Topology, scaling relations and Leonardo's rule in root systems from African tree species

Abstract

Aspects of root architecture, including topology, link length, diameter and scaling relations, were analyzed in excavated coarse root systems of three field-grown fruit tree species (Strychnos cocculoides Bak., Strychnos spinosa Lam. and Vangueria infausta Burch) and the fruit-bearing shrub Grewia flava DC. We investigated the root systems using semi-automatic digitizing and computer-based 3-D reconstruction techniques. Topological analysis was carried out to investigate branching patterns as basic determinants of root architecture. New topological indices were developed and revealed significant differences among the species. The different architectural strategies can be explained in terms of cost-benefit relations and efficiency in soil resource exploration and exploitation. In addition, some well-known hypotheses about geometry and scaling, most of them previously unverified by empirical observations on root systems, were tested. For practical applications, the main emphasis is on the relationship between proximal root diameter, an easily determined parameter, and several parameters describing the size of the whole root system. We also tested the "pipe stem" theory, essentially dating back to Leonardo da Vinci, which underlies many models and which we found conformed to our measurement data with reasonable accuracy. A physiological consequence of the "constant cross-sectional area rule" may be a certain homogeneity of hydraulic architecture throughout root systems.

Root architecture and allocation patterns of eight native tropical species with different successional status used in open-grown mixed plantations in Panama

“…Caution is also required when comparing the data from this study with the existing literature since we studied only coarse roots (d [ 2 mm). Different results might have been obtained if the complete root system had been studied (Oppelt et al 2001). Unfortunately the soils at the research site have a very high clay content making it impossible to extract fine roots without significant damage.…”

“…The manual excavation method in the heavy clay soils of our study site allowed for the removal of roots more than 2 mm in diameter. Although we did not sample fine roots, the distribution of the coarse root system directly affects the extent and location of fine roots and thus it has indeed significant implications for the capacity of the plant to capture resources (Oppelt et al 2001). The complete root system was then washed and the taproot was separated from other roots.…”

“…Yet we found a very strong correlation between height and biomass at this early life-stage (data not show). Few studies have accounted for belowground development in tropical trees because root sampling is generally difficult and very time consuming (Oppelt et al 2001). However, in the context of C storage, prediction of biomass allocation belowground must be considered since it can represent between 18 and 46% of total plant biomass (Sanford and Cuevas 1996) (between 22 and 40% in our study, depending on the species).…”

Below- and aboveground architecture of Androstachys johnsonii prain: topological analysis of the root and shoot systems

“…The majority of the existing studies on root system architecture focus on seedlings (Martínez-Sánchez et al 2003;Trubat et al 2012;Chiatante et al 2004;Berntson 1997;Larkin et al 1995;Nicotra et al 2002;Tworkoski and Scorza 2001;Cortina et al 2008;Riccardo 2007) and saplings (Coll et al 2008;Spanos et al 2008;Salas et al 2004;van Noordwijk and Purnomosidhi 1995;Oppelt et al 2001); this is probably because of the difficulty in excavating the root system of adult trees. Further, if the architecture of the root system of an adult tree is studied, often the root system is not totally removed and is therefore only partially analysed (Kalliokoski 2011;Kalliokoski et al 2008;Soethe et al 2007).…”

“…Field studies of below-and aboveground architecture are relatively scarce in Africa (Oppelt et al 2000(Oppelt et al , 2001). To our knowledge, similar studies in Mozambique and, especially, on Androstachys johnsonii, an commercially important woodland tree species restricted only to Mozambique (Cardoso 1963), are lacking.…”