L. Pagès

Architectural analysis and synthesis of the plum tree root system in an orchard using a quantitative modelling approach

A dynamic 3D representation of the root system architecture of plum is proposed by gathering quantitative and morphological observations of the tree root system in a model. The model includes two information levels: (i) a typology of root axes, based on morphological and developmental characteristics; (ii) a set of basic processes (axial and radial growth, ramification and reiteration, decay). The basic processes are qualitatively identical in space and time. An original approach was used to investigate these processes and to formalize them in the model. Concerning the main roots, a mechanism of reiteration is described that has a substantial influence on the structuring of the root system. Root mortality is assessed using the variation in branching density along the root axes. Radial growth is calculated from the ramification of root axes, using root section conservation properties. This model enables a link between static field observations and a dynamic simulation of the root system architecture. The architectural model allows examination of the global consequences of the basic processes at the level of the root system. The simulations provide useful output, from a simple root depth profile to a simulation of the dynamic 3D root system architecture, to investigate plant functioning and especially water and nutrient uptake.

Correlated responses of root growth and sugar concentrations to various defoliation treatments and rhythmic shoot growth in oak tree seedlings (Quercus pubescens)

BACKGROUND AND AIMS To understand whether root responses to aerial rhythmic growth and contrasted defoliation treatments can be interpreted under the common frame of carbohydrate availability; root growth was studied in parallel with carbohydrate concentrations in different parts of the root system on oak tree seedlings. METHODS Quercus pubescens seedlings were submitted to selective defoliation (removal of mature leaves, cotyledons or young developing leaves) at appearance of the second flush and collected 1, 5 or 10 d later for morphological and biochemical measurements. Soluble sugar and starch concentrations were measured in cotyledons and apical and basal root parts. KEY RESULTS Soluble sugar concentration in the root apices diminished during the expansion of the second aerial flush and increased after the end of aerial growth in control seedlings. Starch concentration in cotyledons regularly decreased. Continuous removal of young leaves did not alter either root growth or apical sugar concentration. Starch storage in basal root segments was increased. After removal of mature leaves (and cotyledons), root growth strongly decreased. Soluble sugar concentration in the root apices drastically decreased and starch reserves in the root basal segments were emptied 5 d after defoliation, illustrating a considerable shortage in carbohydrates. Soluble sugar concentrations recovered 10 d after defoliation, after the end of aerial growth, suggesting a recirculation of sugar. No supplementary recourse to starch in cotyledons was observed. CONCLUSIONS The parallel between apical sugar concentration and root growth patterns, and the correlations between hexose concentration in root apices and their growth rate, support the hypothesis that the response of root growth to aerial periodic growth and defoliation treatments is largely controlled by carbohydrate availability.

Branching patterns of root systems: quantitative analysis of the diversity among dicotyledonous species

BACKGROUND AND AIMS Root branching, and in particular acropetal branching, is a common and important developmental process for increasing the number of growing tips and defining the distribution of their meristem size. This study presents a new method for characterizing the results of this process in natura from scanned images of young, branched parts of excavated roots. The method involves the direct measurement or calculation of seven different traits. METHODS Young plants of 45 species of dicots were sampled from fields and gardens with uniform soils. Roots were separated, scanned and then measured using ImageJ software to determine seven traits related to root diameter and interbranch distance. RESULTS The traits exhibited large interspecific variations, and covariations reflecting trade-offs. For example, at the interspecies level, the spacing of lateral roots (interbranch distance along the parent root) was strongly correlated to the diameter of the finest roots found in the species, and showed a continuum between two opposite strategies: making dense and fine lateral roots, or thick and well-spaced laterals. CONCLUSIONS A simple method is presented for classification of branching patterns in roots that allows relatively quick sampling and measurements to be undertaken. The feasibilty of the method is demonstrated for dicotyledonous species and it has the potential to be developed more broadly for other species and a wider range of enivironmental conditions.

Nitrate availability influence on the growth components of young peach trees

Plant growth may be defined as the combination of two processes: phytomer production (or apparent plastochrone) and phytomer growth (internode elongation). We used this approach in the aim to analyse peach tree growth quantitatively both in space and time and to determine which growth components are influenced by nitrogen availability.