An empirical model that uses light attenuation and plant nitrogen status to predict within-canopy N distribution and upscale photosynthesis from leaf to whole canopy

Modelling the spatial and temporal distribution of leaf nitrogen (N) is central to specify photosynthetic parameters and simulate canopy photosynthesis. Leaf photosynthetic parameters depend on both local light availability and whole-plant N status. The interaction between these two levels of integration has generally been modelled by assuming optimal canopy functioning, which is not supported by experiments. During this study, we examined how a set of empirical relationships with measurable parameters could be used instead to predict photosynthesis at the leaf and whole-canopy levels. The distribution of leaf N per unit area (Na) within the canopy was related to leaf light irradiance and to the nitrogen nutrition index (NNI), a whole-plant variable accounting for plant N status. Na was then used to determine the photosynthetic parameters of a leaf gas exchange model. The model was assessed on alfalfa canopies under contrasting N nutrition and with N2-fixing and non-fixing plants. Three experiments were carried out to parameterize the relationships between Na, leaf irradiance, NNI and photosynthetic parameters. An additional independent data set was used for model evaluation. The N distribution model showed that it was able to predict leaf N on the set of leaves tested. The Na at the top of the canopy appeared to be related linearly to the NNI, whereas the coef- ficient accounting for N allocation remained constant. Photosynthetic parameters were related linearly to Na irrespective of N nutrition and the N acquisition mode. Daily patterns of gas exchange were simulated accurately at the leaf scale. When integrated at the whole-canopy scale, the model predicted that raising N availability above an NNI of 1 did not result in increased net photosynthesis. Overall, the model proposed offered a solution for a dynamic coupling of leaf photosynthesis and canopy N distribution without requiring any optimal functioning hypothesis.Fil: Louarn, Gaëtan. Institut National de la Recherche Agronomique; FranciaFil: Frak, Ela. Institut National de la Recherche Agronomique; FranciaFil: Zaka, Serge. Institut National de la Recherche Agronomique; FranciaFil: Lebon, Eric. Institut National de la Recherche Agronomique. Unité Mixte de Recherche; FranciaFil: Prieto, Jorge Alejandro. Instituto Nacional de Tecnología Agropecuaria (INTA). Estación Experimental Agropecuaria Mendoza; Argentin

What determines the complex kinetics of stomatal conductance under blueless PAR in Festuca arundinacea? Subsequent effects on leaf transpiration

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

Effect of local irradiance on CO2 transfer conductance of mesophyll in walnut

The acclimation responses of walnut leaf photosynthesis to the irradiance microclimate were investigated by characterizing the photosynthetic properties of the leaves sampled on young trees (Juglans nigra3regia) grown in simulated sun and shade environments, and within a mature walnut tree crown (Juglans regia) in the ®eld. In the young trees, the CO2 compensation point in the absence of mitochondrial respiration (G*), which probes the CO 2 versus O 2 speci®city of Rubisco, was not signi®cantly different in sun and shade leaves. The maximal net assimilation rates and stomatal and mesophyll conductances to CO 2 transfer were markedly lower in shade than in sun leaves. Dark respiration rates were also lower in shade leaves. However, the percentage inhibition of respiration by light during photosynthesis was similar in both sun and shade leaves. The extent of the changes in photosynthetic capacity and mesophyll conductance between sun and shade leaves under simulated conditions was similar to that observed between sun and shade leaves collected within the mature tree crown. Moreover, mesophyll conductance was strongly correlated with maximal net assimilation and the relationships were not signi®cantly different between the two experiments, despite marked differences in leaf anatomy. These results suggest that photosynthetic capacity is a valuable parameter for modelling within-canopies variations of mesophyll conductance due to leaf acclimation to light

