Improvement of nitrogen fixation in

Acacia mangiumthrough inoculation with rhizobium

A. GALIANA 1, *, G. M. GNAHOUA2, J. CHAUMONT1, D. LESUEUR1, Y. PRIN1 and B. MALLET1

1

CIRAD-Forêt, Campus international de Baillarguet, Montferrier-Sur-Lez, BP 5035, 34032 Montpellier, Cedex 1, France; 2 Institut des Forêts-Département de la Foresterie(IDEFOR/DFO), 08BP33 Abidjan 08, Côte d’Ivoire (*Author for Correspondence: E-mail:galiana@cirad.fr)

Key words: fallow, humid tropics, nodules, soil fertility, symbiotic association

Abstract. Acacia mangium, a N2-fixing tree legume, has become a major plantation tree speciesin the tropical humid and sub-humid zones. In addition to being a major pulp-wood producer,the tree has a good potential to restore soil fertility as a fallow species in agroforestry systems,and as a fuel species. In this paper, we report an overview of the results from several rhizo-bium inoculation field trials in different edaphic and ecological conditions, conducted by theCIRAD-Forêt (The Forest Program of Centre de Coopération Internationale en RechercheAgronomique pour le Développement) in partnership with national research organizations ofvarious countries of the humid and sub-humid lowlands of West Africa and Cook Islands.Rhizobium inoculation had a positive effect on tree growth up to 39 months after tree planting.Immunological identification of the Bradyrhizobium strains present in the nodules confirmedthe persistence of the more efficient introduced strains up to 42 months after transfer of theinoculated trees to the field. In Côte d’Ivoire, nitrogen derived from atmospheric N2 fixedsymbiotically by A. mangium was 50% in the whole trial and up to 90% in plots with lessfertile soils when the trees were inoculated with an efficient strain.

Introduction

The increasing introduction of Acacia mangium in industrial plantations duringthe last decade is largely due to its good silvicultural potential and its abilityto grow on degraded soils, particularly nitrogen-depleted ones. Large-scaleplantations of A. mangium have been successfully established in tropicalhumid zones, especially in eastern Malaysia (Sabah) and in Indonesia wheremost of them were set up on poor soils and grasslands infested by a noxiousweed, Imperata cylindrica. In 1985, 55,000 hectares were already planted inSabah (Udarbe and Hepburn, 1987). To a lesser extent, expansion of Acaciaplantation in the Philippines, Papua-New Guinea, China and in tropical humidregions of Africa is also documented (National Academy of Science, 1983).The introduction of the species into agroforestry systems has been reportedto be promising in the humid and sub-humid tropics of Asia and Africa (DeTaffin et al., 1991; Dupuy and N’Guessan Kanga, 1991). Due to the increasingimportance of the species, CIRAD-Forêt initiated a research program on theA. mangium-rhizobium symbiosis in 1986. The program, BSFT (Biotechnology

Agroforestry Systems 40: 297–307, 1998. 1998 Kluwer Academic Publishers. Printed in the Netherlands.

Laboratory on Tropical Forest Symbioses, common laboratory betweenCIRAD-Forêt and ORSTOM, Nogent-sur-Marne, France) in association withseveral countries mainly of the West Africa humid lowlands, aims at studyingthe Acacia-rhizobium association in order to increase the productivity of thespecies through nitrogen fixation. Our experience in this domain over thelast decade is summarized below.

Symbiotic characteristics of A. mangium

At the inception of the study in 1986, only one A. mangium strain of rhizo-bium was available. The initial aim of the study was thus to isolate a largenumber of strains from A. mangium root nodules collected from a range oftropical countries. A. mangium was found to nodulate spontaneously in itsnative area (North Queensland, Australia) and in countries to which it hadbeen introduced. About 50 strains were isolated by the BSFT from the nodulescollected in the native area of the species (Souvannavong and Crémière, 1986)and range of other countries (West Africa, French Guyana, China andMalaysia). All these strains were identified as slow-growing Bradyrhizobiumstrains. The host spectrum of these strains was established under controlledconditions by testing their infectivity (ability to form nodules) and effectivity(ability to fix nitrogen) on A. mangium and A.auriculiformis. Prior resultsshowed that A. mangium was a specific host since the effectiveness of thedifferent strains varied considerably according to their origin compared tothe non-specific hosts like Acacia auriculiformis which nodulate and fixnitrogen regardless of the strain (Galiana et al., 1990). Moreover, wheninoculated to A. mangium, the strains originating from Australia were moreefficient than those from other origins or the collection of strains isolated fromother host species.

