Linking water stress effects on carbon partitioning by introducing a xylem circuit into L-PEACH

Background and Aims

Many physiological processes such as photosynthesis, respiration and transpiration can be strongly influenced by the diurnal patterns of within-tree water potential. Despite numerous experiments showing the effect of water potential on fruit-tree development and growth, there are very few models combining carbohydrate allocation with water transport. The aim of this work was to include a xylem circuit into the functional–structural L-PEACH model.

Methods

The xylem modelling was based on an electrical circuit analogy and the Hagen–Poisseuille law for hydraulic conductance. Sub-models for leaf transpiration, soil water potential and the soil–plant interface were also incorporated to provide the driving force and pathway for water flow. The model was assessed by comparing model outputs to field measurements and published knowledge.

Key Results

The model was able to simulate both the water uptake over a season and the effect of different irrigation treatments on tree development, growth and fruit yield.

Conclusions

This work opens the way to a new field of modelling where complex interactions between water transport, carbohydrate allocation and physiological functions can be simulated at the organ level and describe functioning and behaviour at the tree scale.     

Functional–structural plant models: a growing paradigm for plant studies

A number of research groups in various areas of plant biology as well as computer science and applied mathematics have addressed modelling the spatiotemporal dynamics of growth and development of plants. This has resulted in development of functional–structural plant models (FSPMs). In FSPMs, the plant structure is always explicitly represented in terms of a network of elementary units. In this respect, FSPMs are different from more abstract models in which a simplified representation of the plant structure is frequently used (e.g. spatial density of leaves, total biomass, etc.). This key feature makes it possible to build modular models and creates avenues for efficient exchange of model components and experimental data. They are being used to deal with the complex 3-D structure of plants and to simulate growth and development occurring at spatial scales from cells to forest areas, and temporal scales from seconds to decades and many plant generations. The plant types studied also cover a broad spectrum, from algae to trees. This special issue of Annals of Botany features selected papers on FSPM topics such as models of morphological development, models of physical and biological processes, integrated models predicting dynamics of plants and plant communities, modelling platforms, methods for acquiring the 3-D structures of plants using automated measurements, and practical applications for agronomic purposes.     

Small fruit problem in Citrus trees

Summary Physiological causes of the small fruit problem which occurs in certain trees of orange [Citrus sinensis (L.) Osbeck cv. Valencia] were investigated in terms of water relations and gas exchange of fruits during early fruit development as well as tree carbohydrate reserves. These data from cv. Valencia trees with and without a small fruit potential were compared with those of the large fruited cv. Navel. Neither fruit water potential nor fruit transpiration nor tree carbohydrate reserves appeared to be a cause of the small fruit. Yield records showed the small fruit to be assocaited with a large number of fruit per tree. However, fruits from cv. Valencia trees with a small fruit potential respired faster than either fruits of the same cultivar and size from trees without the physiological disorder or fruits of the same size of cv. Navel and also exceeded the dark respiration of the respective leaves. Hence, the small fruit problem in cv. Valencia was partly attributed to inefficient fruit photosynthesis, causing excessive respiration of each of a larger number of fruits compared to fruits of a tree of the same cultivar but without the physiological disorder. Fruits of cv. Valencia respired more in their 2 months longer lifetime on the tree relative to those of cv. Navel. It is concluded that orchard management methods will have to be investigated to balance the fruit load of the cv. Valencia tree utilizing the carbon available for fruit growth and to minimise stress during the early fruit development.     

基于GreenLab的油松结构-功能模型

 植物结构-功能模型(Functional-structural models, FSMs)将结构模型与过程模型结合起来, 用以描述环境机制驱动的植物生长, 输出植物的三维结构。GreenLab是一个近年来不断发展着的基于源-汇关系的通用植物结构-功能模型, 它多应用于农作物, 在树木方面的应用还很少。该文以幼龄油松(Pinus tabulaeformis)为研究对象, 首次将GreenLab模型应用到虚拟树木生长的研究中。采用破坏性取样, 实测了9株油松幼树的形态结构、拓扑结构和器官生物量信息, 根据拓扑编码体系组织数据。模型的直接参数是通过实测数据获得的, 隐含参数是利用非线性最小二乘法拟合反求获得的。对模型的假设进行了验证, 并对模型的模拟效果进行了评估, 结果表明: 节间总鲜质量、树木叶总鲜质量、节间鲜质量、节间长度观测值和模型模拟值建立的回归方程的决定系数在0.78~0.91之间, 因此该模型较真实地反映了油松的结构和生长过程。提出的树木结构和生物量测量及编码方法, 可作为针叶树建立结构-功能模型的参照。     

