Relative Sink Strength Research Articles

Helium bubble formation in additive manufactured L-PBF AlSi10Mg

Laser powder bed fusion additive manufacturing shows great promise for the nuclear industry due to unique and novel metallurgical phenomena and superior properties compared to cast or wrought products. The correlation between the unique microstructure of additively manufactured AlSi10Mg alloy, the radiation damage accumulation and its effect on the mechanical properties is examined. Laser powder bed fusion AlSi10Mg alloy was subjected to He+ ions implantation over an energy range that produced a 2 μm uniform layer within the bulk material to yield a local dose of 2000 appm at the depth of the material. It is shown that for each microstructural component the Helium bubble size, distribution and density depends on its stopping range. Furthermore, the overall increase in nanohardness in the irradiated region is in correlation with the measured defect density. In this unique microstructure interfaces play a diminished role at accumulating Helium bubbles compared to dislocations and dislocation structures indicating their relative sink strength.

A Jasmonate-Induced Defense Elicitation in Mature Leaves Reduces Carbon Export and Alters Sink Priority in Grape (Vitis vinifera Chardonnay).

This work aims to understand how Vitis vinifera (Chardonnay) vines prioritise the export and distribution of recently fixed photoassimilate between root tissue, fruit, and defence, following the elicitation of a defence response. Jasmonic acid (JA) and its methyl ester, MeJA, are endogenous plant hormones, known collectively as jasmonates, that have signalling roles in plant defence and consequently are often used to prime plant defence systems. Here, we use exogenous jasmonate application to mature source leaves of Chardonnay grapevines to elucidate the prioritisation strategy of carbon allocation between plant defence and growth. Our results demonstrate that jasmonate application to Chardonnay leaves can elicit a defence response to Botrytis cinerea, but the effect was localised to the jasmonate-treated area. We found no evidence of a systemic defence response in non-treated mature leaves or young growing tissue. JA application reduced the photosynthetic rate of the treated leaf and reduced the export rate of recently fixed carbon-11 from the leaf. Following JA application, a greater proportion of available recently fixed carbon was allocated to the roots, suggesting an increase in sink strength of the roots. Relative sink strength of the berries did not change; however, an increase in berry sugar was observed seven days after JA treatment. We conclude that the data provide evidence for a “high sugar resistance” model in the mature treated leaves of the vine, since the export of carbon was reduced to ensure an elevated defence response in the treated leaf. The increase in berry sugar concentration seven days after treatment can be explained by the initial prioritisation of a greater portion of the exported carbon to storage in the roots, making it available for remobilisation to the berries once the challenge to defence had passed.

In situ TEM and multiscale study of dislocation loop formation in the vicinity of a grain boundary

Preferential formation of dislocation loops near a grain boundary (GB) in pure magnesium was observed under in-situ TEM 200 KV electron irradiation at 300 K. These loops are vacancy in nature. A rate-theory-based model is presented to explain this observation. Specifically, the model considered an irradiated domain surrounded by GBs and free surfaces. Molecular dynamics (MD) and finite difference methods (FDM) were combined to calibrate and solve the model. The distribution of loops with respect to the GB can be divided into three regions: 1) a defect free zone adjacent to the GB, 2) a region with vacancy loops in the distance range of 10–200 nm from the GB, and 3) a region free of extended defects far away from the GB. The characteristics of the three zones, and the vacancy nature of the loops can be explained by the relative sink strength of the GB to interstitial-type and vacancy-type defects.

Fruit and Leaf Response to Different Source-Sink Ratios in Apple, at the Scale of the Fruit-Bearing Branch.