Effect of inoculation on Acacia mangium growth

The efficiency of the different rhizobium strains was tested in field experi-ments conducted in three countries – Côte d’Ivoire, Cook Islands and Benin.The trial locations differ in both climatic – annual rainfall ranging from 1500mm to 2500 mm – and edaphic – soil types ranging from sandy to clay aswell as acid to neutral – conditions. The results showed that among the fivestrains tested, the Bradyrhizobium strains originating from Australia were themost efficient. Inoculating seedlings in the nursery with Aust 13c and Aust11c had a positive and significant effect on plant height and basal areadevelopment, up to 39 months after transplanting in the field. This was par-ticularly the case in the trials set up at Port-Bouët in Côte d’Ivoire, at Semein Benin and at Turoa and Hospital Hill in Cook Islands. The data obtainedfrom greenhouse experiments and in vitro conditions in laboratory were in

298

agreement with that obtained under field conditions. This observation waswell illustrated in the trial conducted at Seme in Benin. The ranking of theseven Bradyrhizobium strains according to their efficiency on plant shootheight, shoot dry weight, number and dry weight of root nodules obtained atthree months after sowing the seeds in the nursery, with or without a pre-liminary disinfection of the nursery soil was the same as that obtained incontrolled in vitro and greenhouse conditions with plants cultured on nitrogen-free medium (Souvannavong and Galiana, 1991).

In the trial set up at Anguededou in Côte d’Ivoire, the positive and sig-nificant effect of inoculation on tree height observed four months after trans-planting in the field did not persist at 21 month after transplanting. However,the effect on basal area development was still significant (Table 1). Anotherexperiment was conducted at Anguededou in Côte d’Ivoire to test the effectof interaction between different rhizobium strains and four different A.mangium provenances on tree growth. The result showed a significant inter-action effect. The Oriomo provenance (originating from Papua New Guinea)had a mean height (13 m) that was 25% greater than that of the other prove-nances (San Pedro-Côte d’Ivoire, Rex Range-Australia and Piru Ceram-Indonesia) after 19 months of growth in the field (results per provenance notdetailed in Table 1). However, some strain by provenance combinations suchas AG3

× San Pedro, RMBY × Rex Range and RMBY × Piru Ceram had asignificant (P < 0.05) effect on tree height, with performances similar to thecombinations involving the Oriomo provenance. By contrast, other combina-tions such as AG3 × Oriomo had a negative effect on tree growth.

Identification and survival of Bradyrhizobium strains introduced infield experiments

In order to confirm the validity of the in situ inoculation experiments and thepositive effect of certain strains on tree growth, we collected root nodulesat a soil depth of 0–15 cm in the field trials established in Côte d’Ivoire(Anguededou and Port-Bouët sites). The sampling was done at 23 and 42months after transplanting at the Anguededou site and at 19 months for thePort-Bouët site. The purpose was to study the survival of the introduced strainsand their competitive ability against native rhizobium strains. The results ofidentification of the introduced strains with serological typing (indirectimmunofluorescence method described by Somasegaran and Hoben, 1985)showed that the most efficient strain, i.e. Aust 13c, persisted in 100% of thecollected nodules up to two years after transplanting of the inoculated trees(Galiana et al., 1994).

At Anguededou station, the majority of the collected nodules contained theAust 13c strain at 23 and 42 months after tree transplanting. This was the casein all blocks for all A. mangium provenances analyzed (Table 2). All thenodules collected from trees inoculated with Aust 13c strain exclusively

299

300

Table 1. Effect of rhizobium inoculation on Acacia mangium growth: results obtained from several inoculation field trials set up by the CIRAD-Forêtin humid and sub-humid tropics of West Africa and Cook islands.a

Location of Area of Date of Plant age at Rhizobium Disinfection Heightc Basal aread

trials trial planting observation strains tested of nursery (% Increment/ (% Inc./control)(month/year) (months) soilb control)

Côte D’IvoireAnguededou 1.07 ha 3/88 04 Aust 13c + 0+99% 000–

(study of the interaction TAL 72 + +124% 000–provenance × strain) RMBY + +106% 000–

