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Climate change may have important consequences on plant distribution because local environments could change faster than the pace of natural selection and adaptation of wild populations and cultivars of perennial forages. Temperature is a primary factor affecting seed germination and primary heterotrophic growth processes. Medicago sativa (L.) is the most important forage legumes globally. The accelerated breeding of alfalfa cultivars adapted to new ranges of temperature could be necessary under most future climate scenarios. This work aims to explore the genetic diversity of a sample of accessions for responses to temperature during seed germination and seedling heterotrophic growth. Seeds or seedlings were placed in the dark under eight constant temperatures in the range of 5 °C to 40 °C. Germinated seeds were manually counted, while hypocotyl and radicle growth were estimated by using image analysis and curve fitting. Multivariate analyses highlighted links between responses and the origin of accessions. Variability was high, within and between accessions, for all the response variables. Accessions showed significant differences in their non-linear response curves in terms of germinability, germination rates and relative elongation rates. Nevertheless, differences were more noticeable in germination rations and rates compared to seedling heterotrophic growth. Consequently, these could be easier to use as early markers for alfalfa selection and breeding for the future. [ABSTRACT FROM AUTHOR]

Key message: Cocksfoot shows intra-specific variability in its response to constant temperature during germination. Temperature, in conjunction with other environmental factors, controls plant development, including seed germination and its timing, which directly affects seedling survival. Indirectly, seed germination affects recruitment of individuals and hence the genetic dynamics of grasslands communities. Cocksfoot (Dactylis glomerata L.) is a major species growing in temperate and Mediterranean grasslands. Six accessions of D. glomerata, including four natural populations and two commercial varieties were evaluated for their responses to eight constant temperatures, from 5 to 40 ℃, with increases by 5 ℃. Four replicates of one-hundred seeds per accession were put in the dark and counted for germination at variable frequencies and duration that depended on temperature treatments. We estimated maximum germination percentage, maximum germination rate as well as apparent initial time and time when 50% of seed germinate. The F test showed significant difference (P < 0.01) between the response curves of various accessions. At least four types of responses can be distinguished. Temperature for maximum germination ranged from 5 to 25 ℃, depending on accessions. The results of this study reveal the existence of intraspecific genetic variability during germination in D. glomerata for the response to temperature. Such variability could be used to select new varieties adapted to thermal conditions induced by ongoing climate change. [ABSTRACT FROM AUTHOR]

Neonicotinoid insecticides have made possible, for three decades, to protect sugar beet crops against aphids and the viruses they transmit. However, they have been accused of reducing biodiversity, leading the European Union to ban the use of neonicotinoid-coated seeds. The requests for exemptions of use, submitted annually by different member states, might soon no longer be granted. Here, we performed a comprehensive analysis of the available alternatives to neonicotinoids for aphid control in sugar beets, following the PICO framework. The abstracts of 3878 references were consulted to evaluate alternative control methods. Of these, we selected 301 scientific publications, keeping only those which provided indications of treatment efficacy against sugar beet aphids. We identified 75 control strategies (products or methods) as possible alternatives to neonicotinoids. Each control strategy was evaluated based on four criteria: efficacy, durability, applicability and practicability. Using these criteria, we highlight 20 methods or products that have both potential as alternative to neonicotinoids and whose short-term use is feasible. These alternative methods include five synthetic and three natural insecticides, two entomopathogenic fungi, two arthropod natural enemies, organic and mineral oils, two plant defense elicitors, three farming practices and the potential of resistant varieties. Most of them provide important, but arguably insufficient, control of aphids if used alone. However, most of them appear to be complementary and compatible with each other. Therefore, integrating strategies will be needed to maintain beet yields while limiting unintended effects on environment and biodiversity. [ABSTRACT FROM AUTHOR]

