When your neighbor trumps your environment: Patterns of co-occurring, root-associated fungal communities
Biotic and abiotic factors influence the structure of root-associated fungal communities. To understand how plant neighbors and nitrogen addition affect the co-existence of common fungal groups, arbuscular mycorrhizal fungi (AMF) and dark-septate endophytes (DSE), we analyzed root colonization in co-dominant plant species Festuca thurberi and Helianthella quinquenervis. We selected Helianthella that were growing either in close proximity to (within 10 cm) or far from (greater than 20 cm) from Festuca in a pre-established nitrogen addition experiment at the Rocky Mountain Biological Laboratory, Gothic, CO, USA. Additionally, we explored how changes in fungal communities affect plant performance by measuring the stem height of Helianthella individuals growing near and far from Festuca.
We found plant neighbor identity has a larger effect on root colonization rates than nitrogen addition. DSE colonization was 20% higher in roots of both Festuca and Helianthella growing near Festuca, whereas AMF colonization was 21% higher in Helianthella roots far from Festuca (AMF F= 25.09 p < 0.01, Festuca F= 20.921 p < 0.01). We did not see a significant shift in AMF or DSE colonization with nitrogen addition (AMF F = 2.59 p = 0.08, Festuca F = 2.39 p = 0.10). Most surprisingly, the shift in mycorrhizal community abundance comes without any tradeoff in Helianthella performance (t = -0.89, p = 0.38). Thus, even though the fungal community of Helianthella growing near Festuca has shifted significantly (increased DSE, lowered AMF), DSE may be able filling a similar functional role as AMF in this ecosystem. To our knowledge, this is the first study to report neighbor influence of co-occurring fungal functional groups (AMF and DSE) as well as measuring potential feedback on plant performance and indicate there may be more complexity to plant-mycorrhizal interactions than previously known.