Abstract
This study aimed to analyse the topological branching pattern, area-preserving branching, and fractal branching pattern (self-similarity) of the root and shoot systems of 93 Androstachys johnsonii trees with diameter-at-breast heights of 5–32 cm. Topological parameters were calculated. Visual analysis indicated herringbone-like branching pattern for both the root and shoot systems. However, the topological index (TI) and topological trend (TT) suggested otherwise. This discrepancy was attributed to the fact that A. johnsonii has multiple laterals per stem/taproot node, suggesting that the topological indexes (TI and TT) might yield biased conclusions regarding the branching pattern when the main axis has multiple laterals per node. Hence, modified topological index (TIM) that could be applied in the cases of multiple laterals per node while conserving the values of TI for cases with one lateral per node was developed; the modified index was more efficient and realistic than TI. The area preserving branching was confirmed for each stem node confirming thus, the self-similar branching. For the root system, the area-preserving branching was only confirmed for the first node; therefore, self-similarity was not confirmed.
Highlights
Architecture of biological objects refers to the spatial configuration of the assemblage of subunits such that the overall configuration has some functional significance (Lynch 1995)
Root architecture refers to the spatial configuration of the root system (Lynch 1995) and, analogously, shoot architecture refers to the spatial configuration of the shoot system
The branching topology of the root and shoot systems of A. johnsonii can be considered as perfectly to nearly herringbone, respectively, i.e., the stem or taproot is the main axis (Kalliokoski 2011) and the longest and thickest branch (Richardson and zu Dohna 2003; Fig. 2) as opposed to dichotomous branching topology where the parent branch divides into two daughter branches of the same size (Richardson and zu Dohna 2003), i.e., branching occurs with equal probability on all links (Kalliokoski 2011)
Summary
Architecture of biological objects refers to the spatial configuration of the assemblage of subunits such that the overall configuration has some functional significance (Lynch 1995). Root architecture refers to the spatial configuration of the root system (Lynch 1995) and, analogously, shoot architecture refers to the spatial configuration of the shoot system. Root architecture determines the ability of plants to exploit soil resources (Lynch 1995), thereby affecting water and nutrient acquisition, carbon metabolism, and environmental stress resistance (Trubat 2012). Plants are known to respond to nutrient limitation by modifying branching and root system architecture (Trubat et al 2012; Lynch and Ho 2005) towards herringbone-like root system (Fitter 1987; Fitter et al 1991). In a similar way the response to water limitation is by inhibiting lateral branching (Malamy 2005) and promoting herringbone-like root systems (Fitter 1987). During the life of a tree, from seedling to adult stage, the root system can undergo transformations according to the availability of nutrients and water resources
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