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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]

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]

Abstract: The objective of this work was to describe the dynamics of senescence of field-grown maize from silking to harvest, at both leaf and plant level. At the leaf level, the dynamics of symptoms of senescence were considered on each leaf taken individually and described according to zones from the tip to the base of the leaf lamina. At the whole plant level, foliar ranks were each considered as an entity to describe the time course of senescence. To this end, we use a database built-up from field trials conducted during three consecutive years (1994–1996) and thus undergoing variable meteorological and soil water conditions. Leaf chlorophyll content was estimated using two different methods based on the optical properties of the leaves. In Trial I, chlorophyll estimates were based on leaf optical density measured with a MacBeth TR-924 densitometer. In Trial II and Trial III, chlorophyll estimations were based on measurement using a hand-held Minolta SPAD-502 device. In Trial II and Trial III, chlorophyll fluorescence analyses under filed conditions were performed. These analyses focused on the photosystem II (PSII) maximum efficiency (Fv′/Fm′) parameter in the light-adapted state. Measurements were done with a Waltz PAM-2000 portable fluorometer. We report detailed descriptions of the spatio-temporal dynamics of these indicators of senescence. We found that, after silking, a strong relationship exists between available water and leaf chlorophyll content. Further, the maximum efficiency of PSII decreased faster in maize plants undergoing low available soil water than in irrigated plants. The rank of a leaf is determinant of the time for the beginning of the decline in both chlorophyll content and maximum efficiency of PSII. At plant and leaf level, the onset of senescence was marked by a decrease in chlorophyll content that was not concomitant with a dramatic decrease in the maximum efficiency of PSII. Our analyses suggest that a non-linear functional relationship could exist between these two parameters during monocarpic senescence. In the mean time, the results presented in this paper could be used to refine the senescence related modules in plant and crop models. [Copyright &y& Elsevier]

In monocarpic species such as corn, senescence of leaves is coordinated with that of the whole plant and influenced by the reproductive function. The objective of the present study was to describe the evolution of corn senescence along two axes: (1) the whole-plant axis, where all foliar stages were each considered as an entity, and (2) the foliar axis, where the dynamics of three macroscopic symptoms of senescence was considered on each leaf taken individually, according to zones from the apex to the base of the leaf lamina. From a corn field culture, leaves were sampled or whole plants were submitted to a follow-up, from flowering to harvest. Dynamics of water, dry matter, and chlorophyll contents were different along the leaf as well as between ranking of leaves. Moreover, plant chlorophyll content followed a more complex dynamics than that of water and dry matter. From a follow-up of discoloration along leaves of 15 stems from top to bottom, authors have established functional relationships describing the advance of the senescence front for each foliar rank from 7 to top (rank 15 or 16). This quantitative description can be used directly in crop models as well as structure–function plant models. This would allow estimation of leaf-senescence impact on light-radiation interception and, therefore, on photosynthesis and productivity. Results can also be used for interpretation of reflectance measurements on corn canopies by remote sensing. [ABSTRACT FROM AUTHOR]

Abstract: Light quality plays a key role in higher plants’ morphogenesis. In most plant models, light is considered as a consumable resource and plants are assumed blind to light signals. However, prior to any effort for modelling photomorphogenetic mechanisms, it is necessary to characterise the spatial distribution of the Morphogenetically Active Radiation (MAR) over and within plant canopies. Measurements of local photosynthetic photon flux density (PPFD) and broadband irradiance (Es) are easy to carry out by using small sensors. Thus, the distribution of the MAR within a canopy can be estimated whenever the functional relationships between these measurements and the photon flux within any spectral band are known. The objective of this work was to determine these functional relationships from the light spectra received above and at various positions around a target plant within a growing sorghum crop. The MAR components considered in this work are related either to photon flux densities in various wavebands between 330 and 950nm or to the ratio between two photon flux densities. A part of the photon flux-related variables is strictly included in the PAR band and might be estimated from PPFD measurements using linear relationships. The other variables are related to both PPFD and Es by multiple linear relationships. The phytochrome photoequilibrium and the red to far-red ratios were related to the relative transmitted PPFD and to the ratio PPFD/Es within the canopy using a non-linear model. Models were validated against an independent set of data. We demonstrate that the MAR components within a sorghum crop can be accurately estimated with the functional relationships presented in this paper. [Copyright &y& Elsevier]

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]

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]

