Gilles Vercambre

Carbon allocation in fruit trees: from theory to modelling

Carbon allocation within a plant depends on complex rules linking source organs (mainly shoots) and sink organs (mainly roots and fruits). The complexity of these rules comes from both regulations and interactions between various plant processes involving carbon. This paper presents these regulations and interactions, and analyses how agricultural management can influence them. Ecophysiological models of carbon production and allocation are good tools for such analyses. The fundamental bases of these models are first presented, focusing on their underlying processes and concepts. Different approaches are used for modelling carbon economy. They are classified as empirical, teleonomic, driven by source–sink relationships, or based on transport and chemical/biochemical conversion concepts. These four approaches are presented with a particular emphasis on the regulations and interactions between organs and between processes. The role of plant architecture in carbon partitioning is also discussed and the interest of coupling plant architecture models with carbon allocation models is highlighted. As an illustration of carbon allocation models, a model developed for peach trees, describing carbon transfer within the plant, and based on source–sink and Münch transport theory is presented and used for analyzing the link between roots, shoots and reproductive compartments. On this basis, the consequences of fruit load or plant pruning on fruit and vegetative growth can be evaluated.

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.

QualiTree, a virtual fruit tree to study the management of fruit quality. II. Parameterisation for peach, analysis of growth-related processes and agronomic scenarios

In this paper, QualiTree, a fruit tree model designed to study the management of fruit quality, and developed and described in a companion paper (Lescourret et al. in Trees Struct Funct, 2010), was combined with a simple light-interception sub-model, and then parameterised and tested on peach in different situations. Simulation outputs displayed fairly good agreement with the observed data concerning mean fruit and vegetative growth. The variability over time of fruit and vegetative growth was well predicted. QualiTree was able to reproduce the observed response of trees to heterogeneous thinning treatments in terms of fruit growth. A sensitivity analysis showed that the average seasonal growth rates of the different organs were sensitive to changes to the values of their respective initial relative growth rates and that stem wood was the tree organ the most affected by a change in the initial relative growth rates of other organs. QualiTree was able to react to simulated scenarios that combined thinning and pest attacks. As expected, thinning intensity and the percentage damage caused by pests significantly affected fruit yield and quality traits at harvest. These simulations showed that QualiTree could be a useful tool to design innovative horticultural practices.

Metabolomic profiling in tomato reveals diel compositional changes in fruit affected by source–sink relationships

Highlight Using metabolomics in tomato, we confirmed the existence of diel patterns in leaf composition and showed lower but significant diel changes in expanding fruit depending on the potential carbon supply.

Quantification and modelling of the stomatal, cuticular and crack components of peach fruit surface conductance

This study describes the components of fruit surface conductance. It aims to revise a modelling framework examining water loss across the fruit epidermis in relation to time and fruit growing conditions. For this purpose, cuticular crack surface area, healing artificial wounds in vivo, stomatal number and total fruit surface conductance were quantified during nectarine (Prunus persica L. nucipersica) fruit growth under contrasted irrigation regimes or thinning intensities. The contribution of stomatal component to total conductance decreased very early. A sub-model of the specific cuticular conductance according to fruit age was proposed that accounted for the complex temporal variation of the cuticular component. The occurrence of cracks was modelled by considering the relative expansion rate of the cuticle as a function of fruit fresh mass and relative expansion rate of the fruit. Healing decreased with fruit age. The observed temporal variations of fruit surface conductance and cuticular crack surface area were well simulated by the modified model whatever the fruit growing conditions. Tests on independent data revealed that the model was highly sensitive to parameters related to cuticular crack development and to cuticular properties.

Response of photosynthesis and chlorophyll fluorescence to acute ozone stress in tomato (Solanum lycopersicum Mill.)

The crop sensitivity to ozone (O3) is affected by the timing of the O3 exposure, by the O3 concentration, and by the crop age. To determine the physiological response to the acute ozone stress, tomato plants were exposed to O3 at two growth stages. In Experiment I (Exp. I), O3 (500 μg m−3) was applied to 30-d-old plants (PL30). In Experiment II (Exp. II), three O3 concentrations (200, 350, and 500 μg m−3) were applied to 51-d-old plants (PL51). The time of the treatment was 4 h (7:30–11:30 h). Photosynthesis and chlorophyll fluorescence measurements were done 4 times (before the exposure; 20 min, 20 h, and 2–3 weeks after the end of the treatment) using a LI-COR 6400 photosynthesis meter. The stomatal pore area and stomatal conductance were reduced as the O3 concentration increased. Ozone induced the decrease in the photosynthetic parameters of tomato regardless of the plant age. Both the photosystem (PS) II operating efficiency and the maximum quantum efficiency of PSII photochemistry declined under the ozone stress suggesting that the PSII activity was inhibited by O3. The impaired PSII contributed to the reduced photosynthetic rate. The greater decline of photosynthetic parameters was found in the PL30 compared with the PL51. It proved the age-dependent ozone sensitivity of tomato, where the younger plants were more vulnerable. Ozone caused the degradation of photosynthetic apparatus, which affected the photosynthesis of tomato plants depending on the growth stage and the O3 concentration.

Peach water relations, gas exchange, growth and shoot mortality under water deficit in semi-arid weather conditions.

