Biology subjects

Whitman, T.

Publications and source records attributed to Whitman, T..

3 recordsLinked to original sources

bioRxiv2026

Persistent but variable effect of experimental laboratory burns on microbial community resistance, resilience, and function across contrasting boreal forest soils

Boreal forests stretch across vast swaths of the northern hemisphere, are shaped by wildfire, and play an important role in the global carbon cycle. Microorganisms play a critical role in soil nutrient cycling in these ecosystems, yet there are many open questions about the impacts of wildfire on microbially mediated soil biogeochemical cycles. In this study, we used laboratory burns and soil incubations of intact soil cores collected from two distinct soil types -- Histosols and Gleysols -- from boreal forest within Wood Buffalo National Park, Alberta, Canada, to assess burn effects on soil bacterial and fungal community composition and function. We compared resistance and resilience to burning for microbial communities vs. resistance and resilience to burning for soil pH and soil respiration to assess the relationships between burn-induced shifts in microbial community composition, the soil environment, and microbial activity. To link shifts in microbial community composition to potential community function, we measured glucose-specific carbon use efficiency (CUE) and assessed its relationship with weighted mean predicted 16S rRNA gene copy numbers for bacterial communities and FUNGuild-estimated relative abundance of putative symbiotrophic and saprotrophic fungi in burned and unburned soils. Microbial community resistance and resilience to burning varied across soil type with higher resistance of both bacterial and fungal communities from Histosols compared to the O horizons of Gleysols. This may be explained by a larger impact of burning on microbes in the thinner Gleysol O horizons. The relatively low resilience of bacterial and fungal communities to burning as well as the failure of resilience to increase with time since burning supports previous reports of post-burn microbial community recovery occurring over years rather than months. Burning caused a decrease in CUE with larger decreases following longer, hotter burns, which correlated with an increase in weighted mean predicted 16S rRNA gene copy number, raising the possibility that copy number could serve as a proxy for post-fire CUE in boreal forest soils, though more research is needed to constrain the effects of environmental conditions, substrates, and time since fire on this relationship. These findings suggest several ways in which burn-induced shifts in microbial community composition reflect altered microbial community function in meaningful ways for soil carbon cycling.

ecology↗

bioRxiv2017

Microbial community assembly differs by mineral type in the rhizosphere

Inputs of root carbon (C) fuel growth of nearby soil microorganisms. If these microbes associate with soil minerals, then mineral-microbiome complexes near roots could be a gateway towards stabilization of soil carbon and may influence the quantity and quality of persistent SOM. To investigate the interactions between roots, soil minerals, and microbes, we incubated three types of minerals (ferrihydrite, kaolinite, quartz) and a native soil mineral fraction near roots of a common Californian annual grass, Avena barbata, growing in its resident soil. We followed microbial colonization of these minerals for 2.5 months - the plants lifespan. Bacteria and fungi that colonized mineral surfaces during this experiment differed across mineral types and differed from those in the background soil, implying microbial colonization was the result of processes in addition to passive movement with water to mineral surfaces. Null model analysis revealed that dispersal limitation was a dominant factor structuring mineral-associated microbial communities for all mineral types. Once bacteria arrived at a mineral surface, capacity for rapid growth appeared important, as ribosomal copy number was significantly correlated with relative enrichment on minerals. Glomeromycota (a phylum associated with arbuscular mycorrhizal fungi) appeared to preferentially associate with ferrihydrite surfaces. The mechanisms enabling colonization of soil minerals may be foundational to the overall soil microbiome composition and partially responsible for the persistence of C entering soil via plant roots.

microbiology↗

bioRxiv2016

Spatiotemporal Dynamics of the Bacterial Microbiota and Methanotrophic Bacteria on Lotic Cladophora glomerata (Chlorophyta)

The branched periphytic green alga Cladophora glomerata, often abundant in nearshore waters of lakes and rivers worldwide, plays important ecosystem roles, some mediated by epibiotic microbiota that benefit from host-provided surface, organic C, and O2. Previous microscopy and high throughput sequencing studies have indicated surprising epibiont taxonomic and functional diversity, but have not included adequate consideration of sample replication or the potential for spatial and temporal variation. Here we report the results of 16S rRNA amplicon-based phylum-to-genus taxonomic analysis of Cladophora-associated bacterial epibiota sampled in replicate from three microsites and at six times during the open-water season of 2014, from the same lake locale (Picnic Point, Lake Mendota, Dane Co., WI, USA) explored by high throughput sequencing studies in two previous years. Statistical methods were used to test null hypotheses that the bacterial community: 1) is homogeneous across microsites tested, and 2) does not change over the course of a growth season or among successive years. Results indicated a dynamic microbial community that is more strongly influenced by sampling day during the growth season than by microsite variation. A surprising diversity of bacterial genera known to be associated with the key function of methane-oxidation (methanotrophy)-including relatively high-abundance of Crenothrix, Methylomonas, and Methylocaldum-showed intra-seasonal and inter-annual variability possibly related to temperature differences, and microsite preferences possibly related to variation in methane abundance. By contrast, a core assemblage of bacterial genera seems to persist over a growth season and from year-to-year, possibly transmitted by a persistent attached host resting stage.

microbiology↗