L-system-based model of growth of dark coniferous tree species

On the basis of L-systems a mathematical model was designed to describe the growth of a dark coniferous tree. The software models a virtual timber stand composed of single trees and its further development. To eliminate branch crossing of growing trees, the rule forbidding shoot growth into the space already occupied was applied to the model. The model parameters were defined for two dark coniferous species of the southern Sikhote-Alin’ — Jezo spruce (Picea jezoensis) and Khingam fir (Abies nephrolepis). The model describes various modifications of tree crown under the influence of neighbouring trees, height uncertainty of crown starting point, variation of taper and shape of a trunk depending on plantation density, and recovery of normal tree growth after singling. Comparison of the modelled results and empirical observations show that the model succeeds in describing the growth both of single trees and of mixed plantations.     

A Semi-Quantitative Approach to Deriving a Model Structure for the Uptake of Organic Chemicals by Vegetation

An expert elicitation exercise was undertaken to determine those components and processes that are most important for modeling plant uptake of organic chemicals. The state of our knowledge of these processes was also assessed. This semi-quantitative analysis allowed the construction of an idealized model with seven compartments; soil bulk, soil water, roots, stem, leaves, fruit, and air. Three main areas were identified further research: 1) the uptake of organic chemicals by fruit; 2) the internal transfer of organic chemicals between plant structures (e.g., stem and leaves); and 3) the transfer via the soil–air–plant pathway. Until new data becomes available to quantify these processes, it is proposed that an equilibrium partitioning approach is used between plant components other than fruit or that models consist of both an edible and inedible compartment.     

On the canopy structure manipulation to buffer climate change effects on insect herbivore development

Insect pest development is often linearly related to air temperature, without taking into account the multiple interactions between the particular host plant and pest, the microclimatic conditions actually experienced by the insect, and the non-linear response of insect development rate to temperature. In this study, using an integrative biophysical model, we have investigated effects of both climatic and tree structure changes on the development of a phytophagous leaf mining moth (Phyllonorycter blancardella), taking into account the heterogeneous microclimatic conditions provided by its host plant, the domestic apple (Malus domestica), the larval body temperature rather than the ambient air temperature, and a non-linear development rate model. Hourly body temperature dynamics of larvae homogeneously dispersed in tree canopies were simulated from hourly meteorological conditions (medium IPCC climate change scenario) within the canopy of apple trees. To analyse the effect of tree architecture on leaf miner development, both pruned and unpruned trees, and one, two and three scaffold branched trees were used. Body temperature dynamics was used to compute larval development time and mortality following the non-linear developmental model for this insect. The results showed that tree pruning influences significantly larval development time and mortality. Nevertheless, the effects of manipulating tree structure on larval development and survival were relatively weak compared with the impact of chosen climate variations. This survey also showed that the variability in insect development time within a year and insect mortality change markedly with climatic variations, and highlights the importance of using non-linear rate curves and insect body temperatures instead of air temperature in forecasting models of climate-related insect pest outbreaks.     

Interacting effects of pollination,water and nutrients on fruit tree performance

Pollination is critical to fruit production, but the interactions of pollination with plant resources on a plant's reproductive and vegetative features are largely overlooked. We examined the influences of pollination, irrigation and fertilisation on the performance of almond, Prunus dulcis, in northern California. We used a full‐factorial design to test for the effects of pollination limitation on fruit production and foliage variables of whole trees experiencing four resource treatments: (i) normal water and nutrients, (ii) reduced water, (iii) no nutrients, and (iv) reduced water and no nutrients. In each of these combinations, we applied three pollination treatments: hand‐cross pollination, open‐pollination and pollinator exclusion. Pollination strongly affected yield even under reduced water and no nutrient applications. Hand‐cross pollination resulted in over 50% fruit set with small kernels, while open‐pollinated flowers showed over 30% fruit set with moderate‐sized kernels. Pollinator‐excluded flowers had a maximum fruit set of 5%, with big and heavy kernels. Reduced water interacted with the open‐ and hand‐cross pollination treatments, reducing yield more than in the pollinator exclusion treatment. The number of kernels negatively influenced the number of leaves, and reduced water and no nutrient applications interacted with the pollination treatments. Overall, our results indicate that the influences of pollination on fruit tree yield interact with the plant availability of nutrients and water and that excess pollination can reduce fruit quality and the production of leaves for photosynthesis. Such information is critical to understand how pollination influences fruit tree performance.     

