Root system topology and diameter distribution of species from habitats differing in inundation frequency

Abstract

Summary 1.We compared the root systems of seven halophytic species that occur at different elevations on a salt marsh, in order to (i) test the hypothesis that variations in root system architecture reflect adaptation to inundation frequency or nitrogen limitation, and (ii) verify the theoretically predicted relationships between root diameter, link magnitude and root topology. Diameters and lengths of individual laterals were determined along root axes, and branching patterns were quantified by calculating a topological index (TI). 2. Chenopodiaceae (annual dicots) showed that with increasing elevation, the branch density and length of individual first-order laterals tended to increase, so that the relative length of the main axes decreased. Root branching of the Chenopodiaceae at lower elevations was herringbone-like, whereas species from higher elevations had smaller TIs because their branching patterns were more complex. 3. The Gramineae, too, showed a tendency to increased length of individual laterals with increasing elevation. However, TI was not related to elevation, did not indicate a herringbone structure for all species, and was within the same range of that of the Chenopodiaceae. 4. As root topology of the Chenopodiaceae is related to elevation, but that of the grasses is not, topology is not necessarily an important adaptive trait in all plant families that inhabit the salt marsh. Short first-and second-order laterals may represent a more general architectural adaptation to frequent inundation, with longer first-order laterals being favourable to competition for nutrients. 5. Diameters at the root base tended to decrease if root branching was herringbone-like (TI close to 1). Roots of first-order laterals were approximately one-third of the diameter of the main axes; second-order laterals were approximately half the diameter of the firstorder laterals. These ratios illustrate the value of using the developmental segment-ordering system in describing roots. The theoretically predicted relationship between root diameter and link magnitude was not present within individual orders of roots, whereas diameter did slowly increase with magnitude when combining different root orders. 6. In the absence of a clear relationship between root diameter and link magnitude, the predicted high carbon costs associated with herringbone root systems disappear, whereas the advantage of minimized inter-root competition remains. Consequently, herringbone root systems will be most efficient in terms of nutrients gained per carbon invested. However, dichotomous root systems offer a greater potential for exploring the soil, which contributes to the potential competitiveness of plants growing in nutrient limited habitats.

Relationships between root diameter, root length and root branching along lateral roots in adult, field-grown maize

“…The relationships between diameter, length and branching density and their hierarchical connections are discussed below. The positive correlation between daughter root diameter and mother root diameter has been already noted and quantified for several species (Bouma et al, 2001;Lecompte et al, 2005;Bécel et al, 2012;Pagès et al, 2013Pagès et al, , 2014. However, in these studies the sampling methods and definitions of daughter root and bearing root diameter were mostly different from those used here.…”

Mechanisms of vegetation uprooting by flow in alluvial non-cohesive sediment

“…Morphological and functional aspects of plant roots are well documented (e.g., Cannon, 1949;Gregory et al, 1987;Jackson et al, 1996;Fitter, 2002) and also mathematically described (Berntson and Stoll, 1997;Berntson, 1997;Bouma et al, 2001;Sakai, 2001). Attempts at classifying root families can already be found in the pioneering work by Cannon (1949).…”

“…In general, root morphology tends to be determined by site characteristics, soil moisture and nutrients as well as environmental conditions (Bouma et al, 2001;McMichael and Burke, 2002;Portenfield, 2002;Xie et al, 2006). After the work by Schimper (1935) substantial advancements have been made in understanding factors and mechanisms influencing both plants and their below ground biomass (see for instance .…”

“…Schenk and Jackson (2002b) proposed an analysis of rooting depths and lateral spread as a function of climate, soil and vegetation characteristics worldwide. Although the ability of plants to adapt their root length and branching complexity to soil moisture (hydrotropism) and nutrient availability is species dependent (Bouma et al, 2001), on average this feature is present for all species. At least for some species and environments, nutrient concentrations seem to exert a smaller effect on root topology than soil moisture and sediment size distribution (Fitter, 1987;Francis et al, 2005 andPasquale et al(2011)PasqualePasquale (Perona)).…”

Root growth and morphology of four provenances of a perennial grass (Cenchrus ciliarisL.) in rhizotron chamber

“…In the arid zone, root biomass and morphology can play a key role in determining plant functional strategy to cope with drought, particularly for grasses species (Hook & Lauenroth 1991;Tulio & Johonson, 1998;Bouma et al, 2001). Within a species a degree of morphological plasticity is seen as a favourable characteristic for range plants growing in arid and Saharan environments because it allows for greater flexibility in exploring large soil volumes given suitable conditions.…”