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Báo cáo khoa học: "An experimental system for the quantitative C-labelling 14 of whole trees in situ"

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  1. Technical note An experimental system for the quantitative C-labelling 14 of whole trees in situ A A Lacointe FA Daudet, P Archer JS Frossard Kajji, INRA, Université Blaise-Pascal, Unité Associée de Physiologie Intégrée de l’Arbre Fruitier, Domaine de Crouelle, F-63039 Clermont-Ferrand Cedex 02, France 8 10 March April 1992; accepted (Received 1993) Summary —The first part of this paper provides a brief review of the requirements that apply to 14 C- labelling chamber technology, particularly for tree labelling, and of the means that can be used to meet them. Two main points are considered: the quality of the plant chamber environment - the ne- cessity of thermal and hygrometric regulations is discussed - and the possibility of determining the exact amount of 14 assimilated by the plant. The authors then describe a simple system allowing 2 CO the quantitative labelling of entire trees, without temperature- or hygrometry-regulating devices which can be used in the morning. The CO concentration is maintained at its natural level through- 2 out the labelling procedure through an injection of cold CO operated by an IRGA-driven computer. 2 This system was successfully used for the labelling of grafted walnut trees. assimilation chamber I control of CO level I photosynthesis 2 Résumé — Un système expérimental permettant le marquage quantitatif au 14 d’arbres C entiers in situ. Ce système, utilisé pour le marquage de noyers greffés de 3 ans (surface foliaire : 1,7m se compose d’une chambre d’assimilation et d’un dispositif d’injection de CO à commande ), 2 2 électronique permettant une régulation continue de la concentration en CO (fig 1). Ne comportant 2 pas de dispositif de régulation thermique, il n’est utilisé que pendant la matinée. Malgré une aug- mentation significative de la température au cours du marquage (fig 2), la photosynthèse est peu perturbée, comme le montre la figure 3 : le taux d’assimilation (pente des segments décroissants) reste régulier. La chambre d’assimilation, en PVC de 2 mm monté sur un cadre d’acier, forme un cy- lindre fermé (hauteur, 2 m; diamètre, 1,44 m), constitué de 2 moitiés s’accolant l’une à l’autre par un joint de caoutchouc. Lors de la fermeture, le joint est comprimé par une série d’écrous disposés tout au long de la suture. Le cylindre, soutenu par un portique métallique, contient l’ensemble de la fron- daison. Une ouverture à la base du cylindre permet le passage du tronc, l’étanchéité étant assurée par un film de polyéthylène de 0,03 mm et un joint en mastic souple «Terostat». Des considérations Abbreviations: IR: infrared; PAR: photosynthetically active radiations; IRGA: infrared gas analyser; FMW: fresh matter weight. The mention of trade or firm names in this publication does not constitute endorsement or approval by the French Ministry of Agriculture.
