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Made available in DSpace on 2021-06-25T10:27:16Z (GMT). No. of bitstreams: 0 Previous issue date: 2021-07-01 While a recent study showed that significant amounts of the nitrogen (N) requirements of young Eucalyptus trees can be provided by nitrogen-fixing trees (NFTs) in mixed-species plantations through short-term belowground N transfer, the consequences of soil fertility on this facilitation process remain unknown. We assessed the effect of fertilization on the percentage of N derived from transfer (%NDFT) from Acacia mangium trees to Eucalyptus trees in mixed-species plantations. A complete randomized block design with two treatments (fertilized vs unfertilized) and three blocks was set up in mixed-species plantations of A. mangium and Eucalyptus in Brazil, with 50% of each species at 2.5 m × 2.5 m spacing. Collection of litterfall and forest floor made it possible to estimate the annual N release from forest floor decomposition between 46 and 58 months after planting, close to harvest age. 15N-NO3- was injected into the stem of one dominant Acacia tree in each plot, 58 months after planting. The x(15N) values of Acacia and Eucalyptus fine roots sampled within 1.8 m of the labelled A. mangium tree were determined at 7, 14, 30 and 60 days after labelling. The x(15N) values in wood, bark, branch and leaf samples were also determined for the 6 labelled Acacia trees and their two closest Eucalyptus neighbours, just before and 60 days after labelling. The amount of N released from forest floor decomposition was 31% higher in fertilized (F+) than in unfertilized (F-) plots. Sixty days after labelling, the aboveground compartments of Eucalyptus trees were significantly 15N enriched in both treatments. The x(15N) values of Acacia fine roots were higher than background values from 7 days after labelling onwards in F+ and 30 days after labelling in F-. The x(15N) values of Eucalyptus fine roots were higher than background values in both treatments, from 30 days after labelling onwards. Mean %NDFT values were 18.0% in F+ and 33.9% in F- over the first 60 days after labelling, and 22.8% in F+ and 67.7% in F- from 30 to 60 days after labelling. Fertilization decreased short-term transfer belowground of N from Acacia trees to Eucalyptus trees. Our study suggests that belowground facilitation processes providing N from NFTs to Eucalyptus trees in mixed-species plantations are more pronounced in low-fertility soils than in nutrient-supplied stands. USP ESALQ Forest Science Department Eco&Sols INRA CIRAD IRD Montpellier SupAgro University of Montpellier CIRAD UMR Eco&Sols UNESP School of Agriculture São Paulo State University ‘Julio de Mesquita Filho,’ Department of Forest Science and Wood UFES IPEF Instituto de Pesquisas e Estudos Florestais UNESP School of Agriculture São Paulo State University ‘Julio de Mesquita Filho,’

On R&eacute, union Island, a French overseas territory located in the western Indian Ocean, increasing pig livestock farming is generating large quantities of slurry. Most of it is spread on a little agricultural land due to the insular context. Considering the limitation of the quantities that can be spread on agricultural areas (European &ldquo, Nitrate Directive&rdquo, 91/676/EEC), the use of wastewater treatment systems using phytoremediation principles is an attractive option for the pig slurry treatment. A wastewater treatment system using bamboo groves was assessed for the pig slurry treatment. Three field plots were designed on an agricultural area and planted with 40 bamboo clumps on each plot. A total of 67 m3 of pig slurry was spread on two plots in two forms: raw slurry and centrifuged slurry. The latter plot was watered with tap water. The total amount of nitrogen, phosphorus and potassium was 5.3, 1.4 and 5.5 t&middot, ha-1, respectively, for the raw slurry treatment and 4.2, 0.4 and 5.1 t&middot, ha-1, respectively, for the centrifuged slurry treatment. The response of bamboo species to pig slurry application was determined using morphologic parameters, Chlorophyll a fluorescence measurements and biomass yield. Compared to the control, the biomass increased by 1.8 to 6 times, depending on the species and the form of slurry. Depending on the species, the average biomass ranged from 52 to 135 t.DM.ha-1 in two years of experiment.

Uptake, assimilation, and recycling of nutrients are essential for optimal plant growth and development. A large number of studies have contributed significantly to highlight the major features that shape an efficient utilization of nutrients in plants, especially at the transcriptional level. However, only a few examples have explored the epigenetic mechanisms that are intrinsically associated to the transcriptional reprogramming events in response to nutritional fluctuations. In this review, we gather the chromatin-based mechanisms that have been described in response to variations of nutrients availability. At this time of genome and epigenome editing, such mechanisms could potentially represent new targets for crop improvement.

Observations of the vegetative and reproductive biomass produced annually and the mineral element contents have been conducted on diverse oil palm plant materials tested in a genetic test in Indonesia. The results show that the nutrient uptake (for trunk growth, leaf renewal and bunch export) greatly varies (CV = 10% for N uptake and 17% for K uptake) with the origins of the planting materials considered. For equivalent production, the uptake in nutrients of certain plant material may differ very significantly; for the same level of uptake in nutrients, production can vary significantly. This study supports the hypothesis that the optimal nutrient thresholds are intrinsically linked to the plant material. It assumes that some planting materials have different needs and that a fertilizer regime could be adapted to their specific needs without losses in performance. To confirm these assumptions, the need of implementing specific experimental devices with differentiated fertilization regimes is discu...