Temperature is one the most influential environmental factors for the germination and establishment of grass species. The specific objective of this study was to determine the effects of low constant temperature on the time needed to express the full germination capacity of nondormant seedlots. Fifteen accessions, comprising seven of Lolium perenne L., three of Festuca arundinacea Schreb., three of Dactylis glomerata L. and two of Triticum aestivum L., were evaluated at constant temperatures of 5 and 21 °C. As expected, the germination rates were faster at 21 °C than at 5 °C. Indeed, at 5 °C seeds needed up to twenty-one times longer to reach the maximum germination than when tested at 21 °C. The genotypic variability found for the ratio of germination rates between the two temperatures (i.e., germination rate at 5 °C/germination rate at 21 °C) was much more variable than what is found in the literature for perennial cool-season grasses. On the other hand, in most cases, no significant differences were observed in the germinability (the capacity to germinate) response to 5 °C and 21 °C. Within the four species, twelve of the fifteen studied accessions expressed the same germinability at 5 °C and 21 °C, when given enough time. Only three accessions had final germination percentages higher at 21 °C than at 5 °C. Our results suggest that, in general, nondormant seeds at low temperatures germinate as well as nondormant seeds at near-optimal temperatures, provided they have enough time to express their germination capacity. These findings cast doubts on the validity of conclusions drawn in many studies where germination experiments were performed for a period insufficient to obtain full germination at low temperatures. Another major finding in this work concerns the risk of wrongly estimating germinability at low temperatures. [ABSTRACT FROM AUTHOR]

Tall fescue is a major species growing in temperate grasslands. It is a cool-season perennial native of Western Europe and used worldwide as forage for its quality and adaptability to various soils and climates. By its effects on germination and seedling growth, temperature affects the recruitment of individuals and, consequently, the genetic diversity of plant communities. Under most climate change scenarios, breeding cultivars adapted to new ranges of temperature will be necessary. Knowing the variability of the responses to temperature by different accessions is an essential first step towards such breeding. In this work, we (i) analyze the intraspecific variability of tall fescue in response to a constant temperature during germination and (ii) quantitatively describe the response curves. A sample of nine, from 128, accessions of tall fescue was evaluated. Four replicates of 100 seeds per accessions were tested for germination in the dark at eight constant temperatures ranging from 5 to 40 °C with increases of 5 °C. The germinability, lag to start and maximum germination rates were estimated. It was observed that the responses of tall fescue accessions were statistically different (p < 0.05). The optimal temperature for maximum germination ranged from 9 °C to 25 °C. Germination was not observed for any accession at 40 °C. The novelty of this work comes from the duration of the sampling period at low temperatures that was longer than in most published papers. Based on the responses to temperature during germination, our findings suggest that a high intraspecific genetic variability exists in tall fescue that merits further exploration. This variability should be useful to breed new cultivars adapted to the new environmental conditions imposed by the ongoing fast climate change. [ABSTRACT FROM AUTHOR]

Lolium perenne (L.) is one of the most important species in temperate grasslands. Temperature is a major factor controlling plant development. Breeding L. perenne cultivars adapted to new ranges of temperature could be necessary under most climate change scenarios. However, before any breeding effort in such direction, knowing the intraspecific variability of responses to temperature is essential. Our objective was to analyze a sample of accessions of L. perenne for their response to constant temperature during germination and initial heterotrophic growth. Eight accessions were taken out from a genebank containing 160 accessions. Six accessions were wild populations collected in different places in France and the other two were populations from a selection program. For germination, four replicates of 100 seeds per accession were tested in Petri dishes in the dark at eight constant temperatures, from 5 to 40°C with increases of 5°C. Germination countings were carried out at variable time intervals and durations that depended on treatments. For initial heterotrophic growth analysis, seeds were germinated at 25°C. Sets of 30 seedlings per accession were placed in polypropylene boxes on blotter blue paper and transferred to each one of the eight treatments in the dark. They were pictured at variable time intervals for root and shoot growth measurement by image analysis. Neither seed germination nor heterotrophic growth was observed at 40°C, for any accession. Temperature and time course response surfaces were markedly different between accessions. Equally, maximum germinability and the shape of the response curves to temperature were significantly different between accessions. This means that limited similarities between responses were observed. Furthermore, germination rates followed the non-linear beta function with significant differences between some accessions. These also showed significant differences in their root and shoot growth rate in response to temperature. In general, the relative growth rates of roots and shoots were slow at 5°C, peaked between 25 and 30°C, and showed a sharp reduction afterward. These results reveal, for the first time, high genetic variability within L. perenne germplasm for the response to temperature in the initial life phases. This discovered variability should serve breeders to create perennial ryegrass varieties for the future. [ABSTRACT FROM AUTHOR]

