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International audience; We studied the effects of light quality and defoliation on the rate of phytomer appearance and axillary bud outgrowth in white clover. The treatments were applied to one phytomer, a phytomer being defined as the structural unit comprising a node, internode, axillary bud, subtending leaf and two nodal root primordia. Light of a low red:far-red (R:FR) ratio (0.27) was applied to a ''target'' phytomer either (i) within the apical bud and then to the axillary bud after emergence of the phytomer from the apical bud, or (ii) to the axillary bud only after emergence. The Light conditions were directed to these specific parts of the plant by collimating light from small FR light-emitting diodes; with this technique we were able to change the light quality without any change in the level of photosynthetically active radiation. The subtending leaf of the target phytomer was retained or defoliated when it had emerged from the apical bud. FR light applied from the time the phytomer was within the apical bud caused a delay in branch appearance at the target phytomer. In contrast, direct treatment of the axillary bud with FR light after it had emerged from the apical bud did not result in any delay in branch appearance. As the light treatment of the apical bud may have changed the light environment of any of the organs contained in the bud we were unable to ascribe the delay in branch appearance to light perception by any particular organ. However, indirect evidence leads to the conclusion that the likely site of light perception was the developing leaf subtending the axillary bud while it was the outermost phytomer within the apical bud. These results do not support the hypothesis that the R:FR ratio of light incident at an axillary bud site is the environmental factor that controls bud development. Defoliation of the unfolding leaf reduced the rate of phytomer appearance on the main stolen but had no immediate effect on branch appearance. As a consequence there was a reduction in the number of phytomers between the stolen apical meristem and the first phytomer with a branch. This is frequently taken to indicate a relaxation of apical dominance, but in this case was found not to involve a direct effect on bud activity. A current model of white clover growth suggests that there is integration of activity between apical meristems but independence of activity and response to the local micro-environment by axillary buds. In contrast, we found that (i) defoliation reduced phytomer appearance only at the main stolen apical meristem and not at all the meristems in the plant and (ii) that a change in the local light environment of an axillary bud had no discernible effect on bud activity once the bud had emerged from the apical bud but could delay branching if applied before emergence. These results are at variance with the predictions of the model.

International audience; A controlled environment experiment investigated whether the red: far-red (R:FR) ratio of light at the apical bud of the main stolon could alter plant morphogenesis in clonal cuttings of white clover (Trifolium repens L.) The apical bud included the apical meristem, five to six developing leaf primordia with associated axillary bud primordia and stipules and the first emerged folded leaf until development was greater than 0.3 on the Carlson scale. Three light regimes were imposed on the apical bud by collimating light from R or FR light-emitting diodes so that the R:FR ratio of light incident at the apical bud was set at 0.25, 1.6 or 2.1, without significantly altering photosynthetically active radiation. The effect of these light regimes on white clover seedling growth was also tested. At a low R:FR ratio seedling hypocotyl and cotyledon lengths were significantly longer. However, with the cuttings, the light treatments did not alter node appearance rate or internode length of the main stolon, petiole length, area of leaves or total shoot dry matter. There was one significant photomorphogenetic response in the cuttings, a delay of 0.5 of a phyllochron in the appearance of branches from axillary buds in the low R:FR ratio treatment relative to the other treatments. Where branch appearance was delayed plants had fewer branches. This difference could be ascribed solely to a delay in branch appearance as there were no significant treatment effects on either the initiation of axillary bud primordia within the apical bud, the probability of branching or on the rate of growth of branches after appearance. Because treatment of the apical bud induced only one of the many previously observed responses of white clover to a decrease in the R:FR ratio of light, we conclude that other plant organs must also sense the quality of incident light.

