#FEMSmicroBlog: How time affects microbial communities in the rhizosphere

24-10-2021

Microbes and host plants interact in complex ways often through the rhizosphere. In this narrow zone of soil around the roots, both the microbial composition and the microbe-plant interactions change over time. The article “Time outweighs the effect of host developmental stage on microbial community composition” published in FEMS Microbiology Ecology investigates how time alters the microorganisms living in the rhizosphere. Author Reilly Dibner explains for the #FEMSmicroBlog which conditions change this rhizobiome. #FascinatingMicrobes

 

Complex relationships between plants and their microbes

Microbes in the rhizosphere boost the health of plants. As such, the rhizobiome strengthens plant defenses against disease and herbivores, access to nutrients, stress tolerance, host plant fitness, and general productivity.

Interestingly, many plant processes and traits can alter the composition of microorganisms in the rhizosphere. For example, abiotic environmental and soil conditions shape the rhizosphere microbiome. Differences in soil geochemistry and environmental factors such as drought and season influence the composition of soil microbial communities.

Also, biological characteristics of the host plant and its environment shape the microbes in the rhizosphere. These attributes can include the genotype, the diversity of the surrounding ecosystem and the developmental stage of the plant.

Throughout the lifetime of a plant, its activities and needs change. Hence, the relationship between host plant and rhizobiome also changes over time. Understanding this change may be relevant for sustainable crop management while it could also be key to developing effective management strategies.

The developmental stage of a plant ranges from germination to flowering through fruiting and senescence. Throughout each stage, the microbial community in the rhizosphere can look differently. These shifts have been observed in the model plant, Arabidopsis thaliana, in peas, wheat, potatoes, and other species.

Throughout each plant development stage, the microbial community in the rhizosphere can look differently.

However, studying microbial changes throughout plant development is complicated because developmental stages depend on time. Hence, analyzing developmental stages independently of time is a challenge and most studies on this topic do not separate these components.

 

The microbial shift in the rhizosphere depends on time

Based on this background, the article “Time outweighs the effect of host developmental stage on microbial community composition” published in FEMS Microbiology Ecology focused on this shift of the rhizosphere microbiome. The study aimed to answer the following questions: is the rhizosphere microbiome determined primarily by A) developmental stage of the plant, independent of time, or B) time, independent of the developmental stage of the plant?

The study looked at the effects of time and the developmental stage independent of each other by using A. thaliana genotypes that differ in flowering time. Note that the wild type genotype has a typical form found in natural conditions and has no selected mutations.

In addition to the wild type, the study used two mutant genotypes that flower early and two mutant genotypes that flower late. These mutants are engineered to differ only at a single locus that affects flowering time. Hence, the genotype should not affect the rhizosphere microbial community.

Screenshot from the study time development impacts rhizosphere microbiome - or the rhizobiome.
Time impacts the rhizobiome. From Dibner et al. (2021).

The main results of this study showed that rhizosphere microbes shifted over time. And this shift occurred independently of whether host plants were newly vegetative, flowering, fruiting, or senescing. Thus, time—and the potential for microbial succession, not developmental stage—determined microbial community diversity.

 

Potential role of microbial succession in the plant-rhizobiome

Microbial succession is the assembly of communities following a disturbance, which inherently means change. Over the last ten years, the study of succession has expanded from its focus on plants to include a rich body of research focused on microbes.

Succession in microbial communities can occur following disturbances but also to a smaller extent in environments without major changes. In this study, the microbial community was disturbed with soil autoclaving at the beginning, followed by planting, germination and plant growth. The observed changes in soil microbial community may well be explained by succession.

Where possible, future studies that investigate the importance of host developmental stage on rhizosphere diversity would benefit from including a temporal control in their experiments. In this way, they would separate time from developmental stages of the plant. On top of that, these studies may be able to identify patterns of microbial succession and contribute to this exciting and growing body of literature.

 

 

About the author of this blog

Reilly Dibner is an ecologist studying relationships among microbes, plants, soil, and air. She is currently a postdoctoral research associate in the Weinig Lab, in the Botany Department, and Microbial Ecology Collaborative at the University of Wyoming in Wyoming, USA. The Microbial Ecology Collaborative explores the diversity and function of Wyoming’s microbiome; this collaborative group is part of Wyoming’s Established Program to Stimulate Competitive Research (WY EPSCoR), a National Science Foundation (NSF) program to strengthen STEM capabilities throughout the country.

About this blog section

The section #FascinatingMicrobes for the #FEMSmicroBlog explains the science behind a paper and highlights the significance and broader context of a recent finding. One of the main goals is to share the fascinating spectrum of microbes across all fields of microbiology.

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