Various adaptive mechanisms can ensure that seedlings are established at the most favourable time and place. These mechanisms include seed dormancy i.e., incapacity to germinate in any environment without a specific environmental trigger and inhibition i.e., incapacity to germinate in an unfavourable environment (water availability, temperature: thermoinhibition and light). The objective of this research was to study in the temperate range for germination of forage and turf grass species perennial ryegrass, if the thermal requirements for germination are under genetic controlled and could be selectively bred. Two divergent selections of three cycles were realized on a natural population: one to select for the capacity to germinate at 10°C vs. the impossibility to germinate at 10°C, and one to select for the capacity to germinate at 32°C vs. the impossibility to germinate at 32°C. Seeds of all the lots obtained from the two divergent selections were then germinated at constant temperatures from 5 to 35°C to evaluate their germination ability. Concerning the positive selection, the first cycle of positive selection at 10°C was highly efficient with a very strong increase in the germination percentage. However, afterward no selection effect was observed during the next two cycles of positive selection. By contrast, the positive selection at 32°C was efficient during all cycles with a linear increase of the percentage of germination at 32°C. Concerning the negative selection, we observed only a large positive effect of the first cycle of selection at 10°C. These findings demonstrate that seed thermoinhibition at 10 and 32°C observed in a natural population of perennial ryegrass has a genetic basis and a single recessive gene seems to be involved at 10°C. [ABSTRACT FROM AUTHOR]

Perennial ryegrass is an important forage crop in dairy farming, either for grazing or haying purposes. To further optimise the forage use, this study focused on understanding forage digestibility in the two most important cuts of perennial ryegrass, the spring cut at heading and the autumn cut. In a highly diverse collection of 592 Lolium perenne genotypes, the organic matter digestibility (OMD) and underlying traits such as cell wall digestibility (NDFD) and cell wall components (cellulose, hemicellulose, and lignin) were investigated for 2 years. A high genotype × season interaction was found for OMD and NDFD, indicating differences in genetic control of these forage quality traits in spring versus autumn. OMD could be explained by both the quantity of cell wall content (NDF) and the quality of the cell wall content (NDFD). The variability in NDFD in spring was mainly explained by differences in hemicellulose. A 1% increase of the hemicellulose content in the cell wall (HC.NDF) resulted in an increase of 0.81% of NDFD. In autumn, it was mainly explained by the lignin content in the cell wall (ADL.NDF). A 0.1% decrease of ADL.NDF resulted in an increase of 0.41% of NDFD. The seasonal traits were highly heritable and showed a higher variation in autumn versus spring, indicating the potential to select for forage quality in the autumn cut. In a candidate gene association mapping approach, in which 503 genes involved in cell wall biogenesis, plant architecture, and phytohormone biosynthesis and signalling, identified significant quantitative trait loci (QTLs) which could explain from 29 to 52% of the phenotypic variance in the forage quality traits OMD and NDFD, with small effects of each marker taken individually (ranging from 1 to 7%). No identical QTLs were identified between seasons, but within a season, some QTLs were in common between digestibility traits and cell wall composition traits confirming the importance of hemicellulose concentration for spring digestibility and lignin concentration in NDF for autumn digestibility. [ABSTRACT FROM AUTHOR]

