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Document Type
Poster
Publication Date
Fall 10-1-2026
Abstract
Soil microbial communities play critical roles in ecosystem processes such as nutrient cycling and organic matter decomposition, yet it remains unclear how losses in microbial diversity influence these functions independent of total biomass. In this study, we examined how reductions in microbial diversity affect soil metabolic activity while controlling for microbial abundance. We used a dilution-to-extinction approach by inoculating sterilized soil with 10-fold serial dilutions of a soil slurry (10⁰ to 10⁻⁶), followed by a 21-day incubation to allow microbial regrowth. Biomass (measured as phospholipid phosphate), and metabolic activity (measured with BIOLOG EcoPlates) were used to quantify microbial biomass and patterns of carbon utilization. Biomass were similar across all dilution treatments, including 10⁻⁶; however, metabolic activity declined with increasing dilution. Treatments 100 (control) and 10-1 reached higher substrate utilization more quickly, whereas 10⁻⁵ and 10⁻⁶ showed lower overall substrate utilization. Substrate richness decreased from 29 substrates in 10⁰/10⁻¹ to 17 in 10⁻⁵ and to 2 in 10⁻⁶, with parallel declines in Shannon diversity (p < 0.001). These results indicate that recovery of total abundance does not correspond to recovery of ecosystem functional capacity. In addition to overall metabolic activity, patterns of carbon substrate use shifted with decreasing diversity. Canonical variates analysis explained 83.9% of total variation and showed strong separation of sterile and 10⁻⁶ dilution from all treatments, indicating a distinct metabolic profile at the highest dilution. Lower dilutions (10⁰–10⁻¹) were associated with carbohydrate and aromatic substrates (N-acetyl-D-glucosamine, D-galacturonic acid), whereas 10⁻⁶ was characterized by relative enrichment of select carboxylic acids (D-malic acid) and depletion of several carbohydrate and amine utilizers. Heatmap analysis demonstrated progressive loss with dilution: 27 to 31 substrates highly utilized in 10⁰/10⁻¹ but largely absent in 10⁻⁶. Bacterial functional groups present in 10⁻³ and 10⁻⁵ that metabolized carboxylic acids (e.g., D-glucosaminic acid, α-ketobutyric acid), carbohydrates (D,L-α-glycerol phosphate, N-acetyl-D-glucosamine), and amino acids (L-phenylalanine, L-threonine, L-asparagine) were progressively reduced with increasing dilution. At 10⁻⁶, functional groups capable of metabolizing polymers, carbohydrates, and amino acid substrates were largely undetected. Together, these findings support the ecological hypothesis that microbial diversity stabilizes ecosystem functioning by maintaining functional redundancy and expanding metabolic niche space. Diversity loss altered community metabolic profiles even when biomass remained constant, demonstrating partial decoupling between microbial abundance and ecosystem function. This pattern is consistent with biodiversity-ecosystem function theory, where reductions in taxonomic diversity constrain functional capacity despite compensatory population growth of surviving taxa.
Department
Department of Biology, DePauw University, Greencastle, IN
Project Mentor
Professor Philips Akinwole
Recommended Citation
Doan, Thi '27; Le, Uyen '27; Hickman, Crimson; and Akinwole, Philips, "Dilution-to-Extinction Reveals Shifts in Carbon Substrate Utilization and Functional Capacity Following Soil Microbial Diversity Loss" (2026). Annual Student Research Poster Session. 268.
https://scholarship.depauw.edu/srfposters/268
Funding and Acknowledgements
We thank DePauw University’s Biology Department and Dr. Akinwole for the support and lab materials. We thank Dr. Frederick Hendricks, the Biology department, and DePauw’s Student Research & Artistic Grant for funding.