Plant-soil feedback from non-native communities increases pine invasion and re-invasion potential

Abstract Background and aims Individual plants and plant communities leave legacies in the soil that influence the future growth and success of subsequent plants grown in those soils However, direct tests of plant community legacies are rare. Understanding these is especially relevant for sites where invasion or re-invasion of non-native plants threatens restoration success. Methods We used soils modified by experimental plant communities to test which aspects of plant community structure create legacies that affect the initial growth and mycorrhizal community of Pinus contorta, a common invasive pine species in the Southern Hemisphere. These plant communities varied in several factors including presence of Pinus species and the proportion of other non-native species, nitrogen-fixers, and grasses. Results Pinus contorta seedlings grew largest in soils that were previously conditioned by Pinus individuals and by soils conditioned by communities of other non-native plants, or grasses. Ectomycorrhizal fungal diversity on P. contorta roots was 19.7% less in soil with a Pinus legacy than in soil without Pinus legacy. Fungal communities were generally one of three types: dominated by Wilcoxina, or Inocybe, or without a dominant fungal taxon. Conclusion Our results demonstrate that legacy effects of plant communities on the diversity of mutualistic fungi and soil abiotic conditions can change the growth of P. contorta seedlings. This suggests some restoration sites, and particularly those with a previous history of Pinus species or high percentage of grasses or other non-native species, could be more vulnerable to invasion or reinvasion by P. contorta.