Apple fruit growth is the result of several factors: inherent demand (relative sink strength) of the fruit (defined by the demands for cell division and expansion growth, etc.), carbon assimilation by the source leaves (source strength), and the resulting allocation to the organ in question. It is thus a complex process involving source–sink interactions. In the present study, we designed an experimental system in which parts of fruit-bearing branches of two apple cultivars (“Fuji” and “Ariane”) were isolated from the rest of the tree by girdling and then subjected to specific pruning and fruit removal treatments to create a wide range of global (branch-level) source–sink ratios. We monitored not only fruit kinetics but also photosynthesis as a response to light in leaves of the three different shoot types (i.e., the rosette, the bourse, and the vegetative shoots) to 1) study the impact of source–sink distance on carbon partitioning between fruits within the same branch and 2) to investigate the impact of source/sink ratio on fruit growth and leaf photosynthetic activity. Our results indicate 1) no significant differences among lateral fruits belonging to different ranks, and this independent of source availability; 2) that a modification of the source/sink ratio seems to be compensated by an alteration of the photosynthetic rate of leaves, with stronger and weaker values obtained for lower and higher ratios, respectively. Moreover, our results seem to suggest that two growing sinks together will upregulate photosynthesis rate more strongly than one growing sink does on its own, and this with the same leaf area per fruit. These results are discussed, and some hypotheses are put forward to explain them.

Modeling grapevine performance with ‘VitiSim’, a weather-based carbon balance model: Water status and climate change scenarios

Abstract A carbon balance model (VitiSim) was used for assessing the effects of vine water status and different climate scenarios on the dry matter production and partitioning of ‘Tempranillo’ grapevines (Vitis vinifera L.) grown in two different Spanish regions. Inputs included weather daily variables, stem water potential measurements and vineyard system data. Partitioning is based on the supply and demand balance using relative sink strength coefficients when carbon supply is lower than organ demands. A new routine to consider the effect of vine water status on photosynthesis rate was implemented in the model. Experimental data from two Spanish locations, several seasons (2007–2011) and well-watered and water-stressed vines were used for validating the model. A sensitivity analysis showed that model outputs are greatly influenced by those inputs linked to light interception. Simulated dry matter productions were realistic even though in general the amounts were underestimated. VitiSim was able to reproduce the effect of water stress on dry matter production observed in the field. Then, the model was used to estimate vine dry mass in different locations within Spain and worldwide under the standard current meteorological condition and under two climate change scenarios. Results were in accordance with those commonly found in field studies. Hence, this model appears useful to estimate vine dry matter potential from few easily available inputs and to simulate the effects of deficit irrigation strategies on grape yield. Further routines must be implemented to enhance VitiSim predictive capabilities and reliability.

Cavity nucleation and growth in dual beam irradiated 316L industrial austenitic stainless steel

Thin foils of 316L were simultaneously ion irradiated and He implanted in situ in a Transmission Electron Microscope at elevated temperatures. The resulting microstructure is carefully investigated in comparison with previous single ion irradiation experiments with a focus on the nucleation and growth of cavities. Helium is found to strongly enhance the nucleation of cavities in dual beam experiments. On the contrary, it does not induce more nucleation when implanted consecutively to an in situ ion irradiation but rather the growth of cavities by absorption at existing cavities, which shows the importance of synergistic effects and He injection mode on the microstructural changes. In both dual beam and single beam experiments, the characteristics of the populations of cavities, either stabilized by He or O atoms, are in qualitative agreement with the predictions of rate theory models for cavity growth. The evolutions of cavity population as a function of irradiation conditions can be reasonably well explained by the concept of relative sink strength of cavities and dislocations and the resulting partitioning of defects at sinks, or conversely recombination when either of the sinks dominates. The dislocations whose presence is a prerequisite to cavity growth in rate theory models are not observed in all studied conditions. In this case, the net influx of vacancies to cavities necessary to their growth and conversion to voids is believed to result from free surface effects, and possibly also segregation of elements close to the cavity surface. In any studied condition, the measured swelling is low, which is ascribed to the dilution of gaseous atoms among a high density of cavities as well as a high rate of point defect recombination and loss at traps. This high rate of recombination enhanced when dislocations are absent appears to result in the formation of overpressurized He bubbles.

