Biology subjects

West, J. R.

Publications and source records attributed to West, J. R..

3 recordsLinked to original sources

bioRxiv2023

Soil microaggregate bacterial communities following Amynthas tokioensis and Amynthas agrestis earthworm co-invasion

Earthworms restructure the soil environment through burrowing, consumption, and casting behaviors. Though non-native European Lumbricid earthworms are well-studied in North American soils, the Asian pheretimoid Amynthas tokioensis and Amynthas agrestis earthworms exhibit distinct ecological patterns that alter invaded habitats. In particular, bioturbation may affect soil aggregation and microbial community assembly processes, such as dispersal and selection. We aimed to determine the effects of A. tokioensis and A. agrestis co-invasions in woodlands in Madison, WI, U.S. on soil bacterial communities and edaphic characteristics. Using 16S rRNA gene sequencing, we found that the presence and activity of these Amynthas species earthworms significantly affected bacterial community composition. At one site, there was a decrease in sample-to-sample dissimilarity (i.e., decreased beta diversity), with concomitant increases in homogenizing community assembly processes. However, at the other site, we found opposite trends, with evidence for increased compositional dissimilarity between samples and decreased evidence for homogenizing community assembly processes. Overall, inconclusive support for the hypothesized homogenization of bacterial community composition driven by homogenizing community assembly processes indicates that the effects of Amynthas pressure in these systems represent a departure from previously established soil disturbance paradigms. Instead, we conclude that aggregate formation via A. tokioensis and A. agrestis casting activity does not consistently impose a strong selective filter on soil bacterial communities, nor does the heightened earthworm activity necessarily act to meaningfully homogenize soil communities via dispersal. Overall increases in soil C and N under Amynthas spp. activity support previous work indicating enhanced decomposition and incorporation of soil litter, but future work could focus on long-term fate of microaggregate-protected C.

ecology↗

bioRxiv2023

Tillage homogenizes soil bacterial communities in microaggregate fractions by facilitating dispersal

Soil aggregation physically protects soil organic matter and promotes soil carbon persistence through microaggregate formation and organo-mineral associations. Tillage is a ubiquitous disturbance to arable soil that disrupts aggregation, thus affecting microbial resource availability, soil microhabitat conditions, and microbial interactions. We investigated how tillage affects bacterial community composition of soil microaggregate fractions (53-250 {micro}m), specifically the free microaggregate fraction in bulk soil, and the occluded microaggregate fraction from within macroaggregates, using two long-term tillage vs. no-tillage experiments in southern WI, U.S., that represent two different silt loam soils (Alfisol and Mollisol). We applied 16S rRNA gene amplicon sequencing to characterize the effects of tillage on microaggregate bacterial communities by relating compositional changes and ecological community assembly patterns to various tillage-driven changes in the soil environment, including aggregate size distribution and carbon content. Tillage homogenized soil bacterial communities, as quantified by increased compositional similarity at both within-plot and between-plot scales, and community assembly was increasingly influenced by homogenizing dispersal with tillage. We did not identify major distinctions between bacterial communities of the free and occluded microaggregate fractions, thus highlighting how soil microaggregates readily shift between these operationally defined fractions in temperate annual cropping systems, where the soil environment is subject to drastic seasonal changes that are exacerbated by tillage. With this study, we improve our understanding of the microbial response to soil disturbance, and thus the potential mechanisms through which disturbances like tillage affect soil carbon persistence. HighlightsO_LITillage homogenized soil bacterial communities, within and between plots C_LIO_LIHomogenizing dispersal drove community assembly under tillage C_LIO_LIFree and occluded microaggregate fractions hosted similar communities C_LI

ecology↗

bioRxiv2022

Disturbance by soil mixing decreases microbial richness and supports homogenizing community assembly processes

The spatial heterogeneity of soils microhabitats warrants the study of ecological patterns and community assembly processes in the context of community coalescence, or the combining and restructuring of communities and their environment. By mixing soil at various frequencies in a 16-week lab incubation, we explored the effects of mixing disturbance on soil bacterial richness, community composition, and community assembly processes. We hypothesized that well-mixed soil would harbor less richness, dominated by homogenizing dispersal and homogeneous selection. Using 16S rRNA gene sequencing, we inferred ecological processes, estimated richness and differential abundance, calculated compositional dissimilarity, and constructed co-occurrence networks. Findings supported our hypotheses, with >20% decrease in soil bacterial richness in well-mixed soil. While soil mixing resulted in increasingly dissimilar communities compared to unmixed soil (Bray-Curtis dissimilarity; 0.75 vs. 0.25), well-mixed soil communities were increasingly self-similar. Our results imply that vast soil diversity may be attributed to the unmixed and spatially heterogeneous nature of soil, and also provide insight into soil communities following coalescence events. By isolating and better understanding the effect of spatial heterogeneity and dysconnectivity on soil microbial communities, we may better extrapolate how anthropogenic disturbances, such as climate change or land use change, may affect broad soil functions. One sentence summarySoil mixing decreases bacterial richness as several taxa dominate the community, providing evidence for homogenizing community assembly processes.

ecology↗