Spatial heterogeneity of plant–soil feedbacks increases per capita reproductive biomass of species at an establishment disadvantage
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Plant–soil feedbacks have been widely implicated as a driver of plant community diversity, and the coexistence prediction generated by a negative plant–soil feedback can be tested using the mutual invasibility criterion: if two populations are able to invade one another, this result is consistent with stable coexistence. We previously showed that two co-occurring Rumex species exhibit negative pairwise plant–soil feedbacks, predicting that plant–soil feedbacks could lead to their coexistence. However, whether plants are able to reproduce when at an establishment disadvantage (“invasibility”), or what drivers in the soil might correlate with this pattern, are unknown. To address these questions, we created experimental plots with heterogeneous and homogeneous soils using field-collected conditioned soils from each of these Rumex species. We then allowed resident plants of each species to establish and added invader seeds of the congener to evaluate invasibility. Rumex congeners were mutually invasible, in that both species were able to establish and reproduce in the other’s resident population. Invaders of both species had twice as much reproduction in heterogeneous compared to homogeneous soils; thus the spatial arrangement of plant–soil feedbacks may influence coexistence. Soil mixing had a non-additive effect on the soil bacterial and fungal communities, soil moisture, and phosphorous availability, suggesting that disturbance could dramatically alter soil legacy effects. Because the spatial arrangement of soil patches has coexistence implications, plant–soil feedback studies should move beyond studies of mean effects of single patch types, to consider how the spatial arrangement of patches in the field influences plant communities.
KeywordsBlack box Coexistence Invasibility Soil nutrient availability Soil microbes
We thank Squire Valleevue and Valley Ridge Farms, Case Western Reserve University (CWRU), especially A. Aldridge, C. Bond, and A. Locci, for making this experiment possible. We also thank the many students who helped with this experiment, especially C.G. Cope, G.A. del Pino, H. Flanagan, K. Grigsby, L. Huffman, J. Hooks, K. Keisewetter, S.C. Leahy, B. Ochocki, A. Osvaldsson, C. Yu, X. Zhao, and N.M. Zimmerman. Thanks to K.C. Abbott and R.E. Snyder for feedback on the ideas. Thanks to two anonymous reviewers and the editor for constructive feedback on the manuscript. Thanks to Holden Arboretum for lab space and financial support. We thank the National Science Foundation (DEB 1250170 to J.H.B.) and CWRU for funding.
Author contribution statement
JHB, AJB, and AMK designed and performed the experiments. JHB, AJB, JEM, AMK, and DJB collected and managed the data. JHB analyzed the data and wrote the first draft and all authors contributed to revisions.
Data available from the Dryad Digital Repository: http://dx.doi.org/10.5061/dryad.h0p04.
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