Le soleil, architecte des plantes

National audienceLa forme des plantes n'est pas due au hasard : plusieurs mécanismes, induits en particulier par la lumière, contribuent à les façonner et influent sur la longueur des tiges, la courbure des troncs, la densité des branchages ou la taille des feuilles. Des découvertes qui ont donné naissance à des applications jusqu'aux pelouses des stades. Tige, branches, feuilles ou fleurs : l'architecture d'une plante est due à ses caractéristiques génétiques, mais aussi à sa réponse à différents signaux environnementaux. Parmi ces derniers, la lumière tient une place essentielle, contrôlant divers mécanismes. Tout d'abord, la direction de la lumière détermine l'orientation de la plante - ce terme désignant ici les plantes herbacées, au contraire des arbres qui sont des plantes ligneuses. C'est ce qu'on appelle le phototropisme. Dans la plupart des cas, cette lumière est celle du soleil, on parle alors d'héliotropisme. Pour s'orienter vers la lumière, la plante s'appuie sur un moteur : la croissance différentielle, qui fait qu'un côté de ..

Herbivory mitigation through increased water-use efficiency in a leaf-mining moth-apple tree relationship, Plant, Cell and Environment, 29, 2238-2247.

International audienc

LightCue: An Innovative Far-Red Light Emitter for Locally Modifying the Spectral Cue in Outdoor Conditions with Global Consequences on Plant Architecture

Plasticity of plant architecture is a promising lever to increase crop resilience to biotic and abiotic damage. Among the main drivers of its regulation are the spectral signals which occur via photomorphogenesis processes. In particular, branching, one of the yield components, is responsive to photosynthetic photon flux density (PPFD) and to red to far-red ratio (R:FR), both signals whose effects are tricky to decorrelate in the field. Here, we developed a device consisting of far-red light emitting diode (LED) rings. It can reduce the R:FR ratio to 0.14 in the vicinity of an organ without changing the PPFD in outdoor high irradiance fluctuating conditions, which is a breakthrough as LEDs have been mostly used in non-fluctuant controlled conditions at low irradiance over short periods of time. Applied at the base of rapeseed stems during the whole bolting-reproductive phase, LightCue induced an expected significant inhibitory effect on two basal targeted axillary buds and a strong unexpected stimulatory effect on the overall plant aerial architecture. It increased shoot/root ratio while not modifying the carbon balance. LightCue therefore represents a promising device for progress in the understanding of light signal regulation in the field

Effects of N availability, local light regime and leaf rank on the amount and sources of N allocated within the foliage of young walnut (Juglans nigra x regia) trees

Early season leaf growth depends largely on N provided by remobilization from storage and many studies have tested the impact of current-N availability to roots on the amount of leaf N provided by remobilization. While it is well known that the light regime experienced by a leaf influences the amount of N per unit leaf area, the effects on N derived from direct root uptake or remobilization have never been tested at an intra-canopy scale. The objective of this study was to quantify the relative importance of (i) N availability to roots, (ii) local light regime experienced by the foliage (here at shoot scale), and (iii) leaf rank along the shoot, on the total amount of N allocated to leaves and on the proportions of N provided by remobilization and uptake. Potted hybrid walnut trees (Juglans nigra x regia L.) were grown outdoors in sand and fed with a labelled (15N) nutrient solution in order to quantify the importance of uptake and remobilization as sources for leaf N. The trees were manipulated to produce only two shoots by removing the apical bud and an experimental design with two factors was used: (1) N availability for the tree (8 mol N m-3, HN, or 2 mol N m-3, LN), and (2) light level of treated (lower) branch (90%, HL, or 10%, LL, of incident light). Total leaf N per individual tree was not influenced by either N availability or light level. Higher N availability increased the amount of leaf N derived from root uptake at the whole - tree scale (typically around 8% and 2% under HN and LN, respectively). N allocation within the foliage of individual trees was controlled by the local light regime that strongly affected individual leaf characteristics (Ma and Na). Decreasing the light availability to a branch decreased the amount of N allocated to this branch to the benefit of the less shaded branch. In contrast, the local light regime (shading) experienced by the lower branch did not affect the fraction of total leaf N provided by remobilization for both lower, shaded or upper, unshaded branches. These results are discussed in terms of the modelling of tree growth

LightCue: An Innovative Far-Red Light Emitter for Locally Modifying the Spectral Cue in Outdoor Conditions with Global Consequences on Plant Architecture

