Biology subjects

Sigurdsson, B. D.

Publications and source records attributed to Sigurdsson, B. D..

4 recordsLinked to original sources

bioRxiv2026

Who and how much? Quantifying the role of trophic guilds in soil organic carbon mineralization

Understanding the biotic processes that drive soil organic carbon (SOC) mineralization is essential for predicting the climate warming-carbon cycle feedback. Here, we combined Tree-of-life sequencing (TOLseq; cross-domain profiling using ribosomal RNA) with quantitative conversion factors linking rRNA transcript abundance to biomass, to understand how soil food web changes affect SOC mineralization in an in situ soil warming experiment. Field observations showed that warming reduced SOC stocks, but after decades of warming SOC mineralization had acclimated. An energetic soil food web model revealed both bottom-up and top-down controls in the trophic cascades, shifting C flows from fungal and plant-associated channels towards the bacterial channel. This caused an increase in SOC mineralization rate in warmed soils of 30% per-unit biomass across the year.

microbiology↗

bioRxiv2025

Soil trace gas oxidizers divergently respond to short- and long-term warming

The upland soil microbiome is dominated by aerobic bacteria that oxidize atmospheric trace gases, including CO, H2, and CH4. As a result, soils are the largest biological sink for these climate-active gases. Whether global warming will enhance or suppress these processes remains unclear. Here, we studied the warming responses of soil trace gas oxidizers by profiling natural geothermal gradients in a subarctic grassland with over 60 years of field warming at +6{degrees}C. We integrate field flux measurements, ex situ biogeochemical assays, metagenomics, and metatranscriptomics to determine ecosystem and cellular-level responses. Our results show that the oxidation of atmospheric CO and H2, but not CH4, increased with long-term warming due to higher cell numbers. However, at the cellular level, trace gas oxidizers, especially methanotrophs, tended to reduce gas consumption and transcription of gas-metabolizing enzymes in response to long-term warming. Our findings suggest that soils may remain a robust sink for trace gases despite lower per-cell activity. This work establishes a framework for interpreting the relationships between temperature and microbial trace gas oxidation on timescales relevant to Earths climate system.

microbiology↗

bioRxiv2022

Community adaptation to temperature explains abrupt soil bacterial community shift along a geothermal gradient on Iceland

Understanding how and why soil microbial communities respond to temperature changes is important for understanding the drivers of microbial distribution and abundance. A unique area in Iceland, where soil temperatures have increased due to geothermic activity four years prior to sampling, creating a stable gradient of ambient to +40{degrees}C, allowed us to investigate the shape of the response to warming of soil bacterial communities, and their associated community temperature adaptation. We used 16S rRNA amplicon sequencing to profile bacterial communities, and bacterial growth based assays (3H Leu-incorporation) to characterize community adaptation using a temperature sensitivity index (SI, log (growth at 40{degrees}C/4{degrees}C)). Samples were taken from [≥]9 levels of warming (covering almost up to +40{degrees}C above ambient soil temperature), under both grassland (Agrostis capillaris) and forest (Picea sitchensis) vegetation. The soils had very different community composition, but temperature adaptation was the same. Both diversity and community composition as well SI showed similar threshold dynamics along the soil temperature gradient. There were no significant changes up to soil warming of approx. 6-9 {degrees}C, beyond which all indices shifted in parallel. The consistency of these responses gives strong support for a decisive role for direct temperature effects in driving bacterial community shifts along soil temperature gradients.

ecology↗

bioRxiv2017

Prolonged exposure does not increase soil microbial community response to warming along geothermal gradients

Predicting effects of climate change on ecosystem functioning requires knowledge of soil microbial community responses to warming. We used natural geothermal gradients (from +1{degrees}C to +19{degrees}C above ambient) in two subarctic grasslands to test the hypothesis that long-term exposure (>50 years) intensifies microbial community responses to warming compared to short-term exposure (5-7 years). Community profiles from amplicon sequencing of bacterial and fungal rRNA genes did not support this hypothesis: significant changes relative to ambient were observed from +9{degrees}C and upwards in the long-term and from 7{degrees}C to 11{degrees}C / +3{degrees}C to +5{degrees}C and upwards in the short-term, for bacteria and fungi, respectively. Our results suggest that bacterial communities in high-latitude grasslands will not undergo lasting shifts in community composition under the warming predicted for the coming 100 years. Fungal communities do appear to be temperature sensitive to the warming within this range, but only for short-term exposures.

ecology↗