[Departement_IRSTEA]Territoires [TR1_IRSTEA]DTAM; Two agri-environmental measures (MAE) tied to an obligation of result aimed at pastureland management (Herbe_09) and preserving species-rich grassland (Herbe_07) were studied: genesis of these measures in Europe and in France, conditions of implementation in different areas and agroecological relevance. This type of MAE restores a sense of responsibility to farmers. Implementing these measures may generate a positive territorial dynamic in the sometimes contradictory debate over the best interests of farmers vs. ecological biodiversity conservation measures. Results show that their positive impact in terms of social, ecological and agricultural benefits supports the idea that they ought to be implemented on a wider scale, along with improved regulations, a better dialogue between farmers and environmental activists, and progress in technical and scientific knowledge.; Les mesures agri-environnementales (MAE) visant la gestion pastorale (Herbe_09) et le maintien de prairies à forte richesse spécifique (Herbe_07) sont analysées : genèse de ces mesures en Europe et en France, conditions de leur mise en oeuvre dans plusieurs territoires et pertinence agri-écologique. Ce type de MAE est susceptible de redonner aux éleveurs une responsabilité valorisante ; leur mise en oeuvre peut entraîner une dynamique territoriale positive dans le débat parfois contradictoire entre agriculture et conservation de la biodiversité ; enfin, elles permettent de concilier production et biodiversité, mais sont peu propices à d’autres fonctions écologiques (pollinisation, séquestration du carbone...). Au final, leur bilan social, écologique et agricole, positif, incite à les généraliser mais en faisant progresser réglementation, concertation entre acteurs agricoles et environnementaux, et connaissances techniques et scientifiques.

This study was undertaken to determine the effects of root exudates on soil aggregate stability. Root mucilage was collected from two-month old maize plants (Zea mays L.) Mucilage and glucose solutions were added at a rate of 2.45 g C kg−1 dry soil to silty clay and silt loam soils. Amended soils, placed in serum flasks, were incubated for 42 d with a drying-wetting cycle after 21 d. Evolved CO2 was measured periodically as well as the water-stable aggregates and soluble sugar and polysaccharide content of the soil. In mucilage-amended soils CO2 evolution started with a lag phase of 2–3 days, which was not observed in glucose-amended soils. There was then a sharp increase in evolved CO2 up to day 7. During the second incubation period there were only small differences in evolved C between treatments. Incorporation of mucilage in both soils resulted in a spectacular and immediate increase in soil aggregate stability. Thereafter, the percent of water-stable aggregates quickly decreased parallel to microbial degradation. On completion of the incubation, aggregate stability in the silty clay soil was still significantly higher in the presence of mucilage than in the control. This work supports the assumption that freshly released mucilage is able to stick very rapidly to soil particles and may protect the newly formed aggregates against water destruction. On the silty clay, microbial activity contributes to a stabilization of these established organo-mineral bounds.

International audience; Plant growth promotion induced by the antagonistic fungus, Pythiumoligandrum, is the result of a complex interaction which includes an indirect effect through control of pathogens in the rhizosphere and/or a direct one mediated by plant-induced resistance. The present study shows an increased plant growth associated with direct interaction between P. oligandrum and roots, which is mediated by a fungus-produced auxin compound, tryptamine (TNH2). In vitro experiments provided evidence that P. oligandrum metabolised specifically indole derivatives, such as tryptophan and indole-3-acetaldehyde, to produce THN2 through the tryptamine pathway. When P. oligandrum grew in sterile root exudates, it also produced an auxin-like compound. Additional experiments on P. oligandrum– root interaction showed that, in amended nutrient solution of plants, the antagonist metabolised Trp into TNH2 and that root absorption of this newly formed auxin-compound in appropriate concentrations was associated with enhancement of plant growth. This phenomenon was observed only when nutrient solution was amended with low tryptophan (Trp) concentrations, i.e. 0.05 and 0.1 mM; higher concentration (0.5 and 1 mM Trp) induced abnormal root development. Similar experiments were performed with Pythium group F, a minor pathogen known for its ability to produce auxin-compounds through the tryptamine pathway. In this case, irregular root development was always noticed with all Trp concentrations added to the nutrient solution of plants. Moreover, Pythium group F colonization of roots was associated with leakage of auxin-compounds in the nutrient solution. Our results, therefore, highlight that the production of similar auxin-compounds by two Pythium species has contrary effects on plant development.

In order to compare the growth potential of buds of two contrasting cultivars of white clover (Trifolium repens L.) (cv. AberHerald and Grasslands Huia) during the winter–early spring period, we adapted a method to assess the potential for activity of shoot buds and root primordia. The growth potential was evaluated following the excision of individual stolon nodes sampled in the field, from experimental plots located in the eastern part of France. Two populations of nodes were sampled: (i) the youngest node emerged from the apical bud (node 1), (ii) the third node behind the apex (node 3). The excised nodes were placed in controlled conditions and the outgrowth of axillary buds and roots was recorded every day for a week. The study demonstrated a seasonal influence on the potential for activity of axillary buds and root primordia, particularly for buds at node 3. The proportion of potentially active shoot and root buds was less than 50% at the end of March, and then increased from end of March to reach 80% in April. The data indicated a genetic variation in potential for outgrowth during winter. AberHerald had a higher percentage of potentially active buds than Huia during winter, irrespective of the node position. Moreover AberHerald buds had faster rates of outgrowth than Huia buds. Differences between cultivars in winter survival and potential for growth in spring were linked to identified cultivars' differences in developmental characteristics of buds.