Apical dominance, the process by which the growing apical zone of the shoot inhibits bud outgrowth, involves an intricate network of several signals in the shoot. Auxin originating from plant apical region inhibits bud outgrowth indirectly. This inhibition is in particular mediated by cytokinins and strigolactones, which move from the stem to the bud and that respectively stimulate and repress bud outgrowth. The action of this hormonal network is itself modulated by sugar levels as competition for sugars, caused by the growing apical sugar sink, may deprive buds from sugars and prevents bud outgrowth partly by their signaling role. In this review, we analyze recent findings on the interaction between light, in terms of quantity and quality, and apical dominance regulation. Depending on growth conditions, light may trigger different pathways of the apical dominance regulatory network. Studies pinpoint to the key role of shoot-located cytokinin synthesis for light intensity and abscisic acid synthesis in the bud for R:FR in the regulation of bud outgrowth by light. Our analysis provides three major research lines to get a more comprehensive understanding of light effects on bud outgrowth. This would undoubtedly benefit from the use of computer modeling associated with experimental observations to deal with a regulatory system that involves several interacting signals, feedbacks, and quantitative effects.

International audience; One of the challenges of eco-efficient agriculture is the development of operational farming practices to increase the level of agricultural production, maximize the efficiency of resource use and reduce environmental impacts. Based on the efficiency frontier concept and the decomposition of resource use efficiency, we used a three-quadrant framework allowing to carry a functional analysis of the cropping system. Using a data envelope approach, we established boundary curves which represent the maximum achievable performances (yield, N uptake) when N is the only limiting factor. This framework has been first implemented and tested using published data from 112 agronomic situations of rainfed durum wheat in experimental fields in northern Syria and then further applied on a data set of 245 agronomic situations of durum wheat in farmers’ fields in two grain-producing regions of Tunisia. The results demonstrated the impact of preceding crops: durum wheat following legumes or vegetable showed a higher potential for N uptake but with only a minor effect on its conversion into grains. This positive effect of diversified rotation on potential N uptake by durum wheat is partly of-set by increased N uptake gaps in farmer’s fields indicating a higher effect of other limiting factors.

International audience; Rapid adjustment of plant physiology and development to external fluctuations is critical for sessile organism, giving a singular interest to network signaling controlling these mechanisms. Among many adaptation processes, root plasticity is primordial to optimize nutrient acquisition but relies on a complex network integrating local and systemic (root shoot) signaling. Indeed, locally, plants invest resource in soil area where nutrients are available and systemically they adjust nutrient acquisition to the whole plant demand.Our main goal is to decipher systemic signaling underlying the perception of nitrate heterogeneous provision, in Arabidopsis. Using the split-root system, in which physically isolated root systems of the same plant were challenged with different environments, we previously demonstrated that cytokinin biosynthesis constitutes one critical component of root-shoot-root communication. By combining the use of cytokinin mutants with hormone measurements, transcriptomic analysis, nitrate uptake assays, and root growth measurements, we show that root to shoot trans-zeatin (tZ) translocation is likely crucial for long distance signaling controlling rapid sentinel gene regulation and long-term functional acclimation to heterogeneous nitrate supply. Interestingly, shoot transcriptome profiling revealed that glutamate/glutamine metabolism is likely a target of tZ root-to-shoot translocation, prompting an interesting hypothesis regarding shoot-to-root communication. Finally, this study also highlights tZ-independent pathways triggered by variation into nitrogen supply.

Light is a critical environmental factor that influences nutrient uptake in roots and the subsequent use of nutrients, which is necessary to sustain plant growth. The positive effect of red light on phosphorus uptake has now been defined, along with the pivotal role of the phytochrome-B signalling cascades that mediate this effect.

The consequences of diversity on belowground processes are still poorly known in tropical forests. The distributions of very fine roots (diameter < 1 mm) and fine roots (diameter < 3 mm) were studied in a randomized block design close to the harvest age of fast-growing plantations. A replacement series was set up in Brazil with mono-specific Eucalyptus grandis (100E) and Acacia mangium (100A) stands and a mixture with the same stocking density and 50 % of each species (50A:50E). The total fine root (FR) biomass down to a depth of 2 m was about 27 % higher in 50A:50E than in 100A and 100E. Fine root over-yielding in 50A:50E resulted from a 72 % rise in E. grandis fine root biomass per tree relative to 100E, whereas A. mangium FR biomass per tree was 17 % lower than in 100A. Mixing A. mangium with E. grandis trees led to a drop in A. mangium FR biomass in the upper 50 cm of soil relative to 100A, partially balanced by a rise in deep soil layers. Our results highlight similarities in the effects of directional resources on leaf and FR distributions in the mixture, with A. mangium leaves below the E. grandis canopy and a low density of A. mangium fine roots in the resource-rich soil layers relative to monospecific stands. The vertical segregation of resource-absorbing organs did not lead to niche complementarity expected to increase the total biomass production.

Publication 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/256699; International audience; Radopholus similis is a worldwide endoparasitic nematode that greatly hampers banana (Musa acuminata, Cavendish subgroup) productivity. Earthworms are known to closely interact with above-ground and under-ground soil biota and particularly with plants and microfaunal communities. This study was aimed at investigating, under greenhouse conditions, the effects of the earthworm Pontoscolex corethrurus on banana growth and nutrient uptake, and assessing the influences of this earthworm on the development of an inoculated population of R. similis. Six-week-old tissue culture banana plants were submitted to four treatments: with P. corethrurus, R. similis, P. corethrurus+R. similis, and a control with no earthworms or nematodes. At the end of the experiment, the P. corethrurus treatments showed significantly higher leaf surface areas, shoot dry root weights, and root fresh weights than those without earthworms. This root growth enhancement probably contributed to the evident but non-significant decrease in the density of nematodes in the roots, even though earthworms did not reduce the total number of nematodes per whole root system. Moreover, the presence of earthworms slightly alleviated the severity of root damage. N bioavailability in the soil, along with N, Ca, and Mg content of banana plants, were also significantly increased in the presence of earthworms. Our results demonstrated that banana plant growth and nutrition were positively influenced by earthworms. Cropping practices that boost the development of earthworm communities in soil should therefore be promoted to enhance sustainability and to naturally alleviate nematode impact.

