Observing weak adaptation of duckweeds to their local microbiome depends on local pondwater

Populations can locally adapt to the biotic and abiotic factors of environments. However, detecting adaptation to biotic factors can depend on the abiotic conditions in which the adaptation is tested, and vice versa. The microbiome is one important aspect of the biotic environment: Interactions between microbiomes and their hosts are critical for host fitness and trait expression. If hosts adapt to local microbiomes, they may therefore depend on interactions with local microbes to express trait values adapted to the local abiotic environment.

Using Lemna minor (duckweed) as a model host, we examined differences in host fitness when grown in local and nonlocal microbiomes and in local and nonlocal water. We experimentally recombined duckweeds, microbes, and water from four ponds around Durham, New Hampshire (United States) in well-plate microcosms in a growth chamber.

The source of duckweeds, microbes, and water all affected microbial growth, duckweed growth, and duckweed traits. However, weak, marginally significant local adaptation resulted in higher frond area only when duckweeds were paired with their local water and local microbes. Microbial growth was also marginally reduced when duckweeds were paired with microbes and water from their local site.

While microbiome impacts on duckweed growth and traits varied across abiotic contexts, local microbiomes provided only limited growth benefits. Harnessing the effects of plant microbiomes is an exciting area of applied research. Despite our findings, bioprospecting in local microbiomes could still be fruitful: It may be ecologically safer, and other plants may locally adapt to microbiomes.