Table S1: Plant groups, plant names and seed sources per conditioning and greenhouse treatments

Plant group / Plant species / Seed source
Conditioning treatment
Native / big bluestem (Andropogon gerardii Vitmann) / 1
Native / Canada wild rye (Elymus canadensis L.) / 1
Native / native polyculture 1 - Mixture of big bluestem, Canada wild rye, slender wheatgrass (Agropyron trachycaulum (Link) Malte ex H.F. Lewis), maximilian sunflower (Helianthus maximiliani Schrad.), partridge pea (Chamaecrista fasciculate (Michx.) Greene), switchgrass (Panicum virgatum L.), Canada milkvetch (Astragalus canadensis L.) and yellow coneflower (Ratibida pinnata Vent. (Barnh.). / 1
Exotic / crested wheatgrass (Agropyron cristatum (L.) Gaertn.) / 2
Exotic / smooth brome (Bromus inermisLeyss. ssp. inermis) / 3
Zea / corn (Zea mays L.) in 2010 and 2012, soybean (Glycine max(L.) Merr.) in 2011 / 4
Response treatment
Native / big bluestem (Andropogon gerardii Vitmann) / 1
Native / Canada milk vetch (Astragalus canadensis L.)* / 1
Native / switchgrass (Panicum virgatum L.) / 5
Exotic / crested wheatgrass (Agropyron cristatum (L.) Gaertn.) # / 2
Exotic / smooth brome (Bromus inermis Leyss.) / 3
Exotic / spotted knapweed (Centaureastoebe ssp. micranthos (S.G. Gmel. ex Gugler) Hayek)† / 6
Exotic / Bird's Foot Trefoil (Lotus corniculatus L.)** / 7
1 Prairie Moon Nursery, Winona, MN
2 variety Hycrest, Agassiz Seed, Fargo, ND
3 Albert Lea Seedhouse, Albert Lea, MN
4 UMORE park field station, MN
5 variety Sunburst, Kaste Seed, Fertile, MN
6 hand-picked in western Minnesota
7 variety MSP3535, University of Minnesota, St Paul, MN / * legume-specific rhizobia from Prairie Moon Nursery
** rhizobium from Albert Lea Seed House
# Experiment 2 only
† Experiment 1 only

Fig. S1 The effect of field N fertilization on plant biomass in soils conditioned by natives, exotics or maize-soybean in Experiment 1 (Conditioning Group x Field N, F = 3.2, p =0.04). Untransformed shoot biomass, averaged across species per group, and standard errors are shown. Native conditioning group: Andropogon, Elymus and native plant mixture; exotic conditioning group: Agropyron and Bromus

Fig. S2The effect of greenhouse N fertilization on plant biomass for native and exotic greenhouse response plants in Experiment 1 (Greenhouse Response Group x Field N, F = 4.5, p = 0.034). Untransformed shoot biomass, averaged across species per group, and standard errors are shown. Native greenhouse response group: Andropogon, Astragalus and Panicum; exotic greenhouse response group: Bromus, Centaurea and Lotus

Fig. S3The effect of field N addition on plant biomass per conditioning species andgreenhouse response species in Experiment 1 (Conditioning Species x Greenhouse Response Species x Field N, F = 2.4, p < 0.001). Untransformed mean shoot biomass, averaged across greenhouse N additions,and standard errors are shown. The top three graphs show native and the bottom three show exotic greenhouse response species. In all graphs, the first three conditioning species (Andropogon, Elymus and native mix) are native, while the fourth and fifth (Agropyron and Bromus)are exotic conditioning species