Abstract
Research in the field of plant biology has recently demonstrated that inter- and intra-specific interactions belowground can dramatically alter root growth. Our aim was to answer questions related to the effect of inter- vs. intra-specific interactions on the growth and utilization of undisturbed space by fine roots within three dimensions (3D) using micro X-ray computed tomography. To achieve this, Populus tremuloides (quaking aspen) and Picea mariana (black spruce) seedlings were planted into containers as either solitary individuals, or inter-/intra-specific pairs, allowed to grow for 2 months, and 3D metrics developed in order to quantify their use of belowground space. In both aspen and spruce, inter-specific root interactions produced a shift in the vertical distribution of the root system volume, and deepened the average position of root tips when compared to intra-specifically growing seedlings. Inter-specific interactions also increased the minimum distance between root tips belonging to the same root system. There was no effect of belowground interactions on the radial distribution of roots, or the directionality of lateral root growth for either species. In conclusion, we found that significant differences were observed more often when comparing controls (solitary individuals) and paired seedlings (inter- or intra-specific), than when comparing inter- and intra-specifically growing seedlings. This would indicate that competition between neighboring seedlings was more responsible for shifting fine root growth in both species than was neighbor identity. However, significant inter- vs. intra-specific differences were observed, which further emphasizes the importance of biological interactions in competition studies.
Highlights
Plants sharing a finite amount of space will inevitably interact with each other either above or belowground in the pursuit of essential resources
specific root length (SRL) and specific root area (SRA) depict the cost of root construction, and can be highly informative in establishing whether a treatment had an effect on root morphology
We could not conclude with any certainty that intra- and inter- growing seedlings differed in terms of root system architecture and use of 3D space
Summary
Plants sharing a finite amount of space will inevitably interact with each other either above or belowground in the pursuit of essential resources. Recent advances in three dimensional (3D) imaging technology such as ground penetrating radar, laser imaging, nuclear magnetic resonance imaging (MRI), neutron radiography (NT), and X-ray computed tomography (CT) have made the observation of undisturbed root systems possible (Macfall et al, 1991; Butnor et al, 2001; Gregory et al, 2003; Kaestner et al, 2006; Perret et al, 2007; Tracy et al, 2010; Moradi et al, 2011; Mairhofer et al, 2012) Innovations in software such as Rootviz, Root track (Tracy et al, 2010; Mairhofer et al, 2012), RootReader3D (Clark et al, 2011), and Avizo (Saoirse et al, 2010), and specific filtering algorithms (Perret et al, 2007) have helped improve 3D image resolution and stream-line the quantification of anatomical parameters such as lateral root length, lateral root number, root-system surface area, and volume of undisturbed root systems. Studies have already begun to explore the 3D spatial distribution of fine and coarse roots in forests (Pierret et al, 1999; Butnor et al, 2001), mechanical buckling in plant roots (Silverberg et al, 2012), and water uptake at the root-soil interface (Moradi et al, 2011)
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