Recent findings point to plant root traits as potentially important for shaping the boundaries of biomes and for maintaining the plant communities within. We examined two hypotheses: 1) Thin-rooted plant strategies might be favored in biomes with low soil resources; and 2) these strategies may act, along with fire, to maintain the sharp boundary between the Fynbos and Afrotemperate Forest biomes in South Africa. These biomes differ in biodiversity, plant traits, and physiognomy, yet exist as alternative stable states on the same geological substrate and in the same climate conditions. We conducted a 4-y field experiment to examine the ability of Forest species to invade the Fynbos as a function of growth-limiting nutrients and belowground plant–plant competition. Our results support both hypotheses: First, we found marked biome differences in root traits, with Fynbos species exhibiting the thinnest roots reported from any biome worldwide. Second, our field manipulation demonstrated that intense belowground competition inhibits the ability of Forest species to invade Fynbos. Nitrogen was unexpectedly the resource that determined competitive outcome, despite the long-standing expectation that Fynbos is severely phosphorus constrained. These findings identify a trait-by-resource feedback mechanism, in which most species possess adaptive traits that modify soil resources in favor of their own survival while deterring invading species. Our findings challenge the long-held notion that biome boundaries depend primarily on external abiotic constraints and, instead, identify an internal biotic mechanism—a selective feedback among traits, plant–plant competition, and ecosystem conditions—that, along with contrasting fire regime, can act to maintain biome boundaries.
|Original language||American English|
|Journal||Proceedings of the National Academy of Sciences of the United States of America|
|State||Published - 1 Mar 2022|
Bibliographical noteFunding Information:
ACKNOWLEDGMENTS. This work was supported by grants from Princeton University and the Princeton Global Collaborative Network Fund (to L.O.H.), and a grant from the Andrew W. Mellon Foundation (to L.O.H. and E.C.F.). M.L. acknowledges the generous support of the Princeton University Petrie Fellowship and the Santa Fe Institute Omidyar Fellowship. We thank Dali Guo and Hongbo Liu for helpful discussions on root trait analyses; Anastas Belev, Jeremy Midgley, Simon Power, and Heath Beckett for helping with compiling biome properties; Dawood Hattas, Desmond Barnes, Anthea Stain, and Awot Gebregziabher from the University of Cape Town for administrative help; Elton Le Roux, Patrick Shone, Johanita Alberts, and Abri de Buys from the South African National Biodiversity Institute, Cape Nature, and the South African Environmental Observation Network for their support with our fieldwork; Douglas Euston-Brown for species classification and field assistance; Dunja MacAlister for assisting with the measurement of root traits; and Edward Chirwa, Josh van der Ploeg, Jacques Nel, Keenan Davids, Francois Johannes, Lyndall Swarts, Sonjia Erasmus, Musemo Mweemba, Stefan Goets, and David Gwynne-Evans for helping with various stages of the nutrient manipulation experiment.
© 2022 National Academy of Sciences. All rights reserved.
Copyright © 2022 the Author(s). Published by PNAS.
- Biome boundary
- Resource competition
- Root traits
- Trait-by-resource feedback
- Plant Roots/physiology
- South Africa
- Plant Physiological Phenomena