  2. théoriques permettent d’estimer à quelque 3% la radioactivité perdue par fuites lors du marquage. La régulation de la teneur en CO répond à un double but. D’une part, en limitant l’écart par rapport aux 2 conditions naturelles, on perturbe le moins possible la répartition biochimique et spatiale des assimi- lats. D’autre part, la totalité du 14 étant injectée instantanément dès le début de l’opération, la régu- C lation consiste à injecter du carbone «froid» pour compenser la photosynthèse, et l’équation (1 ) (para- graphe «Injection de CO donne à tout moment la quantité totale de 14 restant dans la chambre. C ») 2 Ainsi, 99,3% de la radioactivité a disparu lorsqu’on a renouvelé 5 fois la totalité du CO présent dans 2 la chambre, ce qui était réalisé en 4 h environ. Le CO est fourni par la réaction d’une solution de 2 Na gouttant dans un flacon d’acide sulfurique à 33% (fig 1). L’efficacité du dégagement gazeux 3 CO 2 est améliorée par une agitation magnétique et un barbotage de l’air de la chambre prélevé par une pompe. L’injection initiale du carbonate marqué, de forte radioactivité spécifique (1,85 GBq/mmole; 74 MBq par arbre, pesant chacun 2 kg de MS) ne modifie pas la teneur totale en CO de la chambre. 2 Puis le réservoir de carbonate est empli de solution «froide», 1 M, délivrée selon les besoins de la régulation par une électrovanne. Celle-ci est pilotée par un micro-ordinateur (fig 1) munie d’une carte d’acquisition de données (Micromac 4000, Analog Devices) qui enregistre par ailleurs la température, le PAR incident et la teneur en CO de la chambre mesurée par un IRGA. Ce système libère 2 quelques gouttes de carbonate dès que la teneur en CO descend au-dessous de 350 vpm, ce qui 2 permet une régulation efficace (fig 3). Les aspects quantitatifs des marquages ont été validés par 2 moyens indirects : d’une part, en vérifiant que la radioactivité résiduelle de l’air à la fin du marquage est conforme à l’équation (1); d’autre part, en retrouvant dans les arbres traités, quelques heures après marquage, 90% de la radioactivité injectée. chambre d’assimilation / régulation de la concentration 2 CO / photosynthèse en INTRODUCTION This labelling system was designed to investigate carbon flows in 3- to 4-yr old walnut trees. Particularly, our aim was to During the past 40 years 14 has been C trace the incorporation of photosynthate- widely used as a tracer in studies of car- derived carbon into carbohydrate reserves bon flows in biological or biochemical sys- vs structural compounds at different times, tems, in which its radiations be used can as well as spring remobilization of the la- in imagery (autoradiography) or quantita- belled reserves (Lacointe et al, 1993). tively counted in liquid scintillation or gas- flow counters. We will here discuss only global studies of carbon flows, in which the GENERAL CONSTRAINTS RELATED C 14 enters the plant system through the TO 14 LABELLING C natural pathway, ie photosynthesis. The basic procedure in this case consists of Airtight chambers are utilised in the quanti- feeding the plants with 14 CO C-enriched 2 . tative feeding of plants with labelled CO2 After a brief review of the constraints re- ( or 13 Enclosing plants in a ). 2 CO 2 CO 14 lated to 14 labelling, and of the main C closed illuminated chamber leads to rapid progress made in labelling chamber tech- modification of the atmosphere due to de- nology in order to meet them, particularly pletion of CO by photosynthesis and ac- 2 for trees, this paper presents a system al- cumulation of a significant amount of heat lowing quantitative labelling which has and water vapour; the rate of photosynthe- been used successfully at our laboratory in sis can be significantly altered by these Clermont-Ferrand. modifications in the environment.