Ideal sinks are not always ideal: Radiation damage accumulation in nanocomposites

Designing radiation tolerant materials is one of the primary challenges associated with advanced nuclear energy systems. One attractive route that has received much attention world-wide is to introduce a high density of sinks, often in the form of interfaces or secondary phases. Here, we develop a simple model of such nanocomposites and examine the ramifications of various factors on the overall radiation stability of the material. In particular, we determine how the distribution of secondary phases, the relative sink strength of those phases, and the irradiation temperature influence the radiation tolerance of the matrix. We find that the best scenario is one in which the sinks have intermediate strength, transiently trapping defects before releasing them back into the matrix. Neither perfect sinks nor the complete absence of sinks perform as well. This provides new insight into the optimal properties of nanocomposites for radiation damage environments.

Temporal and spatial variability of the stable isotopic composition of atmospheric molecular hydrogen: observations at six EUROHYDROS stations

Abstract. Despite the potential of isotope measurements to improve our understanding of the global atmospheric molecular hydrogen (H2) cycle, few H2 isotope data have been published so far. Now, within the EUROpean network for atmospheric HYDRogen Observations and Studies project (EUROHYDROS), weekly to monthly air samples from six locations in a global sampling network have been analysed for H2 mixing ratio (m(H2)) and the stable isotopic composition of the H2 (δ(D,H2), hereafter referred to as δD). The time series thus obtained now cover one to five years for all stations. This is the largest set of ground station observations of δD so far. Annual average δD values are higher at the Southern Hemisphere (SH) than at the Northern Hemisphere (NH) stations; the maximum is observed at Neumayer (Antarctica), and the minimum at the non-arctic NH stations. The maximum seasonal differences in δD range from ≈18 ‰ at Neumayer to ≈45 ‰ at Schauinsland (Southern Germany); in general, seasonal variability is largest at the NH stations. The timing of minima and maxima differs per station as well. In Alert (Arctic Canada), the variations in δD and m(H2) can be approximated as simple harmonic functions with a ≈5-month relative phase shift. This out-of-phase seasonal behaviour of δD and m(H2) can also be detected, but delayed and with a ≈6-month relative phase shift, at Mace Head and Cape Verde. However, no seasonal δD cycle could be observed at Schauinsland, which likely reflects the larger influence of local sources and sinks at this continental station. At the two SH stations, no seasonal cycle could be detected in the δD data. If it is assumed that the sink processes are the main drivers of the observed seasonality in m(H2) and δD on the NH, the relative seasonal variations can be used to estimate the relative sink strength of the two major sinks, deposition to soils and atmospheric oxidation by the hydroxyl (OH) radical. For the NH coastal and marine stations this analysis suggests that the relative contribution of soil uptake to the total annual H2 removal increases with latitude.

Contrasted Responses to Root Hypoxia in Tomato Fruit at Two Stages of Development

The biochemical consequences of root hypoxia have been documented in many sink organs, but not extensively in fruit. Therefore, in the present study, the response to root hypoxia in tomato fruit (Solanum lycopersicum L.) was investigated at two developmental stages, during the cell division and the cell expansion phases. Our results showed that in dividing fruit, root hypoxia caused an exhaustion of carbon reserves and proteins. However, ammonium and major amino acids (glutamine, asparagine and γ–aminobutyric acid (GABA)) significantly accumulated. In expanding fruit, root hypoxia had no effect on soluble sugar, protein and glutamine contents, whereas starch content was significantly decreased, and asparagine and GABA contents slightly increased. Metabolite contents were well correlated with activities of the corresponding metabolising enzymes. Contrary to nitrogen metabolising enzymes (glutamine synthetase, asparagine synthetase and glutamate decraboxylase), the activities of enzymes involved in sugar metabolism (invertase, sucrose synthase, sucrose phosphate synthase and ADP glucose pyrophosphorylase) were significantly reduced by root hypoxia, in diving fruit. In expanding fruit, only a slight decrease in ADP glucose pyrophosphorylase and an increase in asparagine synthetase and glutamate decarboxylase activities were observed. Taken together, the present data revealed that the effects of root hypoxia are more pronounced in the youngest fruits as it is probably controlled by the relative sink strength of the fruit and by the global disturbance in plant functioning.

