In the latest in our series of blogs for the Toward prediction in the restoration of biodiveristy Special Feature, Jonathan Bauer discusses his article, Effects of between-site variation in soil microbial communities and plant-soil feedbacks on the productivity and composition of plant communities. All articles from the Special Feature are available in issue 54.4 of Journal of Applied Ecology.

Microorganisms in the soil have strong effects on plant communities, and variation in the composition of soil microbial communities can lead to differences in plant communities and associated ecosystem services.  Aspects of a site’s history can cause variation in soil microbial communities, and this may be especially important in ecological restoration, where long histories of intensive agriculture or other human-caused disturbances have created soil communities that are altered from reference conditions.  Soil microbial communities may also change in association with the plant species that grow at a site via plant-soil feedbacks.

Due to the importance of soil microbial communities, there has been increasing interest in incorporating soil microorganisms into ecological restoration efforts, and it is clear that soil microbial communities can shape restoration outcomes.  However, understanding where variation in soil microbial community compositions arises is essential to including soil microbial communities into restoration effects.  If between-site differences in soil microbial communities is important, then restoration efforts may need to introduce plant species that are adapted to these soil conditions or reintroduce appropriate soil microbial communities if important microorganisms are absent.  On the other hand, if plant-soil feedbacks overwhelm any initial effects of soil microbial communities at a restoration site, then the focus should be on reintroducing plants that will host a desirable soil community, for example, by promoting microbial mutualists.

We tested these two alternatives with a two-phase plant-soil feedback experiment.  We collected soil from two recently restored prairies and from two remnant prairies.  We then inoculated seedlings of nine prairie species with these soils, allowing the soil microbial communities to change in association with these different plants for one growing season.  Then, we inoculated prairie mesocosms with these soils to determine if the site where soil was originally collected or plant-soil feedbacks had more important effects on plant community composition and productivity.

Soils associated with different plant species supported different levels of productivity and changed the relative success of seedlings in our mesocosms.  However, we were also able to detect effects of where the soil was originally collected.  The effects of different sites and of plant-soil feedbacks were similarly important for total community productivity.  However, plant-soil feedbacks had stronger effects on community composition.  This was mostly a result of strong effects of a single species, Tradescantia ohiensis.

We conducted a parallel experiment to test the role of mycorrhizal fungi and rhizobia in these feedback effects.  Both of these groups of microbial mutualists were affected by the presence of different plant species, and the resulting variation was associated with changes in plant community composition.  The effects of mycorrhizal fungi were stronger, and the lowest abundance of mycorrhizae was associated with soils conditioned by Tradescantia ohiensis, explaining this species’ strong effects on community composition and productivity.

Overall, we found that the differences in soil microbial communities between sites and the plant-soil feedbacks that occur within a site can cause differences in plant community composition.  As a result, the effects of plant-soil feedbacks on soil microbial communities could be considered as a way to alter restoration outcomes.  For example, in our study system, most plant species are highly depended on mutualisms with mycorrhizal fungi.  So, introducing plant species that promote the abundance of mycorrhizae could improve soil conditions for the desired plant communities within a restoration.  However, plant-soil feedbacks do not overwhelm the initial effects of a site’s soil microbial communities.  Consequently, some plant species may be better suited to the microbial community at different sites, so that plants should either be chosen that are compatible with these conditions or missing components of the soil microbial community could be reintroduced along with the plant species that depend on these microorganisms.

Effects of between-site variation in soil microbial communities and plant-soil feedbacks on the productivity and composition of plant communities is a part of the Special Feature, Toward prediction in the restoration of biodiversity and available in read in the Journal of Applied Ecology.

Read other blogs from the series:

• Toward prediction in the restoration of biodiversity by Lars Brudvig
• Every restoration is unique by Katharine Stuble 
• A common currency for connecting the goals of restoration: plant traits can help us understand how plant communities form and help ecosystems function by Chad Zirbel
• Resilience: advancing a deceptively simple concept by Loralee Larios
• Tree islands for tropical forest restoration: the outlook is rosy after 10 years by Leighton Reid (shared from Natural history of Ecological Restoration)
• Finding missing branches: Phylogenetic patterns of plant community diversity in restored and remnant tallgrass prairies by Rebecca Barak