  3. Although the aim of feeding experi- 2.5 and 25 μm; Dogniaux and Nisen, ments is generally not to evaluate the pho- 1975), and low convection (closed circuit conditions), the temperature of the air in- tosynthetic rate (well known gas exchange side the chambers can be increased by 5 methods are far more suitable for this pur- to 15°C with respect to the outside in con- pose), it is necessary to maintain a suffi- ditions of high solar irradiance. When ex- ciently high rate of photosynthesis in order cessive, this increase in temperature can to achieve maximal exhaustion of the la- lead to reduced or even negative net pho- belled CO by the plants. Furthermore, a 2 tosynthetic rates, the latter rendering im- significantly reduced assimilation rate possible any labelling experiment in the could disturb the natural pattern of chemi- absence of an additional cooling system. cal and spatial partitioning of assimilated C (Geiger and Fondy, 1991).Then at least A few authors have tried to solve this partially regulating the most critical param- problem which can become critical for long eters of the environment may become nec- feeding periods especially when intense essary even for feeding periods of short encountered. radiative conditions are duration. For long-term feeding experi- Lister et al (1961) interposed water fil- ments, due to significant alteration in most ters to absorb part of the IR radiations from of the physiological functions when the en- the light source. This system is viable for vironmental conditions are changed, the indoor labelling but unsuitable in the field. temperature and humidity of the air will Palit (1985) used occasional spraying of have to be regulated. cold water, whereas Lister et al (1961), Warembourg and Paul (1973), Geiger and Shieh (1988) made use of different types A within-chamber environment of heat exchangers to regulate the temper- allowing photosynthesis ature. All these systems, well adapted to small-sized chambers (a few litres), would become problematical if used with cham- Light conditions bers several cubic meters in size, as nec- essary to label whole trees. The materials used to construct the cham- bers (transparent plastics) have photosyn- However, even for small chambers, thetically-active radiation (PAR) transmis- since the only requirement is that of no sig- sion factors ranging between 70 and 90% nificant reduction in photosynthesis, most (Dogniaux and Nisen, 1975), which in- authors did not include any cooling device volves some reduction in the photosynthet- in their feeding system and tried simply to ic rate with respect to open air conditions. limit overheating, ie to operate preferential- In labelling experiments this reduction is ly in the morning. This is approach that assumed to have only little effect (if any) was adopted for our system. on the fate of the incorporated C in the plant (which is the question under study). Air humidity conditions For reasons of cost and ease of handling PVC was chosen. When exposed to high solar irradiance, well watered plants inside a closed cham- Air temperature conditions ber convert a large proportion of the inci- dent radiative energy into latent heat by Due to very low transmittance of the plastic transpiration, leading complete satura- to tion of the volume of the chamber materials in the thermal IR range (between by water
  4. vapour in a few min and to heavy conden- Making the labelling quantitative sation on the walls which constitute the cold elements of the system. Since the of the the experi- Depending objectives on leaves absorb most radiation, they be- ment, it may or may not be important to come warmer so that no condensation oc- regulate the isotopic ratio of the assimilat- curs on them. These physical conditions at CO (specific activity in case of 14 ). 2 CO ed 2 leaf level (high temperature and low water In long-term labelling experiments saturation deficit) are known to be general- steady state has to be reached, hence the ly favourable to photosynthesis (provided isotopic ratio of the photosynthetic CO 2 the temperatures do not become exces- must be held constant, but the total sive). Then one can assume that regulat- amount of incorporated C is generally of ing the humidity of the air per se would no importance. On the other hand, in generally be unnecessary for feeding ex- short-term labelling experiments achieving periments of short duration. On the con- quantitative labelling, ie knowing how trary, for long-duration feeding experi- much 14 the plant has actually taken up C ments, a system of complete air may be of importance, particularly for ex- conditioning (temperature and hygrometry) periments with destructive sampling; but is necessary. A few authors (Webb, 1975; keeping the isotopic ratio constant is gen- Kuhn and Beck, 1987; Geiger and Shieh, erally unnecessary. 