Supplementary information : http://www.nature.com/article-assets/npg/nplants/2015/nplants201515/extref/nplants201515-s1.pdf Voir communiqué de presse http://presse.inra.fr/Ressources/Communiques-de-presse/Les-strategies-des-plantes-pour-optimiser-l-utilisation-des-nitrates; International audience; In Arabidopsis the plasma membrane nitrate transceptor (transporter/receptor) NRT1.1 governs many physiological and developmental responses to nitrate. Alongside facilitating nitrate uptake, NRT1.1 regulates the expression levels of many nitrate assimilation pathway genes, modulates root system architecture, relieves seed dormancy and protects plants from ammonium toxicity. Here, we assess the functional and phenotypic consequences of point mutations in two key residues of NRT1.1 (P492 and T101). We show that the point mutations differentially affect several of the NRT1.1-dependent responses to nitrate, namely the repression of lateral root development at low nitrate concentrations, and the short-term upregulation of the nitrate-uptake gene NRT2.1, and its longer-term downregulation, at high nitrate concentrations. We also show that these mutations have differential effects on genome-wide gene expression. Our findings indicate that NRT1.1 activates four separate signalling mechanisms, which have independent structural bases in the protein. In particular, we present evidence to suggest that the phosphorylated and non-phosphorylated forms of NRT1.1 at T101 have distinct signalling functions, and that the nitrate-dependent regulation of root development depends on the phosphorylated form. Our findings add to the evidence that NRT1.1 is able to trigger independent signalling pathways in Arabidopsis in response to different environmental conditions.

Developing and deploying cotton cultivars with high nutrient uptake, use efficiency and tolerance to nutrient related soil stresses is desirable to assist sustainable soil management. Genetic variation, heritability, selection response and quantitative trait loci (QTLs) were investigated for five macronutrients (P, K, Ca, Mg, S) and five micronutrients (Fe, Mn, B, Zn, and Cu) in a recombinant inbred line (RIL) population from an inter-specific cross between Gossypium hirsutum cv. Guazuncho 2, and G. barbadense accession VH8-4602. Na and K/Na ratio were also studied as the imbalance between Na and other nutrients is detrimental to cotton growth and development. The concentrations of nutrients were measured for different plant parts of the two parents and for leaf samples of the whole population collected at early to peak flowering in field experiments over two years in a sodic Vertosol soil. Parental contrast was large for most nutrient concentrations in leaves when compared with other plant parts. Segregation for leaf nutrient concentration was observed within the population with transgression for P, K, K/Na ratio and all micronutrients. Genotypic difference was the major factor behind within-population variation for most nutrients, while narrow sense heritability was moderate (0.27 for Mn and Cu, and 0.43 for B). At least one significant QTL was identified for each nutrient except K and more than half of those QTLs were clustered on chromosomes 14, 18 and 22. Selection response was predicted to be low for P and all micronutrients except B, high for K, Na and B, and very high for K/Na ratio. Correlations were more common between macronutrients, Na and K/Na ratio where the nature and strength of the relations varied (r=-0.69 to 0.76). We conclude that there is sufficient genetic diversity between these two tetraploid cotton species that could be exploited to improve cotton nutrient status by introgressing species-unique favourable alleles.

The validity of the modifications in the source code of EPIC for simulation of crop development in semiarid conditions, described in de Barros et al. [de Barros, I., Williams, J.R., Gaiser, T. Modeling soil nutrient limitations to crop production in semiarid NE of Brazil with a modified EPIC version. I. Changes in the source code of the model. Ecol. Modell., submitted for publication] was tested against the results of 3 years, field experiment with nutrient omission using intercropping between maize and cowpea. The plant biomass production, grain yield, N, P, and K uptake by both crops were measured during the period of 1998-2000 and compared with simulated values. Reasonably good agreement and accuracy was obtained between the measured and simulated values for all evaluated parameters. Slight overestimation of grain yield by the simulations was attributed to high rates of floral abortion caused by dry spells during the flowering periods of 1998 and 1999, since this factor is not considered in the model yet. Improvements of the accuracy of the model may also be obtained by more comprehensive understanding of soil resource use by component plants in mixed cropping systems. Therefore, it is necessary to generate more knowledge about the partitioning of the resources by the crops before being incorporated into modeling approaches. The model was sensitive to climate variations and changes in soil chemical properties due to the application of fertilizers and/or lime under the tropical semiarid conditions of the NE of Brazil. Once calibrated and validated for different crops and soil types of this region, the model will be appropriate as tool for regional planning.

The negative relationship between intake and digestibility of an unchanging diet has been widely described. The review of the different processes of ruminai digestion shows that the main cause of the variation in digestibility is the retention time of particles in the rumen. However, most experiments have been carried out at levels of intake higher than maintenance. For this reason, a special attention is paid to experiments carried out at low levels of intake. In these conditions, the response of digestibility to a decrease in intake is variable: it can increase, be stable or decrease. Up till now, it has not been possible to determine the animal or nutritional factors which influence the way of variation, and especially the unexpected decrease in digestibility. However, it has been clearly shown that these decreases are not due to an insufficient retention time of particles in the rumen, or to an insufficient reduction of particle size. Differences in microbial activity have not been exhibited by in situ measurements. It is hypothesised that a reduction of bacterial growth, or of the expression of microbial degradation potential occurs at very low intakes, but mechanisms are still not elucidated. The decrease in weight and oxygen uptake by the digestive tract contributes to the adaptation of animals maintenance requirements. At short term, the proportion of metabolisable energy intake which is recovered in the portal vein remains unchanged when animals are underfed but the supply of absorbable amino acids (AAs) cannot keep up with the gut requirements. The consequences of underfeeding on nutrition and absorption do not differ between small ruminants and cattle. © 2003 Elsevier Science B.V. All rights reserved.