Reduced blue light irradiance is known to enhance leaf elongation rate (LER) in grasses, but the mechanisms involved have not yet been elucidated. We investigated whether leaf elongation response to reduced blue light could be mediated by stomata-induced variations of plant transpiration. Two experiments were carried out on tall fescue in order to monitor LER and transpiration under reduced blue light irradiance. Additionally, LER dynamics were compared with those observed in the response to vapour pressure deficit (VPD)-induced variations of transpiration. Finally, we developed a model of water flow within a tiller to simulate the observed short-term response of LER to various transpiration regimes. LER dramatically increased in response to blue light reduction and then reached new steady states, which remained higher than the control. Reduced blue light triggered a simultaneous stomatal closure which induced an immediate decrease of leaf transpiration. The hydraulic model of leaf elongation accurately predicted the LER response to blue light and VPD, resulting from an increase in the growth-induced water potential gradient in the leaf growth zone. Our results suggest that the blue light signal is sensed by stomata of expanded leaves and transduced to the leaf growth zone through the hydraulic architecture of the tiller. [ABSTRACT FROM AUTHOR]

Lucerne (Medicago sativa), a major perennial pasture legume, belongs to a species complex that includes several subspecies with wild and cultivated populations. Stand establishment may be compromised by poor germination. Seed scarification, deterioration and temperature have an impact on germination. The objective of this study was to analyse the genetic diversity of lucerne germination in response to three factors: (1) temperature, with seven constant temperatures ranging from 5 to 40°C, was tested on 38 accessions, (2) seed scarification was tested on the same accessions at 5 and 22°C, (3) seed deterioration was tested on two accessions and two seed lots at the seven temperatures. The germination dynamics of seed lots over time was modelled and three parameters were analysed: germinability (germination capacity), maximum germination rate (maximum% of seeds germinating per time unit), and lag time before the first seed germinates. Seed scarification enhanced germinability at both temperatures and its effect was much higher on falcata and wild sativa accessions. Incomplete loss of the hardseededness trait during domestication and selection is hypothesised, indicating that the introduction of wild material in breeding programmes should be followed by the selection for germinability without scarification. Seed lots with altered germinability had low germination at extreme temperatures, both cold and hot, suggesting that mild temperatures are required to promote germination of damaged seed lots. A large genetic diversity was revealed for germination (both capacity and rate) in response to temperature. All accessions had an optimal germination at 15 or 22°C and a poor germination at 40°C. The sativa varieties and landraces had a high germination from 5 to 34°C while the germination of falcata and the wild sativa accessions were weakened at 5 or 34°C, respectively. These differences are interpreted in terms of adaptation to the climate of their geographical origin regions in order to escape frost or heat/drought risks. These new findings give insights on adaptation and domestication of lucerne in its wide geographic area. They suggest further improvement of germination is needed, especially when introducing wild material in breeding pools to remove scarification requirements and to limit differences in response to temperature. [ABSTRACT FROM AUTHOR]

In grassland plant communities, the ability of individual plants to regrow after defoliation is of crucial importance since it allows the restoration of active photosynthesis and plant growth. The aim of this study was to evaluate the effects of increasing defoliation intensity (0, 25, 65, 84, and 100% of removed leaf area) on sugar remobilization and N uptake, remobilization, and allocation in roots, adult leaves, and growing leaves of ryegrass over 2 days, using a 15N tracer technique. Increasing defoliation intensity decreased plant N uptake in a correlative way and increased plant N remobilization, but independently. The relative contribution of N stored before defoliation to leaf growth increased when defoliation intensity was severe. In most conditions, root N reserves also contributed to leaf regrowth, but much less than adult leaves and irrespective of defoliation intensity. A threshold of defoliation intensity (65% leaf area removal) was identified below which C (glucose, fructose, sucrose, fructans), and N (amino acids, soluble proteins) storage compounds were not recruited for regrowth. By contrast, nitrate content increased in elongating leaf bases above this threshold. Wounding associated with defoliation is thus not the predominant signal that triggers storage remobilization and controls the priority of resource allocation to leaf meristems. A framework integrating the sequential events leading to the refoliation of grasses is proposed on the basis of current knowledge and on the findings of the present work. [ABSTRACT FROM AUTHOR]