Contrasted Effects of Prolonged Root Hypoxia on Tomato Root and Fruit (Solanum lycopersicum) Metabolism

AbstractThe decrease in growth rate of the root system, or the complete cessation of its growth, in fruiting tomato plants is a known phenomena. It has been suggested that a limited supply of carbohydrates to this organ, because of its relative weakness in competition with the developing fruitlets is the main cause for these disorders. This hypothesis was tested in this study with tomato plants (Solanum lycopersicum cv Micro‐Tom) submitted to gradual root hypoxia (1–2 % oxygen) at first flower anthesis and with limited fruit number (six fruits per plant). To this end, a range of physiological and biochemical parameters was evaluated. Our results showed that under oxygen deficiency, root growth was severely affected. In contrast to fruits, root protein and carbohydrate contents decreased significantly, concomitantly with a significant decrease in photosynthesis. Together the present data revealed that, at the fruiting stage, the effect of flooding on root growth and metabolism is probably controlled by the relative sink strength of the fruit.

ENDOTHELIALISATION AND CELL RETENTION ON BIOLOGICAL AND SYNTHETIC MATERIALS

Designing radiation tolerant materials is one of the primary challenges associated with advanced nuclear energy systems. One attractive route that has received much attention world-wide is to introduce a high density of sinks, often in the form of interfaces or secondary phases. Here, we develop a simple model of such nanocomposites and examine the ramifications of various factors on the overall radiation stability of the material. In particular, we determine how the distribution of secondary phases, the relative sink strength of those phases, and the irradiation temperature influence the radiation tolerance of the matrix. We find that the best scenario is one in which the sinks have intermediate strength, transiently trapping defects before releasing them back into the matrix. Neither perfect sinks nor the complete absence of sinks perform as well. This provides new insight into the optimal properties of nanocomposites for radiation damage environments.

Source–sink balance of wheat determines responsiveness of grain production to increased [CO 2] and water supply

Manipulation of source (flag-leaf removal) and sink (ear trimming) was conducted in a factorial CO 2-irrigation field chamber experiment with spring wheat ( Triticum aestivum L.) in south-west Sweden to test the hypothesis that responsiveness of grain production and biomass partitioning to CO 2 concentration ([CO 2]) and water supply is dependent on the source–sink balance of the plant. Negative effects of doubled [CO 2] on both individual grain mass (IGM) and harvest index (HI) were strongly related to decreasing relative sink strength (i.e. increasing source:sink ratio), probably as a result of feedbacks from sink limitation on source activity under elevated [CO 2] being relatively more important as relative sink strength decreases. Substantial down-regulation of photosynthetic capacity in elevated [CO 2], resulted in lack of significant stimulation of grain yield (GY) of unmanipulated shoots growing under elevated [CO 2]. GY was even reduced by elevated [CO 2] in sink-manipulated shoots, implying that high source:sink ratio may result in a down-regulation of photosynthetic capacity that more than offsets the direct stimulating effect of elevated [CO 2]. High irrigation positively affected IGM and HI in source-manipulated shoots only, probably as a result of the timing of irrigation treatment effects on soil moisture during, but not before, grain filling. Irrigation thus probably affected source activity during grain filling rather than potential sink capacity determined before and around anthesis, an effect that should be more pronounced for shoots with low source:sink ratio. We conclude that effects of [CO 2] and irrigation on grain production and biomass partitioning of wheat are strongly modified by source–sink balance of the plant, and that sink limitation is a major constraint on CO 2-induced GY enhancement of spring wheat under Scandinavian climatic conditions. These findings may explain earlier observations of decreased CO 2 responsiveness of GY in modern wheat cultivars, with lower whole-plant sink strength before and around anthesis compared to old cultivars, and call into question current attempts of molecular plant breeding to maximise photosynthetic activity before and around anthesis in order to enhance GY in a world with rising atmospheric [CO 2].

