Abstract
The complexity of natural soils presents a challenge to the systematic identification and disentanglement of governing processes that shape natural bacterial communities. Studies have highlighted the critical role of the soil aqueous phase in shaping interactions among soil bacterial communities. To quantify and improve the attributability of soil aqueous-phase effects, we introduced a synthetic and traceable bacterial community to simple porous microcosms and subjected the community to constant or dynamic hydration conditions. The results were expressed in terms of absolute abundance and show species-specific responses to hydration and nutrient conditions. Hydration dynamics exerted a significant influence on the fraction of less-abundant species, especially after extended incubation periods. Phylogenetic relationships did not explain the group of most abundant species. The ability to quantify species-level dynamics in a bacterial community offers an important step toward deciphering the links between community composition and functions in dynamic terrestrial environments.IMPORTANCE The composition and activity of soil bacteria are central to various ecosystem services and soil biogeochemical cycles. A key factor for soil bacterial activity is soil hydration, which is in a constant state of change due to rainfall, drainage, plant water uptake, and evaporation. These dynamic changes in soil hydration state affect the structure and function of soil bacterial communities in complex ways often unobservable in natural soil. We designed an experimental system that retains the salient features of hydrated soil yet enables systematic evaluation of changes in a representative bacterial community in response to cycles of wetting and drying. The study shows that hydration cycles affect community abundance, yet most changes in composition occur with the less-abundant species (while the successful ones remain dominant). This research offers a new path for an improved understanding of bacterial community assembly in natural environments, including bacterial growth, maintenance, and death, with a special focus on the role of hydrological factors.
Highlights
The complexity of natural soils presents a challenge to the systematic identification and disentanglement of governing processes that shape natural bacterial communities
Species abundance was expressed as the number of genome equivalents (Ϸindividual cell numbers) calculated from quantitative real-time PCR amplification of genomic DNA
The processes that govern changes in soil microbial community composition in natural environments are inherently complex and difficult to decipher due to numerous interactions that are neither easy to measure nor controllable [26]
Summary
The complexity of natural soils presents a challenge to the systematic identification and disentanglement of governing processes that shape natural bacterial communities. A key factor for soil bacterial activity is soil hydration, which is in a constant state of change due to rainfall, drainage, plant water uptake, and evaporation These dynamic changes in soil hydration state affect the structure and function of soil bacterial communities in complex ways often unobservable in natural soil. The mechanisms by which soil hydration dynamics affect microbial community composition and function remain poorly understood due to the complexity of natural soil-microbe systems In their natural environments, bacterial communities respond to dynamic changes in hydration status by rapid changes in community composition and functioning, such as following a rainfall event in desert soil [1] or after simulated dry-wet cycles of soil cores [2,3,4].
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