Sink Strength Of Organs Research Articles

Breaking Buds—Stop and Go? Acid Invertase Activities in Apple Leaf Buds during Dormancy Release until Bud Break

Bud dormancy enables deciduous fruit trees to endure unfavorable conditions during winter, and considerably impacts growth and reproduction in spring. We investigated acid invertase activities during dormancy release until bud break under natural (orchard) conditions in two consecutive years. Our aim was to relate the activity patterns to the developmental progression and to air temperature, which is a major factor influencing the developmental processes at that stage. The enzyme assays were performed on extracts from leaf buds of the cultivar Idared, sampled from early March to April in the years 2020 and 2021. The air temperature was continually monitored during the observation periods. cwINV activity showed a trend of slight increase at the earlier developmental stages and sharply increased during bud break in both years. cwINV is known to contribute to organ sink strength. Its up-regulation may, therefore, be related to the increasing developmental demand for carbohydrates in apple leaf buds during dormancy release until bud break. vacINV activity was relatively constant at the earlier stages and also showed a pronounced increase in activity during bud break in both years. However, in both years, we observed drops in vacINV activity following cold spells. vacINV activity has been associated with growth via cell elongation through the regulation of cell turgor and may, thus, be involved in bud break. Therefore, we suggest that the down-regulation of vacINV activity as a consequence of cold spells might contribute to a delay in bud break to protect young leaf tissues from exposure to cold stress conditions.

Magnitude and mechanisms of nitrogen‐mediated responses of tree biomass production to elevated CO2: A global synthesis

Abstract Elevated atmospheric CO2 concentration (eCO2) typically stimulates tree growth, which is mediated by nitrogen (N) availability; but how N regulates tree biomass responses to eCO2 remains uncertain, which limits our prediction of forest carbon (C) cycling under future global change scenarios. A meta‐analysis of a global dataset including 3,399 observations from 283 papers published from 1980s to February 2021 was conducted with the aim of elucidating N‐mediated responses of tree biomass production to eCO2 and the underlying mechanisms. We found that eCO2 stimulated tree biomass production (+32.0%), while it induced accumulation of non‐structural carbohydrates in leaves rather than in woods and roots, suggesting that the production may be C‐limited but depend on the sink strength of organs. Biomass responses to eCO2 of N‐fertilized trees (+39.6%) were 68.4% greater than those of non‐fertilized trees (+23.5%), confirming that tree growth is also N‐limited. Such N limitation was alleviated by the eCO2‐induced increases in N uptake and N‐use efficiency (NUE), with the former being more important. Increases in tree N pool arose from the enhanced production of fine roots with a lower specific root length, whereas increases in NUE resulted from the flexibility in tissue C:N ratios instead of N resorption efficiency. The positive responses of tree biomass production to eCO2 were greater for ectomycorrhizal trees and conifers than for arbuscular mycorrhizal trees and angiosperms, respectively. Synthesis. Our findings suggest that eCO2 stimulates tree biomass production by increasing C availability, and alleviating N limitation in a feedback way via enhancing N uptake and NUE, and they improve our mechanistic understanding of responses of forest productivity and C sequestration to eCO2 under global change.

Estimating Sink Parameters of Stochastic Functional-Structural Plant Models Using Organic Series-Continuous and Rhythmic Development.

Functional-structural plant models (FSPMs) generally simulate plant development and growth at the level of individual organs (leaves, flowers, internodes, etc.). Parameters that are not directly measurable, such as the sink strength of organs, can be estimated inversely by fitting the weights of organs along an axis (organic series) with the corresponding model output. To accommodate intracanopy variability among individual plants, stochastic FSPMs have been built by introducing the randomness in plant development; this presents a challenge in comparing model output and experimental data in parameter estimation since the plant axis contains individual organs with different amounts and weights. To achieve model calibration, the interaction between plant development and growth is disentangled by first computing the occurrence probabilities of each potential site of phytomer, as defined in the developmental model (potential structure). On this basis, the mean organic series is computed analytically to fit the organ-level target data. This process is applied for plants with continuous and rhythmic development simulated with different development parameter sets. The results are verified by Monte-Carlo simulation. Calibration tests are performed both in silico and on real plants. The analytical organic series are obtained for both continuous and rhythmic cases, and they match well with the results from Monte-Carlo simulation, and vice versa. This fitting process works well for both the simulated and real data sets; thus, the proposed method can solve the source-sink functions of stochastic plant architectures through a simplified approach to plant sampling. This work presents a generic method for estimating the sink parameters of a stochastic FSPM using statistical organ-level data, and it provides a method for sampling stems. The current work breaks a bottleneck in the application of FSPMs to real plants, creating the opportunity for broad applications.

