title: Belowground legacies of Pinus contorta invasion and removal result in multiple mechanisms of invasional meltdown.
abstract: Plant invasions can change soil biota and nutrients in ways that drive subsequent plant communities, particularly when co-invading with belowground mutualists such as ectomycorrhizal fungi. These effects can persist following removal of the invasive plant and, combined with effects of removal per se, influence subsequent plant communities and ecosystem functioning. We used field observations and a soil bioassay with multiple plant species to determine the belowground effects and post-removal legacy caused by invasion of the non-native tree Pinus contorta into a native plant community. Pinus facilitated ectomycorrhizal infection of the co-occurring invasive tree, Pseudotsuga menziesii, but not conspecific Pinus (which always had ectomycorrhizas) nor the native pioneer Kunzea ericoides (which never had ectomycorrhizas). Pinus also caused a major shift in soil nutrient cycling as indicated by increased bacterial dominance, NO3-N (17-fold increase) and available phosphorus (3.2-fold increase) in soils, which in turn promoted increased growth of graminoids. These results parallel field observations, where Pinus removal is associated with invasion by non-native grasses and herbs, and suggest that legacies of Pinus on soil nutrient cycling thus indirectly promote invasion of other non-native plant species. Our findings demonstrate that multi-trophic belowground legacies are an important but hitherto largely unconsidered factor in plant community reassembly following invasive plant removal.
authors.affiliation: Landcare Research, Lincoln, New Zealand Bio-Protection Research Centre, Lincoln University, Lincoln, New Zealand ian.dickie@lincoln.ac.nz.
authors.forename: Ian A
authors.initials: IA
authors.lastname: Dickie
authors.affiliation: Landcare Research, Lincoln, New Zealand Agriculture and Agri-Food Canada, Ottawa, Canada.
authors.forename: Mark G
authors.initials: MG
authors.lastname: St John
authors.affiliation: Landcare Research, Lincoln, New Zealand.
authors.forename: Gregor W
authors.initials: GW
authors.lastname: Yeates
authors.affiliation: Landcare Research, Lincoln, New Zealand.
authors.forename: Chris W
authors.initials: CW
authors.lastname: Morse
authors.affiliation: Landcare Research, Lincoln, New Zealand.
authors.forename: Karen I
authors.initials: KI
authors.lastname: Bonner
authors.affiliation: Landcare Research, Lincoln, New Zealand.
authors.forename: Kate
authors.initials: K
authors.lastname: Orwin
authors.affiliation: Landcare Research, Lincoln, New Zealand.
authors.forename: Duane A
authors.initials: DA
authors.lastname: Peltzer
keywords: Biogeochemical processes; biological invasions; ecosystem function; ectomycorrhizas; facilitation; fungal : bacterial ratio; legacy effects; plant–soil interactions; removal effects