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International audience; Since several years, accelerated decline of Aleppo pine (Pinus halepensis) forests has been observed in mediterranean areas. In fact, the combination of various environmental factors (photochemical oxidants, drought, high light,...) was suspected to cause this decline. In this study, three year-old Aleppo pines were exposed during 3 months to ozone fumigation (100 ppb) combined or not with mild drought to study the effects of these combined factors on some sequences linked to carbon partitioning and primary carbon metabolism within the tree. After a cumulative ozone exposure of 132 ppm . h, ozone induced a significant decrease in specific activity of the whole-plant (-38%) combined with a disequilibrium of the carbon transfer between root and shoot in favour of the shoots (non significant). Moreover, while the same cumulative dose of ozone had no effect on total Rubisco activity in one year-old needles, mitochondrial NAD malic enzyme activity increased significantly (+32%). By combining ozone with mild drought, the ozone-induced responses of all the parameters were significantly amplified and Rubisco activity was significantly decreased (by 44%). These results allowed us to conclude that at 132 ppm . h, ozone alone led to an increase in dark respiration. Moreover, by the combination of ozone and mild drought, a decrease carbon fixation capacity was associated to a decrease of the carbon transfered to the roots, leading to a reduced root growth. Thus, there are indications that high levels of ozone during the summer months may impair the ability of Pinus halepensis to withstand severe water stress in its natural environment.

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* INRA Department d'Agronomie, Grignon; National audience

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Le comportement du trèfle blanc (Trifolium repens L cv Crau) est étudié en situation de contrainte hydrique et après réhydratation en liaison avec la fertilisation potassique. Le déficit en eau occasionne une décroissance progressive importante du potentiel hydrique des feuilles et une fermeture rapide des stomates. Ces manifestations sont accompagnées d’une chute de l’activité photosynthétique et de la fixation symbiotique de l’azote. En présence de potassium, la diminution de l’activité fixatrice est significativement ralentie. L’action favorable du potassium est également observée lors de la réhydratation des plantes soumises au déficit. Le rétablissement du potentiel hydrique et de la fixation symbiotique d’azote est plus important en présence de potassium. La fertilisation potassique exerce un effet positif sur la production de matière sèche aérienne aussi bien dans le cas des plantes soumises au déficit que des plantes régulièrement arrosées. Les résultats montrent qu’un apport de potassium favorise la résistance du trèfle blanc au manque d’eau., The effects of successive water stress and irrigation on white clover (Trifolium repens L cv Crau) photosynthetic activity, nitrogen fixation, predawn leaf water potential and stomatal resistance were studied in relation to potassium supply. Water deficit induced a gradual decrease in the predawn leaf water potential and a rapid stomatal closure (figs 1 and 2). Nitrogen fixation and photosynthetic activity were also reduced (fig 4 and table I). The decrease in nitrogen fixation activity was significantly lower with K supply (fig 4). For the same water potential and the same stomatal resistance, nitrogen fixation activity (ARA’s method) was higher in presence of potassium fertilization (fig 5 a, b). The positive effect of K was also observed for the rehydrated plants. Water potential and symbiotic nitrogen fixation recovery was more significant with K supply. Potassium fertilization increased dry matter production in stressed plants as in controls (fig 3). These results showed that K supply increased white clover resistance to water stress.

The pectic nature of root mucilages suggests a hypothetical action of these substances on heavy metal flux into the root. In this study the existence of relations between heavy metals and root mucilages were verified and quantified. In order to obtain substantial amounts of pure root mucilages, two methods of collection were developed, using: (1) maize plants grown in the field and (2) hydroponic axenic cultures. The study of mucilage-metal binding was conducted using the dialysis method, which was developed in a previous work. Results show that root mucilages are able to bind metals. The importance of the binding depends on the nature of the cation, following the order Pb > Cu > Cd. These reactions could be due to exchange processes involving mucilage cations (Ca2+, Mg2+) and heavy metals. The role of mucilages on the retention of heavy metals in the rhizosphere is also discussed.

