7/10/2023 UPDATE: I have discovered other authors came up with this idea before me, as noted by Press and Phoenix¹¹. At least two authors have mentioned it: in the context of mistletoes¹²; and a North American root hemiparasite, Triphysaria ¹³. However, as far as I can tell the hypothesis has never been tested.

Today I had the opportunity to work as a field assistant with a PhD student, Thomas Marquand. He is researching CO₂ and methane dynamics in soil in restored and reclaimed fens in East Anglia (with the Centre for Landscape Regeneration). We took samples from the fen exhibit in the Cambridge Botanic Gardens and used a spectrometer to measure CO₂ and methane concentration, and also δ¹³C-CO₂.