Search

A field manipulation study was established to demonstrate effects of simulated wet N and S deposition on a young (planted 1986) stand of Sitka spruce growing on a predominantly organic soil in an area of low (8–10 kg N ha-1 yr-1) background N deposition in the Scottish borders. From 1996, treatments (six) were applied to the canopies of ten-tree plots in each of four blocks. N was provided as NH4NO3, either with H2SO4 (pH 2.5) at 48 or 96 kg N ha-1 yr-1 inputs or without, at 48 kg N ha-1 yr-1 along with wet (rain water) and dry controls (scaffolding) and a S treatment (Na2SO4). Positive responses (+ >20% over 5 years) with respect to stem area increment were measured in response to N inputs, irrespective of whether acid was included. The positive response to N was not dose related and was achieved against falling base cation concentrations in the foliage, particularly with respect to K. The results suggest young trees are able to buffer the low nutrient levels and produce new growth when there is sufficient N. Inputs of 96 kg N ha-1 yr-1, in addition to ambient N inputs, on this site exceeded tree demand resulting in elevated foliar N, N2O losses and measurable soil water N. These excessive N inputs did not reduce stem area growth. Keywords: acid, canopy application, nitrogen, acid organic soil, simulated wet deposition, soil water, sulphur, young Sitka spruce

With tuberculosis the leading bacterial killer worldwide and other mycobacterial diseases on the increase, the search for new antimycobacterial agents is timely. In this study, extracts from plants, lichens and fungal endophytes of Scottish provenance were screened for activity against Mycobacterium aurum and M. tuberculosis H37Rv. The best activity against M. aurum was observed for extracts of Juniperus communis roots and Cladonia arbuscula (MIC = 4 µg/mL), and a fungal endophyte isolated from Vaccinium myrtillus (MIC = 8 µg/mL). The best activity against M. tuberculosis was observed for extracts of C. arbuscula, Empetrum nigrum, J. communis roots, Calluna vulgaris aerial parts, Myrica gale roots and stems (93 to 99% inhibition at 100 µg/mL). Potent antitubercular activity (90 to 96% inhibition at 100 µg/mL) was also observed for the ethanol extracts of Xerocomus badius, Chalciporus piperatus, Suillus luteus and of endophytes isolated from C. vulgaris, E. nigrum, Vaccinium vitis-idaea and V. myrtillus. The results obtained this study provide, in part, some scientific basis for the traditional use of some of the selected plants in the treatment of tuberculosis. They also indicate that fungal endophytes recovered from Scottish plants are a source of antimycobacterial agents worthy of further investigation

This paper describes a field manipulation experiment where the effects of a simulated decline in acidified S inputs on the fate of N on Sitka spruce growing on an organo‐mineral soil were investigated, alongside those of the original treatments: ammonium nitrate, with and without sulphuric acid and sodium sulphate. Five years of treatment, at canopy height, with up to 100 kg N and S ha−1y−1 were extended for a further three years, for half the plots, while the remaining plots were deprived of N, sulphuric acid or S. Stem area increment was unresponsive, whereas foliar N and Mg concentrations and fine roots were sensitive to the removal of N and acidity. This recovery experiment confirmed that the presence of acidified S modifies the fate of N and suggests that the reduction in acidified S deposition will increase the bioavailability of N.

The spread of arbuscular mycorrhizal (AM) fungi from tree to crop roots was examined by molecular and microscopic methods in a glasshouse study. Growth of Calliandra calothyrsus Meissner trees inoculated with isolates of the AM fungi Glomus etunicatum Becker and Gerdemann and Gigaspora albida Schenck and Smith was monitored over an 18-month period. Three successive ‘intercrops’ of beans or maize were sown at 25, 50 and 75 cm distances from the tree and harvested during this period. At each crop harvest, the distribution of tree and crop roots and the spread of the inoculant fungi were determined using traditional microscopic methods and fungal specific primers. Both inoculants greatly improved the growth of the trees and colonization spread to the crops once the trees were 6 months old. However, benefits of inoculation to crop growth were not observed due to increased competition from the larger inoculated trees growing in a restricted soil volume. Of the two inoculant fungi, Glomus etunicatum appeared to be more mobile as it spread more rapidly, formed higher levels of colonization at increasing distances from the tree and was responsible for most of the mycorrhizal cross-contamination. In contrast, colonization of tree and crop roots by Gigaspora albida was higher nearest the tree. This work demonstrated the benefits of mycorrhizal fungus inoculation for tree growth and confirmed that trees and crops share the same AM fungi. Trees may therefore act as reservoirs of mycorrhizal fungi, either inoculant or indigenous, for surrounding crops or other annual vegetation. It was also shown that tree pruning, the normal practice in agroforestry systems, did not reduce mycorrhizal colonization or prevent spread to crops. However, the slow rates of inoculant spread found here suggest that it may take years before inoculants benefit the growth of crops sown several metres from the tree. The work also demonstrated that microscopic quantification of mycorrhizal colonization and the use of molecular probes to identify specific fungi within roots can complement each other effectively. Molecular probes were more sensitive at detecting mycorrhizal fungi than microscopic methods, but did not discriminate between full mycorrhizal structures and traces of hyphae.