1988) regulated the relative humidity in the In order to make a short-term labelling labelling chamber, using a cooled vapour trap. For our feeding experiments which the first step is to accurately quantitative, determine the total quantity of 14 in- 2 CO 4 h it was decided were designed to last = jected into the labelling system. The CO to leave the hygrometry unregulated. 2 can be directly injected as gas from a sy- ringe (Balatinecz et al, 1966) or a pressur- Regulating the CO concentration 2 ized cylinder (Webb, 1975; Kuhn and Beck, 1987). Alternatively, it can be re- Since exhaustion of the ambient CO by 2 leased from the reaction of 14 C-carbonate photosynthesis in feeding experiments with excess acid (Lister et al, 1961; Han- leads to decreased photosynthetic rates, sen, 1967; Warembourg and Paul, 1973; maintaining the CO concentration at nor- 2 Glerum and Balatinecz, 1980; Langenfeld- mal values is necessary. Achieving accu- Heyser, 1987; Smith and Paul, 1988; La- rate regulation of CO requires continuous 2 cointe, 1989; Schneider and Schmitz, measurement of its concentration (using 1989; and many others). In the latter case, an IRGA) and an injection system. Rough due to the higher density of CO as com- 2 control of the ambient CO can be 2 pared to air, the atmosphere in the reac- achieved by temperate injection of chemi- tion vessel must be chased efficiently. This cal reactants (Warembourg and Paul, problem was solved by forcing the cham- 1973; Smith and Paul, 1988; Schneider ber atmosphere into the reacting solution and Schmitz, 1989) or by the use of cylin- (fig 1). ders of diluted CO and mass-flow regula- 2 Secondly, the injected CO must not 2 tors (Webb, 1975; Geiger and Shieh, leave the system during the labelling. 1988; Hansen and Beck, 1990). Though Hence the chamber - and circuit when less accurate, the former solution was cho- must be airtight, which is also present - sen for our system because of its simplici- to avoid pollution problems, par- important ty of operation. ticularly indoors. Air-tightness is generally
  5. the chamber (eg 6 h for Hansen, 1967; 30 real problem with solid chambers, but not a min for Palit, 1985). However, some au- be with chambers made of plastic film, can thors further investigated the actual due to the possibility of small tears or amount of 14 taken up by measuring the C holes and rather large changes in volume level of 14 still in the system at the end 2 CO allowed. The above-mentioned materials of the labelling period. Before opening the including plastic films, generally exhibit a chamber, they forced its atmosphere into a sufficient impermeability to CO eg, 2 CO circuit generally containing -4 3 1.04·10 cm for a 0.03- ·Pa -1 ·min -2 · -trapping 2 KOH or Ba(OH) (a common procedure to 2 mm polyethylene film (Daudet, 1987). avoid pollution, particularly indoors) and not carried out more Many authors have then measured the radioactivity trapped by were not in- controls, either because they the alkali (Glerum and Balatinecz, 1980). quantity incorporated terested in the exact Further progress was achieved through (Balatinecz et al, 1966; Langenfeld- measuring the 14 level not only at the 2 CO Heyser, 1987), or because they allowed end of the labelling, but continuously dur- 14 for a time which they ei- C-assimilation ing the labelling period. Lister et al (1961) ther assumed or knew to be long enough used both an IR gas analyser for estimat- for a complete exhaustion of the 14 in 2 CO
  6. ing the total CO level and a Geiger-Müller The chamber used for the local labelling 2 open cylinder made of 2-mm PVC tube for volumic radioactivity, whereas was an Kuhn and Beck (1987) used only an IRGA (PAR transmission factor 85%). Its = to measure the decrease in the CO level height was 0.50 m and its diameter 0.34 m 2 (and calculate that of the 14 within the ) 2 CO (vol 45 I). This cylinder was extended at = chamber. As mentioned above (see Regu- each end by a 0.03-mm polyethylene film lating the CO concentration), some au- junction, allowing gas-tight sealing on the 2 thors used an IRGA to regulate the CO branch with Terostat 9010 sealing profile 2 level inside the chamber throughout the la- (Teroson, France). belling period. The chamber used for global labelling closed cylinder (height 2 m; diam- When the injected CO was of constant 2 was a = 3.25 m made of 2- ), 3 1.44 m; vol eter specific radioactivity, this allowed long- = = mm PVC set on a steel frame. It consisted duration labelling under steady-state