Partitioning of 13C-photosynthates from different current shoots neighboring with fruiting spur in later-maturing Japanese pear during the period of rapid fruit growth

To elucidate the fate of photosynthates from different current shoots and their influence on fruit growth and bud differentiation in neighboring spur complex during the period of rapid fruit growth in two late-maturing Japanese pear cultivars: ‘Atago’ and ‘Shinkou’ with contrasting fruit size, 13C labeling of single shoot was done to investigate of C-relations in fruit branches of eight shoot-combinations. The results showed that all of the current shoots investigated (bourse shoots of nonfruiting spur, bourse shoots of fruiting spur, extension shoot, nonfruiting spur, vegetative shoot, and water sprout) could export photosynthates to the neighboring fruit and buds. Water sprouts together with vegetative shoots, bourse shoots, and extension shoots are important source for fruit growth after shoot growth termination during the period of rapid fruit growth in production of late-maturing pears. The carbon transfer rate from the neighboring to the fruit bearing spur is depent (i) on the types of shoot which acts as C source, (ii) on the position of the fruiting spur and (iii) on the source-sink distance. Furthermore, the cultivar difference in carbon partitioning from different current shoot-combinations confirmed that the movement of photosynthates into the fruit was determined by sink strength of the fruit, and ‘Atago’ exhibited a greater relative sink strength of fruit than ‘Shinkou’. In addition, vegetative shoots are very important C sources for fruit growth in ‘Atago’ and the growth pattern of bourse shoot seriously affects C allocated to fruit in ‘Shinkou’.

Parameter Optimization and Field Validation of the Functional-Structural Model GREENLAB for Maize at Different Population Densities

Plant population density (PPD) influences plant growth greatly. Functional-structural plant models such as GREENLAB can be used to simulate plant development and growth and PPD effects on plant functioning and architectural behaviour can be investigated. This study aims to evaluate the ability of GREENLAB to predict maize growth and development at different PPDs. Two field experiments were conducted on irrigated fields in the North China Plain with a block design of four replications. Each experiment included three PPDs: 2.8, 5.6 and 11.1 plants m(-2). Detailed observations were made on the dimensions and fresh biomass of above-ground plant organs for each phytomer throughout the seasons. Growth stage-specific target files (a description of plant organ weight and dimension according to plant topological structure) were established from the measured data required for GREENLAB parameterization. Parameter optimization was conducted using a generalized least square method for the entire growth cycles for all PPDs and years. Data from in situ plant digitization were used to establish geometrical symbol files for organs that were then applied to translate model output directly into 3-D representation for each time step of the model execution. The analysis indicated that the parameter values of organ sink variation function, and the values of most of the relative sink strength parameters varied little among years and PPDs, but the biomass production parameter, computed plant projection surface and internode relative sink strength varied with PPD. Simulations of maize plant growth based on the fitted parameters were reasonably good as indicated by the linearity and slopes similar to unity for the comparison of simulated and observed values. Based on the parameter values fitted from different PPDs, shoot (including vegetative and reproductive parts of the plant) and cob fresh biomass for other PPDs were simulated. Three-dimensional representation of individual plant and plant stand from the model output with two contrasting PPDs were presented with which the PPD effect on plant growth can be easily recognized. This study showed that GREENLAB model has the ability to capture plant plasticity induced by PPD. The relatively stable parameter values strengthened the hypothesis that one set of equations can govern dynamic organ growth. With further validation, this model can be used for agronomic applications such as yield optimization.

