Belowground Invasions: Co-invasion of pine trees and their ectomycorrhizal fungi

HORTON, THOMAS R; NUÑEZ, MARTIN A.; POLICELLI, NAHUEL; PAUCHARD, ANÍBAL; BRUNS, THOMAS D.

San Carlos de Bariloche

Simposio; II International Symposium Mycorrhizal Symbiosis in South America; 2019

Belowground biota is known to drive the invasion of non-native plant species, however, it is unclear whether the identity of belowground organisms or its mere presence are determinant of the invasion process, and the impact that non-native belowground biota may have on native species. Pine invasions in the Southern Hemisphere are an ideal system to study these two questions as the invasion is not possible without the co-introduction of ectomycorrhizal fungi (EMF). To evaluate if the presence of any compatible fungi was enough for pines to invade or if the identity of the EMF matters, we conducted a global systematic review of the literature. We found that only one group of EMF, suilloid fungi, is able to act as a global driver of pine invasions. We identified the main ecological traits of suilloid fungi that may explain their key role at pine invasions related to their long-distance dispersal capacity and exploration type, their capacity to generate a resistant spore bank, and their rapid colonization of roots. Knowing that not only pines but also their associated symbionts have invasive traits, we asked whether non-native invasive EMF could be replacing native EMF communities and how that would affect the growth of native ectomycorrhizal plant species. We also evaluated the possibility of crossed colonization between hosts and EMF (native vs non-native). In a greenhouse experiment we planted native Nothofagus species and non-native invasive Pinus contorta in soil from stands where invasive pine trees were highly abundant (invaded soil) and from stands were pine trees were absent and Nothofagus was the dominant tree species (uninvaded soil). We also collected root tips of both species from the field along a pine invasion gradient over a Nothofagus forest. We evaluated the identity of the EMF species associated with the roots using RFLP and sequencing. We found that both host species (Nothofagus and P. contorta) grew equally well in both soil types (invaded and uninvaded) with a high percentage of root colonization. We did not find cross-colonization. Suillus luteus was predominantly driving the invasion of pines together with a few less dominant EMF species. Nothofagus was able to associate with native EMF, predominantly Cortinarius sp., in both soil types. We obtained similar results for field root tips. Together, our results show that the identity of mycorrhizal fungi and their functional traits, rather than simply the presence of compatible fungi and their diversity, are key to the understanding of plant invasion processes and their success or failure. For plant species invasion, belowground biota can both drive the invasion into non-invaded native forests and enhance restoration possibilities of previously invaded habitats