Climate and plant trait strategies determine tree carbon allocation to leaves and mediate future forest productivity

Forest leaf area has enormous leverage on the carbon cycle because it mediates both forest productivity and resilience to climate extremes. Despite widespread evidence that trees are capable of adjusting to changes in environment across both space and time through modifying carbon allocation to leaves, many vegetation models use fixed carbon allocation schemes independent of environment, which introduces large uncertainties into predictions of future forest responses to atmospheric CO₂ fertilization and anthropogenic climate change. Here, we develop an optimization‐based model, whereby tree carbon allocation to leaves is an emergent property of environment and plant hydraulic traits. Using a combination of meta‐analysis, observational datasets, and model predictions, we find strong evidence that optimal hydraulic–carbon coupling explains observed patterns in leaf allocation across large environmental and CO₂ concentration gradients. Furthermore, testing the sensitivity of leaf allocation strategy to a diversity in hydraulic and economic spectrum physiological traits, we show that plant hydraulic traits in particular have an enormous impact on the global change response of forest leaf area. Our results provide a rigorous theoretical underpinning for improving carbon cycle predictions through advancing model predictions of leaf area, and underscore that tree‐level carbon allocation to leaves should be derived from first principles using mechanistic plant hydraulic processes in the next generation of vegetation models.     

Photosynthesis and transpiration of an isolated tree: model and validation

Abstract. A model for the distribution of radiation incident on leaves in an isolated apple tree is presented. The simulated area of shadow cast by a tree compared well with measured values. The radiation model is combined with leaf models of photosynthesis and stomatal behaviour to simulate diurnal variations in the exchanges of carbon dioxide and water by the tree. Satisfactory correspondence was obtained when observed rates of transpiration and photosynthesis were compared with simulations. Further simulations indicated the diurnal patterns of transpiration and photosynthesis to be expected for trees with various shapes and leaf areas.     

Changes of Starch and Sorbitol in Leaves Before and After Removal of Fruits from Peach Trees

Changes in contents of nonstructural carbohydrates in leaves,as well as some characteristics of leaves before and after fruitremoval, were investigated in potted peach (Prunus persica L.)trees. Leaf area and dry mass per unit leaf area (SLW) at thefruit-maturation stage decreased with increasing numbers ofpeaches per tree, whereas the chlorophyll content per unit areain leaves of fruiting trees increased. The chlorophyll contentdecreased more rapidly upon removal of fruit than that in leavesof fruiting trees. The starch content per unit dry mass in leavesof fruiting trees at the fruit-maturation stage was lower thanthat in leaves of non-fruiting trees. Starch accumulated significantlyin leaves within 1 d of removal of fruit during the fruit-maturationstage and continued to increase thereafter. The accumulationof starch after removal of fruit occurred more rapidly thanthe decrease in chlorophyll content. Reducing and non-reducingsugars (total sugars) per unit dry mass in the leaves were higherin fruiting trees than in non-fruiting trees. After fruit removal,the total sugar content of leaves increased temporarily andthen gradually decreased. The sorbitol content per unit freshmass in leaves of fruiting trees during the fruit-maturationstage was slightly higher than that in leaves of non-fruitingtrees. One day after removal of fruit, the sorbitol contentincreased in parallel with the accumulation of starch and remainedhigh. The sucrose content of leaves did not change markedlyupon removal of fruit. Prunus persica L.; peach leaves; nonstructural carbohydrate; starch and sorbitol; fruit removal     

