<b>Do plant strigolactones follow macroecological patterns? The seed-borne endomicrobiome shapes two global gradients in an invasive plant </b>

We tested two competing macroecological predictions using strigolactone concentrations from 42 populations of the globally invasive <i>Taraxacum officinale</i>, comparing plants with an intact or an experimentally reduced seed-transmitted endomicrobiome.

A cold-tolerance hypothesis predicts a U-shaped distribution with latitude, while an enemy-release hypothesis (EICA) predicts a monotonic decline with distance from the species' region of origin. Distance from the region of origin predicted strigolactone decline consistently in both hemispheres, and this decline was significantly steeper in plants with an intact than a reduced endomicrobiome. Latitude predicted strigolactone levels only in the Northern Hemisphere, where the endomicrobiome again amplified the response.