#FEMSmicroBlog: Repeated long-term droughts change the interactions between plants and microbes
Within the rhizosphere, plants and microbes have intimate relationships. Yet, changing environmental conditions threaten their interactions. The research article “The effect of successive summer drought periods on bacterial diversity along a plant species richness gradient” in FEMS Microbiology Ecology explores the relationships between soil microbes and their associated plants over a period of nine years, as explained by Yuri de Souza. #FascinatingMicrobes
Environmental microbes benefit plant communities
Plants and microbes interact intensively in the rhizosphere – the soil zone around plant roots. Here, plants transform CO2 into organic molecules, like sugar, and either use or share them with the microbiota through their roots. In turn, microbes provide essential nutrients to plants.
Unfortunately, intensifying drought events due to climate change threaten the well-being of plant communities. The lack of water causes stress on plant tissue and can, in extreme cases, lead to plant death.
But microbes and an increasing biodiversity can help mitigate the negative consequences of drought on plant health. Plant-associated microbes produce osmolytes, modulate root morphology, interact with the plant hormone system, and produce exopolysaccharides. All of these processes improve water and nutrient capturing for the plant to withstand drought conditions.
Additionally, plants growing in monoculture, that is crops consisting of one species, lack metabolites provided by other plants and their associated microbes. This makes them more vulnerable to drought stress. That’s why the study “The effect of successive summer drought periods on bacterial diversity along a plant species richness gradient” in FEMS Microbiology Ecology investigated the changes in plant richness and bacterial communities during prolonged and repeated periods of drought.
The protective effect of biodiversity during drought
For this, the study used the experimental setup of the Jena Experiment in Germany. Started in spring 2002, this biodiversity experiment looks at the long-term interactions between plant diversity and ecosystem processes.
In plots of 20×20 meters, plant communities grow in varying numbers of plant species. Plots start with single species, with further plots containing two, four, eight, sixteen, and sixty species.
The experiment is maintained via careful weeding three times a year to keep only species that originally belonged to the plot. Ongoing for over 20 years, this richness gradient deeply embedded the effects of plant richness into the soil of each plot.
For the here described study and during the summer months from 2008 to 2017, 80 plots in the Jena Experiment field were divided. One sub-plot served as a control and received water equivalent to the natural rainfall. The other sub-plot was covered to shelter it from rain, thus enduring drought.
In 2018, 160 soil samples were collected to investigate long-term effects of repeated periods of drought on bacterial community composition. 16S rRNA gene metabarcoding helped identify the bacteria in the rhizosphere.
Microbial diversity increases after drought periods
The number of different bacterial species in each plot, the so-called bacterial richness, slightly but steadily increased under drought conditions. This result was consistent regardless of the level of plant richness; a rather surprising result since microbial richness was expected to decrease due to the loss of species caused by drought.
Yet, the hypothesis is that water connects small soil particles to each other. With decreasing water levels, these connections break and isolate the soil compartments and trapped microbes. This isolation reduces the homogenization of nutrients among the soil particles and leaves more space filled with air.
To adapt to this condition, bacterial communities recruit other species to diversify and share functions. As a result, the soil samples were colonized by Gemmatimonadota, Verrucomicrobiota, Patescibacteria, Myxococcota, Bacteroidota, Chloroflexi, Acidobacteriota, Actinobacteriota, Proteobacteria, and Planctomycetota as the most predominant phyla. Yet, their abundance shifted between drought-exposed and control plots.
It seems that microbial communities respond differently to acute and chronic drought. Previous research showed that acute drought drastically reduces soil bacterial diversity. Yet here, chronic drought led to an increase in diversity as potentially a consequence of reduced soil connectivity.
- Read the article “The effect of successive summer drought periods on bacterial diversity along a plant species richness gradient” by de Souza et al. in FEMS Microbiology Ecology (2024).
Yuri Pinheiro is a Brazilian microbiologist living in Germany. There, he developed his PhD thesis on microbial ecology, investigating the interactions between soil and plant microbes with biodiversity and stress. He is passionate about astrobiology and loves extremophilic microbes
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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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