Intraspecific competition is an important plant interaction that has been studied extensively aboveground, but less so belowground, due to the difficulties in accessing the root system experimentally. Recent in vivo and in situ automatic imaging advances help understand root system architecture. In this study, a portable imaging platform and a scalable transplant technique were applied to test intraspecific competition in Arabidopsis thaliana. A single green fluorescent protein labeled plant was placed in the center of a grid of different planting densities of neighboring unlabeled plants or empty spaces, into which different treatments were made to the media. The root system of the central plant showed changes in the vertical distribution with increasing neighbor density, becoming more positively kurtotic, and developing an increasing negative skew with time. Horizontal root distribution was initially asymmetric, but became more evenly circular with time, and mean direction was not affected by the presence of adjacent empty spaces as initially hypothesized. To date, this is the first study to analyze the patterns of both vertical and horizontal growth in conspecific root systems. We present a portable imaging platform with simplicity, accessibility, and scalability, to capture the dynamic interactions of plant root systems.

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Published in Plants, v. 6, issue 4, 46, p. 1-17.

© 2017 by the authors. Licensee MDPI, Basel, Switzerland.

This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (http://creativecommons.org/licenses/by/4.0/).

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This work is funded by an NSF Information and Intelligent Systems grant (Award# 1238125) that was awarded to Qiang Cheng. Marisa Blake Szubryt was supported by the Undergraduate Research Assistantship (UGA) program at SIUC in 2015–2016, and Xian Liu by a Graduate Research Assistantship through the SIUC Environmental Resources and Policy program. The authors wish to thank the four undergraduate students, Jacob Gerfen (2012–2013), Robert Higgins (2013–2014), Jesse Kays (2014–2015) and Kelsey Reed (2015–2016), for their assistance in imaging roots. They were supported by the SIUC Undergraduate Research Assistantships.

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The following are available online at www.mdpi.com/2223-7747/6/4/46/s1, Figure S1: Experimental setups with two densities and four treatments, Figure S2: Setup of fluorescence imaging, Figure S3: Image processing, Figure S4: Histograms of two roots in the D3 density at 26 DAP, Figure S5: 3D heatmaps of root horizontal distribution, Figure S6: 2D root density windroses, Figure S7: Inorganic nitrogen nutrients of diffusion assays and effects of densities and treatments, Method S1: Root recognition and image digitalization, Method S2: Assignment of polar coordinates and windrose plots.

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