Seasonal Differences in Effects of Microbial Communities on Duckweed Traits

Host-associated microbiomes shape the expression of a diverse suite of host traits, ranging from longevity in animals to flowering time in plants. Despite their importance to host traits, the composition of host-associated microbiomes can fluctuate, and microbiomes of differing composition often have differing impacts on hosts. Fluctuations in microbiome composition can include seasonal shifts that correlate with seasonal phenotypic changes in hosts. Yet, identifying whether these correlated seasonal changes in hosts and microbial communities are causally linked remains difficult because it requires separating the effects of the abiotic environment and host or tissue age from the effects of seasonally altered microbial communities. Here, we used microcosm experiments simultaneously reinoculating axenic duckweeds with microbial communities cultured from different seasons to compare their effects on duckweed growth and trait expression. We found seasonal differences in the effects microbial communities had on duckweeds. Microbial communities cultured from duckweeds in the summer shifted duckweed fronds to be more aggregated (by 5.7%) and slightly more green (by 0.7%) than microbial communities cultured from duckweeds in other seasons, and nonsignificantly increased duckweed growth rates. Inoculation with microbial communities cultured from summer collections also resulted in more total microbial growth in microcosms. These findings enhance our understanding of the influence of seasonality on the complex relationship between microbes and their hosts, with potential future applications in agriculture and medicine.