In this study the sensitivity of peach tree (Prunus persica L.) to three water stress levels from mid-pit hardening until harvest was assessed. Seasonal patterns of shoot and fruit growth, gas exchange (leaf photosynthesis, stomatal conductance and transpiration) as well as carbon (C) storage/mobilization were evaluated in relation to plant water status. A simple C balance model was also developed to investigate sink-source relationship in relation to plant water status at the tree level. The C source was estimated through the leaf area dynamics and leaf photosynthesis rate along the season. The C sink was estimated for maintenance respiration and growth of shoots and fruits. Water stress significantly reduced gas exchange, and fruit, and shoot growth, but increased fruit dry matter concentration. Growth was more affected by water deficit than photosynthesis, and shoot growth was more sensitive to water deficit than fruit growth. Reduction of shoot growth was associated with a decrease of shoot elongation, emergence, and high shoot mortality. Water scarcity affected tree C assimilation due to two interacting factors: (i) reduction in leaf photosynthesis (-23% and -50% under moderate (MS) and severe (SS) water stress compared to low (LS) stress during growth season) and (ii) reduction in total leaf area (-57% and -79% under MS and SS compared to LS at harvest). Our field data analysis suggested a Ψstem threshold of -1.5 MPa below which daily net C gain became negative, i.e. C assimilation became lower than C needed for respiration and growth. Negative C balance under MS and SS associated with decline of trunk carbohydrate reserves – may have led to drought-induced vegetative mortality.

In-silico analysis of water and carbon relations under stress conditions. A multi-scale perspective centered on fruit.

Fruit development, from its early stages, is the result of a complex network of interacting processes, on different scales. These include cell division, cell expansion but also nutrient transport from the plant, and exchanges with the environment. In the presence of nutrient limitation, in particular, the plant reacts as a whole, by modifying its architecture, metabolism, and reproductive strategy, determining the resources available for fruit development, which in turn affects the overall source-sink balance of the system. Here, we present an integrated model of tomato that explicitly accounts for early developmental changes (from cell division to harvest), and use it to investigate the impact of water deficit and carbon limitation on nutrient fluxes and fruit growth, in both dry and fresh mass. Variability in fruit response is analyzed on two different scales: among trusses at plant level, and within cell populations at fruit level. Results show that the effect of stress on individual cells strongly depends on their age, size, and uptake capabilities, and that the timing of stress application, together with the fruit position on the plant, is crucial in determining the final phenotypic outcome. Water deficit and carbon depletion impacted either source size, source activity, or sink strength with contrasted effects on fruit growth. An important prediction of the model is the major role of symplasmic transport of carbon in the early stage of fruit development, as a catalyst for cell and fruit growth.

Water scarcity conditions affect peach fruit size and polyphenol contents more severely than other fruit quality traits

BACKGROUND The literature abounds with the impacts of drought conditions on the concentration of non-structural compounds (NSC) in peach fruits without distinction as to the direct effect of drought on fruit metabolism and its indirect effect through dilution. Moreover, there is a need to investigate the sensitivity of the fruit composition to progressive water deficit in semi-arid conditions, as well as the origin of variations in fruit composition - not only in carbohydrates and organic acids, but also in secondary metabolites such as polyphenols. RESULTS The increase in stress intensity resulted in smaller fruits and a reduction in yield. Drought increased fruit dry matter content, structural dry matter (SDM) content and firmness due to lower water import to fruits, although drought reduced fruit surface conductance and its transpiration. Drought significantly affected the concentrations of each NSC either through the decrease in dilution and/or modifications of their metabolism. The increase in hexoses and sorbitol concentrations of fruits grown under drought conditions resulted in an increase in the sweetness index but not near harvest. Malic acid concentration and content:SDM ratio increased as drought intensified, whereas those of citric and quinic acids decreased. Polyphenol concentration and content increased under severe drought. CONCLUSION The increase in stress intensity strongly affected fruit mass. The concentration of total carbohydrates and organic acid at harvest increased mainly through a decrease in fruit dilution, whereas the concentrations of polyphenols were also strongly affected through an impact on their metabolism.

Nitrogen and water supplies affect peach tree–green peach aphid interactions: the key role played by vegetative growth

The availabilities of water and nitrogen resources are among the main abiotic factors modifying plant physiology and growth. Consequently, via bottom‐up processes, they also can have an impact on the performance of herbivorous insects. However, the extent to which the modification of plant growth is responsible for such an impact remains unclear. We conducted a factorial experiment quantifying Myzus persicae aphid abundance and the vegetative growth of Prunus persica peach tree shoots under contrasting levels of nitrogen and water supplies. We used a hierarchical analysis of multiple regression models to determine whether the consequences of the availability of nitrogen and water on aphid abundance could be the result of a modification of plant growth. Maximum aphid abundance was achieved under nitrogen and water comfort conditions. The best model explaining variance in aphid abundance took into account vegetative growth and water supply, as well as their interaction. The results of the present study suggest that a higher nitrogen supply increases aphid abundance by fostering plant growth. Additionally, the positive response of aphid abundance to vegetative growth is lower in the case of water restriction because, under such conditions, aphids cannot take full advantage of tree vigour. Such a result provides new insights into aphid control in agriculture, as well as on the possible effects of climate change.