International audience; Resource acquisition within the soil is a complex process, which consists of several sub-processes involving both the soil and the plant. A brief analysis of the whole system is presented, first by focusing on the components of the system, and then on the successive events. This analysis stresses the diversity and specificity of the components involved, as well as their interactive roles, at several organisation levels, both in space and time. Therefore, a systemic approach using dynamic models is defended in order to gather available knowledge and gain new insight within the whole system. In comparison to many of the traditional modelling approaches, which tended to over-simplify the plant part of the system, some new and promising attempts are presented. These new models give a good illustration of what can be expected to be gained by associating structural and functional characteristics of the plant components.; Introduction sur l'environnement souterrain et l'acquisition des ressources, avec références particulières aux arbres. Les modèles de simulation devraient inclure la structure et les fonctions de la plante. L'acquisition des ressources du sol est un processus complexe, que l'on peut subdiviser en plusieurs processus plus élémentaires faisant intervenir conjointement la plante et le sol. Nous faisons une brève analyse de ce système, en insistant d'abord sur ses composants, puis sur les événements successifs. Cette analyse révèle la diversité et la spécificité des composants impliqués, ainsi que leurs rôles interactifs, à plusieurs niveaux d'organisation dans le temps et dans l'espace. Aussi, nous défendons une approche systémique, utilisant la modélisation dynamique, pour synthétiser les connaissances disponibles, et obtenir ainsi un nouvel éclairage sur le système pris dans sa globalité. En comparaison avec les approches de modélisation traditionnelles, qui tendent à simplifier outrageusement la partie plante du système, nous présentons quelque démarches nouvelles et prometteuses. Ces derniers modèles illustrent bien les progrès que l'on peut escompter en associant davantage les caractéristiques structurales et fonctionnelles des composants de la plante.

We compare the effects of minimum and conventional tillage on banana growth, under irrigated and rain-fed conditions. Measurements of leaf growth, root length density and soil water depletion were made. We used a crop simulation model to understand and explain the differential behavior of banana plants in the experiments. Our approach consisted of (i) an adaptation of the STICS model, initially developed for temperate crops, to the banana crop grown under tropical conditions and (ii) use of the integrative ability of the model to identify the respective roles of irrigation and tillage. The adaptation of the model concerned the phasic development, and leaf and root growth. Some specific characteristics of the tropical environment were also introduced. The model points out that under irrigated conditions crop water requirements were always satisfied whatever the tillage depth. In that case, the difference in terms of leaf growth and yield between shallow and deep tillage treatments can be explained by the nitrogen deficit due to a poor root system. Rain-fed crops suffered from water shortage, but the increase in soil exploration, allowed by conventional tillage, compensated for the absence of irrigation. This work improves knowledge of the agro-physiology of the banana crop. It demonstrates the fundamental part played by the root system, which appears as an important limiting factor for a correct water and nutrient supply. It provides an opportunity to elaborate a global model for the banana crop. (Resume d'auteur)

Solution pH, temperature, nitrate (NO3-)/ammonium (NH4+) ratios, and inhibitors effects on the NO3- and NH4+ uptake rates of coffee (#Coffea arabica# L.) roots were investigated in short-term solution culture. At intermediate pH values (4.25 to 5.75) typical of coffee soils, NH4+ and NO3- uptake rates were similar and nearly independent of pH. Nitrate uptake varied more with temperature than did ammonium. Nitrate uptake increased from 0.05 to 1.01 micromol/g FW/h between 4 and 16°C, and increased three-fold between 16 to 22°C. Between 4 to 22°C, NH4+ uptake rate increased more gradually from 1.00 to 3.25 micromol/g FW/h. In the 22-40°C temperature range, NH4+ and NO3- uptake rates were similar (averaging 3.65 and 3.56 micromol/g FW/h, respectively). At concentrations ranging from 0.5 to 3 mM, NO3- did not influence NH4+ uptake rate. However, NO3- uptake was significantly reduced when NH4+ was present at 3 mM concentration. Most importantly, total uptake(NO3- + NH4+) at any NO3-/NH4+ ratio was higher than that of plants fed solely with either NH4+ or NO3-. Anaerobic conditions reduced NO3- and NH4+ uptake rate by 50 and 30%, respectively, whereas dinitrophenol almost completely inhibited both NH4+ and NO3- uptake. These results suggest that Arabica coffee is well adapted to acidic soil conditions and can utilize the seasonally prevalent forms of inorganic N. These observations can help optimizing coffee N nutrition by recommending cultural practices maintaining roots in the temperature range optimum for both NH4+ and NO3- uptake, and by advising N fertilization resulting in a balanced soil inorganic N availability.

Uptake and compartmentation of Al in the roots tips were investigated in two corn ( Zea mays L.) cultivars (HS7777 single sensitive hybrid and C525-M single tolerant hybrid). Seedlings were grown for 24 h in nutrient solution at pH 4.4 characterized by low ionic strength (2,06 μM) and low Al 3+ activity (10.3 μM). The root elongation decreased strongly for the sensitive cultivar. There were no differences in the contents of total Al in the entire roots between cultivars. Nonexchangeable-Al and exchangeable-Al contents were higher in the root tips of HS7777. The sensitive cultivar also showed higher total and exchangeable-Al contents in excised root tips in 180 min of Al uptake. Al uptake for both cultivars increased in solution containing 0.1 mM of 2,4-dinitrophenol. Al contents were higher for the tolerant cultivar.