Plasticity of plant architecture is a promising lever to increase crop resilience to biotic and abiotic damage. Among the main drivers of its regulation are the spectral signals which occur via photomorphogenesis processes. In particular, branching, one of the yield components, is responsive to photosynthetic photon flux density (PPFD) and to red to far-red ratio (R:FR), both signals whose effects are tricky to decorrelate in the field. Here, we developed a device consisting of far-red light emitting diode (LED) rings. It can reduce the R:FR ratio to 0.14 in the vicinity of an organ without changing the PPFD in outdoor high irradiance fluctuating conditions, which is a breakthrough as LEDs have been mostly used in non-fluctuant controlled conditions at low irradiance over short periods of time. Applied at the base of rapeseed stems during the whole bolting-reproductive phase, LightCue induced an expected significant inhibitory effect on two basal targeted axillary buds and a strong unexpected stimulatory effect on the overall plant aerial architecture. It increased shoot/root ratio while not modifying the carbon balance. LightCue therefore represents a promising device for progress in the understanding of light signal regulation in the field

Herbivory mitigation through increased water-use efficiency in a leaf-mining moth-apple tree relationship

Correspondence: [email protected] Inra prise en compte dans l'analyse bibliométrique des publications scientifiques mondiales sur les Fruits, les Légumes et la Pomme de terre. Période 2000-2012. http://prodinra.inra.fr/record/256699Herbivory alters plant gas exchange but the effects depend on the type of leaf damage. In contrast to ectophagous insects, leaf miners, by living inside the leaf tissues, do not affect the integrity of the leaf surface. Thus, the effect of leaf miners on CO2 uptake and water-use efficiency by leaves remains unclear. We explored the impacts of the leaf-mining moth Phyllonorycter blancardella (Lepidoptera: Gracillariidae) on light responses of the apple leaf gas exchanges to determine the balance between the negative effects of reduced photosynthesis and potential positive impacts of increased water-use efficiency (WUE). Gas exchange in intact and mined leaf tissues was measured using an infrared gas analyser. The maximal assimilation rate was slightly reduced but the light response of net photosynthesis was not affected in mined leaf tissues. The transpiration rate was far more affected than the assimilation rate in the mine integument as a result of stomatal closure from moderate to high irradiance level. The WUE was about 200% higher in the mined leaf tissues than in intact leaf portions. Our results illustrate a novel mechanism by which plants might minimize losses from herbivore attacks; via trade-offs between the negative impacts on photosynthesis and the positive effects of increased WU

Effects of N availability, local light regime and leaf rank on the amount and sources of N allocated within the foliage of young walnut (Juglans nigra x regia) trees

Early season leaf growth depends largely on N provided by remobilization from storage and many studies have tested the impact of current-N availability to roots on the amount of leaf N provided by remobilization. While it is well known that the light regime experienced by a leaf influences the amount of N per unit leaf area, the effects on N derived from direct root uptake or remobilization have never been tested at an intra-canopy scale. The objective of this study was to quantify the relative importance of (i) N availability to roots, (ii) local light regime experienced by the foliage (here at shoot scale), and (iii) leaf rank along the shoot, on the total amount of N allocated to leaves and on the proportions of N provided by remobilization and uptake. Potted hybrid walnut trees (Juglans nigra x regia L.) were grown outdoors in sand and fed with a labelled (15N) nutrient solution in order to quantify the importance of uptake and remobilization as sources for leaf N. The trees were manipulated to produce only two shoots by removing the apical bud and an experimental design with two factors was used: (1) N availability for the tree (8 mol N m-3, HN, or 2 mol N m-3, LN), and (2) light level of treated (lower) branch (90%, HL, or 10%, LL, of incident light). Total leaf N per individual tree was not influenced by either N availability or light level. Higher N availability increased the amount of leaf N derived from root uptake at the whole - tree scale (typically around 8% and 2% under HN and LN, respectively). N allocation within the foliage of individual trees was controlled by the local light regime that strongly affected individual leaf characteristics (Ma and Na). Decreasing the light availability to a branch decreased the amount of N allocated to this branch to the benefit of the less shaded branch. In contrast, the local light regime (shading) experienced by the lower branch did not affect the fraction of total leaf N provided by remobilization for both lower, shaded or upper, unshaded branches. These results are discussed in terms of the modelling of tree growth