con- of 2 halves hanging from a portable sup- ditions (Warembourg and Paul, 1973; port, which could be joined together via Webb, 1975; Geiger and Shieh, 1987; rubber joints. Airtightness was achieved by Smith and Paul, 1988). On the other hand, compressing the joints with screws. There when all the 14 was injected at the be- 2 CO was an opening in the cylinder bottom for ginning of the experiment and the conti- the stem, and airtightness was achieved nously injected CO was only 12 (Han- 2 CO 2 through plastic film junction and sealing as and Beck, 1990), this allowed a sen for the small chamber. precise calculation of the total 14 taken C up by the plant under conditions of mini- Despite ample precautions, we could mum perturbation. This was the basis of not assume that airtightness was absolute, the system we designed for the labelling of either for the large or for the small cham- whole trees. ber, due to preexisting small holes in the plastic film parts and/or leaks induced by differential thermal dilatation of the rigid DESCRIPTION AND PERFORMANCES parts of the chambers. No precise meas- OF THE LABELLING SYSTEM urement of leakage was made for the chambers but an estimate of the upper lim- it of total radioactivity lost due to these leaks The labelling system is composed of an can be given, assuming equipressure be- assimilation chamber and an electronical- tween the inside of the chamber and atmos- ly-controled CO injection device allowing 2 phere, when thermal dilatation of the air in continuous regulation of the inside CO2 the chamber occurs. In such conditions, an concentration (fig 1).Ithas been used on increase in temperature of 15-20°C during 3-yr-old grafted walnut trees with 1 trunk the course of feeding (cf fig 2), could lead to and 4/5 branches and a total leaf area of= a leakage of 6% of the air in the chamber; 1.7 m The trees were grown outdoors in . 2 we can expect a lesser relative loss of total 200-I containers. radioactivity (= 3%) since the specific radio- activity of the CO decreases continuously 2 The assimilation chambers during the feeding period. In both chambers the atmosphere was homogeneized by a fan, and there were 4 Two chambers were used alternatively, al- openings for the in- and outlet tubes of 2 lowing either local labelling of a branch closed circuits: one for CO level monitor- 2 section or global labelling of the whole ing and one for CO injection (fig 1).The 2 above-ground part.
  7. made of polyamide (Rilsan), 14 had been assimilated. Provided the 2 CO tubing was which CO level in the chamber remained chosen for its impermeability to total 2 was constant, the radioactivity still present at . 2 CO any time could be easily calculated: CO injection 2 R being the radioactivity still present, R the i Total amount of RA required per tree initial radioactivity injected, n the total amount of CO injected from cold carbonate 2 The total amount of radioactivity required since the beginning, and N the amount of was determined according to the sensitivity CO constantly present in the chamber. 2 of the least sensitive method used for 14 C From this equation it can be derived that measurement. Two methods were used in the radioactivity was exhausted by 99.3% the experiment: liquid scintillation for solu- 5N, which was achieved within 4- for n = ble compounds, and argon-methane flow 5 h in the large chamber, or < 1 h in the counting for insoluble compounds. The small chamber. less sensitive method is the latter, which The CO level was continuously meas- 2 was used in a previous experiment on wal- ured with an IRGA (Mark III, ADC, UK). A nut seedlings (Lacointe, 1989). This study data processor system (Micromac 4000, showed that an accurate measurement of Analog Devices, USA) connected to a mi- the RA incorporated in all organs (includ- crocomputer allowed the recording of 1 &mu;Ci new spring organs) required ing = physical parameters such as air tempera- (37 kBq) 14 fed per g plant DM as an 2 CO ture, incident PAR (Daudet, 1987) and order of magnitude. Since the DM weight monitoring of a magnetic valve. Whenever 2 kg, the amount injected was deter- was = the CO level dropped below 350 vpm, the 2 mined as 74 MBq for each tree. valve opened and an unlabelled sodium carbonate solution was dropped into the Control of acid, injecting cold CO into the chamber. CO injection 2 2 The molarity of the