AG3 + 0+82% 000–Control + 0+28% 000–Control – 000– 000–

21 Aust 13c + 00+4% 0+24%TAL 72 + 00+3% 0+23%RMBY + 00+8% 0+12%AG3 + 00–5% 0+15%Control + 00–1% 0+13%Control – 0 (10.90 m) 000–

Abidjan (nursery) 4/90 42 PBG3 + 00+7% 000–(study of the interaction Aust 13c + 00+3% 000–strain × soil type) TAL 582 + 00+3% 000–

Control + 000– 000–

Port-Bouët 0.78 ha 4/90 20 Aust 13c + 0+15% 0+20%CB 756 + 0000.1% 00–2%Control + 00 (5.37 m) 000–

301

BENIN Seme (nursery) 3/89 03 Aust 13c +/– 0+41% 000–Aust 11c +/– 0+30% 000–RMBY +/– 0+14% 000–AG 3 +/– 00+1% 000–PBG 3 +/– 00+9% 000–TAL 72 +/– 00–6% 000–CB 756 +/– 00–6% 000–Control +/– 000– 000–

Seme 1.56 ha 6/89 20 Aust 11c – 0+28% 000–Aust 11c + 00–9% 000–Control – 00 (2.58 m) 000–Aust 13c + 00+5% 000–Control + 00 (2.38 m) 000–CB 756 + 00+9% 000–

Cook IslandsTuroa 590 m2 7/88 39 Aust 11c – 00+7% 0+30%

AG 3 – 0+11% 0+18%Control – 00 (7.87 m) 000–

Hospital Hill 590 m2 7/88 39 Aust 11c – 0+37% +128%AG 3 – 0+16% 0+40%Control – 00 (4.90 m) 000–

a Sources: Ehrhart (1991); Galiana (1990); Galiana et al. (1994); Lesueur et al. (1994); Mallet and Gnahoua (1989); Messant (1991).b + = soil disinfected, – = soil not disinfected, +/- = disinfected and not disinfected soil treatments combined, ( ) = Height of uninoculated controltrees.c Percentages shown in bold characters refer to values significantly higher than those of the control treatments. d Control = Uninoculated control trees.

302Table 2. Nodule occupancy of inoculated and uninoculated trees in field inoculation trial at Anguededou, Côte d’Ivoire.

Months after tree Block Tree Inoculated strain Number of nodules reacting positively with antiseruma

transplanting provenanceAust 13c RMBY TAL 72 AG3

23 I San-Pedro Aust 13c 10 00 00 00RMBY 06 04 05 00TAL 72 09 00 00 00AG3 10 00 00 00Uninoculated Db 09 00 00 00Uninoculated NDc 09 00 00 00

42 I Rex range Aust 13c 10 ndd nd ndRMBY 10 02 02 00TAL 72 10 01 00 02AG3 10 00 01 00Uninoculated D nd nd nd ndUninoculated ND nd nd nd nd

42 II Rex range Aust 13c 10 01 00 00RMBY 10 00 00 00TAL 72 07 00 00 00AG3 10 00 00 00Uninoculated D 09 00 00 00Uninoculated ND 07 00 00 00

a Nodules were analyzed by the indirect immunofluorescence technique (Somasegaran and Hoben, 1985); 10 nodules per tree were tested and eachnodule was analyzed with each of the four antisera.b Uninoculated D; uninoculated control trees initially grown at the nursery on soil disinfected with metam sodium.c Uninoculated ND; uninoculated control trees initially grown at the nursery on non disinfected soil; trees inoculated with the four Bradyrhizobiumstrains were grown on soil initially disinfected with metam sodium.d nd = not determined.

contained Aust 13c and no native strain was detected. Among the other threeintroduced strains, only RMBY strain was recovered at a significant rate, with40% of the nodules exclusively containing the RMBY inoculant strain at 23months after field transplanting. All the other plots that were inoculated withTAL 72 and AG3 strains and the plots with uninoculated control trees werebroadly contaminated by Aust 13c strain in all the blocks for all A. mangiumprovenances that were analyzed – 70 to 100% of the nodules contained Aust13c from each randomly sampled tree. The overall contamination andnodulation of trees by Aust 13c in this experiment could explain the gradualreduction in differences between treatments with time as the positive effectof inoculation on height growth observed at 4 months was no longer visible19 months after tree transplantation.