Nitrate in the unsaturated zone between the soil surface and the water table was studied in agroforestry Parklands in north western Senegal by examination of samples obtained by hand auger. Depending on location, water tables existed at depths between 10 and 35m below ground. Previous studies of groundwater in this region had found that large concentrations of nitrate were unconnected with anthropogenic activity. The objective of this study was to determine whether nitrogen fixing vegetation had a role in groundwater nitrate accumulation and whether roots of trees were located deeply enough to access the nitrate. Accordingly, sample profiles were augered close to stems of nitrogen fixing trees, non-nitrogen fixing trees and also in adjacent areas that were unaffected by tree presence. These adjacent areas were typically open pasture or cultivated fields. Tree fine roots were quantified in the samples and examined for the presence of mycorrhizas. Similarly, sand/soil samples were examined and tested for the presence of nitrogen fixing rhizobia that were capable of forming functional nodules on appropriate host plants. Concentrations of nitrate were greatest in soils beneath nitrogen fixing trees and nitrate was more plentiful in profiles augered beneath nitrogen fixing crops than it was elsewhere suggesting that N-fixation was the source of the nitrate. The concentrrations of nitrate that were found in the unsaturated zone were greatly in excess of the WHO recommended limit for nitrate in drinking water. High NO3-N/Cl ratios confirm insitu production of nitrate, and indicate that this is a natural baseline occurrence related to N-fixation. The nitrate is moving down the profile and impacts the groundwater unless it can be intercepted by plant roots. NO3-N amounts in solution in the soil profile varied between 75 and 1000kg ha−1 beneath trees and between 120 and 400kg ha−1 in areas outwith tree crowns. Although these quantities of N occupy the lower end of the range of N values obtained in north American deserts, they comprise a considerable dryland resource where amounts of organic fertilizer are limited and where cost prohibits the use of commercial fertilizers. Roots of both nitrogen fixing and non-nitrogen fixing trees were deep enough to access the nitrate but the small amounts of available water at intermediate depths suggest that large scale uptake of nitrate will only be possible in the wetter zones located close to the water table. Shallow roots tended to be more heavily colonized by mycorrhizas than deeper roots but mycorrhizas were recovered from roots located 22m below ground. Tree roots and rhizobia had similar patterns of distribution. They were commonest close to the soil surface, less frequent at intermediate depths and tended to increase in frequency close to the water table.

Survival, biomass production, nutrient use and fertility of soil were examined in experimental stands of 10-year-old N-fixing indigenous Acacia nilotica (L.) Del. (eight provenances), A. senegal (L.) Willd. (one provenance), Acacia tortilis (Forsskal) Hayne (six provenances), Acacia raddiana syn A. tortilis (Forssk.) Hayne ssp. raddiana (Savi) Brenan (three provenances) and exotic N-fixing A. holosericea A. Cunn. ex G. Don (one provenance), A. cowleana Tate (one provenance), Acacia aneura F. Muell. ex Benth. (twelve provenances), Prosopis juliflora (Sw.) DC. (one naturalised provenance), Prosopis cineraria (L.) Druce (five provenances) and P. chilensis (Molina) Stuntz (two provenances) growing on a coastal site in semi-arid Senegal. Similar data were obtained for the non-N-fixing fast-growing exotic species Azadirachta indica Adr. Juss. and Eucalyptus camaldulensis Dehnh. of the same age that were growing on adjacent plots. P. juliflora produced more biomass than the other species and showed the greatest potential for use as a multipurpose tree. A. aneura showed the greatest potential for fodder production and despite its small stature, it ranked second for biomass among the N-fixing species. Of the indigenous species, A. nilotica was the most efficient user of non-renewable elements in biomass production. A. raddiana seemed profligate in its consumption of both N and P in wood production. E. camaldulensis was efficient in its use of N in wood but its wood contained large concentrations of P and K. A. aneura, P. juliflora and A. nilotica had the smallest concentrations of P in wood. A. raddiana and A. indica contained large concentrations of K in their wood in contrast to A. aneura and A. nilotica which were the most efficient users of K in wood production. There were few significant differences in fertility in soils beneath the differing tree species. Nevertheless, plots containing P. juliflora and P. cineraria tended to be the most fertile. Soil beneath A. indica was more fertile than soil beneath some N-fixing species. The extent of removal of plant nutrients in biomass suggests that without inputs of nutrient elements, harvest of wood and foliage is unlikely to be sustainable at the measured rate of production for more than two tree rotations of 10 years duration.