L’étude de l’assimilation photosynthétique et du transport des assimilats chez le trèfle blanc a pour objet de préciser le rôle de la feuille dans l’établissement des relations source-puits. Des marquages courts au 14CO2 sont effectués sur les 8 limbes initiés par le stolon obtenu en conditions contrôlées par bouturage d’apex. Le profil photosynthétique de l’ensemble des limbes du stolon met en évidence un effet « âge du limbe source» pour l’assimilation du 14CO2. Les limbes 2, 3 et 4 sont les plus efficients, les limbes plus âgés sont le siège d’une perte d’activité assimilatrice. Le plus jeune limbe montre un niveau photosynthétique faible et le taux de distribution de carbone le plus bas. Il est également un puits majeur d’assimilats issus des autres limbes. Il s’établit des relations source-puits privilégiées entre les jeunes feuilles et l’apex en croissance. L’allocation de carbone aux racines nodulées est le fait des feuilles plus âgées. Quelle que soit la position de la feuille marquée, le stolon est l’organe qui accumule le plus de carbone néosynthétisé ; il régit les flux vers l’apex et vers les nodosités. Il n’a pas été observé de corrélation positive nette entre assimilation et transport du carbone récent par les limbes source., The authors have studied photosynthetic assimilation and assimilate transport in white clover to try to determine the role of leaf position on the establishment of source-sink relations. Short pulse labelling with 14CO2 was applied to the 8 leaves formed on stolons obtained by suckering of a stem apex. An effect of "age of the source" was shown on 14CO2 assimilation. Leaf numbers 2, 3 and 4 were the most efficient, the youngest leaf showing a low photosynthetic level and the lowest carbon assimilation rate. It was also a major sink for assimilate coming from the other leaves. Preferential source-sink relations were established between the growing apex and the young leaves. Carbon allocation to nodulated roots was due to the oldest leaves. Whatever the position of the labelled leaf, the stolon was the organ which accumulated the most newly synthesized carbon. The stolon governed carbon flow towards the apex and the nodules. We did not observed a clear positive correlation between assimilation and the transport of new carbon by the source leaf.

Les assimilats formés par les limbes et distribués vers les organes puits jouent un rôle capital dans la construction des organes végétatifs. De plus, l’allocation de carbone aux nodosités est garante d’un système fixateur efficient. A l’aide d’un «phytomodèle» et de marquages courts au 14C02, nous avons déterminé le rôle de la ramification sur les flux de photoassimilats chez le trèfle blanc. Les données montrent clairement que l’interaction «âge de la ramification-position de la feuille source« gère les relations entre les puits. La force du puits nodosités tend à chuter en présence d’une ramification surnuméraire en cours de développement. L’étude confirme le rôle tampon du stolon : l’activité de l’ensemble de l’organe de réserve est peu modifiée, quelles que soient les modalités du marquage. En revanche, la part allouée au stolon-fils est d’autant plus importante que la ramification est âgée, avec comme conséquence une moindre distribution au stolon parent. Un point végétatif à 4 feuilles reçoit encore du carbone issu des feuilles sources du stolon parent., Assimilates synthetized by the lamina and translocated to the sink organs play an important role in the building of the vegetative organs. Especially, the efficiency of nitrogen fixation depends on the carbon supply to the nodules. With the help of a white clover "phytomodel" and short pulse labelling of single leaf with 14C02, we have determined the role of ramifications on assimilate flux to various plant organs. Two cases were distinguished (Figure 1): - stolon without ramification, with only 8 leaves and 1 apex - stolon with 1 ramification, 2 apices; - ramification with 2 leaves (R4) - ramification with 4 leaves (R8) near the nodulated roots Different leaves were chosen (Table l) in order to determine assimilate distribution : - from the main stolon towards the ramification (fed leaves F4 and F8; - from the ramification towards the main stolon (fed leaves F1 and F2 : ramification R4 ; fed leaves F1 and F4 ; ramification R8). The ramifications R4 and R8 imported significant assimilates -14C (Tables IIa & llb) from leaves of the main stolon. Consequently the sink strength of nodules decreased (Table III). 14C-photosynthate exportation from the ramifications towards the main stolon was high, with 38-52°% of the exported activity according to the labelled leaf (Table IVa). Position of the labelled leaf and of the branch stolon played a role in the assimilate distribution to the organs (Table IVb) which influenced the sink strength of nodules and ramification. Branch stolon showed a high sink strength especially in the case of R4 labelled leaf f2 (Table V). Whatever the labelled leaf position, this study confirms the buffering power of the whole stolon (main stolon + stolon of the ramification; Figure 2). On the other hand, the older the daughter branch, the higher the assimilate supply, and consequently the lower the allocation to the parent stolon.

