If you've ever seen bilberries https://en.wikipedia.org/wiki/Bilberry https://en.wikipedia.org/wiki/Bilberry growing in the wild then you'll know that they grow

If you've ever seen bilberries https://en.wikipedia.org/wiki/Bilberry https://en.wikipedia.org/wiki/Bilberry growing in the wild then you'll know that they grow in "poor" acidic soils. Often alongside other similar acid loving plants like heather and rhododendrons. It would not have been much of a "discovery" to realise that need an acidic soil but maybe more of a discovery that they grow better when aided by fungi.