A great variety of legume species are used for forage production and grown in multi-species grasslands. Despite their close phylogenetic relationship, they display a broad range of morphologies that markedly affect their competitive abilities and persistence in mixtures. Little is yet known about the component traits that control the deployment of plant architecture in most of these species. During the present study, we compared the patterns of shoot organogenesis and shoot organ growth in contrasting forage species belonging to the four morphogenetic groups previously identified in herbaceous legumes (i.e., stolon-formers, rhizome-formers, crown-formers tolerant to defoliation and crown-formers intolerant to defoliation). To achieve this, three greenhouse experiments were carried out using plant species from each group (namely alfalfa, birdsfoot trefoil, sainfoin, kura clover, red clover, and white clover) which were grown at low density under non-limiting water and soil nutrient availability. The potential morphogenesis of shoots characterized under these conditions showed that all the species shared a number of common morphogenetic features. All complied with a generalized classification of shoot axes into three types (main axis, primary and secondary axes). A common quantitative framework for vegetative growth and development involved: (i) the regular development of all shoot axes in thermal time and a deterministic branching pattern in the absence of stress; (ii) a temporal coordination of organ growth at the phytomer level that was highly conserved irrespective of phytomer position, and (iii) an identical allometry determining the surface area of all the leaves. The species differed in their architecture as a consequence of the values taken by component traits of morphogenesis. Assessing the relationships between the traits studied showed that these species were distinct from each other along two main PCA axes which explained 68% of total variance: the first axis captured a trade-off between maximum leaf size and the ability to produce numerous phytomers, while the second distinguished morphogenetic strategies reliant on either petiole or internode expansion to achieve space colonization. The consequences of this quantitative framework are discussed, along with its possible applications regarding plant phenotyping and modeling. [ABSTRACT FROM AUTHOR]

Background and Aims Predicting light partitioning in crop mixtures is a critical step in improving the productivity of such complex systems, and light interception has been shown to be closely linked to plant architecture. The aim of the present work was to analyse the relationships between plant architecture and light partitioning within wheat–pea (Triticum aestivum–Pisum sativum) mixtures. An existing model for wheat was utilized and a new model for pea morphogenesis was developed. Both models were then used to assess the effects of architectural variations in light partitioning. Methods First, a deterministic model (L-Pea) was developed in order to obtain dynamic reconstructions of pea architecture. The L-Pea model is based on L-systems formalism and consists of modules for ‘vegetative development’ and ‘organ extension’. A tripartite simulator was then built up from pea and wheat models interfaced with a radiative transfer model. Architectural parameters from both plant models, selected on the basis of their contribution to leaf area index (LAI), height and leaf geometry, were then modified in order to generate contrasting architectures of wheat and pea. Key results By scaling down the analysis to the organ level, it could be shown that the number of branches/tillers and length of internodes significantly determined the partitioning of light within mixtures. Temporal relationships between light partitioning and the LAI and height of the different species showed that light capture was mainly related to the architectural traits involved in plant LAI during the early stages of development, and in plant height during the onset of interspecific competition. Conclusions In silico experiments enabled the study of the intrinsic effects of architectural parameters on the partitioning of light in crop mixtures of wheat and pea. The findings show that plant architecture is an important criterion for the identification/breeding of plant ideotypes, particularly with respect to light partitioning. [ABSTRACT FROM AUTHOR]

