Belowground carbon transfer across mycorrhizal networks among trees: Facts, not fantasy

The mycorrhizal symbiosis between fungi and plants is among the oldest, ubiquitous and most important interactions in terrestrial life on Earth. Carbon (C) transfer across a common mycorrhizal network (CMN) was demonstrated over half a century ago in the lab (Reid and Woods 1969), and later in the field (Simard et al . 1997). Recent years have seen ample progress in this research direction, including evidence for ecological significance of carbon transfer (Klein et al . 2016). Furthermore, specific cases where the architecture of mycorrhizal networks have been mapped (Beiler et al . 2015) and CMN-C transfer from mature trees to seedlings has been demonstrated (Orrego 2018) have suggested that trees in forests are more connected than once thought (Simard 2021). In a recent Perspective , Karst et al . (2023) offered a valuable critical review warning of over-interpretation and positive citation bias in CMN research. It concluded that while there is evidence for C movement among plants, the importance of CMNs remains unclear, as noted by others too (Henriksson et al . 2023). Here we argue that while some of these claims are justified, factual evidence about belowground C transfer across CMNs is solid and accumulating.