基于GreenLab原理构建油松成年树的结构-功能模型

 林木的结构-功能模型(functional-structural tree modeling, FSTMs)是基于器官级组件构建的将植物结构和功能结合起来的一类模型, 在应用于成年树时需要解决拓扑结构复杂性和年轮分配模式普适性的问题。该文以18年生和41年生的油松 (Pinus tabulaeformis)成年树为研究对象, 将GreenLab模型应用到成年树的模拟中。采用破坏性取样, 实测了2株油松成年树的形态结构, 利用子结构模型解决成年树拓扑结构复杂性的问题, 引入年轮影响系数λ, 将全局分配模式和Pressler模式结合起 来, 解决年轮分配模式在不同年龄和环境条件下不同的问题。模型的直接参数通过实测数据获得, 隐含参数利用非线性最小二乘法拟合反求获得。通过实测数据与模拟数据的对比、模拟数据与经验模型模拟数据的对比, 对模型的模拟效果进行了评估, 发现节间总重、针叶总重、树高、树干节间重观测值和模型模拟值建立的回归方程的决定系数为0.84–0.98, 结构-功能模型与经验模型对总生物量模拟的决定系数为0.95, 表明该模型能较真实地反映油松的结构和生长过程。     

果树成花转变途径与调控研究进展

植物成花转变是营养生长向生殖生长转变的过程,木本果树过长的童期严重制约了育种的进程。相对于模式植物,目前对果树成花转变与调控的研究相对较少。因此,了解并掌握果树成花转变的途径及调控方法,对于缩短果树童期、调控开花,加速果树育种具有重要意义。基于近年来国内外相关研究,本文系统总结了果树的成花途径,阐述了果树栽培措施、植物生长调节剂等成花调控方法,以及果树中成花调控的相关基因及网络机制。最后,本文还对以修饰组学为主的多组学以及嫁接和植物生长调节剂在果树成花调控中的研究前景进行了展望。     

Influence of plant ontogeny on compensation to leaf damage

Ontogenetic changes in architecture, carbohydrate reserves, and resource allocation can constrain the ability of plants to compensate for herbivore damage. To evaluate ontogenetic changes in compensation, saplings and reproductive individuals of the tropical tree Casearia nitida were subjected to three levels of defoliation (0, 25, and 75% leaf area removed) and regrowth was quantified. The impact of defoliation on fruit production was evaluated in reproductive trees. In addition, the influence of defoliation on carbohydrate reserves and on the production of phenolic compounds was assessed. Plants at both stages were able to compensate for 25% leaf area loss, but only saplings were able to compensate at the 75% defoliation level. Negative impacts of defoliation on reproductive trees were also suggested by their tendency to produce fewer fruits when defoliated. The concentration of nonstructural carbohydrates decreased with damage in saplings but not in reproductive trees, suggesting an ontogenetic stage-dependent impact of defoliation on carbohydrate reserves. The concentration of phenolic compounds in leaves decreased with increasing leaf damage in both ontogenetic stages. This suggests a resource based trade-off between defense and compensation. The results from this study suggest that ontogeny needs to be considered when assessing plant responses to herbivore damage.     

In Loquat (Eriobotrya japonica Lindl.) Return Bloom Depends on the Time the Fruit Remains on the Tree

In loquat (Eriobotrya japonica Lindl.), the comparison of fruiting trees and defruited trees carried out covering a range of developmental fruit stages reveals a significant reduction in flowering due to fruit from its early stage of development, being higher when it changes color and becomes senescent, which coincides with the floral bud inductive period. This effect occurred both at the tree and at the shoot level. Furthermore, although current shoots almost always develop into panicles, those from fruiting trees develop fewer flowers, suggesting that fruit also affects at the floral bud level. In our experiment, the gibberellin concentration at the floral bud inductive period was significantly higher in bark tissues (periderm, cortex and phloem tissues) of fruiting trees, compared with defruited trees that tend to flower more. The lower concentration of IAA in the bark tissues of defruited trees also contributes to increase their flowering intensity. On the contrary, the zeatin concentration was higher. Accordingly, at bud burst, the IAA/zeatin ratio, an indication of effect on flowering, was significantly higher for fruiting trees. Some disruption in the nitrate reduction process in fruiting tree was also observed. The process of floral bud induction and differentiation was not associated with either reducing or translocating and reserve carbohydrate concentration. Hence, loquat flower intensity depends on the time the fruit is maintained on the tree. The intensity is affected indirectly, by reducing the number of shoots, and directly, by reducing the number of flowers per panicle, and these effects are linked to endogenous plant hormone contents.     