Intact soil cores were sampled from around three leguminous tree species (Acacia nilotica, Acacia tortilis and Prosopis juliflora) in 10-year-old alley-cropping plots at Thienaba, Senegal. Cores were removed from two depths (0–25 and 25–50 cm) and at two distances from the trunk (1 and 5 m). Duplicate soil cores were taken for assessment of root concentration (cm/100 cm3 soil), mycorrhizal infection (% of infected root length) and spore concentration in the soils. In order to determine the mycorrhizal inoculum potential (MIP) of the soils, a mycorrhizal bioassay of the soil cores was conducted in the greenhouse using millet seedlings. For all plots, seedlings grown in soils from the surface layer (0–25 cm) were larger and formed higher levels of infection than those grown in soils from 25 to 50 cm depth. Mycorrhizal infection of the seedlings was greatest in soil from the A. tortilis plots and, unlike the other tree species, also the greatest in soil collected near the tree. Positive relationships were found between the growth and infection of the bioassay seedlings and the root and spore concentrations in the field soils. Seedling growth and infection may also have been related to higher levels of carbon in the field soils. The results indicated that root and spore concentrations in the field soils were good indicators of MIP, but that levels of root infection were not. The results also indicated the potential benefit to crop yield of maintaining high levels of mycorrhizal propagules in alley-cropping soils and a possible role of the trees in maintaining these sources of inoculum.

As Eucalyptus globulus (Labill.) seedlings are being widely outplanted to sites characterised by both high and low rainfall, this study describes the effect of soil moisture availability on mycorrhizal development and growth of seedlings inoculated with three different fungi. The information generated by this study should enable the nurseryman to target which mycorrhizal fungi to select as suitable inoculants for dry and wet sites. Mycorrhizal and non-mycorrhizal seedlings of E . globulus , grown under non-nutrient limiting conditions, were subjected to two different watering regimes from nine weeks after inoculation. During the following eight weeks, weekly measurements of stomatal conductance were made. All fruit bodies were collected, as they were formed, and the plants were harvested at 17 weeks. Of the three fungi used as inoculants, an isolate of Laccaria fraterna (Cooke and Mass.) Peg. formed the highest level of infection on seedlings that were watered normally whereas, on seedlings that were water-stressed, Pisolithus tinctorius (Pers.) Coker and Couch (syn. P . arhizus (Pers.) Raus.) achieved greatest mycorrhizal development. However, this isolate of L . fraterna sustained high levels of infection (>50%) on E . globulus seedlings in both `wet' and `dry' regimes. Seedlings subjected to drought conditions possessed significantly less stem and leaf biomass. Although there was a negative correlation between mycorrhizal development and shoot growth on seedlings watered normally, for those raised in the drier regime, benefits attributable to mycorrhizal inoculation were detected. In particular, the stomatal conductances of inoculated plants, raised in the `dry' regime, were found to be greater than those of non-inoculated plants growing in the same conditions.

In order to improve the procedure for selecting effective mycorrhizal inoculants for fast-growing eucalypts, a wide range of isolates associated with Eucalyptus globulus Labill. was tested at two contrasting nutrient regimes, representative of that present following outplanting (i.e, post-fertilization) and that likely to occur one or two years later when soil nutrient concentrations will have returned to a much lower level. It was felt that this would provide a more accurate prediction of a selected isolate's potential performance during early plantation establishment. As a consequence, during an initial 12-week period, representative of the nursery phase, seedlings of Eucalyptus globulus, pre-inoculated with 10 different mycorrhizal fungi, were given optimal nutrients to encourage the development of mycorrhizas. At the end of this period, six of the 18 replicate plants were harvested and assessed for shoot growth and mycorrhizal infection while the remainder received for a further 12 weeks two different nutrient solutions (10 and 3 mg l(-1) phosphorus (P)). When these plants were harvested at 24 weeks, shoot growth and mycorrhizal development were again assessed. At the end of the first phase (0-12 weeks), all seedlings, irrespective of fungal inoculant, had become mycorrhizal. However, the extent of mycorrhizal infection achieved by the 10 different fungi ranged from 1.4% to 40.7%. Significant differences were also found between the fungi in their effect on stem diameter, stem dry weight, and shoot dry weight but not stem height or leaf dry weight. When assessed at 24 weeks, mycorrhizal development ranged from 22.3% to 77.7% on seedlings given 10 mg l(-1) P and 23.1-77.3% for those given 3 mg l(-1) P. Three of the 10 fungi formed >50% infection on seedlings, irrespective of the nutrient regime applied. Most of the fungi formed higher levels of infection on seedlings given 10 mg l(-1) P; however, two isolates formed higher levels of infection on seedlings given 3 mg l(-1) P. Infection by nine of the 10 isolates led to a significant increase in leaf and shoot dry weight by seedlings given 10 mg l(-1) P in comparison to those which received 3 mg l(-1) P. However. inoculation with the remaining fungus, an isolate of Pisolithus tinctorius, led to seedlings given 3 mg l(-1) P forming shoots as large as those attained by plants given the higher P regime. The results indicate that isolates can be selected with the potential to achieve significant gains over a broad spectrum of nutrient concentrations. The implications for improving the establishment of E. globulus plantations at a wide spectrum of outplanting sites is discussed.