In the Port-Bouët field experiment, the immunological identification ofstrains in the nodules also showed the persistence of Aust 13c at 19 monthsafter transplanting of the inoculated trees in all the blocks for all the treesanalyzed (Table 3). All the nodules collected from the trees inoculated withAust 13c reacted positively with the homologous antiserum. All of theobserved bacteroids under UV microscope were identified as Aust 13c strain.

303

Table 3. Nodule occupancy of inoculated and uninoculated trees in field inoculation trial atPort-Bouët, Côte d’Ivoire, after 19 months of field growth.

Inoculated strain Block Tree no. Number of nodules reacting positively with antiseruma

Aust 13c CB 756 PBG 3

Aust 13c I 1 10 0 002 10 0 00

II 1 10 0 002 10 0 00

III 1 10 0 002 ndb 0 00

CB 756 I 1 00 1 012 00 0 00

II 1 00 0 002 02 0 00

III 1 02 0 002 09 0 00

Uninoculated I 1 00 0 002 01 0 00

II 1 01 2 002 00 2 00

III 1 06 0 002 02 0 nd

a Nodules were analyzed by the indirect immunofluorescence technique: 10 nodules per treewere tested and each nodule was analyzed with each of the three antisera.b nd = not determined.

The two plots of block III containing trees inoculated with the CB756 strainand uninoculated control, respectively, were largely contaminated by Aust13c. By contrast, CB756 was not identified in the nodules collected from treesinoculated with the corresponding strain. However, CB 756 was found in fewnodules from two uninoculated control trees located in block II. All othernodules collected from trees inoculated with CB 756 or those not inoculatedcontained a majority of indigenous strains. At Port-Bouët, contrary to the trialat Anguededou, the plots inoculated with CB 756 and the uninoculatedcontrols were still slightly contaminated by Aust 13c that occurred in theadjacent plots after 19 months. This is probably due to the fact that, theadjacent plots at Port-Bouët were separated from each other by three to fiverows of border Eucalyptus urophylla whereas a single row of A. mangiumseparated the different ‘strain’ treatments in the Anguededou field trial.Consequently, the positive effect of inoculation with Aust 13c on tree growthcould still persist after 19 months at Port-Bouët. This suggests that indige-nous rhizobium strains are less efficient than the introduced Aust 13c strain.

Estimation of nitrogen fixed by Acacia mangium in plantation

The percentage of nitrogen derived from atmospheric N2 (Ndfa %) and fixedby A. mangium was evaluated in the rhizobium inoculation field trial set upat Port-Bouët that is reported above (see Tables 1 and 2). The treatmentswere trees inoculated with Aust 13c, CB 756 and control (uninoculated trees).Each treatment was replicated three times in 3 blocks in a RandomizedComplete Block Design. The Ndfa% was calculated following the 15N naturalabundance method described by Amarger et al. (1977) and Bardin et al. (1977).Eucalyptus (Eucalyptus urophylla) was included in the trial both as a borderrow to avoid cross contamination of Bradyrhizobium species strains betweenplots and as a non-fixing reference plant for the determination of Ndfa%.

Table 4 shows a positive and highly significant effect (P < 0.05) of inoc-ulation with Aust13c on tree growth at 19 months after transplanting in thefield. The height of trees inoculated with Aust 13c was about 10% greaterthan that of the trees inoculated with the CB 756 strain and the uninoculatedones. Similarly, the diameter at ground level of trees inoculated with Aust 13cwas about 15% greater than that measured in the two other ‘strain’ treatmentplots. Furthermore, the growth of the trees inoculated with Aust 13c was thegreatest compared to that of the trees in the other treatment plots in each ofthe three blocks. The block effect on tree growth was also highly significant(P < 0.01 for height and P < 0.05 for diameter, respectively). Tree heightwas greater in block I than in blocks II and III by 6.7% and 15.8%, respec-tively whereas tree diameter was greater in block II than in blocks I and IIIby 10% and 18.3%, respectively.