Progress in the biotechnology of trees

An increasing world population and rise in demand for tree products, especially wood, has increased the need to produce more timber through planting more forest with improved quality stock. Superior trees are likely to arise from several sources. Firstly, forest trees can be selected from wild populations and cloned using macropropagation techniques already being investigated for fruit tree rootstocks. Alternatively, propagation might be brought aboutin vitro through micropropagation or sustained somatic embryogenesis, with encapsulation of the somatic embryos to form artificial seeds. Tree quality could be improved through increased plant breeding and it is likely that experienced gained, to date, in the breeding of fruit species will be useful in devising strategies for forest trees. Since the development of techniques to regenerate woody plants from explant tissues, cells and protoplasts, it is now feasible to test the use of tissue culture methods to bring about improvements in tree quality. Success has already been achieved for tree species in the generation of somaclonal and protoclonal variation, the formation of haploids, triploids and polyploids, somatic hybrids and cybrids and the introduction of foreign DNA through transformation. This review summarizes the advances made so far in tree biotechnology, and suggests some of the directions that it might take in the future.     

Arterial branching within the confines of fractal L-system formalism

Parametric Lindenmayer systems (L-systems) are formulated to generate branching tree structures that can incorporate the physiological laws of arterial branching. By construction, the generated trees are de facto fractal structures, and with appropriate choice of parameters, they can be made to exhibit some of the branching patterns of arterial trees, particularly those with a preponderant value of the asymmetry ratio. The question of whether arterial trees in general have these fractal characteristics is examined by comparison of pattern with vasculature from the cardiovascular system. The results suggest that parametric L-systems can be used to produce fractal tree structures but not with the variability in branching parameters observed in arterial trees. These parameters include the asymmetry ratio, the area ratio, branch diameters, and branching angles. The key issue is that the source of variability in these parameters is not known and, hence, it cannot be accurately reproduced in a model. L-systems with a random choice of parameters can be made to mimic some of the observed variability, but the legitimacy of that choice is not clear.     

Herbivore effects on developmental instability and fecundity of holm oaks

Plants are able to compensate for loss of tissue due to herbivores at a variety of spatial and temporal scales, masking detrimental effects of herbivory on plant fitness at these scales. The stressing effect of herbivory could also produce instability in the development of plant modules, and measures of such instability may reflect the fitness consequences of herbivory if instability is related to components of plant fitness. We analyse the relationships between herbivory, developmental instability and production of female flowers and fruits of holm oak Quercus ilex trees by means of herbivore removal experiments. Removal of leaf herbivores reduced herbivory rates at the tree level, but had no effect on mean production of female flowers or mature fruits, whereas herbivory tended to enhance flower production and had no effect on fruit abortion at the shoot level. Differences in herbivory levels between shoots of the same branch did not affect the size and fluctuating asymmetry of intact leaves. These results indicate compensation for herbivory at the tree level and over-compensation at the shoot level in terms of allocation of resources to female flower production. Removal of insect herbivores produced an increase in the mean developmental instability of leaves at the tree level in the year following the insecticide treatment, and there was a direct relationship between herbivory rates in the current year and leaf fluctuating asymmetry the following year irrespective of herbivore removal treatment. Finally, the production of pistillate flowers and fruits by trees was inversely related to the mean fluctuating asymmetry of leaves growing the same year. Leaf fluctuating asymmetry was thus an estimator of the stressing effects of herbivory on adult trees, an effect that was delayed to the following year. As leaf fluctuating asymmetry was also related to tree fecundity, asymmetry levels provided a sensitive measure of plant performance under conditions of compensatory responses to herbivory.     

FATE‐HD: a spatially and temporally explicit integrated model for predicting vegetation structure and diversity at regional scale

During the last decade, despite strenuous efforts to develop new models and compare different approaches, few conclusions have been drawn on their ability to provide robust biodiversity projections in an environmental change context. The recurring suggestions are that models should explicitly (i) include spatiotemporal dynamics; (ii) consider multiple species in interactions and (iii) account for the processes shaping biodiversity distribution. This article presents a biodiversity model (FATE‐HD) that meets this challenge at regional scale by combining phenomenological and process‐based approaches and using well‐defined plant functional groups. FATE‐HD has been tested and validated in a French National Park, demonstrating its ability to simulate vegetation dynamics, structure and diversity in response to disturbances and climate change. The analysis demonstrated the importance of considering biotic interactions, spatio‐temporal dynamics and disturbances in addition to abiotic drivers to simulate vegetation dynamics. The distribution of pioneer trees was particularly improved, as were all undergrowth functional groups.