A number of investigations have demonstrated that balanced fertilizer applications can improve shoot growth of E. globulus plantations. Similar information on the impact of balanced N + P fertilizers on mycorrhizal development is lacking. This study was thus undertaken to determine the combinations of N and P which promote greatest mycorrhizal development and growth of seedlings of E. globulus. The overall objective was to generate information which might be translated into protocols for improved nursery and plantation management. Factorial combinations of two ectomycorrhizal fungi (Hydnangeum carneum Wall. apud Klotz. and Laccaria fraterna (Cooke and Mass.) Peg.) and eight fertilizer regimes containing different combinations of nitrogen (N) and phosphorus (P) were applied to Eucalyptus globulus seedlings. The four concentrations of nitrogen in the solutions ranged from 62.5 up to 250 mg l(-1) while those of phosphorus were 10 and 25 mg l(-1). Plants were harvested 12 weeks after inoculation. When given the lower P regime (10 mg l(-1) P), increasing amounts of applied N resulted in increasing percentages of infected roots, irrespective of fungal inoculant. Maximum colonization, including frequency of mycorrhizal branching, was observed at 250 mg l(-1) N/10 mg l(-1) P, with no indication that mycorrhizal infection had peaked. For seedlings given the higher P (25 mg l(-1)) concentration, increasing amounts of nitrogen tended to decrease per cent root infection. Seedlings given 25 mg l(-1) P grew larger (leaf, stem and shoot dry weight) with increasing concentrations of nitrogen. Those that were given the lower P concentration responded less to N. With the exception of leaf number, a strong positive relationship was found between seedling growth variables and percentage mycorrhizal infection at 10 mg l(-1) P. No such relationship was found at 25 mg l(-1) P. The implications of these findings for the development of a balanced N:P fertilizer regime in eucalypt nurseries and plantations are discussed.

Nine months after logging, seedlings of S. parvifolia were sampled from beneath open, closed and partially closed canopies, which resulted from the different logging treatments. Logging was done manually with minimal soil disturbance, compaction or damage to the vegetation. Assessments were made of seedling growth and ectomycorrhizal populations present on the roots. Seedlings growing under the closed canopy were smaller and possessed lower levels of mycorrhizal infection than those under open or partially closed canopies. Twenty-six ectomycorrhizal types were distinguished, with diversity greatest on seedlings growing under open and partially closed canopies. Although most mycorrhizal types occurred in less than half of the samples, occurrence of individual types was related to canopy type. Based on their frequency (number of seedlings having a mycorrhizal type) and abundance (% infection of a mycorrhizal type if present), mycorrhizal types were categorized into two main groups; those which occurred predominantly under the closed canopy and those which occurred under both open and partially closed canopies. Many of the fungi which dominated under the open and partially closed canopies are thought of as pioneer fungi and their occurrence is discussed in relation to their methods of dispersal and sensitivity to disturbance. Implications for forest management are considered.

The ectomycorrhizal (ECM) colonisation of seedling Sitka spruce (Picea sitchensis) was examined in an uneven-aged plantation forest in southern Scotland. The extent of ECM colonisation of individual seedlings was 43.8–97.2%, with an overall mean of 80.3 ± 1.1%. A total of 13 ECM morphotypes were differentiated, with 1–4 ECM types colonising an individual seedling. ECM colonisation was dominated by a single species, Tylosporafibrillosa, which accounted for 72.4–97.7% of the ECM colonisation recorded, on a plot mean basis. Other ECM types appeared to be distributed very patchily, only two types (Lactarius sp. and Mycelium radicis atrovirens Melin) exceeding a mean of 10% colonisation in any one plot. No significant correlations were recorded between ECM colonisation and seedling growth, or between ECM colonisation and soil pH, loss-on-ignition, or water content.

Ectomycorrhizal formation between Thel- ephora terrestris and Eucalyptus globulus is reported for the first time. The mycorrhizas are described and compared with those formed by Thelephora terrestris on other tree species. Ecological and practical impli- cations of the association are discussed.

A greenhouse experiment was conducted to assess the arbuscular mycorrhizal (AM) fungi inoculum potential for Leucaena leucocephala in a range of nutrient-depleted farm soils in western Kenya. Leucaena was grown in 12 uninoculated farm soils with pH 5.0–6.7, with or without rock P and farmyard manure. Root infection, nodulation, and shoot and root weight were determined 25, 46, and 69 days after planting. Spore concentrations in the farm soils at the start of the experiment ranged from 44 to 126 live spores per 100 g dry soil with 6–10 species per soil, principally Scutellospora spp. and Acaulospora spp. Nodulation was absent or poor in all soils, indicating the need for rhizobial inoculation of species belonging to the leucaena crossinoculation group in this agrosystem. Rock-P alone increased final shoot dry weight by a factor of 1.4, manure alone by 1.8, and rock-P plus manure by 1.9, compared with no ameliorant. Root infection with AM fungi was detected in all soils 25 days after planting and increased linearly in the different farm soils to values of 33–65% 69 days after planting. Soil pH and root infection 25 days after planting accounted for much of the variation in final shoot weight among soils with no amelioront (87%). As early root infection increased from 20 to 40% at soil pH 5.0, the predicted final shoot dry weight was doubled, and the response to ameliorants was reduced by two-thirds. The growth responses to increased infection became smaller as pH increased from 5.0 to 6.5.