Relationships between biomass allocation, axis organogenesis and organ expansion under shading and water deficit conditions in grapevine.

The relationships between whole-plant growth and morphogenetic processes under abiotic stresses are still partly unknown. Whole-plant biomass growth can be decreased by many abiotic stresses, including water deficit and shading. Two experiments were performed on potted plants of one grapevine cultivar (Vitis vinifera L. cv. Syrah) subjected to watering and shading treatments. Under water stress, plants reduced their primary and secondary axis leaf production rate, whereas secondary axis budburst was relatively unaffected. Individual leaf area was reduced and a strong decrease in leaf expansion rate was observed. Under shading, primary axis organogenesis was maintained, both secondary axis budburst rate and phytomer appearance rate were decreased, and individual leaf area slightly increased. Specific leaf area did not change under soil water deficit, whereas it increased under shading. These results confirm the existence of dynamic changes in organ sink strength and biomass allocation patterns to favour plant leaf area growth under shading, and to reduce plant leaf area and water losses by transpiration under water stress. From a modelling point of view, this study shows that functional structural models based on a C balance are not fully relevant for simulating plant growth under abiotic constraints if they do not include non-trophic relationships (hormonal signalling or plant hydraulic properties) that modify organ sink strength according to abiotic constraints.

Condensed tannin biosynthesis and polymerization synergistically condition carbon use, defense, sink strength and growth in Populus

The partitioning of carbon for growth, storage and constitutive chemical defenses is widely framed in terms of a hypothetical sink-source differential that varies with nutrient supply. According to this framework, phenolics accrual is passive and occurs in source leaves when normal sink growth is not sustainable due to a nutrient limitation. In assessing this framework, we present gene and metabolite evidence that condensed tannin (CT) accrual is strongest in sink leaves and sequesters carbon in a way that impinges upon foliar sink strength and upon phenolic glycoside (PG) accrual in Populus. The work was based on two Populus fremontii × angustifolia backcross lines with contrasting rates of CT accrual and growth, and equally large foliar PG reserves. However, foliar PG accrual was developmentally delayed in the high-CT, slow-growth line (SG), and nitrogen-limitation led to increased foliar PG accrual only in the low-CT, fast-growth line (FG). Metabolite profiling of developing leaves indicated comparatively carbon-limited amino acid metabolism, depletion of several Krebs cycle intermediates and reduced organ sink strength in SG. Gene profiling indicated that CT synthesis decreased as leaves expanded and PGs increased. A most striking finding was that the nitrogenous monoamine phenylethylamine accumulated only in leaves of SG plants. The potential negative impact of CT hyper-accumulation on foliar sink strength, as well as a mechanism for phenylethylamine involvement in CT polymerization in Populus are discussed. Starch accrual in source leaves and CT accrual in sink leaves of SG may both contribute to the maintenance of a slow-growth phenotype suited to survival in nutrient-poor habitats.