The percentage of nitrogen derived from atmospheric N2 (Ndfa %) con-tained in A. mangium leaves at 19 months after field planting varied from 19.4

304

to 90.6% depending on the different blocks and the Bradyrhizobium straintreatments. The trees inoculated with Aust 13c strain had Ndfa % slightlyhigher (61.7%) than that of the trees inoculated with CB 756 strain (54.9%)and the uninoculated trees (41.5%). However, the difference was not statisti-cally significant at P = 0.05. Nitrogen fixation was markedly enhanced onthe N-deficient blocks (Blocks II and III). The Ndfa % of the A. mangium inblocks II (64.4%) and III (66.5%) was 2.4 times higher than that of the treesin Block I (27.1%). The non-significant differences were due to the largevariation in Ndfa% values within each plot as shown by the relatively highcoefficients of variation (Galiana et al., 1996). This could be due to theheterogeneity of the soils and/or high genetic variability within the A. mangiumprovenances as in the E. urophylla that was used as reference tree to calcu-late the Ndfa%.

Although the A. mangium inoculated with Aust 13c fixed more nitrogenand had a better growth than the A. mangium inoculated with CB 756 andthe uninoculated ones, in each of the three blocks of the trial, there was nosignificant correlation between Ndfa % and the growth parameters – heightand diameter – measured for A. mangium. By contrast, we observed highlypositive and significant correlation coefficients between A. mangium heightand the concentration of different soil chemical properties including total N(r = 0.85 at P ≤ 0.005), nitrate-N (r = 0.88 at P < 0.005), available P (Olsenmethod) (r = 0.86 at P ≤ 0.005), and other soil properties such as organic Cor the percentage of organic matter. Although nitrogen fixation by legumi-nous plants is known to be inhibited by high concentration of combinednitrogen, especially nitrate-N (Vessey and Waterer, 1982) in the soil, corre-lation between the soil nutrients and Ndfa % was not statistically significant.

305

Table 4. Effects of ‘Bradyrhizobium strain’ and ‘block’ factors on tree height, diameter andpercentage of nitrogen derived from nitrogen fixation in Acacia mangium, 19 months after treetransplantion at Port-Bouët, Côte d’Ivoire.

Height Diameter at ground Nitrogen fixed(m. tree–1) level (cm. tree–1) (%)

Strain effecta

Aust 13c 5.92 a 11.1 a 61.7CB 756 5.34 b 09.6 b 54.9Uninoculated 5.37 b 09.7 b 41.5

Block effectb

Block I 5.93 a 10.0 b 27.1Block II 5.56 b 11.0 a 64.4Block III 5.12 c 09.3 c 66.5

In each column, the values (means obtained from 90 trees for height and diameter and from 24trees for nitrogen fixed) followed by a same letter are, according to Newman and Keuls test(Dagnélie, 1969) not significantly different at P = 0.01.a All ‘block’ treatments combined.b All ‘strain’ treatments combined.

Ndfa % was negatively correlated (r = –0.72 at P ≤ 0.05) to height anddiameter of the intercalary E. urophylla close to the A. mangium plots. Theeucalyptus, which does not fix N2 but only assimilates mineral N is knownto be a reliable indicator of soil fertility. This implies that nitrogen fixationby A. mangium is inversely proportional to the soil fertility status as in a givenplot the A. mangium and the adjacent eucalyptus were planted on soils of thesame soil fertility conditions. The absence of correlation between Ndfa % andgrowth parameters measured in A. mangium thus suggests the possibility ofsimultaneous action and the interdependency of the N2-fixing and N-assimi-lating processes – complementary and synergistic – during the 19 months ofgrowth.

The result showed that A. mangium had a high nitrogen-fixing ability asNdfa % reached more than 50% over the whole trial in a soil which is notparticularly poor in nitrogen. This N2-fixing potential was especially high inthe less fertile plots of the trial, located in block III, and when the trees wereinoculated with the most efficient strain Aust 13c as Ndfa % reached 90%when these two conditions were fulfilled.

Conclusion

All the field trials conducted in different countries and on different soil typesshowed a positive effect of inoculation on tree growth with A. mangiumrhizobium strains isolated from the natural distribution area of the host species(Australia). Moreover, this positive effect of inoculation was maintained aftertwo to three years of planting the trees in the field. Immunological identifi-cation of the rhizobium strains that were present in the nodules confirmedthe persistence and the high competitivity of the most efficient introducedstrains (originating from Australia) two to three years and half after inocula-tion. The studies showed in particular the high N2-fixing potential of A.mangium. The percentage of nitrogen derived from atmospheric N2 fixed byA. mangium and then from a symbiotic origin was 50% over the whole trialand reached 90% on the less fertile plots and when trees were inoculatedwith an efficient strain. Further research is necessary to quantify the N fluxesand N input to the soil with particular reference to N derived from symbioticN2 fixation after litter decomposition.