Seedbeds at two Scottish nurseries (Forfar and Newton) were inoculated with the ectomycorrhizal fungus Laccariaproximo (Boud.) Pat. and sown with Sitka spruce (Piceasitchensis (Bong.) Carr.) seed. Numbers of emergent seedlings were affected by both inoculum and fertilizer treatments. Up to 114% more seedlings were found in plots inoculated with live fungus in a vermiculite–peat carrier than in control plots with or without the same carrier. A similar, although reduced, effect was found when the live fungus was encapsulated in alginate beads. Application of fertilizer (to the seedbed before sowing and subsequently as a top dressing) reduced numbers of emergent seedlings at both nurseries; at Forfar, numbers in the treatments that had received fertilizer were 40–50% of the numbers in the analogous unfertilized treatments, while at Newton, the plots that had received live inoculum and fertilizer contained seedling numbers that were 66–72% of those in the comparable unfertilized treatment. The effect of inoculant on seedling numbers occurred within the first few weeks after inoculation and was independent of mycorrhizal formation.

Ectomycorrhizas of 5-month-old Pinus patula plants grown in autoclaved shola soil (forest soil) inoculated with basidiospores of Rhizopogon luteolus and Scleroderma citrinum are described. The main emphasis is on the organisation of the mantle tissue as seen in plan view and the features of associated hyphae and strands. The different layers in the mantle produced by the different fungi are described and illustrated.

Effects of vesicular-arbuscular mycorrhizal inoculation and the incorporation of water-holding polymer to the rooting zone, on tree survival and early growth have been assessed at two semi-arid sites in Kenya. Mycorrhizal inoculation was generally beneficial to plant growth in the nursery while polymer had few effects. Survival 30 weeks after planting was significantly affected by the experimental treatments in three out of four tree species at each site; inoculation enhanced survival, while polymer reduced it. Improvements in survival of up to 80% were achieved. Mycorrhizal effects on growth of Acacia tortilis and Prosopis juliflora after outplanting occurred with increases of up to 36% being obtained. The detrimental effects of polymer were unexpected.

This preliminary study investigated the effects of enhanced nitrogen (NH4NO3 at 48 kg ha(-1) y(-1)), sulphur (Na2SO4 at 50 kg ha(-1) y(-1)), acidified nitrogen and sulphur (H2SO4 + NH4NO3) at pre-stated doses (pH 2.5), and acidified nitrogen and sulphur deposition at double these doses on the ectomycorrhizal community associated with a 13-year-old Sitka spruce (Picea sitchensis) forest. Sulphur deposition had little impact on below ground ectomycorrhizal diversity, but stimulated sporocarp production. Nitrogen inputs increased below ground colonisation compared to acidified nitrogen and sulphur, largely due to an increase in Tylospora fibrillosa colonisation. Sporocarp production and ectomycorrhizal root colonisation by Lactarius rufus were reduced in the nitrogen treated plots. These observations suggest that nitrogen deposition to a young plantation may suppress ectomycorrhizal fungi producing large sporocarps. It is proposed that enhanced nitrogen deposition increases ectomycorrhizal nitrogen assimilation, consuming more carbon and leaving less for extrametrical mycelium and sporocarp development.