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National audience; Assimilates synthetized by the lamina and translocated to the sink organs play an important role in the building of the vegetative organs. Especially, the efficiency of nitrogen fixation depends on the carbon supply to the nodules. With the help of a white clover "phytomodel" and short pulse labelling of single leaf with 14C02, we have determined the role of ramifications on assimilate flux to various plant organs. Two cases were distinguished (Figure 1): - stolon without ramification, with only 8 leaves and 1 apex - stolon with 1 ramification, 2 apices; - ramification with 2 leaves (R4) - ramification with 4 leaves (R8) near the nodulated roots Different leaves were chosen (Table l) in order to determine assimilate distribution : - from the main stolon towards the ramification (fed leaves F4 and F8; - from the ramification towards the main stolon (fed leaves F1 and F2 : ramification R4 ; fed leaves F1 and F4 ; ramification R8). The ramifications R4 and R8 imported significant assimilates -14C (Tables IIa & llb) from leaves of the main stolon. Consequently the sink strength of nodules decreased (Table III). 14C-photosynthate exportation from the ramifications towards the main stolon was high, with 38-52°% of the exported activity according to the labelled leaf (Table IVa). Position of the labelled leaf and of the branch stolon played a role in the assimilate distribution to the organs (Table IVb) which influenced the sink strength of nodules and ramification. Branch stolon showed a high sink strength especially in the case of R4 labelled leaf f2 (Table V). Whatever the labelled leaf position, this study confirms the buffering power of the whole stolon (main stolon + stolon of the ramification; Figure 2). On the other hand, the older the daughter branch, the higher the assimilate supply, and consequently the lower the allocation to the parent stolon.; Les assimilats formés par les limbes et distribués vers les organes puits jouent un rôle capital dans la construction des organes végétatifs. De plus, l’allocation de carbone aux nodosités est garante d’un système fixateur efficient. A l’aide d’un «phytomodèle» et de marquages courts au 14C02, nous avons déterminé le rôle de la ramification sur les flux de photoassimilats chez le trèfle blanc. Les données montrent clairement que l’interaction «âge de la ramification-position de la feuille source« gère les relations entre les puits. La force du puits nodosités tend à chuter en présence d’une ramification surnuméraire en cours de développement. L’étude confirme le rôle tampon du stolon : l’activité de l’ensemble de l’organe de réserve est peu modifiée, quelles que soient les modalités du marquage. En revanche, la part allouée au stolon-fils est d’autant plus importante que la ramification est âgée, avec comme conséquence une moindre distribution au stolon parent. Un point végétatif à 4 feuilles reçoit encore du carbone issu des feuilles sources du stolon parent.

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International audience; The response to water stress was studied on white clover grown hydroponically. Two varieties (Crau and Huia) were both subjected to a moderate and a more-severe stress, induced by polyethylene glycol (10 and 20% respectively), in the presence of a nutrient solution poor in potassium (K1=0.005 mM), or abundantly supplied (K2=5mM). Dawn water potential and nitrogen fixation (acetylene reduction activity) decreased with the increasing stress. Conversely, the stomatal resistance increased whenosmoticum was added. Crau had a lower stomatal resistance to the deficit, than did Huia. In relation with the K supply, treatment K2 confirmed the superiority of Crau. Crau also showed greater nodule mass and number than Huia. The data show relationships between dawn water potential, stomatal resistance and nitrogen fixation activity.