A FUNCTIONAL-STRUCTURAL MODEL OF CHRYSANTHEMUM FOR PREDICTION OF ORNAMENTAL QUALITY

An integration of structural and physiological models is used to simulate 3D plant growth and visual appearance of cut chrysanthemum, reacting on environmental factors. Measurements to calibrate the model include 3D data of digitised plants as well as a number of measurements and observations on harvested plants, including biomass per organ. The structural module is based on the L-systems algorithm. This L-system calculates temperature and light driven development, branching pattern, and flower formation. In this 3D structural model existing rules for physiological processes are incorporated, enabling calculation of carbon dynamics. A 3D radiosity method is used to calculate light absorption of every organ (leaf) at an hourly basis. Hourly photosynthesis per leaf is calculated according to the biochemical model of Farquhar taking into account absorbed light, CO2, and temperature at hourly intervals. A relative sink strength approach is used to distribute the available assimilates among organs at a daily basis. Simulated growth response to temperature is based on various trial data. Modelling of light interception and photosynthesis is currently tested for one plant density only. Since the 3D crop consists of a set of individual plants, simulation of plant to plant competition for light is enabled. The model is able to visualise different flower qualities in terms of flower number, flower size and branching patterns per plant. The results show the effects of local growth of organs on the structure and ornamental quality at plant level.

Spur Characteristics, Fruit Growth, and Carbon Partitioning in Two Late-maturing Japanese Pear (Pyrus pyrifolia Nakai) Cultivars with Contrasting Fruit Size

The aim of this study was to investigate the roles of spur characteristics and carbon partitioning in regulating cultivar differences in fruit size of two late-maturing japanese pear cultivars, `Atago' and `Shinkou'. The study of spur characteristics showed that the two cultivars displayed different patterns in leaf development, flower characteristics, fruit growth, and shoot type. In contrast to `Atago' with dramatically larger fruit, `Shinkou' is a heavily spurred cultivar with a higher total leaf area and leaf number per spur early in fruit growth, less vegetative shoots, and smaller fruit but larger core. No significant differences were obtained in specific leaf weight, leaf thickness, chlorophyll content, and net photosynthesis of mature leaves, and seed number per fruit between the two cultivars. The results of trace experiment with 13C revealed that on a spur basis, there were no significant differences in the amount of 13C assimilate produced by spur leaves on each labeling date except at 190 days after anthesis, however, there were highly significant differences in the amount of 13C allocated to fruit between cultivars. Moreover, a higher amount of 13C assimilates was allocated to `Atago' flesh (or fruit) than that in `Shinkou'. Analysis of relative sink strength (RSS) indicates that the sink strength of fruit was dominant over those of other organs in the spur measured in both cultivars except at the early stage of fruit growth. `Atago' exhibited a greater RSS of fruit and lower losses of 13C for respiration and export than `Shinkou'. These results suggest that the movement of photosynthates into the fruit was determined by sink strength of the fruit rather than the source strength in the two cultivars.

A Dynamic, Architectural Plant Model Simulating Resource-dependent Growth

Physiological and architectural plant models have originally been developed for different purposes and therefore have little in common, thus making combined applications difficult. There is, however, an increasing demand for crop models that simulate the genetic and resource-dependent variability of plant geometry and architecture, because man is increasingly able to transform plant production systems through combined genetic and environmental engineering. GREENLAB is presented, a mathematical plant model that simulates interactions between plant structure and function. Dual-scale automaton is used to simulate plant organogenesis from germination to maturity on the basis of organogenetic growth cycles that have constant thermal time. Plant fresh biomass production is computed from transpiration, assuming transpiration efficiency to be constant and atmospheric demand to be the driving force, under non-limiting water supply. The fresh biomass is then distributed among expanding organs according to their relative demand. Demand for organ growth is estimated from allometric relationships (e.g. leaf surface to weight ratios) and kinetics of potential growth rate for each organ type. These are obtained through parameter optimization against empirical, morphological data sets by running the model in inverted mode. Potential growth rates are then used as estimates of relative sink strength in the model. These and other 'hidden' plant parameters are calibrated using the non-linear, least-square method. The model reproduced accurately the dynamics of plant growth, architecture and geometry of various annual and woody plants, enabling 3D visualization. It was also able to simulate the variability of leaf size on the plant and compensatory growth following pruning, as a result of internal competition for resources. The potential of the model's underlying concepts to predict the plant's phenotypic plasticity is discussed.