The Uptake and Partitioning of Nitrogen in Phalaenopsis Sogo Yukidian ‘V3’ as Shown by 15N as a Tracer

Phalaenopsis is currently the world’s number one potted flower crop. It is a slow-growing plant that responds slowly to nitrogen (N) fertilization and is noted for great resilience against N deficiency. Despite the great significance of N during the cultivation of Phalaenopsis, little has been studied on the uptake and partitioning of N in this crop. The stable isotope 15N was used as a tracer to investigate the uptake and partitioning of N and the roles of organs in sink and source relationship of N partitioning during different stages in Phalaenopsis. Fertilizer labeled with 15N was applied to Phalaenopsis Sogo Yukidian ‘V3’ during the vegetative growth stage on different parts of plants. Both leaves and roots were able to take up N. Nitrogen uptake efficiency of young roots was the highest, followed by old roots, whereas that of leaves was lowest. No difference of N uptake efficiency was found between the upper and lower leaf surfaces. Movement of fertilizer N to the leaves occurred as early as 0.5 day after fertilizer application to the roots. The partitioning of N depended on organ sink strength. During the vegetative growth stage, newly grown leaves and newly formed roots were major sinks. Sink strength of leaves decreased with the increase in leaf age. Stalks and flowers were major sinks during the reproductive growth stage. Mature leaves were a major location where N was stored and could serve as a N source during the reproductive growth stage and also for new leaf growth.

Impact of eastern dwarf mistletoe (Arceuthobium pusillum) on host white spruce (Picea glauca) development, growth and performance across multiple scales

Infection by eastern dwarf mistletoe (Arceuthobium pusillum) modifies needle and branch morphology and hastens white spruce (Picea glauca) mortality. We examined potential causal mechanisms and assessed the impacts of infection-induced alterations to host development and performance across scales ranging from needle hormone contents to bole expansion. Needles on infected branches (IBs) possessed higher total cytokinin (CK) and lower abscisic acid contents than needles on uninfected branches (UBs). IBs exhibited greater xylem growth than same-aged UBs, which is consistent with the promotive effect of CKs on vascular differentiation and organ sink strength. Elevated CK content may also explain the dense secondary and tertiary branching observed at the site of infection, i.e. the formation of 'witches' brooms' with significantly lower light capture efficiencies. Observed hormone perturbations were consistent with higher rates of transpiration, lower water use efficiencies (WUEs) and more negative needle carbon isotope ratios observed for IBs. Observed reductions in needle size allowed IBs to compensate for reduced hydraulic conductivity. Severe infections resulted in dramatically decreased diameter growth of the bole. It seems likely that the modifications to host hormone contents by eastern dwarf mistletoe infection led white spruce trees to dedicate a disproportionate fraction of their photoassimilate and other resources to self-shaded branches with low WUE. This would have decreased the potential for fixed carbon accumulation, generating a decline in the whole-tree resource pool. As mistletoe infections grew in size and the number of IBs increased, this burden was manifested as increasingly greater reductions in bole growth.

Correlation between dynamic tomato fruit-set and source-sink ratio: a common relationship for different plant densities and seasons?

It is widely accepted that fruit-set in plants is related to source-sink ratio. Despite its critical importance to yield, prediction of fruit-set remains an ongoing problem in crop models. Functional-structural plant models are potentially able to simulate organ-level plasticity of plants. To predict fruit-set, the quantitative link between source-sink ratio and fruit-set probability is analysed here via a functional-structural plant model, GreenLab. Two experiments, each with four plant densities, were carried out in a solar greenhouse during two growth seasons (started in spring and autumn). Dynamic fruit-set probability was estimated by frequent observation on inflorescences. Source and sink parameter values were obtained by fitting GreenLab outputs for the biomass of plant parts (lamina, petiole, internode, fruit), at both organ and plant level, to corresponding destructive measurements at six dates from real plants. The dynamic source-sink ratio was calculated as the ratio between biomass production and plant demand (sum of all organ sink strength) per growth cycle, both being outputs of the model. Most sink parameters were stable over multiple planting densities and seasons. From planting, source-sink ratio increased in the vegetative stage and reached a peak after fruit-set commenced, followed by a decrease of leaf appearance rate. Fruit-set probability was correlated with the source-sink ratio after the appearance of flower buds. The relationship between fruit-set probability and the most correlated source-sink ratio could be quantified by a single regression line for both experiments. The current work paves the way to predicting dynamic fruit-set using a functional structure model.

