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Access Type

Open Access Thesis

Document Type


Degree Program

Molecular & Cellular Biology

Degree Type

Master of Science (M.S.)

Year Degree Awarded


Month Degree Awarded



The year 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. Rising temperatures are largely attributed to increasing CO2 levels from the widespread burning of fossil fuels. Terrestrial ecosystems make up the largest global carbon reservoir. In the soil, microorganisms play major roles in carbon and nutrient cycling, decomposition, and mediation of plant health, among several others. Involvement in such important processes makes soil microbial communities incredibly insightful for understanding earth’s changing climate.

The Harvard Forests in Petersham, MA implement belowground heating cables to warm experimental soils 5°C above the ambient soil temperature. With this dramatic temperature difference, researchers intended to simulate a worst-case scenario for earth’s climate. However, upward trends in global warming make this projection not as far out of reach as originally thought.

In 2017, the heating cables in experimental soil plots were turned off after approximately 15 consecutive years of warming and the soil was allowed to re-equilibrate to the ambient temperature. Experimental soils took around 2 months to reach the same temperature as the control soils. Significant changes in soil respiration levels and moisture were observed, raising the question as to whether soil microbial gene expression levels changed as well. Soil samples were collected for bulk RNA extraction from both heated and control soil plots on the day the heating cables were turned off (Day 0) and sequenced on the Illumina NextSeq platform at the Department of Energy’s Joint Genome Institute.

Here I present a metatranscriptomic analysis of the Harvard Forest soil microbiome on Day 0 to uncover the soil microbial community’s transcriptional response to long-term warming. Major phyla that were less transcriptionally active in response to warming include Basidiomycota, Pseudomonadota, Bacteroidetes, and Acidobacteria, which have essential roles in decomposition, nutrient cycling, mediating plant health, and more. Phyla that were more transcriptionally active in response to warming include Actinobacteria, Ascomycota, and Chloroflexota, which participate in biogeochemical cycling, polymer breakdown, antimicrobial activity, and more. These changes in activity reflect the ways in which the soil microbiome responds to chronic warming.


First Advisor

Jeffrey Blanchard

Second Advisor

Laura Katz

Third Advisor

Jessica Rocheleau

Fourth Advisor

Samuel Hazen