A greenhouse experiment was conducted to investigate the effects of a root-lesion nematode, #Pratylenchus coffeae#, two arbuscular mycorrhizal (AM) fungi, #Acaulospora mellea# and #Glomus clarum#, and timing of inoculation on the growth and nutrition of a nematode-susceptible Arabica coffee cultivar. The late AM inoculation (added simultaneously with nematodes) did not enhance coffee tolerance to #P. coffeae#. In the presence of #P. coffeae#, late-mycorrhizal plants were P deficient during the entire experiment and their foliar P concentration remained as low as that of non-mycorrhizal plants. After 7.5 months, nematodes decreased AM colonization of late-mycorrhizal plants by half and their biomass was only 20-30% that of the controls. In contrast, early AM inoculation (4 months before nematode inoculation) with either AM species improved the tolerance of coffee to #P. coffeae#. Root colonization by AM was not significantly reduced by #P. coffeae#. Despite higher densities of nematodes, root lesions were less numerous and more localized in early AM inoculated plants than in those of non-mycorrhizal plants. In the presence of #P. coffeae#, early AM-inoculated plants remained P sufficient and their biomass was still 75-80% that of their nematode-free controls. This study shows that in soils with low P levels, enhanced tolerance to #P. coffeae# seems limited to mycorrhizal coffee plants with well established AM symbiosis and improved P status.

International audience; Recent reports suggest that significant fractionation of stable metal isotopes occurs during biogeochemical cycling and that the uptake into higher plants is an important process. To test isotopic fractionation of copper (Cu) and zinc (Zn) during plant uptake and constrain its controls, we grew lettuce, tomato, rice and durum wheat under controlled conditions in nutrient solutions with variable metal speciation and iron (Fe) supply. The results show that the fractionation patterns of these two micronutrients are decoupled during the transport from nutrient solution to root. In roots, we found an enrichment of the heavier isotopes for Zn, in agreement with previous studies, but an enrichment of isotopically light Cu, suggesting a reduction of Cu(II) possibly at the surfaces of the root cell plasma membranes. This observation holds for both graminaceous and nongraminaceaous species and confirms that reduction is a predominant and ubiquitous mechanism for the acquisition of Cu into plants similar to the mechanism for the acquisition of iron (Fe) by the strategy I plant species. We propose two preliminary models of isotope fractionation processes of Cu and Zn in plants with different uptake strategies

Correspondance auteur: Hinsinger P. philippe.hinsinger@supagro.inra.fr ; In the context of increasing global food demand, ecological intensification of agroecosystems is required to increase nutrient use efficiency in plants while decreasing fertilizer inputs. Better exploration and exploitation of soil resources is a major issue for phosphorus, given that rock phosphate ores are finite resources, which are going to be exhausted in decades from now on. We review the processes governing the acquisition by plants of poorly mobile nutrients in soils, with a particular focus on processes at the root-soil interface. Rhizosphere processes are poorly accounted for in most plant nutrition models. This lack largely explains why present-day models fail at predicting the actual uptake of poorly mobile nutrients such as phosphorus under low input conditions. A first section is dedicated to biophysical processes and the spatial/temporal development of the rhizosphere. A second section concentrates on biochemical/biogeochemical processes, while a third section addresses biological/ecological processes operating in the rhizosphere. New routes for improving soil nutrient efficiency are addressed, with a particular focus on breeding and ecological engineering options. Better mimicking natural ecosystems and exploiting plant diversity appears as an appealing way forward, on this long and winding road towards ecological intensification of agroecosystems.

Mes travaux de recherche, au travers de 3 approches distinctes, se focalisent sur l'analyse du développement d'Arabidopsis thaliana. Ainsi, ma thèse a porté sur la caractérisation génétique, physiologique, cytologique et moléculaire d'une classe de mutants de développement d'Arabidopsis thaliana : les mutants " tonneau " et a permis de montrer que les gènes TON, impliqués dans l'ancrage du cytosquelette cortical à la membrane jouaient un rôle majeur dans le développement de la plantule. Au cours de mon stage post doctoral j'ai étudié le rôle de la protéine KNOLLE dans le trafic vésiculaire et plus précisément dans la formation du phragmoplaste et de son impact sur la division cellulaire et la formation de l'embryon d'Arabidopsis. Depuis mon recrutement à l'INRA, je me suis plus particulièrement intéressé au développement racinaire adaptatif tout d'abord en réponse à une carence en phosphore puis en réponse à l'apport de nitrate. Au travers d'approches combinées de génétique, transcriptomique, physiologie, biologie cellulaire et moléculaire, j'ai pu caractériser les réponses adaptatives et identifier plusieurs gènes clés. L'évolution récente de mon activité de recherche m'a conduit à aborder un des aspects majeurs de la nutrition minérale que constituent les mécanismes de détection et de signalisation d'un élément nutritif. Nous avons ainsi pu identifier que le transporteur de nitrate NRT1-1 jouait un rôle de senseur de nitrate et activait une voie de signalisation impliquant l'auxine conduisant à une modification de l'architecture du système racinaire. Le programme de recherche que je vais développer dans les prochaines années concerne la caractérisation des bases moléculaires impliquées dans les signalisations nitrate NRT1-1-dépendantes.

Background previous studies have shown that non-digestible inulin-type fructan intake can increase intestinal mineral absorption in both humans and animals. However, this stimulatory effect on intestinal absorption may depend on experimental conditions such as duration of fermentable fiber intake, mineral diet levels and animals' physiological status, in particular their age. Objectives the aim of this study was to determine the effect of inulin intake on Ca and Mg absorption in rats at different age stages. Methods eighty male Wistar rats of four different ages (2, 5, 10 and 20 months) were randomized into either a control group or a group receiving 3.75% inulin in their diet for 4 days and then 7.5% inulin for three weeks. The animals were fed fresh food and water ad libitum for the duration of the experiment. Intestinal absorption of Ca and Mg was determined by fecal monitoring using stable isotopic tracers. Ca and Mg status was also assessed. Results absorption of Ca and Mg was significantly lower in the aged rats (10 and 20 mo) than in the young and adult rat groups. As expected, inulin intake increased Ca and Mg absorption in all four rat groups. However, inulin had a numerically greater effect on Ca absorption in aged rats than in younger rats whereas its effect on Mg absorption remained similar across all four rat age groups. Conclusion the extent of the stimulatory effect of inulin on absorption of Ca may differ according to animal ages. Further studies are required to explore this effect over longer inulin intake periods, and to confirm these results in humans.