Des échantillons de sol ont été prélevés à l'aide d'une tarière autour de quatre légumineuses arborescentes de dix ans cultivées en couloirs dans la station agroforestière de Thiénaba, au Sénégal. Les échantillons ont été collectés à cinq profondeurs et à trois distances du tronc des arbres. Pour déterminer le potentiel mycorhizien des sols, un essai biologique a été conduit en serre avec du mil. Un échantillonnage de sols a été également effectué au nord (Tunisie) et au sud (Sénégal) du Sahara. L'effectivité de souches de Rhizobium et de champignons endomycorhiziens a été testée en pépinière sur Prosopis juliflora, Prosopis chilensis et deux provenances d'Acacia raddiana. Pour toutes les parcelles, les plants élevés sur les sols prélevés en surface (0-25 cm) sont plus grands et sont plus infectés que ceux élevés sur les sols prélevés en profondeur. Le taux d'infection des plants est plus élevé pour les sols prélevés sous Acacia raddiana et près du tronc, contrairement aux autres espèces. L'infection mycorhizienne ne dépend ni du climat, ni des formations végétales. Par contre, elle diminue avec les perturbations du sol. La réponse à l'inoculation des espèces arborescentes est très variable. Cependant, les courbes de nodulation et d'infection mycorhizienne sont similaires pour les deux provenances d'Acacia raddiana. Soil cores were sampled from around four leguminous tree species in 10-year-old alley cropping plots at Thiénaba, Senegal. Samples were collected from five depths and at three distances from the trunk. To determine the inoculum potential of the soils, mycorrhizal biossay was conducted in the greenhouse using millet seedling. Soil sampling was also conducted in the North (Tunisia) and the South (Senegal) of the Sahara desert. In order to test the effectiveness of rhizobial and mycorrhizal inocula, an experiment was conducted with Prosopis juliflora, Prosopis chilensis and two provenances of Acacia raddiana. For all plots, seedlings grown in soils from the surface (0-25 cm) were larger and formed higher levels of infection than those grown in soils from 25 to 50 cm depth. Mycorrhizal infection of the seedlings was greatest in soil from Acacia raddiana plots and, unlike the other tree species, also the greatest in soil collected near the tree. Mycorrhizal infection depended neither on climate nor on plant cover. In contrast, it decreased with soil disturbance. Inoculation test showed great variation between the tree species. However, nodulation and mycorrhizal infection of the two provenances of Acacia raddiana were similar.

The overall aim of this paper is to describe the selection of effective rhizobia and arbuscular mycorrhizas (AM), which after inoculation, will significantly improve the forage production of Calliandra calothyrsus under field conditions. To achieve this objective, the following activities were carried out: (i) establishment from both nodules and soil samples of a collection of microsymbionts (rhizobium and AM) of C. calothyrsus from Central America (Mexico, Honduras, Guatemala, Nicaragua and Costa Rica), also from outside its native range in Cameroon, Kenya and New Caledonia; (ii) identification under glasshouse conditions of the most effective rhizobia and AM isolates; (iii) production of a solid selected inoculum for field trials; (iv) examination of the impact of the inoculation on the growth of C. calothyrsus monitored under nursery conditions. We have screened 446 rhizobia strains in the nursery and identified six as being very effective at nodulating the host plant. They originated from Costa Rica (CCCR15 and CCCR1), from New Caledonia (CCNC26), from Cameroon (CCC22) and from Kenya (KWN35 and KCC6). In relation to AM, five isolates have been selected for the ability to infect and promote growth of the host plant--two isolates of Gigaspora albida isolated from Kenya (GA1b and GA2); one isolate of Scutellospora verrucosa isolated from Kenya (SV2c); one isolate of Scutellospora calospora isolated from Guatemala (SC2) and one isolate of Glomus etunicatum isolated from Honduras (GE1). Further experiments will test these selected inocula, singly and in mixtures, in order to obtain an inoculant which significantly improves the growth of C. calothyrsus and to enable its distribution to farmers who use this woody legume for forage production on their farms.

Roots and soil were sampled from around four leguminous tree species in 10-year-old plots at Bandia, Senegal. Assessments of root concentration (cm per 100 cm3 soil) and mycorrhizal colonisation (% of root length) were made and related to the abundance of spores in the soil and the above ground growth (stem diameter at 30 cm height) of the trees. Root concentrations in Acacia nilotica and Acacia tortilis plots were greater than those found in Prosopis juliflora and Acacia aneura plots at all three depths examined (0–10, 10–25, 25–50 cm). Root concentration decreased with soil depth in all plots and was greatest nearest the tree in the Acacia nilotica and Acacia tortilis plots. Mycorrhizal colonisation was highest on Prosopis juliflora roots and lowest on Acacia tortilis roots. Colonisation was not affected by distance from the tree and decreased with depth only in the Acacia aneura plot. Numbers of spores recovered from soils were generally low (27 per 100 g dry wt. soil) and were concentrated in the upper 10 cm of soil. Spores were most numerous in the Acacia aneura plot and least numerous in the Prosopis juliflora plot. Positive relationships were found between spore numbers and root concentration in the Prosopis juliflora plot and between spore numbers and mycorrhizal colonisation in the Acacia aneura plot. Of the four tree species examined, root and mycorrhizal distributions of Prosopis juliflora and Acacia nilotica showed most promise for use in agroforestry systems.