The Derivation of Sink Functions of Wheat Organs using the GREENLAB Model

In traditional crop growth models assimilate production and partitioning are described with empirical equations. In the GREENLAB functional-structural model, however, allocation of carbon to different kinds of organs depends on the number and relative sink strengths of growing organs present in the crop architecture. The aim of this study is to generate sink functions of wheat (Triticum aestivum) organs by calibrating the GREENLAB model using a dedicated data set, consisting of time series on the mass of individual organs (the 'target data'). An experiment was conducted on spring wheat (Triticum aestivum, 'Minaret'), in a growth chamber from, 2004 to, 2005. Four harvests were made of six plants each to determine the size and mass of individual organs, including the root system, leaf blades, sheaths, internodes and ears of the main stem and different tillers. Leaf status (appearance, expansion, maturity and death) of these 24 plants was recorded. With the structures and mass of organs of four individual sample plants, the GREENLAB model was calibrated using a non-linear least-square-root fitting method, the aim of which was to minimize the difference in mass of the organs between measured data and model output, and to provide the parameter values of the model (the sink strengths of organs of each type, age and tiller order, and two empirical parameters linked to biomass production). The masses of all measured organs from one plant from each harvest were fitted simultaneously. With estimated parameters for sink and source functions, the model predicted the mass and size of individual organs at each position of the wheat structure in a mechanistic way. In addition, there was close agreement between experimentally observed and simulated values of leaf area index.

MODELLING FRUIT SET, FRUIT GROWTH AND DRY MATTER PARTITIONING

This paper discusses how fruit set, fruit growth and dry matter partitioning can be simulated by models where sink strength (assimilate demand) and source strength (assimilate supply) are the key variables. Although examples are derived from experiments on fruit vegetables such as tomato, sweet pepper and cucumber, the theoretical basis holds for a wide range of crops including fruit trees. Dry matter partitioning is the end result of the flow of assimilates from source organs via a transport path to the sink organs. It appears to be primarily regulated by the sink strength of the sinks, with fruits being the major sinks in fruit trees or fruit vegetables. Source strength has only an indirect effect on dry matter partitioning through effects on the number of fruits on a plant. The transport path is only of minor importance for the regulation of dry matter partitioning at the whole plant level. The growth rate of a fruit depends on the source strength and the fraction of the assimilates partitioned into it. Dry matter partitioning was modelled as a function of the sink strengths of the plant organs, where sink strength of an organ is defined by its potential growth rate (potential capacity to accumulate assimilates). The potential growth rate has been shown to quantitatively reflect the sink strength of an organ. The potential growth of a fruit is a function of both its age and temperature. In several experiments and for different treatments it was shown that dry matter partitioning into a fruit can be simulated as a function of its sink strength relative to that of the other plant organs. The number of fruits set per plant has a great impact on the dry matter partitioning and fruit growth. Several experiments have shown that fruit set increases with source strength and decreases with sink strength. Consequently fruit set could be reasonably successful modelled as a function of sink and source strength. Finally it is shown how a photosynthesis-based model combined with submodels for fruit set, fruit growth and dry matter partitioning can be used for predictions of yield and fruit size.