Background and Aims Most studies dealing with light partitioning in intercropping systems have used statistical models based on the turbid medium approach, thus assuming homogeneous canopies. However, these models could not be directly validated although spatial heterogeneities could arise in such canopies. The aim of the present study was to assess the ability of the turbid medium approach to accurately estimate light partitioning within grass–legume mixed canopies. Methods Three contrasted mixtures of wheat–pea, tall fescue–alfalfa and tall fescue–clover were sown according to various patterns and densities. Three-dimensional plant mock-ups were derived from magnetic digitizations carried out at different stages of development. The benchmarks for light interception efficiency (LIE) estimates were provided by the combination of a light projective model and plant mock-ups, which also provided the inputs of a turbid medium model (SIRASCA), i.e. leaf area index and inclination. SIRASCA was set to gradually account for vertical heterogeneity of the foliage, i.e. the canopy was described as one, two or ten horizontal layers of leaves. Key Results Mixtures exhibited various and heterogeneous profiles of foliar distribution, leaf inclination and component species height. Nevertheless, most of the LIE was satisfactorily predicted by SIRASCA. Biased estimations were, however, observed for (1) grass species and (2) tall fescue–alfalfa mixtures grown at high density. Most of the discrepancies were due to vertical heterogeneities and were corrected by increasing the vertical description of canopies although, in practice, this would require time-consuming measurements. Conclusions The turbid medium analogy could be successfully used in a wide range of canopies. However, a more detailed description of the canopy is required for mixtures exhibiting vertical stratifications and inter-/intra-species foliage overlapping. Architectural models remain a relevant tool for studying light partitioning in intercropping systems that exhibit strong vertical heterogeneities. Moreover, these models offer the possibility to integrate the effects of microclimate variations on plant growth. [ABSTRACT FROM PUBLISHER]

Light quality and, in particular, its content of blue light is involved in plant functioning and morphogenesis. Blue light variation frequently occurs within a stand as shaded zones are characterized by a simultaneous decrease of PAR and blue light levels which both affect plant functioning, for example, gas exchange. However, little is known about the effects of low blue light itself on gas exchange. The aims of the present study were (i) to characterize stomatal behaviour in Festuca arundinacea leaves through leaf gas exchange measurements in response to a sudden reduction in blue light, and (ii) to test the putative role of Ci on blue light gas exchange responses. An infrared gas analyser (IRGA) was used with light transmission filters to study stomatal conductance (gs), transpiration (Tr), assimilation (A), and intercellular concentration of CO2 (Ci) responses to blueless PAR (1.80 μmol m−2 s−1). The results were compared with those obtained under a neutral filter supplying a similar photosynthetic efficiency to the blueless PAR filter. It was shown that the reduction of blue light triggered a drastic and instantaneous decrease of gs by 43.2% and of Tr by 40.0%, but a gradual stomatal reopening began 20 min after the start of the low blue light treatment, thus leading to new steady-states. This new stomatal equilibrium was supposed to be related to Ci. The results were confirmed in more developed plants although they exhibited delayed and less marked responses. It is concluded that stomatal responses to blue light could play a key role in photomorphogenetic mechanisms through their effect on transpiration. [ABSTRACT FROM PUBLISHER]

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The canopy structure of grasslands is a major determinant of their use-value, as it affects the quantity and quality of the forage removed when mowed or grazed. The structure of this canopy is determined by individual plant architecture, which is highly sensitive to both environmental variations and management practices such as cutting regimes. In the case of perennial ryegrass (Lolium perenneL.), this architectural plasticity may partially be mediated by a self-regulation process, i.e. the actual state of the architecture (e.g. length of the pseudostem) may indirectly control some morphogenetic processes. To test the robustness of this hypothesis, we designed an exploratory model of ryegrass morphogenesis exhibiting this cybernetic behaviour. This functional-structural model is based on the L-system formalism. It was able to capture satisfactorily the major quantitative architectural traits of ryegrass under non-limiting growing conditions and under a cutting constraint. From these simulation results it appears that (i) self-regulation rules could be of practical use to ryegrass modelling, and (ii) when activated in an integrated model, they are not markedly incompatible with observations. [ABSTRACT FROM AUTHOR]