SynopsisSequential observations were made of the effects on root development of inoculating Betula pendula seedlings during propagation with sheathing mycorrhizal fungi, Amanita muscaria, Hebeloma sacchariolens or Paxillus involutus. After propagation, the seedlings were grown for two seasons in four different soils (two mineral soils and two peats) which were not sterilised.While all inoculated seedlings had similar numbers of mycorrhizas at planting, numbers subsequently increased most rapidly with P. involutus and least rapidly with A. muscaria. From the end of the first season onwards, the uninoculated controls had as many mycorrhizas as seedlings inoculated with either A. muscaria or H. sacchariolens. These numbers were, however, usually exceeded on plants inoculated with P. involutus.The mycorrhizas developing on the controls, and on seedlings inoculated with A. muscaria, were attributable after planting into the unsterile soils, to naturally occurring soil-borne inocula of species of Cenococcum, Hebeloma, Inocybe, Laccaria, Paxillus and Thelephora etc. Those developing on seedlings inoculated with P. involutus were all attributable to this inoculant fungus in the first year but, in the second year, the proportions decreased to 19—14%. With H. sacchariolens, at least 90% of the mycorrhizas in the two mineral soils and one of the peats (a sedge peat) were attributable in years 1 and 2 to the inoculant fungus. In the other peat (Sphagnum peat), the proportion of mycorrhizas attributable to H. sacchariolens decreased to 25% by the end of the first year and totally disappeared in the second.The continued ability of H. sacchariolensto form mycorrhizas in a range of unsterile soils, to the virtual exclusion of mycorrhizas attributable to other fungi, is thought to be characteristic of fungi that occur early in mycorrhizal successions. In contrast,A. muscaria(a late-stage fungus), was unable to form mycorrhizas after inoculated seedlings were transferred from controlled axenic conditions to unsterilised field soils.Two arbiters of root growth were measured—numbers of roots and their dry weights. Whereas inoculations with H. sacchariolens significantly decreased numbers in the latter part of the first season, they either had no effects on dry weights as in the mineral soils or significantly increased them as in the peats. In the second season, there was further evidence, sometimes contradictory, showing that inoculations can appreciably alter the structure of developing root systems.

The potential benefits of inoculation of Piceasitchensis (Bong.) Carr. seedlings with ectomycorrhizal fungi are being explored in trials on two first-rotation forest sites (at Wealside and Gleedlee) in Northumberland. Trials have been initiated on two contrasting soil types at each site, using plants inoculated with isolates of fungi that occur early in the mycorrhizal succession (Hebelomacrustuliniforme (Bull, ex St. Amans) Quélet, H. subsaponaceum Karst., Laccarialaccata (Scop, ex Fr.) Cooke, L. proximo (Boud.) Pat., L. tortilis (Bolt.) S. F. Gray, Paxillusinvolutus (Batsch) Fr., and Thelephoraterrestris Ehrenb. ex Fr.), together with appropriate control treatments. Inoculation treatments produced significant differences in growth on both sites. At Wealside, and on one soil type at Gleedlee, height increment was positively correlated with the proportion of the root system that was mycorrhizal at planting, rather than to the type of inoculum perse. In contrast, on the other soil at Gleedlee, increment was positively correlated with root/shoot ratio at the time of planting, not with mycorrhizal infection. Examination of root systems at Wealside suggested that inoculant fungi could infect new roots on site for at least 4 years and that, despite proximity of established woodland, mycorrhizal formation with indigenous fungi was slow. The data suggest that further work on mycorrhizal inoculation for British forestry and elsewhere is justified.

Observations extended to the twelfth after season after planting Betula pendula into a brown earth confirmed that the production of fruitbodies by associated sheathing mycorrhizal fungi followed distinctive patterns in time and space. The temporal sequence progressed Hebeloma crustuliniforme (4th year) → Lactarius pubescens → Hebeloma fragilipes → Cortinarius sp. and Russula ‘grisea’ (12th year). Whereas the radius of the ‘ring’ of L. pubescens fruitbodies was 58 cm in the 7th year, it was 182 cm in the 12th year — an annual rate of increase of 24.8 cm year −1 , exceeding those, when measurable, of H. crustuliniforme (15.3 cm year −1 ), Cortinarius sp. (7.0) and R. ‘grisea’ (17.0).

The assemblages of fruitbodies produced by sheathing mycorrhizal fungi associated with clones of Betula spp. were affected by ‘host’ genotype and the origin of propagating soil during the first 6 years after transplanting into a groundwater gley with mull humus. Significantly more fruitbodies were produced when rooted cuttings were propagated in soil A than in soil B, on average 19.5 compared with 4.5 per tree. The larger numbers in soil A were associated with a preponderance of fruitbodies of Laccaria tortilis; Hebeloma spp. being relatively more abundant in soil B. Appreciably more fruitbodies were associated with clone 12.5D of B. pendula than with clone 9.3D of B. pubescens , 19.9 compared with 4.6, the difference being largely attributable to the ‘substitution’ of the prolific L. tortilis by the sparse Inocybe petiginosa . Whereas soil type had a significant effect on numbers of fruitbodies associated with the three more productive clones, it had no effect on numbers of fruitbodies associated with clone 9.3D.

