Dynamics of heterorhizic root systems: protoxylem groups within the fine‐root system of Chamaecyparis obtusa

Abstract

Summary• To understand the physiology of fine-root functions in relation to soil organic sources, the heterogeneity of individual root functions within a fine-root system requires investigation. Here the heterogeneous dynamics within fine-root systems are reported.• The fine roots of Chamaecyparis obtusa were sampled using a sequential ingrowth core method over 2 yr. After color categorization, roots were classified into protoxylem groups from anatomical observations.• The root lengths with diarch and triarch groups fluctuated seasonally, whereas the tetrarch root length increased. The percentage of secondary root mortality to total mortality increased with increasing amounts of protoxylem. The carbon : nitrogen ratio indicated that the decomposability of primary roots might be greater than that of secondary roots. The position of diarch roots was mostly apical, whereas tetrarch roots tended to be distributed in basal positions within the root architecture.• We demonstrate the heterogeneous dynamics within a fine-root system of C. obtusa . Fine-root heterogeneity should affect soil C dynamics. This heterogeneity is determined by the branching position within the root architecture.

Atlas of woody plant roots: morphology and anatomy with special emphasis on fine roots

“…The shape of primary xylem is sometimes barely evident or not evident at all. Arrangement of primary xylem in roots in general rarely corresponds with the ideal disposition shown in textbooks (Schweingruber 2007), while in the apical roots the situation is even more complicated, as the apical roots have a lesser amount of primary xylem/ protoxylem than roots that are positioned more basally (Hishi & Takeda 2005), and pioneer roots have more protoxylem groups than do fibrous roots (Zadworny Anatomy fibrous roots (Zadworny & Eissenstatt 2011), but their beginning of primordial tracheary element formation starts later (Bagniewska-Zadworna et al 2012). However, the functional xylem vessel elements were developed at the same time in fibrous and pioneer roots of the same age, but the secondary vascular development proceeded much more rapidly in pioneer roots (Bagniewska-Zadworna et al 2012).…”

“…It is not necessarily the case that each primary root undergoes secondary growth. Many roots die before they advance to secondary growth and the longevity of the root is believed to be related to the amount of primary xylem (protoxylem) (Hishi & Takeda 2005). It must be emphasized that the thickness of the root itself does not necessarily mean that the root is in a later ontogenetic stage than thinner roots that occur in the same root system.…”

“…In all remaining investigated species two resin ducts corresponding to diarch primary xylem were observed. Although thicker roots in P. sylvestris can be di-, threeor tetra-arch, it is believed that root architecture affects the disposition of primary xylem within the root, with diarch roots positioned apically relative to triarch or tetrarch roots (Hishi & Takeda 2005). (Fig 2.4.2 b-d), the more characteristic anatomical structures are formed.…”

Considerations in the study of tree fine-root turnover with minirhizotrons

“…The diameter of 'fine roots' can also differ along root branching orders: roots with an apex (root tip) are thinner than the axis roots to which they are attached (Pregitzer et al, 2002;Guo et al, 2004), suggesting shorter life spans in thinner apical roots. Further, in addition to carbon-fraction concentrations, such as cellulose and lignin, the C/N ratio can also differ among root branching orders (Pregitzer et al, 2002;Guo et al, 2004;Hishi and Takeda, 2005b), suggesting that roots in different branching orders have different decomposition rates.…”

Characteristics of Fine Roots of Pinus massoniana in the Three Gorges Reservoir Area, China

“…Moreover, morphological characteristics and physiological functions differ significantly among fine roots of different sizes, and roots of different diameter classes showed significant differences in their respiration rates as root respiration rate decreased with root diameter increase [30]. In most tree species, mounting evidence shows that fine roots <2 mm diameter can be divided into smaller diameter classes, due to their wide range of variability in root functions, according to root diameter size class or root branching order [9,[31][32][33]. Hence, the traditional category of fine roots as a single root diameter class of <2 mm might be inherently arbitrary for predicting variation in root characteristics [9,30,34,35].…”