features. Changes in functional processes were linked to several biogeochemical processes, including changes in carbohydrates, aromatics, sulfur (S), nitrogen (N), phosphorus (P), and potassium (K) metabolism. For instance, the transcriptional abundance of carbon metabolism, respiration, and cellular processes increased with the temperature effect in the organic horizon. In contrast, S and P metabolism in conjunction with viral related pathways decreased in abundance. In this study we demonstrated that long-term warming has resulted in significant changes in soil biodiversity and soil biogeochemical cycling specifically in the organic horizon.