Résumés des communications * INRA Centre d'Avignon, Documentation, Domaine St Paul, Site Agroparc, 84914 Avignon cedex 9 Diffusion du document : INRA Centre d'Avignon, Documentation, Domaine St Paul, Site Agroparc, 84914 Avignon cedex 9; Influence de la disponibilité en nitrate sur les composantes du développement de jeunes pêchers. 1. Rencontres

CORRECTION; International audience

Les déficiences en magnésium sont généralement spéctaculaires et facilement identifiables. L'objectif de cette communication est d'examiner les résultats obtenus lors de plusieurs expérimentations dans différents pays afin d'émettre des recommandations pour des apports raisonnés de magnésium basés sur les résultats d'analyses foliaires effectuées régulièrement. Après avoir rappelé les symptômes des carences en magnésium chez le palmier, on étudie l'effet d'apport d'engrais à base de magnésium sur le rendement; l'absorption du magnésium en fonction des traitements; les effets du magnésium sur la nutrition azotée et potassique; les types d'engrais et doses utilisés pour compenser la déficience en magnésium

Salinity is a major yield-reducing stress in many and and/or coastal irrigation systems for rice. Past studies on salt stress have mainly addressed the vegetative growth stage of rice, and little is known on salt effects on the reproductive organs. Sodium and potassium uptake of panicles was studied for eight rice cultivars in field trials under irrigation with saline and fresh water in the hot dry season and the wet season 1994 at WARDA in Ndiaye, Senegal. Sodium and potassium content was determined at four different stages of panicle development and related to salt treatment effects on yield, yield components and panicle transpiration. Yield and yield components were strongly affected by salinity, the effects being stronger in the HDS than in the WS. The cultivars differed in the amount of salt taken up by the panicle. Tolerant cultivars had lower panicle sodium content at all panicle development stages than susceptible ones. Panicle potassium concentration decreased with panicle development under both treatments in all cultivars, but to a lesser extent in salt treated susceptible cultivars. Grain weight reduction in the early panicle development stages and spikelet sterility increase in the later PDS were highly correlated (p < 0.01) with an increase in panicle sodium concentration in both seasons, whereas reduction in spikelet number was not. The magnitude of salt-induced yield loss could not be explained with increases in sodium uptake to the panicle alone. It is argued that the amount of sodium taken up by the panicle may be determined by two different factors. One factor (before flowering) being the overall control mechanism of sodium uptake through root properties and the subsequent distribution of sodium in the vegetative plant, whereas the other (from flowering onwards) is probably linked to panicle transpiration.

La dépendance mycorhizienne a été évaluée chez 13 arbres fruitiers (#Zizyphus mauritiana#, #Tamarindus indica#, #Parkia biglobosa#, #Balanites aegyptiaca#, #Sclerocaria birrea#, #Adansonia digitata#, #Cordyla pinnata#, #Saba senegalensis#, #Landolphia heudelotii#, #Dialium guineensis#, #Anarcadium occidentale#, #Afzelia africana# et #Aphanas senegalensis#) à usages multiples dans les systèmes agroforestiers soudano-sahéliens. #Z. mauritiana# (jujubier) est le fruitier qui répond le mieux à la mycorhization avec une dépendance d'environ 77%. Certains fruitiers comme #T. indica#, #D. guineensis#, #P. biglobosa# et #C. pinnata# ont une dépendance mycorhizienne respectivement de 53,80%, 44,80%, 32,33% et 28,50%, alors que d'autres tels que #A. digitata#, #S. birrea#, #B. aegyptiaca#, #A. senegalensis# #A. occidentale# répondent moins bien. Les fruitiers #S. senegalensis#, #L. heudilotii# et #A. africana# ne forment pas de mycorhizes à arbuscules. L'inoculation a d'ailleurs un effet dépressif sur la croissance d'#A. africana#. Le jujubier a été donc retenu comme fruitier modèle pour étudier la capacité des mycorhizes à arbucules à mobiliser des phosphates naturels (PN), ressource minérale dont regorgent la plupart des pays d'Afrique de l'Ouest. Les jujubiers mycorhizés utilisent plus efficacement le phosphore du sol et le phosphore des PN que les jujubiers non mycorhizés. Les réponses du jujubier à la mycorhization sont plus marquées avec le PN de Tilemsi (Mali). Ces travaux s'inscrivent dans une perspective d'amélioration de la production fourragère et fruitière du jujubier dont l'importance est considérable pour le Sahel.

Des semenceaux d'Arabica cv Catuai ont été utilisés pour déterminer les effets du pH, de la température, de la disponibilité en NH 4+ et NO 3- et de conditions anaérobies sur l'absorption de NH+ et de NO dans des expériences de courtes durées (3 heures) en solution hydroponique. Les résultats montrent que l'absorption de NH 4+ et de NO 3- par le Catuai est peu sensible aux pH allant de 4,00 à 6,00, les plus fréquents en arabicaculture. Par contre, l'absorption est réduite de 50 % pour NO 3- et de 30 % pour NH 4+ par des conditions anaérobies. Entre 4°C et 16°C, le Catuai absorbe plus de NH 4+ que de NO3-. Entre 16°C et 22°C, l'absorption de NO 3- augmente très fortement pour devenir équivalente à celle du NH 4+ entre 22°C et 34°C. A 40°C, les absorptions de NO 3- et de NH 4+ s'infléchissent. L'expérience sur les rapports NH 4+/NO3- montrent qu'aucune des 2 formes n'a d'effet inhibiteur marqué. Au contraire, l'absorption est plus forte en présence d'une solution azotée mixte (NH 4+ + NO 3-) que lorsqu'une seule forme (NH 4+ ou NO3-) est disponible. Ces résultats montrent que le caféier Catuai est bien adapté aux sols acides et qu'il possède une grande capacité à utiliser la ou les formes azotées minérales disponibles suivant les conditions ambiantes. Néanmoins, la fertilisation azotée du caféier peut être optimisée par le maintien dans l'environnement racinaire de températures intermédiaires et d'une disponibilité équilibrée entre NH 4+ et NO 3-.