Developmental responses to temperature are critical to yield formation in crops and perennial grassland species. However, their characterisation over a broad range of temperatures relevant to climate change studies has been limited in these species. The present study sought to determine the non-linear developmental responses to temperature of two major grassland species, tall fescue ( Festuca arundinacea ) and alfalfa ( Medicago sativa ), and to assess i) whether a coordinated response occurred between different developmental processes, ii) if genotypes from contrasting origins differed in their responses, and iii) to quantify how a lack of coordination and genetic variability might affect estimates of thermal time progression under present and future climate scenarios. Two series of experiments were carried out under controlled conditions with eight constant temperatures ranging from 5 °C to 40 °C applied to seedlings and mature plants. Different growth and developmental processes were characterized, including shoot development and radicle, leaf and stem growth. Once normalized to a temperature of 20 °C, the temperature responses of the different processes displayed no significant variability between temperate and Mediterranean genotypes. On the other hand, not all developmental processes within a genotype displayed a coordinated response to temperature. Significant departures from the response of shoot development in mature plants were observed regarding several processes, particularly at low and supra-optimal temperatures (up to ±5 °C and ±2 °C for minimal and maximal temperature estimates, respectively). Differences were particularly marked relative to node and stem elongation responses. Overall, when using the temperature dependencies of different processes to estimate cumulative thermal time, significant bias was observed in alfalfa when considering stem elongation by comparison with other processes. The consequences for improvements to forage crop models, and for the meta-analyses often used to calibrate them, are discussed. [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]

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]

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]

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]

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]

The European Food Safety Authority concluded in February 2018 that " most uses of neonicotinoid insecticides represent a risk to wild bees and honeybees ". In 2016, the French government passed a law banning the use of the five neonicotinoids previously authorized: clothianidin, imidacloprid, thiamethoxam, acetamiprid and thiacloprid. In the framework of an expert assessment conducted by the French Agency for Food, Environmental and Occupational Health and Safety to identify possible derogations, we performed a thorough assessment of the available alternatives to the five banned neonicotinoids. For each pest targeted by neonicotinoids use, we identified the main alternative pest management methods, which we then ranked for (i) efficacy for controlling the target pest, (ii) applicability (whether directly useable by farmers or in need of further research and development), (iii) durability (risk of resistance in targeted pests), and (iv) practicability (ease of implementation by farmers). We identified 152 authorized uses of neonicotinoids in France, encompassing 120 crops and 279 pest insect species (or genera). An effective alternative to neonicotinoids use was available in 96% of the 2968 case studies analyzed from the literature (single combinations of one alternative pest control method or product × one target crop plant × one target pest insect). The most common alternative to neonicotinoids (89% of cases) was the use of another chemical insecticide (mostly pyrethroids). However, in 78% of cases, at least one non-chemical alternative method could replace neonicotinoids (e.g. microorganisms, semiochemicals or surface coating). The relevance of non-chemical alternatives to neonicotinoids depends on pest feeding habits. Leaf and flower feeders are easier to control with non-chemical methods, whereas wood and root feeders are more difficult to manage by such methods. We also found that further field studies were required for many promising non-chemical methods before their introduction into routine use by farmers. Our findings, transmitted to policymakers, indicate that non-chemical alternatives to neonicotinoids do exist. Furthermore, they highlight the need to promote these methods through regulation and funding, with a view to reducing pesticide use in agriculture. • Five neonicotinoids were banned in France, which were used to protect 120 crops from 279 pest insect species. • In 96% of cases, neonicotinoids can be replaced by effective and directly useable alternative pest control methods. • In 78% of cases, at least one non-chemical alternative method can replace neonicotinoids. • Leaf and flower feeders are easier to control with non-chemical methods than wood and root feeders. [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]

• Characterisation of alfalfa production and electricity generation in agriphotovoltaics conditions. • Alfalfa biomass increased by 10% in average in the shade of the Agri-PV system for shading between 29% and 44%. • Photovoltaic production reduced by 15% due to the optimised tracking for plant growth. • This combined production allowed an increase in total productivity per unit area (LER) of 51% Agriphotovoltaic systems, consisting of the combination of crops and photovoltaic panels (PVPs) on the same area, have recently emerged as an opportunity to solve the competition for land use between food and energy production. Various crops, pedoclimatic contexts and structures and both fixed and mobile panels have been studied. Over a period of two years, this research has been investigating an agriphotovoltaic (APV) system with mobile panels along two axes of rotation. The studied crop is alfalfa, a grassland species that has received little attention under these conditions. In our experimental set-up, the alfalfa biomass increased by an average of 10 % over the two years of the experiment in the shade of the APV plant (between 29 % − 44 %) in comparison to full sunlight (835 g.m−2.year−1), but in a different way depending on the climatic year. The nutritional qualities were preserved while the canopy's morphology was adapted through an increase in the length of the stems and the surface area of the leaflets. Photovoltaic production was reduced by 15 % due to the optimised tracking for plant growth. This combined production allowed an increase in total productivity per unit area of 51 % (LER: 1.51). The positive agronomic results are explained by a decrease in evapotranspiration caused by the panels in a context where the crop is highly sensitive to water deficit with thin soil. To reach a more general conclusion on synergy, these results need to be completed over several years and compared with other studies in different soil and climatic contexts, as well as with modelling studies. [ABSTRACT FROM AUTHOR]

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]

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]

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]