Contrasted responses to carbohydrate limitation in tomato fruit at two stages of development

AbstractThe metabolic consequences of long‐term carbohydrate depletion have been well documented in many sink organs but not extensively in fruit. Therefore, in the present study the response to sugar limitation in tomato fruit (Lycopersicon esculentum Mill.) was investigated at two developmental stages; during the cell division and cell expansion phases. First, the response in excised fruit cultured in vitro was characterized. Sugar depletion caused an arrest of growth and an exhaustion of carbon reserves. The proteins that were degraded and the nitrogen released was transiently stored as asparagine and glutamine in both developmental stages and also as γ ‐aminobutyric acid (GABA) in expanding fruit. Fruit at the cell division stage appeared to be more sensitive to sugar limitation. The response to sugar depletion was then characterized in fruit from plants submitted to extended darkness. In planta, the effects of sugar‐limitation were similar to those described in vitro but much more attenuated, especially in expanding fruit, which still accumulated dry matter. The expression of cell cycle genes, sugar‐ and nitrogen‐related genes was reduced by darkness. Only asparagine synthetase gene expression was induced in both dark‐treated fruit. Together the present data revealed that the effects of the carbon limitation are more pronounced in the youngest fruits as it is probably controlled by the relative sink strength of the fruit.

OSYAQ, an organ‐specific growth model for forage grasses

The effects of different stem‐to‐leaf proportions on the yield and quality of forage grasses is a question of importance to plant breeders. This paper describes the growth submodule of OSYAQ, an organ‐specific yield and quality model. The model input includes daily average air temperature, precipitation, potential evapotranspiration and incoming global radiation. The major processes implemented in the growth submodule are photosynthesis, maintenance and growth respiration, recycling of senescent plant material and remobilization of reserves. The model calculates separately yield formation for stem, leaf and ear. Available assimilates are partitioned to the various plant parts according to the concept of relative sink strength. Calibration and validation were based on a 2‐year and a 1‐year field trial, respectively, carried out under long‐ and short‐day conditions withLolium multiflorumssp.gaudini. These tests indicated a good performance of the model for the long‐day growth but showed some deficiencies for regrowth after defoliation under conditions of extreme water shortage. The paper discusses these results and possible improvements. It concludes that the growth module of OSYAQ provides a suitable tool for the analysis of the effects of varied stem‐to‐leaf ratios on yield.

Growth, flowering and partitioning of 14C-assimilate in oriental lily ‘Star Gazer’ as affected by light level and flower removal

SummaryOriental hybrid lily ‘Star Gazer’ plants were forced in a greenhouse during winter months under natural conditions or with artificial lighting. Supplemental lighting improved plant quality expressed as greater plant fresh weight, longer flower buds and earlier flowering. Lilies grown with supplemental lighting were shorter than control plants. To determine how light conditions and the presence of buds affect growth, whole lily shoots were exposed to 14CO2 at flowering time. Removing lily buds two weeks before flowering in conjunction with higher light level significantly increased the specific 14C radioactivity in mother and daughter scales in lily bulbs when harvested 24 h after exposure. The specific radioactivity in the upper leaves and stems was always higher than in the bottom parts. Bottom leaves showed lower specific 14C radioactivity in the presence of buds but it was not influenced by light level. The highest 14C radioactivity in the bottom and upper parts of the stem was observed in non-irradiated plants without buds. Sink activity of the anthers of irradiated plants was 14 times lower than that of non-irradiated plants. These results demonstrate that the maturation of pollen grains was not completed due to insufficient light level in greenhouse during forcing. Regardless of the light treatment, the specific 14C radioactivity in perianth segments was not affected but the relative sink strength (RSS) was four times higher on plants grown with supplementary lighting than in the control.