International audience; White Clover is often present in permanent pastures, but in amounts which vary very widely with the locations. the conditions of the sail and the climate, the management and manuring practices, and the years. This paper summarizes the results of various experimental studies made in France on this subject. Reference is made to the various techniques which influence the part played by claver and legumes in the sward: rates of nitrogen application, harvesting frequencies. methods of utilization... This study makes also evident the fact that when a pasture is first cut at the grazing stage. the proportion of legumes by weight is rather heavily dependent on certain factors of the sail and the c1imate' such as the pH of the layer between the depths of 5 and 20 cm, the mean temperature during the period elapsed since the last cut, and the climatic excesses or deficiencies of the previous year distributed over a period extending between the months of May to September and the month of October. This analysis constitutes a first approach, and should be investigated more deeply.; Le trèfle blanc est fréquemment présent dans les prairies permanentes mais son importance est extrêmement variable selon les lieux, les conditions pédoclimatiques, les pratiques d'exploitation et de fertilisation, et les années. Cet article fait le point des différents résultats d'essais conduits en France sur ce thème. Il rappelle l'intérêt de différentes techniques pour favoriser la participation du trèfle blanc et des légumineuses : dose d'azote, rythme d'exploitation, mode de récolte... Ce travail met également en évidence que la contribution pondérale des légumineuses d'une première coupe réalisée au stade de pâture dépend assez fortement d'un certain nombre de facteurs pédologiques et climatiques tels que le pH du substrat entre 5 et 20 cm, la température moyenne depuis la dernière coupe, les excédents ou déficits climatiques de l'exercice précédent répartis entre les mois de mai à septembre et le mois d'octobre. Cette analyse représente une première approche qui serait à approfondir.

International audience; The authors have studied photosynthetic assimilation and assimilate transport in white clover to try to determine the role of leaf position on the establishment of source-sink relations. Short pulse labelling with 14CO2 was applied to the 8 leaves formed on stolons obtained by suckering of a stem apex. An effect of "age of the source" was shown on 14CO2 assimilation. Leaf numbers 2, 3 and 4 were the most efficient, the youngest leaf showing a low photosynthetic level and the lowest carbon assimilation rate. It was also a major sink for assimilate coming from the other leaves. Preferential source-sink relations were established between the growing apex and the young leaves. Carbon allocation to nodulated roots was due to the oldest leaves. Whatever the position of the labelled leaf, the stolon was the organ which accumulated the most newly synthesized carbon. The stolon governed carbon flow towards the apex and the nodules. We did not observed a clear positive correlation between assimilation and the transport of new carbon by the source leaf.; L’étude de l’assimilation photosynthétique et du transport des assimilats chez le trèfle blanc a pour objet de préciser le rôle de la feuille dans l’établissement des relations source-puits. Des marquages courts au 14CO2 sont effectués sur les 8 limbes initiés par le stolon obtenu en conditions contrôlées par bouturage d’apex. Le profil photosynthétique de l’ensemble des limbes du stolon met en évidence un effet « âge du limbe source» pour l’assimilation du 14CO2. Les limbes 2, 3 et 4 sont les plus efficients, les limbes plus âgés sont le siège d’une perte d’activité assimilatrice. Le plus jeune limbe montre un niveau photosynthétique faible et le taux de distribution de carbone le plus bas. Il est également un puits majeur d’assimilats issus des autres limbes. Il s’établit des relations source-puits privilégiées entre les jeunes feuilles et l’apex en croissance. L’allocation de carbone aux racines nodulées est le fait des feuilles plus âgées. Quelle que soit la position de la feuille marquée, le stolon est l’organe qui accumule le plus de carbone néosynthétisé ; il régit les flux vers l’apex et vers les nodosités. Il n’a pas été observé de corrélation positive nette entre assimilation et transport du carbone récent par les limbes source.

White clover has a plagiotropic shoot system : it is a typical 'shade avoider' species. In this environment, white clover often experiences competition for light and nutrients from neighbouring plants. This paper reports a study in controlled environments on the effect of light quality on assimilate partitioning between source and sinks and the consequences on plant morphogenesis. The results demonstrated that the source-sink relationships were modified ; far-red plants partitioned more 14 C-assimilates to petioles and leaves than did control plants, at the expense of stolons and roots. These modifications in the transport of 14 C-labelled assimilates were evident less than 4 days after the commencement of the light treatments. Adding far-red at the end of each photosynthetic period modified plant morphogenesis ; far-red radiation decreased stolon branching and promoted the extension of petioles and internodes. Thus, the strategy of white clover in response to far-red is to redirect its development through a modification of its source-sink relationships in order to allow young leaves to be kept out of the shade. The shoot-root ratio was increased by far-red radiation ; thus phytochrome may act indirectly on nitrogen fixation and nutrient uptake by reducing carbohydrate allocation to the roots.

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