Abstract
Background
The ecological study of root systems lags behind the understanding of the aboveground components of plant communities, mainly due to methodological challenges. As ecological root theory develops complexity, root investigation methods are required to meet higher standards of quantitative and detailed data.
Scope
Spatial root density distribution of plants represents one of the main features pursued in ecological studies, as it provides insight into root foraging behavior and belowground competition. To study root density, ecologists should preferably use and develop methods with the potential to provide the most comprehensive information: Individual Root Density Distribution (IRDD), i.e. individual-level and spatially-explicit root density maps. Here, we review the existing methods to detect roots in the field (detection methods), and to infer the identity of these roots (identification methods). We discuss potential combinations of Detection and Identification (DI) methods, and the data quality that these combinations yield in respect to IRDD.
Conclusion
We anticipate that root field ecologists progressively may want to adopt DI methods showing the highest potential to provide high-quality IRDD. These methods are (i) ground-penetrating radar or acoustic tomography in combination with tracking the roots to the individual plant (i.e. skeleton method sensu lato), (ii) soil sampling in combination with in situ root staining (for physiological individuals), or (iii) soil sampling in combination with DNA microsatellites or single nucleotide polymorphism sequencing (for genetic individuals).
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Acknowledgments
We thank three anonymous reviewers and editors for their constructive comments on earlier drafts of the manuscript and L F Wait for reviewing the English grammar and style. We are grateful to F.M. Padilla, H. de Kroon, S. Hosegood, J. Butnor, A. de Castro Aguilar, A. Illuminati and C. Díaz for their data and images. CC acknowledges funding from The May Fellowship in the Department of Ecology and Evolutionary Biology, Princeton University. HDD was supported by a fellowship of the Belgian American Educational Foundation. SM is supported by a Ramón y Cajal postdoctoral fellowship (MINECO, Spain).
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Glossary
Glossary
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[1]
Individual Root Density Distribution (IRDD): The individual-level spatial distribution of root density in the soil relative to the location of the aboveground part of the plant, ecologically equivalent to the map of a plant’s complete root system.
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[2]
Root density: A measure of root mass or volume per soil volumetric unit (generally root dry weight per soil cubic meters).
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[3]
Root detection method: A technique that allows the identity of a root fragment to be resolved, either at the species level or, with higher resolution, at the individual plant level.
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[4]
Root identification method: A technique that allows the identity of a root fragment to be resolved, either at the species level or, with higher resolution, at the individual plant level.
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[5]
Detection-Identification (DI) method: Any particular pairing of a root detection method with a root identification method that allows researchers to extract, visualize, or infer the presence of roots of a given species or individual in a patch of soil.
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[6]
Soil sample: A portion of soil whose spatial information –such as the position where the sample was collected and the sample volume– is known.
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[7]
Rhizotron: Windows or transparent surfaces that allow visualization of a soil wall and the roots growing therein.
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[8]
Tomography: An imaging technique that produces a tomogram, i.e. a group of images arranged in space. Different technologies can be used for tomographic mapping of plant root systems in the field, such as electric currents, electromagnetic waves, or acoustic signals.
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[9]
Physiological individual: A group of plant organs that are connected and share active transportation of water and nutrients through transport tissues.
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[10]
Genetic individual: A group of plant organs sharing a genotype originated from a single sexual reproduction event; because some plants can reproduce vegetatively, a single genetic individual may represent multiple physiological individuals.
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Cabal, C., De Deurwaerder, H.P.T. & Matesanz, S. Field methods to study the spatial root density distribution of individual plants. Plant Soil 462, 25–43 (2021). https://doi.org/10.1007/s11104-021-04841-z
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DOI: https://doi.org/10.1007/s11104-021-04841-z