Quantifying and simulating the relationships between crop growth, total‐nitrogen (total‐N) and nitrate‐N (NO3–‐N) concentration can improve crop nutritional husbandry. In this study, the relationship between shoot relative growth rate (RGR) and shoot total‐N, organic‐N and NO3–‐N concentration of hydroponically‐grown lettuce (Lactuca sativa var. capitata L. cv. Kennedy) was described and simulated. Plants were grown hydroponically for up to 74 d. Nitrogen was supplied throughout (control; T1), or removed at 35 d (T2) and 54 d (T3), respectively, after sowing. The organic‐N and NO3–‐N concentration declined in the shoots of control plants with growth, until commercial maturity approached when organic‐N and NO3–‐N concentration increased. There were sub‐linear relationships between both total‐N and organic‐N concen tration, and shoot RGR, in the N‐limited treatments, i.e. shoot RGR approached an asymptote at high shoot N concentration. The proportional effects of total‐N and organic‐N concentration on shoot RGR were independent of plant age. A dynamic simulation model (‘Nicolet’), derived previously under different conditions, was used to simulate the growth, dry matter content, organic‐N, and NO3–‐N concentration of lettuce grown under the extreme N‐stress conditions experienced by the plants. In view of the largely successful fitting of the model to experimental data, the model was used to interpret the results. Suggestions for model improvement are made. [ABSTRACT FROM PUBLISHER]

Caesium (Cs) is an alkali metal with chemical properties similar to potassium (K). It has no known role in plant nutrition and it is not toxic to plants at the micromolar concentrations occurring naturally in soil solutions. However, two radioisotopes of Cs (134Cs and 137Cs) are of environmental concern due to their relatively long half-lives, emissions of β and γ radiation during decay, and rapid incorporation into biological systems. There is considerable interest in remediating sites contaminated by these isotopes using phytoextraction and, since the produce from radiocaesium-contaminated areas may enter the food chain, the introduction of `safe' crops that do not accumulate Cs. This article reviews the molecular mechanisms of Cs uptake by plants, and provides a perspective on strategies to develop: (1) plants that extract Cs efficiently from soils (for the phytoremediation of land), or (2) `safe' crops that minimise the entry of radiocaesium directly into the human food chain. [ABSTRACT FROM AUTHOR]

Summary: • C assimilation (A) has been shown to limit the growth of young Lactuca sativa (lettuce) plants following an interruption in their external N supply. Further data from these plants were used to test two hypotheses: that N‐limited growth of lettuce is associated with lower stomatal conductance (gs); and that reductions in gs result from adjustments to stomatal frequency or distribution.• The photosynthetic characteristics, nitrate and organic N‐concentrations, as well as epidermal and stomatal distributions, were determined in leaves of hydroponically grown lettuce plants supplied continuously with N or with N removed for up to 14 d.• Although N‐limited plants had lower maximum rates of A, comparisons at equivalent values of gs showed that A was not directly limited by organic‐N but by gs. Reductions in gs under N‐limiting conditions did not associate with adjustments to stomatal frequency or distribution.• Associations between plant N and A could arise either through stomata responding directly to signals induced by N deprivation or to increased CO2 partial pressure at the sites of carboxylation. [ABSTRACT FROM AUTHOR]

Summary • C assimilation (A) has been shown to limit the growth of young Lactuca sativa (lettuce) plants following an interruption in their external N supply. Further data from these plants were used to test two hypotheses: that N-limited growth of lettuce is associated with lower stomatal conductance (gs); and that reductions in gs result from adjustments to stomatal frequency or distribution. • The photosynthetic characteristics, nitrate and organic N-concentrations, as well as epidermal and stomatal distributions, were determined in leaves of hydroponically grown lettuce plants supplied continuously with N or with N removed for up to 14 d. • Although N-limited plants had lower maximum rates of A, comparisons at equivalent values of gs showed that A was not directly limited by organic-N but by gs. Reductions in gs under N-limiting conditions did not associate with adjustments to stomatal frequency or distribution. • Associations between plant N and A could arise either through stomata responding directly to signals induced by N deprivation or to increased CO2 partial pressure at the sites of carboxylation. [ABSTRACT FROM AUTHOR]

