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

Populations can locally adapt to both the biotic and abiotic factors of an environment, but observing adaptation to biotic factors can sometimes depend on the abiotic conditions, and vice versa. One important aspect of the biotic environment is the microbiome: interactions between microbiomes and their hosts are critical for host fitness and trait expression. Hosts may adapt to their local microbiomes, and hosts may depend on interactions with microbes for adaptation to the local environment. Using Lemna minor (duckweed) as a model host organism, 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 4 different ponds around Durham, New Hampshire in well-plate microcosms in a growth chamber. Duckweed, microbe, and water source all affected microbial and duckweed growth, as well as duckweed traits. However, we observed only weak positive local adaptation that resulted in higher frond final area when duckweeds were paired with their local water and microbes. We also found that microbial growth was reduced when duckweeds were paired with microbes or water from their local site.