Stable Isotope Probing Reveals Microbial Responses to Changing Redox Conditions in a Tropical Forest Soil
Abstract
In many wet tropical forest soils, fluctuating redox conditions constrain a metabolically diverse microbial community that mediates C turnover and critical ecosystem processes. However, global climate change has led to inconsistent redox periodicity in these systems. We conducted a 44-day incubation with wet tropical soils to assess microbial response to static oxic, static anoxic, and fluctuating redox regimes. We used 13C-enriched plant litter, biogeochemical analyses, and a multi-omics approach to distinguish C flows and microbial consumers of fresh litter versus native soil organic matter. Gross soil respiration was highest under static oxic conditions, while litter C respiration was highest under static anoxic conditions. The dissolved organic C pool was also largest under static anoxic conditions and increased immediately following an oxic-anoxic transition. Isotope-resolved metabolomics revealed distinct litter-derived decomposition products and microbial metabolites under oxic versus anoxic conditions. Similarly, metagenome-assembled genomes indicated diverse genomic potential, with distinct differences between community capacity under static oxic versus anoxic conditions. Quantitative stable isotope probing provided evidence for phylogenetically conserved trends in litter C assimilation. Most notably, bacteria of the phylum Firmicutes increased in relative abundance and assimilated more litter C under static anoxic conditions. However, several taxa exhibited a surprising tolerance to all redox regimes, indicating that some organisms do not conform to obligate aerobic or anaerobic lifestyles in this naturally dynamic system. Furthermore, many of the taxa that actively assimilated litter C were not abundant. This highlights the potential contribution of `rare' organisms to the terrestrial C cycle. Together, these findings show that shifting redox periodicity influences C cycling in tropical forest soils through its effects on microbial community composition and activity.
Work at Lawrence Livermore National Laboratory was conducted under the auspices of Contract DE-AC52-07NA27344 and SCW1478 and SCW1632.- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2020
- Bibcode:
- 2020AGUFMB125...06H
- Keywords:
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- 0414 Biogeochemical cycles;
- processes;
- and modeling;
- BIOGEOSCIENCES;
- 0428 Carbon cycling;
- BIOGEOSCIENCES;
- 0465 Microbiology: ecology;
- physiology and genomics;
- BIOGEOSCIENCES;
- 0470 Nutrients and nutrient cycling;
- BIOGEOSCIENCES