Dry Matter Partitioning in Tomato: Validation of a Dynamic Simulation Model

A model for dynamic simulation of dry matter distribution between reproductive and vegetative plant parts and the distribution among individual fruit trusses in glasshouse tomato, is validated. The model is part of the crop growth model TOMSIM and is based on the hypothesis that dry matter distribution is regulated by the sink strengths of the plant organs, quantified by their potential growth rates, i.e. the growth rates at non-limiting assimilate supply. Within the plant, individual fruit trusses are distinguished and sink strength of a truss is described as a function of its development stage. Truss development rate is a function of temperature only. The same potential growth curve, proportional to the number of fruits per truss, is adopted for all trusses. In a simple version of the model, vegetative plant parts are lumped together as one sink with a constant sink strength. In a more detailed version, vegetative sink strength is calculated as the sum of sink strengths of vegetative units (three leaves and stem internodes between two trusses). The model was validated for six glasshouse experiments, covering effects of planting date, plant density, number of fruits per truss (pruning at anthesis), truss removal (every second truss removed at anthesis), single- and double-shoot plants and a temperature experiment conducted in climate rooms at 17, 20 or 23 °C. Daily increase in above-ground dry weight, average daily temperatures and number of set fruits per truss were inputs to the model. Both the simple and the more detailed model showed good agreement between measured and simulated fraction of dry matter partitioned into the fruits over time. For the simple version of the model, the slope of the lines relating simulated to measured fraction partitioned into the fruits (16 data sets), varied between 0.92 and 1.11, on average it was 1.04, implying 4% over-estimation for this fraction. For the detailed model these numbers were slightly better: 0.89, 1.08 and 1.01, respectively. The temperature experiment revealed no important direct influence of temperature on the ratio between generative and vegetative sink strength. Simulated truss growth curves showed reasonable agreement with the measurements, although both models over-estimated (17% on average) final dry weight of the lower trusses (truss 1 –3) on a plant. Modelling dry matter partitioning based on sink strengths of organs is promising, as it is a general, dynamic and flexible approach, showing good agreement between measurements and simulation for a range of conditions. Applicability of the model is, however, still limited as long as the number of fruits per truss (flower and /or fruit abortion) is not simulated, as this is a major feedback mechanism in plant growth.

A Simulation Model for Dry Matter Partitioning in Cucumber

A dynamic model is developed for the simulation of the daily dry matter distribution between the generative and vegetative plant parts and the distribution among individual fruits in greenhouse cucumber. The model is based on the hypothesis that dry matter partitioning is regulated by the sink strengths of the plant organs. The sink strength of an organ is defined here as its potential growth rate, i.e. the growth rate at non-limiting assimilate supply. The sink strength of each individual fruit is described as a function of its temperature sum after anthesis and the actual temperature, that of the vegetative plant parts as a function of actual temperature only. The formation rate of non-aborting fruits is essentially a function of the source/sink ratio.Model results agreed well with the measured fluctuating distribution of dry matter between fruits and vegetative parts. The measured effects of three intensities of fruit removal were also simulated satisfactorily. When simulating the partitioning among individual fruits the final fruit size was simulated quite well. However, the growth rate of young fruits was usually overestimated and that of old fruits underestimated, because of dominance among fruits. This phenomenon could be accounted for by incorporating priority functions into the model. Finally, a sensitivity analysis of the model was performed to investigate the effects of some climatic factors, manipulations of the number of fruits on a plant and model parameters on dry matter distribution. Strategies to manipulate the dry matter distribution are discussed.

A Simulation Model for Dry Matter Partitioning in Cucumber

A dynamic model is developed for the simulation of the daily dry matter distribution between the generative and vegetative plant parts and the distribution among individual fruits in greenhouse cucumber. The model is based on the hypothesis that dry matter partitioning is regulated by the sink strengths of the plant organs. The sink strength of an organ is denned here as its potential growth rate, i.e. the growth rate at non-limiting assimilate supply. The sink strength of each individual fruit is described as a function of its temperature sum after anthesis and the actual temperature, that of the vegetative plant parts as a function of actual temperature only. The formation rate of nonaborting fruits is essentially a function of the source/sink ratio. Model results agreed well with the measured fluctuating distribution of dry matter between fruits and vegetative parts. The measured effects of three intensities of fruit removal were also simulated satisfactorily. When simulating the partitioning among individual fruits the final fruit size was simulated quite well. However, the growth rate of young fruits was usually overestimated and that of old fruits underestimated, because of dominance among fruits. This phenomenon could be accounted for by incorporating priority functions into the model. Finally, a sensitivity analysis of the model was performed to investigate the effects of some climatic factors, manipulations of the number of fruits on a plant and model parameters on dry matter distribution. Strategies to manipulate the dry matter distribution are discussed.