Jacques Berthelin

Arbuscular mycorrhizal contribution to heavy metal uptake by maize (Zea mays L.) in pot culture with contaminated soil

In two pot-culture experiments with maize in a silty loam (P2 soil) contaminated by atmospheric deposition from a metal smelter, root colonization with indigenous or introduced arbuscular mycorrhizal (AM) fungi and their influence on plant metal uptake (Cd, Zn, Cu, Pb, Mn) were investigated. Soil was γ-irradiated for the nonmycorrhizal control. In experiment 1, nonirradiated soil provided the mycorrhizal treatment, whereas in experiment 2 the irradiated soil was inoculated with spores of a fungal culture from P2 soil or a laboratory reference culture, Glomus mosseae. Light intensity was considerably higher in experiment 2 and resulted in a fourfold higher shoot and tenfold higher root biomass. Under the conditions of experiment 1, biomass was significantly higher and Cd, Cu, Zn and Mn concentrations significantly lower in the mycorrhizal plants than in the nonmycorrhizal plants, suggesting a protection against metal toxicity. In contrast, in experiment 2, biomass did not differ between treatments and only Cu root concentration was decreased with G. mosseae-inoculated plants, whereas Cu shoot concentration was significantly increased with the indigenous P2 fungal culture. The latter achieved a significantly higher root colonization than G. mosseae (31.7 and 19.1%, respectively) suggesting its higher metal tolerance. Zn shoot concentration was higher in both mycorrhizal treatments and Pb concentrations, particularly in the roots, also tended to increase with mycorrhizal colonization. Cd concentrations were not altered between treatments. Cu and Zn, but not Pb and Cd root-shoot translocation increased with mycorrhizal colonization. The results show that the influence of AM on plant metal uptake depends on plant growth conditions, on the fungal partner and on the metal, and cannot be generalized. It is suggested that metal-tolerant mycorrhizal inoculants might be considered for soil reclamation, since under adverse conditions AM may be more important for plant metal resistance. Under the optimized conditions of normal agricultural practice, however, AM colonization even may increase plant metal absorption from polluted soils.

Differential tolerance to Cd and Zn of arbuscular mycorrhizal (AM) fungal spores isolated from heavy metal-polluted and unpolluted soils

Spores of arbuscular mycorrhizal fungi were isolated from two soils of field trials at INRA-Bordeaux (France) polluted by long-term application of a zinc-polluted sewage sludge (S2 soil) or treated with cadmium nitrate (Cd40 soil) and from corresponding unpolluted soils (F and Cd0 soils). These AM fungi were tested for their tolerance to Cd and Zn added as salt solutions with increasing concentrations (0 to 10 mg L−1) in a simple spore germination device.According to preliminary identification the predominant species in S2 and F cultures was Glomus mosseae, whereas Cd40 and Cd0 cultures contained a mixture of at least G. mosseae and G. etunicatum. Germination of Cd40 spores was more tolerant to Cd and Zn than for Cd0 spores, with EC50 values of 73 and 158 μmol L−1 added Cd and Zn corresponding to approximately 10 and 13 μmol L−1 remaining in solution in the device. The S2 spores from the sludge contaminated soil were more tolerant to Zn (EC50=87 μmol L−1), but not to Cd (EC50=7.5 μmol L−1), than the spores from the farmyard manure-treated F soil (EC50=38 and 8.8 μmol L−1, respectively). Thus, S2 culture exhibited a specific tolerance to Zn, which was lower than the unspecific tolerance of Cd40 culture to both Cd and Zn, despite the much higher Zn availability in S2 soil.These results indicate that AM fungi from different soils may differ in their metal susceptibility and that both metal specific and unspecific tolerance mechanisms may be selected in metal polluted soils.

Rhizodeposition and net release of soluble organic compounds by pine and beech seedlings inoculated with rhizobacteria and ectomycorrhizal fungi

SummaryA lysimetric experiment was performed in a greenhouse to evalute root deposition and net release of soluble organic compounds after 1 and 2 years from pine and beech seedlings inoculated with an ectomycorrhizal fungus (Laccaria laccata) and/or rhizobacteria (Agrobacterium radiobacter for beech and Agrobacterium sp. for pine). Total C compounds released in the rhizosphere of both plants increased after inoculation with the bacteria or ectomycorrhizal fungus. The rhizobacteria increased root and plant growth and rhizodeposition, but the mycorrhizal fungi appeared to increase only root deposition. Soluble C compounds, collected after 2 years, represented only 0.1–0.3% of the total C compounds released into the rhizosphere, and were modified by inoculation with the microorganisms. After inoculation with the bacteria, levels of sugars and amino acids decreased in pine and beech rhizospheres, whereas organic acids increased, especially in the pine rhizosphere. In the rhizosphere of mycorrhizal beeches, sugar and amino acids increased, and organic acids differed from those released from non-mycorrhizal beeches. In the mycorrhizal pine rhizosphere, however, all compounds decreased. Following dual inoculations, mycorrhizal colonization increased, no effect on plant growth was observed, and virtually no organic acids were detected.