carbonate solution was 1 M for the large and 0.125 M for the small CO was generated through dropping a so- 2 chamber. dium carbonate solution from a burette into excess 33% sulfuric acid. The efficiency of An example of the time course of CO 2 CO evolution was improved by a magnet- 2 concentration during feeding is given in fig- ic stirrer and by forcing the chamber at- ure 3. One can see that the stability of CO 2 mosphere through the reacting solution was correct during most of the feeding pe- with a pump. riod. Some dysfunction could occur due to poor stability of the flow of the sodium car- The first the of all the injection step was bonate solution through the precision cock C-carbonate 14 which induced only slight a (see fig 1). increase in the total CO concentration 2 within the chamber (< 0.1 % for the large, 6% for the small chamber) due to the high Variation of air temperature specific radioactivity of the carbonate (1.85 GBq/mmol ref CMM 54, CEA, France). The procedure then consisted of maintaining In order to limit temperature increase, the total CO concentration between 330 performed in the morning, 2 labellings were and 360 vpm until 99% of the injected and lasted 5 h. Figure 2 shows the <
  8. tion around 350 vpm (parts with positive slopes). This indicates that no major distur- bance of photosynthesis and presumably of the general plant physiology occurred. In fact, the photosynthesis of walnut trees appears quite resistant to high tempera- ture; nevertheless, negative values of net assimilation were observed one day when the inside temperature reached 45°C. increase of temperature inside the large Validating the quantitative aspects chamber during a labelling day with very of thefeedings high solar irradiance. Although the air temperature reached 38°C inside the Two indirect means could be used to esti- chamber at the end of the feeding period mate the amount of total radioactivity actu- (> 12°C increase with respect to the ambi- ally absorbed by the trees and compare it ent temperature), there was no significant to the theoretical value as given in equa- alteration in photosynthesis as can be tion [1]: seen from figure 3: the assimilation rate, measuring the radioactivity that re- as derived from the parts with negative - mained in the atmosphere of the chamber slopes, remained relatively regular and in the different vessels at the end of throughout the labelling procedure. So did the feeding period. At the end of a few lo- the kinetics of cold CO injection operated 2 cal labellings, which according to equation by the system to keep the CO concentra- 2
  9. but it can also be stopped at any time [1] were > 99.5% complete, the chamber , 2 CO atmosphere was forced into a KOH solu- (eg in case of excessive temperature in- tion, then an aliquot was evaporated and crease) allowing the accurate amount of assessed for radioactivity in an argon- C 14 taken up to be determined; methane flow counter (NU 20, Numelec, a CO level constantly maintained at its 2 - France). This method, although rapid, is natural value, thus limiting changes in the not accurate for relatively concentrated so- within-leaf partitioning between sucrose lutions; however, it provides an order of and starch which could affect export dy- magnitude. About 0.25% of the initially in- namics. jected 14 was still in the chamber, 2 CO This system allowed us to investigate the which was in accordance with the theoreti- and chemical partitioning of assimi- spatial cal value. The reaction vessel also re- lated carbon in walnut trees in August and tained a slight but measurable radioactivi- October, when the trees exhibited contrast- ty:&ap; 0.3%, which stresses the importance ing daily net assimilation rates (Kajji, 1992). of efficient stirring; We also obtained interesting results on the sampling the tree soon after feeding in - long-term fate of the labelled carbon re- order to estimate the total radioactivity in- serves, eg a differential mobilization rate of corporated. Seven h after local labelling, in the starch reserves according to their for- August 1989, 2 trees were harvested, fixed mation time (Lacointe et al, 1993). in liquid nitrogen and freeze-dried. After For the sake of simplicity tempera- no grinding, their total radioactivity was meas- included in our system regulation ture was ured with the gas-flow counter: respective- and we