Abstract
AbstractFor over a half a century, researchers have been aware of the fact that the physical and chemical characteristics of microenvironments in soils strongly influence the activity, growth and metabolism of microorganisms. However, many aspects of the effect of soil physical characteristics, such as the pore geometry, remain poorly understood. Therefore, the objective of the present research was to determine the influence of soil pore characteristics on the spread of bacteria, observed at the scale relevant to microbes. Pseudomonas fluorescens was introduced in columns filled with 1–2 mm soil aggregates, packed at different bulk densities. Soil microcosms were scanned at 10.87 μm voxel resolution using X‐ray computed tomography (CT) to characterize the geometry of pores. Thin sections were prepared to determine the spread and colonization of bacteria. The results showed that average bacterial cell density was 174 cells mm−2 in soil with bulk density of 1.3 g cm−3 and 99 cells mm−2 in soil with bulk density of 1.5 g cm−3. Soil porosity and solid‐pore interfaces influence the spread of bacteria and their colonization of the pore space at lower bulk density, resulting in relatively higher bacterial densities in larger pore spaces. The study also demonstrates that thin sectioning of resin‐impregnated soil samples can be combined with X‐ray CT to visualize bacterial colonization of a 3D pore volume. This research therefore represents a significant step towards understanding how environmental change and soil management impact bacterial diversity in soils.Highlights We used a quantitative approach to study bacterial spread in soil at scales relevant to microbes. The rate of pseudomonas spread decreased with increased bulk density of soil. Soil porosity and soil‐pore interface influence Pseudomonas in lower bulk density soil. Soil structure with different pore characteristics effects spread and activity of bacteria in soil.
Highlights
Soil microorganisms are intimately involved in numerous processes occurring in soils, including the supply of nutrients to plants, the stimulation of plant growth through production of growth hormones, controlling the activity of plant pathogens, maintaining soil architecture, and contributing to the leaching of inorganics and the mineralization of organic pollutants (Baveye et al, 2018; Burd, Dixon, & Glick, 2000; Hayat, Ali, Amara, Khalid, & Ahmed, 2010; Zaidi, Khan, Ahemad, & Oves, 2009; Zhuang, Chen, Shim, & Bai, 2007)
We provide evidence that bacteria spread though soil in the absence of water movement
We showed that soil physical conditions and pore architecture in particular affect the rate and extent of spread of bacteria through soil
Summary
Soil microorganisms are intimately involved in numerous processes occurring in soils, including the supply of nutrients to plants, the stimulation of plant growth through production of growth hormones, controlling the activity of plant pathogens, maintaining soil architecture, and contributing to the leaching of inorganics and the mineralization of organic pollutants (Baveye et al, 2018; Burd, Dixon, & Glick, 2000; Hayat, Ali, Amara, Khalid, & Ahmed, 2010; Zaidi, Khan, Ahemad, & Oves, 2009; Zhuang, Chen, Shim, & Bai, 2007) These microbial communities have immense metabolic and physiological heterogeneity, which enables them to live, adapt and proliferate in soil environments that exhibit an extremely high level of structural and chemical heterogeneity (Madigan, Clark, Stahl, & Martinko, 2010). In a review, Kuzyakov and Blagodatskaya (2015) argue that most of the biogeochemical processes are taking place in these hotspots Such hotspots are transient in nature and originate from complex interactions between physical, chemical and microbial processes. Of these examples of hotspots, the rhizosphere is the most dynamic, with hotspots lasting days, whereas hotspots associated with soil structure can be more persistent and last for months
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