Community coalescence news

In the last couple of days, two new papers themed around community coalescence have appeared: Calderon et al. in ISME Journal studying the effects of mixing different soil microbial communites experimentally, and Tikhonov presenting some theory underlying community coalescence in eLife.

This is quite exciting and hopefully more studies will begin to address the idea that entire microbial assemblages (and their environments) can encounter each other.

The work by Calderon et al. is in a restoration ecology context, a field where the focus has historically been on plants rather than the soil microbes. They used soil microbial communities from two different soils, which were added to a sterlized third soil; in their experiment they then added various concentrations of these soil microbial communities to resident soil microbial communities, constituting the community coalescence treatments. The results indicated that in the¬† less diluted, more diverse target communities¬† few changes occurred with the addition of the “rescue” microbial communities, most likely because of priority effects. The picture changed in the more depauperate target communities: here many OTUs from the added soil community could establish in the resulting coalescent community. Also communties from one soil had a stronger effect than from the other. Interestingly, a smaller number of species added did have a stronger effect than adding a larger number of species (when added to the most diluted target community). The authors also monitored functional consequences in terms of ammonium and nitrate concentrations in soil. Inoculation was done with soil suspensions in all cases, so aspects of habitat mixing were therefore mostly disentangled from the interaction of the communities. The type of coalescence event examined was the “addition” type, with various addition ratios/ strengths (see Rillig et al. 2015). A very nice study serving as a template for similar experimental work!

The paper by Tikhonov examined community-level competition from a theoretical perspective, directly and explicitly addressing the community coalescence concept. He showed that the ability of a species to persist through a community coalescence event is predicted by a community-level performance of its own community rather than the performance of the species itself.

Favorite sentence: “(…)we observe that community coalescence can be usefully described as an interaction between two entities, characterized macroscopically at the whole-community level”. The paper is very interesting because it highlights a community-level phenotype, placing comparatively less emphasis on the nature and identity of individual species. It is exciting to see such modeling exercises, and I hope there is more to come.

Calderon K,  Spor A, Breuil MC,  Bru D, Bizouard F, Violle C, Barnard RL,
Philippot L. (2016). The ISME Journal; doi:10.1038/ismej.2016.86

Tikhonov M. (2016). Community-level cohesion without cooperation. eLife;
doi: 10.7554/eLife.15747