Afin d'améliorer le procédé de culture #in vitro# d'embryons zygotiques de cocotier, ce projet de recherche a pour objectifs de générer des données afin d'expliquer la base physiologique de la croissance #in vitro# et d'identifier les lacunes des protocoles utilisés couramment. L'approche méthodologique prendra en compte plusieurs techniques permettant de mesurer différents paramètres physiologiques et biochimiques : mobilisation des principaux composés organiques par l'haustorium pendant la germination #in situ#, quantification des phytohormones pendant le développement des noix, détermination de la capacité photosynthètique des vitroplants en pépinière en comparaison avec les plantules en champ. Un projet important pour les Philippines concerne la caractérisation des noix Makapuno au niveau biochimique, histologique et génétique afin d'en comprendre la particularité. D'autres projets pour améliorer le système de culture pourraient être conduits comme l'étude de l'influence de l'immersion temporaire en système RITA sur la germination de l'embryon et le développement des plantules, ou l'étude du développement du système racinaire en conditions #in vitro# et de la quantité d'éléments nutritifs absorbés

Ce projet mené aux Philippines en quatre sites différents a pour but : de sélectionner différentes variétés de maïs, haricot-mungo, patate douce et niébé et de sélectionner différentes espèces de cultures associées avec le cocotier sous différentes intensités lumineuses ; de connaître l'effet de la radiation photosynthètique active (PAR) sur la croissance et le rendement de ces cultures. Les expérimentations ont donné les résultats suivants : on trouve une relation linéaire positive entre le rayonnement PAR et la croissance ou le rendement de ces cultures intercalaires. Plus le rayonnement reçu par la plante est élevé, plus le développement et la production sont importants. Les rendements en maïs doublent avec une augmentation du nombre d'épis par parcelle et du poids des graines par épis, alors que le rendement du haricot triple avec un nombre plus important de gousses par plant et de graines par gousse. La compétition pour l'absorption des éléments nutritifs du sol n'a que peu d'influence entre le cocotier et les cultures associées. Les variations dans le rendement du cocotier ne sont pas dues aux changements de rayonnement PAR résultant d'un éclaircissage mais plutôt à la densité de plantation. En culture associée, le cocotier a 5% de rendement de plus en coprah par hectare. L'augmentation de la croissance végétative de ces cultures intercalaires lors d'une intensité lumineuse plus élevée, accroit la teneur en matière organique du sol. Cependant le pH du sol diminue avec le temps

The architecture and growth dynamics of the oil palm root system were observed, described and analyzed through architectural analysis. Following a transitional juvenile phase, eight different morphological types of roots have been distinguished according to their developmental pattern and state of differentiation: the primary vertical roots (RI VB) and the primary horizontal roots (RI H), the secondary horizontal roots (RII H), upward growing vertical roots (RII VH) and downward growing vertical roots (RII VB), the superficial RIIIs) and the deep (RIIIp) tertiary roots and the quaternary roots (RIV). The relative position of these types of roots represents a morphological and functional unit of the root system, called "root architectural unit" of the oil palm. The identification of the edification sequence of these different roots allowed us to establish the basis of a mathematical formalization of the functioning of root meristems. The mathematical models used in this work were based on stochastic processes (graphs, automata, laws of probability). The processes of growth, branching and mortality and their geometrical parameters were formalized and put together in a synthetic model: the reference axis. Simulation provides tridimensional numerical mock-ups, the validation of which appears satisfactory. These models help to estimate root biomass and distribution, to locate and quantify the absorbing parts of roots and to assess the volume of soil explored by assimilating roots. These various applications offer a promising future in the study of carbon allocation patterns between above- and below-ground parts of plants, or the approach of the intricate phenomena of root competition. (Texte intégral)

The aim of this study was to quantify the long-term effects of Al in solution on mineral ion uptake and associated H + release by the roots of maize cultivated in conditions compatible with field data. Two maize (Zea mays L.) cvs of differing sensitivity to Al were compared. The culture was conducted in hydroponic conditions for culture periods of 2-5 in the presence of 0-30 μM Al. Proton fluxes were localized along the roots using a videodensitometry method with bromocresol green on agarose gel. Aluminium reduced the uptake of anions, particularly NO 3 - , whereas the uptake of K + and NH 4 + was unaffected. These effects were accompanied by an increase in net H + release which was quantitatively comparable with the reduction in NO 3 - uptake. The reduction in NO 3 - uptake and the concomitant increase in H + release increased with the quantity of Al accumulated in the roots, which was itself dependent on the concentration of Al in solution. The Al-sensitive cultivar bound more Al to its roots than the Al-tolerant one; the reduction in NO 3 - uptake and the increase in H + release were also greater in the Al-sensitive cv. Dye indicator videodensitometry showed that the increased H + release was general all along the roots. These results led us to specify the relation between the Al deposition in roots, the reduction in NO 3 - uptake and the stimulation in rhizosphere acidification by the plants. They show that, with maize, Al induces an inhibition in NO 3 - uptake and an increase in net H + release in a 1:1 ratio. These concomitant effects suggest that inhibition in NO 3 - /OH - exchange unmasks active H + excretion which is otherwise insensitive to Al. Both these effects are closely related to the Al content in roots expressed per unit root length.