assumed that in most cases this ly, 88% and 91 % of the injected radioactivi- lack of thermal regulation had no effect on ty were recovered. The missing 10% was the process of redistribution of assimilates attributed to respiratory losses, although within the trees. Nevertheless, it is clear an experimental error of a few percent in that incorporating such an improvement in assessing the total radioactivity of an en- the system would be of interest, as it would tire tree cannot be discarded. permit long-term labelling experiments or/ and feeding during the warmest days. CONCLUSION ACKNOWLEDGMENT Use and performances of the system The authors are most grateful to M Crocombette for providing technical assistance. The labelling system described exhibits 3 characteristics which have already been separately described by other workers, as REFERENCES mentioned above, but not together: a large assimilation chamber (> 3 m al- ) 3 - Balatinecz JJ, Forward DF, Bidwell RGS (1966) lowing the labelling of large trees, namely Distribution of photoassimilated 14 in young C grafted walnuts bearing some fruit. It re- jack pine seedlings. Can J Bot 44, 362-364 mains handy enough to allow the labelling Daudet FA (1987) Un système simple pour la of a different tree every day; mesure in situ des échanges gazeux de cou- quantitative labelling. This can guarantee verts végétaux de quelques mètres carrés de - the complete assimilation of the injected surface foliaire. Agronomie 7, 133-139
  10. Physiology (E Dreyer, G In: Forest Tree Dogniaux R, Nisen A (1975) Traité de Aussenac, M Bonnet-Masimbert, P Dizengre- l’Eclairage Naturel des Serres et Abris pour mel, JM Favre, JP Garrec, F Le Tacon, F Végétaux. Institut Royal Météorologique, Brussels Martin, eds). Ann Sci For 46 (suppl), 832s- 836s BR (1991) Regulation of car- Geiger DR, Fondy bon allocation and partitioning: status and re- Lacointe A, Kajji A, Daudet FA, Archer P, Fros- sard JS (1993) Mobilization of carbon re- search agenda. In: Recent Advances in serves in young walnut trees. Bull Soc Bot Fr Phloem Transport and Assimilate Compart- mentation (JL Bonnemain, S Delrot, WJ Lucas, Act Bot Gall 140 (in press) J Dainty, eds) Ouest Editions, Nantes, 1-9 R (1987) Distribution of leaf Langenfeld-Heyser assimilates in the stem of Picea abies L. Shieh WJ (1988) Analysing parti- Geiger DR, tioning of recently fixed and of reserve car- Trees 1, 102-109 bon in reproductive Phaseolus vulgaris L Lister GR, Krotkov G, Nelson CD (1961) A plants. Plant Cell Environ 11, 777-783 closed-circuit apparatus with an infrared CO 2 Glerum C, Balatinecz JJ (1980) Formation and analyzer and a Geiger tube for continuous measurement of CO exchange in photosyn- distribution of food reserves during autumn 2 thesis and respiration. Can J Bot 39, 581-591 and their subsequent utilization in jack pine. Can J Bot 58, 40-54 (1985) Translocation and distribution of Palit P Hansen P (1967) 14 studies on apple trees. I. C C-labelled 14 assimilate associated with growth of jute (Corchorus olitorius L). Aust J The effect of the fruit on the translocation and distribution of photosynthates. Physiol Plant Physiol 527-534 12, Plant 20, 382-391 Schneider A, Schmitz K (1989) Seasonal course of translocation and distribution of 14 C- Hansen J, Beck E (1990) The fate and path of labelled photoassimilate in young trees of La- assimilation products in the stem of 8-year- old Scots pine (Pinus sylvestris L) trees. rix decidua Mill. Trees 3, 185-191 Trees 4, 16-21 Smith JL, Paul EA (1988) Use of an in situ label- (1992) Gestion du carbone chez le jeune A ling technique for the determination of sea- Kajji sonal 14 distribution in Ponderosa pine. C noyer. Doctoral thesis, Université Blaise Pas- cal, Clermont-Ferrand Plant Soil 106, 221-229 Kuhn U, Beck E (1987) Conductance of needle Warembourg FR, Paul EA (1973) The use of and twig axis phloem of damaged and intact 14 canopy techniques for measuring car- 2 CO bon transfer through the plant soil system. Norway spruce (Picea abies (L) Karst) as in- vestigated by application of in situ. Trees C 14 Plant Soil 38, 331-345 1, 207-214 Webb WL (1975) The distribution of photoassim- Lacointe A (1989) Assimilate allocation and car- ilated carbon and the growth of Douglas fir seedlings. Can J For Res 5, 68-72 bon reserves in Juglans regia L seedlings.
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