Naturally-occurring fine roots ( Betula spp. were sampled to a depth of 30 cm at seven locations on each of two transects across a heap of coal spoil in parts subject to after-burn. In the top 20 cm of substrate, 87% of the root pieces occurred. Irrespective of depth, sheathing mycorrhizas were found on 83% of the root pieces. While the percentages of Paxillus -type mycorrhizas decreased with soil depth, those of a Scleroderma -type significantly increased. Total numbers of mycorrhizas counted at the end-of-season were independent of substrate temperatures. However, numbers of Paxillus -type mycorrhizas were inversely related to both annual mean and spring substrate temperatures, whereas those of the Scleroderma -type were directly related. Vegetative cultures of Scleroderma citrinum grew on an agar medium at 30°C, whereas those of Paxillus involutus did not; at lower temperatures the two fungi responded similarly to temperature changes. The evidence suggests that the observed patterns of mycorrhizal development reflect the changing competitive abilities of Scleroderma and Paxillus and/or host influences at different temperatures in the range 8–16°C.

When stydying the growth of different provenances of Betula pendula and B. pubescens it was noted that fruitbody production by many sheathing (ecto-)mycorrhizal fungi followed distinctive patterns in time and place. When saplings of B. pendula and B. pubescens, from seed collected from ranges of locations in western Europe, were grown on a brown earth at latitude 55° 52′ N, autumnal yellowing and defoliation occurred sooner on saplings originating from northern locations (Scandinavia, 60°–66°N) than on those from the south (United Kingdom and Germany, 50°–55°N); the latter group of trees, particularly of B. pubescens, tended to be taller than the former. In the first 6 years after planting Betula spp., more than 90% of the fruitbodies (toadstools, earth-fans of Thelephora terrestris and elf-cups of Peziza badia), usually appearing in the autumn, were of fungi known, or suspected, to form sheathing mycorrhizas with Betula spp. Mean numbers of fruitbodies increased from 0.4 to 28 and 170 per tree in the 2nd, 4th and 6th years respectively after planting. Numbers of fungal species producing fruitbodies progressively increased from one, Hebeloma crustulvniforme, in the 2nd year to 14 (B. pubescens) and 18 (B. pendula) in the 6th year when Hebeloma spp. accounted for 79% of fruitbodies; Laccaria ‘laccata’, 15%; Inocybe lanuginella, 5% and Lactarius pubescens, 1%. Of the 6th year Hebeloma total, H. crustuliniforme, H. fragilipes, H. mesophaeum and H. sacchariolens accounted for 32, 33, 13 and 11% repectively. Mean distances between fruitbodies and the stems of trees widened at c. 0.16 m year−1 for Hebeloma crustuliniforme; for Laccaria ‘laccata’ they increased by 0.27 to 0.87 m year−1 between the 4th and 5th years after planting but remained virtually unchanged in the 6th year. Distributions differed within and between concentric 10 cm annuli. In the 6th year appreciably more Hebeloma fruitbodies, except those of H. sacchariolens, were found in intermediate annuli than in annuli nearest and furthest from trees. In contrast those of Laccaria ‘laccata’ and Inocybe lanuginella developed at densities of 1500 m−2 and 500 m−2 in most annuli. Fruitbodies of Laccaria ‘laccata’ were significantly clustered in sectors of the differing annuli possibly reflecting associations with radially growing secondarily thickened roots, whereas those of I. lanuginella occurred at random. From 2 to 6 years after planting the mean annual production of toadstools and elf-cups averaged 55 and 0.1 per tree originating from latitude 50° N and 66° N respectively. Earth fans of Thelephora terrestris were likewise less commonly associated with trees of northern origin. B. pubescens, unlike many provenances of B. pendula, seemed to resist invasion by the leaf rust Melampsoridium betulinum. The northern provenances of B. pendula were significantly more seriously infected than southern provenances.

MOST of the intimate and often beneficial associations formed between plant roots and some soil fungi can be classified as either endomycorrhizas of various types or sheathing (ecto-) mycorrhizas1,2. The latter, in which colonised roots are shorter and thicker than their uncolonised counterparts, are mainly attributed to basidiomycetous fungi that produce sporophores (toadstools) typical of the Agaricales. Sometimes fungi forming sheathing mycorrhizas produce large numbers of sporophores. P. Larsen, quoted by Romell3, estimated sporophore production by the mycorrhizal Suillus bovinus (Fries) O. Kuntze to be about 180 kg (dry weight) per hectare per yr. Although their evidence is questionable, experiments done by Romell4 and Laiho5 suggest that the mycorrhizal Boletus subtomentosus Fries and Paxillus involutus (Batsch ex Fr.) Fr. usually form sporophores only if they are organically linked to living trees. Hacskaylo6 found that shading foliage of Pinus virginiana Mill decreased sporophore formation by Thelephora terrestris Fr. The results reported here extend the understanding of this relation by showing that sporophore production by some mycorrhizal associates of birch (Betula spp.) is strongly dependent, in the field, on the presence of green foliage.

dépliant *INRA, Centre de Clermont-Ferrand (FRA) Diffusion du document : INRA, Centre de Clermont-Ferrand (FRA)

dépliant *INRA, Centre de Clermont-Ferrand (FRA) Diffusion du document : INRA, Centre de Clermont-Ferrand (FRA)