Dans les écosystèmes soudano-sahéliens, la gestion des mycorhizes requiert la prise en compte d'au moins trois facteurs : la dépendance mycorhizienne de la plante hôte, le niveau de fertilité (P assimilable) et le potentiel mycorhizien des sols. Les objectifs du travail visent à évaluer la dépendance mycorhizienne de quelques arbres fruitiers dans le but de proposer un modèle d'étude des interactions entre plante et microorganismes du cycle du phosphore, étudier la capacité de l'espèce #Zizyphus mauritiania# jujubier mycorhizé à utiliser le phosphore des phosphates naturels. Le jujubier est, parmi treize arbres fruitiers, l'espèce qui répond le mieux à la mycorhization avec une dépendance d'environ 80%. La nutrition minérale en P, N, K, Ca et Mg de ce fruitier est également nettement améliorée grâce à la mycorhization controlée dans un sol pauvre en P assimilable. En l'absence de processsus biologiques de fixation, le renouvellement durable en P de la solution du sol dépend, pour une large part, d'apports d'éléments minéraux. Pour cela, on peut envisager l'utilisation d'intrants à faible coût comme les phosphates naturels, ressource minérale dont regorgent la plupart des pays d'Afrique de l'Ouest. Les jujubiers mycorhizés utilisent plus efficacement le phosphore du sol et le phosphore des phosphates naturels que les jujubiers non mycorhizés. Les réponses du jujubier à la mycorhization sont plus marquées avec le phosphate naturel originaire du Mali. Ces travaux s'inscrivent dans une perspective d'amélioration de la production fourragère et fruitière du jujubier dont l'importance est considérable pour le Sahel.

L'architecture et la dynamique de croissance du système racinaire sont décrites. Après une phase juvénile transitoire, 8 types morphologiques de racine sont distingués selon leur état de différenciation et leur schéma de développement. La position relative de ces types de racine représente une unité morphologique et fonctionnelle appelée unité architecturale racinaire. En identifiant la séquence d'édification de ces différentes racines, il a été possible d'établir les bases d'une formalisation mathématique du fonctionnement des méristèmes racinaires. Les modèles utilisés sont basés sur des processus stochastiques. Les processus de croissance, de ramification et de mortalité des axes ainsi que les paramètres géométriques ont été formalisés puis rassemblés dans un modèle synthétique : l'axe de référence. La simulation fournit des maquettes numériques tridimensionnelles dont la validation est satisfaisante. Ces maquettes permettent d'estimer et de localiser la biomasse racinaire, les surfaces absorbantes et le volume de sol exploré. Ces applications sont prometteuses pour l'étude de la répartition du carbone entre les parties aérienne et souterraine des plantes ou une approche du phénomène complexe de la concurrence racinaire

L'endomycorhization du caféier Arabica a des effets bénéfiques en pépinière (augmentation de la croissance et donc raccourcissement du temps de résidence) et au champ (gains importants de production). Elle favorise également l'acclimatation des vitroplants (croissance améliorée et quantité d'engrais phosphaté nécessaire diminuée). Enfin, la tolérance aux nématodes est nettement augmentée par la mycorhization précoce (4 à 6 mois avant l'addition des nématodes au milieu de culture) des plants

Cette thèse est constituée de 4 études différentes. La 1ère concerne les effets résiduels sur le rendement, la nutrition et la croissance de jeunes caféiers Robusta replantés, et sur la colonisation mycorhizienne et la densité de spores, des apports NPK après 15 ans d'essai en champ. La 2ème s'intéresse aux interactions des mycorhizes à vésicules et arbuscules (MVA) (Acaulospora mellea et Glomus clarum) et des nématodes (Pratylenchus coffeae et Meloidogyne sp.), inoculés successivement ou simultanément, avec le caféier Arabica. La 3ème étude concerne les effets de divers paramètres (pH de la solution, température racinaire, inhibiteurs, infection par les nématodes et les MVA) sur l'absorption de l'ammonium et du nitrate chez des caféiers Arabica cultivés in vitro. La dernière étude est celle des effets de l'inoculation par les MVA sur la nutrition et la croissance de caféiers Arabica multipliés in vitro et cultivés en pot dans des sols présentant différents niveaux de P disponible

Une analyse architecturale détaillée du système racinaire du palmier à huile a permis de mettre en évidence 8 grands groupes de racines et de définir pour chacun les processus de croissance, de ramification et de mortalité. Des modèles stochastiques ont ensuite été appliqués aux observations. Les différentes étapes nécessaires au passage de ces données aux maquettes virtuelles tridimensionnelles sont d'abord présentées. Une des applications agronomiques de ce travail est l'estimation du volume de sol utile (rhizocylindre), réalisée pour une plantation de 1 ha, âgée de 1 an, et pour 2 éléments indispensables : le potassium et le phosphore. Les zones d'excrétion de protons, considérées par hypothèse comme équivalentes aux zones d'absorption, ont été mises en évidence à l'aide d'un logiciel d'analyse d'images, et étudiées au niveau anatomique. Les caractéristiques morpho-anatomiques de ces zones étant connues, on peut les repérer sur une maquette virtuelle, ce qui permet de calculer par simulation les surfaces absorbantes. Si on estime le rayon du rhizocylindre à 1 mm pour l'ion P et à 1 cm pour l'ion K, on peut alors estimer le volume de sol prospecté (ou utile) pour l'absorption de ces 2 éléments

Effects of N sources (ammonium, nitrate and ammonitrate) and VA mycorrhizae (Glomus intraradices) on rhizosphere soil characteristics (pH, exchangeable acidity, exchangeable cations, inorganic N concentrations) growth and nutrient acquisition of coffee seedlings (Coffea arabica L. cv guatemala) were investigated in a pot study with an acid soil (Red Bluff Loam) sterilized by autoclaving. Ammonium addition decreased rhizosphere pH while nitrate and ammonitrate additions both increased rhizosphere pH. Mycorrhizae induced a higher pH, a lower exchangeable acidity and higher values of exchangeable cations in the rhizosphere. Ammonium addition resulted in a lower mycorrhizal infection than the two other N sources. Mycorrhizal plants grew better and accumulated more N, Ca and Mg than non-mycorrhizal plants.