Sorbitol, together with sucrose and starch, is a major final product of photosynthesis in most species of the Rosaceae. However, little is known concerning the factors affecting the carbon fluxes into these three carbohydrates. The aim of this study was to investigate the effect of net photosynthetic CO2 assimilation rate (NAR) on primary carbon partitioning between sorbitol, sucrose, starch and other metabolites, and on the kinetic pattern of labelling in mature leaves of peach (Primus persica [L.] Batsch). A pulse-chase labelling experiment was conducted on a group of peach seedlings showing a range of NAR's that were obtained by using five photosynthetic photon flux density treatments. Mature leaves undergoing one of these treatments were subjected to a 4-min pulse of 14CO2 followed by a 2- to 120-min chase under 12CO2. The radioactivity in lipids, proteins and in a residual nonsoluble fraction was negligible. After a 2-min chase the organic ions were strongly labelled, accounting for up to 40% of the total incorporated radioactivity at NAR's below 10.4 µmol CO2 m-2s-1. After a 30-min chase, most label was found in sorbitol, sucrose and starch with very little radioactivity in the ionic fractions. The analysis of the partitioning of the newly-fixed carbon showed that at low NAR the 14C flux was mostly into sorbitol rather than into sucrose (ratio = 2.6) or starch. When the NAR was lower than 6.1 µmol CO2 m-2s-1, starch was lightly labelled. As the NAR increased above 10.4 µmol CO2 m-2s-1 the 14CO2 diverted into starch increased dramatically. This study demonstrates that at low NAR's the newly-fixed CO2 is mainly used for sorbitol synthesis. However, as NAR increases, the participation of sucrose and starch in CO2 partitioning are favoured. These results support the hypothesis that primary carbon partitioning depends on photosynthetic rate. [ABSTRACT FROM AUTHOR]

Functional–structural plant models (FSPMs) explore and integrate relationships between a plant's structure and processes that underlie its growth and development. In recent years, the range of topics being addressed by scientists interested in functional–structural plant modelling has expanded greatly. FSPM techniques are now being used to dynamically simulate growth and development occurring at the microscopic scale involving cell division in plant meristems to the macroscopic scales of whole plants and plant communities. The plant types studied also cover a broad spectrum from algae to trees. FSPM is highly interdisciplinary and involves scientists with backgrounds in plant physiology, plant anatomy, plant morphology, mathematics, computer science, cellular biology, ecology and agronomy. This special issue of Annals of Botany features selected papers that provide examples of comprehensive functional–structural models, models of key processes such as partitioning of resources, software for modelling plants and plant environments, data acquisition and processing techniques and applications of functional–structural plant models for agronomic purposes. [ABSTRACT FROM PUBLISHER]

Growing mixtures of annual arable crop species or genotypes is a promising way to improve crop production without increasing agricultural inputs. To design optimal crop mixtures, choices of species, genotypes, sowing proportion, plant arrangement, and sowing date need to be made but field experiments alone are not sufficient to explore such a large range of factors. Crop modeling allows to study, understand, and ultimately design cropping systems and is an established method for sole crops. Recently, modeling started to be applied to annual crop mixtures as well. Here, we review to what extent crop simulation models and individual-based models are suitable to capture and predict the specificities of annual crop mixtures. We argued that (1) the crop mixture spatio-temporal heterogeneity (influencing the occurrence of ecological processes) determines the choice of the modeling approach (plant or crop centered). (2) Only few crop models (adapted from sole crop models) and individual-based models currently exist to simulate annual crop mixtures. Crop models are mainly used to address issues related to both crop mixtures management and the integration of crop mixtures into larger scales such as the rotation. In contrast, individual-based models are mainly used to identify plant traits involved in crop mixture performance and to quantify the relative contribution of the different ecological processes (niche complementarity, facilitation, competition, plasticity) to crop mixture functioning. This review highlights that modeling of annual crop mixtures is in its infancy and gives to model users some important keys to choose the model based on the questions they want to answer, with awareness of the strengths and weaknesses of each of the modeling approaches. [ABSTRACT FROM AUTHOR]