Topological scaling and plant root system architecture: developmental and functional hierarchies

Abstract

SUMMARYTopology is an important component of tbe arcbitecture of wbole root systems. Unfortunately, most commonly applied indices used for characterizing topology are poorly correlated witb one anotber and thus reflect different aspects of topology. In order to understand better bow different methods of cbaracterizing topology vary, tbis paper presents an exploration of several different methods for assigning order witbin branched root systems on tbe basis of (a) developmental (centrifugal) vs. functional (centripetal) ordering sequences and (b) wbetber orders are assigned to individual links or groups of adjacent links (segments). For eacb ordering system, patterns of scaling in relation to various aspects of link and segment size are explored using regression analyses. Segment-based ordering systems resulted in better fits for simple scaling relationships with size, but these patterns varied between developmental vs. functional ordering as well as tbe different size metrics examined. Tbe functional (centripetal), link-based ordering system sbowed complex, non-linear scaling in relation to numbers of links per order. Using a simple simulation model of root growth, it is demonstrated tbat this metbod of cbaracterizing root topology in relation to root size migbt be a more powerful tool for cbaracterizing root system arcbitecture tban in the use of simple, single-index cbaracterizations of topology.

<b>Aluminum toxicity in roots of legume seedlings assessed by topological analysis

“…The other indices, which also include the root system altitude instead of the primary root value, were in agreement, showing no differences in root topology between Al treatments. This result is in contrast to that reported by Berntson (1997), in which the indices used to describe the root topology were poorly correlated with one another. Table 4.…”

“…The criteria most often utilized for evaluating Al toxicity are measurements of the growth, number, color and branching pattern of the root. However, other aspects are also examined, such as the root topology, which is an important component of the entire root system architecture (BERNTSON, 1997). To the best of our knowledge, there has been no published studies on root topology in response to Al toxicity, and knowledge of root morphology and architecture would be very useful both for efforts to breed plants for nutrient efficiency (CRUSH et al, 2005) and for ecological studies on the adaptation of species to acid soils.…”

Root architecture adaptation of Pistacia atlantica subsp. atlantica according to an increasing climatic and edaphic gradient: case of a north–south transect in Algeria

“…• counted the number of branches in the centrifugal direction (developmental) (Berntson, 1997); therefore, we distinguish between the number of branches of superficial roots (BSR), that of deep roots (BDR), and that of total root branches (TRB); • measured root length, which corresponds to the sum of the lengths of the constituent segments of roots; therefore, we distinguish between the total length of the superficial roots (TLSR), that of deep roots (TLDR), and total length of roots (TLR); • measured root average circumference, which corresponds to the average of circumferences of constituent segments of each superficial or deep root; therefore, we distinguish between the average circumference of the superficial roots (ACSR), that of deep roots (ACDR), and that of total roots (ACR). Finally, we transformed in percentages the results of different root measurements to weight differences in the strength of our 4 stations.…”

Correcting for finite spatial scales of self–similarity when calculating fractal dimensions of real–world structures

“…It is likely that this di¤culty is largely driven by variations in D within real-world structures. For example, fracture and fault lines in the Earth's crustal plates (Hatton et al 1994), spatial and temporal variability in zooplankton biomass (Pascual et al 1995), borders between disturbed and non-disturbed habitats (Krummel et al 1987), and the above- (Morse et al 1985) and belowground (Berntson 1997) branching structures of plants, can all exhibit either discrete or continuous scaledependent variations in D. This scale-dependent variation in real-world structures has been acknowledged since the beginning of work with fractal geometry. Early work in soil science, for example, referred to this phenomenon as`partial self-similarity' (Burrough 1981(Burrough , 1983.…”