References

Amarger N, Mariotti A and Mariotti F (1977) Essai d’estimation du taux d’azote fixé symbio-tiquement chez le lupin par le traçage isotopique naturel (15N). Comptes Rendus del’Académie des Sciences, Série D 284: 2179–2182

Bardin R, Domenach AM and Chalamet A (1977) Rapports isotopiques naturels de l’azote. II.Application à la mesure de la fixation symbiotique de l’azote in situ. Revue d’Ecologie etde Biologie des Sols 14: 395–402

306

Dagnélie P (1969) Théorie et méthodes statistiques. Gembloux, Belgique, Duculot. Tomes I etII

De Taffin G, Zakra N, Pomier M, Braconnier S and Weaver RW (1991) Search for a stablecropping system combining coconut and nitrogen-fixing trees. Oléagineux 46: 489–500

Dupuy B and N’Guessan Kanga A (1991) Utilisation des acacias pour régénérer les anciennescocoteraies. Bois et Forêts des Tropiques 230: 15–29

Ehrhart Y (1991) Maintien de l’environnement et production de bois dans le Pacifique Sud.Six-monthly activity report, CTFT, 104 pp

Galiana A (1990) La symbiose Acacia mangium-rhizobium. Centre de coopération internationalen Recherche Agronomique por le Développement-Centre Technique Forestier tropical,nogent-surmarne, france, 246 pp

Galiana A, Chaumont J, Diem HG and Dommergues YR (1990) Nitrogen fixation potential ofAcacia mangium and Acacia auriculiformis seedlings inoculated with Bradyrhizobium andRhizobium spp. Biology and Fertility of Soils 9: 261–267

Galiana A, N’Guessan Kanga A, Gnahoua GM, Balle P, Dupuy B, Domenach AM and MalletB (1996) Fixation de l’azote chez Acacia mangium en plantation. Bois et Forêts desTropiques, 249: 51–62

Galiana A, Prin Y, Mallet B, Gnahoua GM, Poitel M and Diem HG (1994) Inoculation of Acaciamangium with alginate beads containing selected Bradyrhizobium strains under fieldconditions: long-term effect on plant growth and persistence of the introduced strains insoil. Appl Environ Microbiol 60: 3974–3980

Lesueur D, Yacouba T, Galiana A and Mallet B (1994) Croissance et Nodulation d’A. mangium.Bois et Forêts des Tropiques 241: 29–38

Mallet B and Gnahoua G (1989) Etude comparative de l’effet d’inoculation de différentes souchesde rhizobium sur diverses provenances d’A. mangium et A. auriculiformis en pépinière etplantation. Internal report, CTFT-Côte d’Ivoire, 20 pp

Messant D (1991) Rapport annuel campagne 1990. Internal report, Unité de recherchesForestières, Cotonou, Bénin, 25 pp

National Academy of Sciences (1983) In Mangium and other fast-growing Acacias for the humidtropics, pp. 18–19. US National Academy Press, Washington, DC, USA

Somasegaran P and Hoben J (1985) Methods in Legume-Rhizobium Technology, University ofHawaii, NifTAL and Mircen Project, Paia

Souvannavong O and Crémière L (1986) Récolte de provenances d’acacias dans le nord duQueensland (Australie). Internal report, Centre Technique Forestier Tropical, Nogent-Sur-Marne, France, 30 pp

Souvannavong O and Galiana A (1991) Acacia mangium-rhizobium symbiosis: selection andpropagation of the host plant and the micro-organism. In: Taylor DA et Mac Dicken KG(éd) Research on Multipurpose Tree Species in Asia, pp 216–222. Winrock InternationalInstitute for Agricultural Development, Bangkok, Thaïland

Udarbe MP and Hepburn AJ (1987) Development of Acacia mangium as a plantation speciesin Sabah. In: Turnbull JW (ed) Australian Acacias in Developing Countries, ACIARProceedings No. 16, pp. 157–159. Australian Center for International Agricultural Research,Canberra, Australia

Vessey JK and Waterer J (1982) In search of the mechanism of nitrate inhibition of nitrogenaseactivity in legume nodules: recent developments. Physiologia Plantarum 84: 171–176

307