Bioavailability of heavy metals and abundance of arbuscular mycorrhiza in a soil polluted by atmospheric deposition from a smelter

The bioavailability of heavy metals (Cd, Zn, Pb, Cu) and the abundance of arbuscular mycorrhiza (AM) were studied in two agricultural fields close to a Pb-Zn smelter and three fields outside the pollution zone all cultivated with maize (Zea mays L.). Metal extractability with ethylenediaminetetraacetic acid (EDTA)-NH4OAc and Ca(NO3)2, plant metal uptake, and mycorrhizal parameters (spore number, root colonization) were assessed at two growth stages (six-leaf and maturity). Despite regular liming, the availability of Cd, Zn, and Pb was markedly higher in the two metal-polluted fields than in the three uncontaminated fields. However, the AM abundance was not correlated with metal availability. Root colonization and spore numbers in the metal polluted fields were relatively high, though at plant maturity the former was significantly lower than in one of the uncontaminated fields. The very low AM abundance in the two other unpolluted fields was related to other factors, particular soil and plant P status and soil pH. AM root colonization did not substantially prevent plant metal accumulation, since the metal concentrations in maize grown on the polluted fields strongly exceeded normal values, and for Cd and Pb reached the limits of toxicity for animal feed.

Bacterial and Chemical Reductive Dissolution of Mn-, Co-, Cr-, and Al-Substituted Goethites

Goethite samples in which 5% of the iron atoms were replaced with different noniron metal (NIM) atoms (Mn, Co, Al, Cr) were synthesized and characterized by X-ray diffraction. Their dissolution (a) by bacterial (enzymatic) reduction and (b) by chemical dissolution through reduction and complexing with a citrate-bicarbonate-dithionite reagent was investigated and compared with the response of similarly treated nonsubstituted goethite. Chemical dissolution differed in rate of iron solubilization depending on NIM substituents. Initial rates of iron dissolution were faster with goethite-lacking metal substituents than with Al-goethite. Bacterial fermentation and reduction processes were not significantly modified by the presence of Mn, Co, Al, or Cr, but the dissolution rates of iron decreased with substitution. During bacterial iron reduction, Al-goethite was more resistant than Mn-goethite, Co-goethite, Cr-goethite, and pure goethite. Both chemical and bacterial reduction of iron resulted in simultaneous so...

Oxide weathering and trace metal release by bacterial reduction in a New Caledonia Ferralsol

Bacterial reduction of Fe- and Mn-oxides was studied in a surfacehorizon of a New-Caledonian Ferralsol in batch experiments. Twotreatments were imposed containing different sources of organicmatter (soil organic matter with or without glucose addition) tolink organic matter biodegradation with reduction process. Theconcomitant solubilization of Ni and Co was also studied. Resultsshowed that anaerobic Fe- and Mn-reducing bacterial activity wasresponsible for Fe- and Mn-oxide solubilization by anaerobicrespiration or fermentation. When C was more available, oxidereduction was enhanced. Mn-oxide appeared as the major reduciblephase and metal source rather than goethite. Co and Ni weresolubilized with Fe and Mn but their amounts in solutiondecreased at the end of experiment. The bioavailability of heavymetals in this soil was increased by biological reduction but waslimited by adsorption or precipitation phenomena.

Mn-oxide: a major source of easily mobilisable Co and Ni under reducing conditions in New Caledonia Ferralsols

Chemical and bacterial reduction and dissolution of Fe and Mn-oxide and the concomitant solubilisation of Co and Ni were studied in a surface horizon of a New-Caledonia Ferralsol. Chemical extractions showed that Mn and Co were in a large part associated in Mn-oxides. The main part of Ni was associated with goethite, but a very small fraction was also associated with Mn-oxides. Anaerobic reducing bacterial activity was responsible for Fe solubilisation at a smaller extent than for Mn solubilisation and consequently for associated metal release. Submicroscopic investigations revealed the presence of a Mn-oxide containing Co, Ni and Al, close to a lithiophorite–asbolane mixed-layers Mn-oxide, which can be considered as a main source of easily available metals in this soil. To cite this article: C. Quantin et al., C. R. Geoscience 334 (2002) 273–278.

Ability of symbiotic and non-symbiotic rhizospheric microflora of maize (Zea mays) to weather micas and to promote plant growth and plant nutrition

SummaryMaize was grown under axenic conditions in laboratory devices, in a K+-deficient medium, where biotite was the K+ source. In different treatments plants were inoculated by symbiotic (Glomus mosseae) and/or non symbiotic microflora. In those treatments inoculated byGlomus mosseae, the percentage of roots infection after 7 weeks plant growth was 65%. Rhizospheric bacterial population was approximately 108/g (dry weight). Endomycorrhizae stimulated growth and K uptake. Non-symbiotic microflora increased also plant growth but promoted much more biotite weathering and K uptake. Endomycorrhizae and more particularly non-symbiotic microflora increased also Ca and Mg absorption by plants. Possible mechanisms involved and implications in plant growth and pedogenesis are discussed.

Distribution of microorganisms, biomass ATP, and enzyme activities in organic and mineral particles of a long-term wastewater irrigated soil.

The aim of the study was to elucidate the spatial distribution of soil microorganisms and enyzme activities in a long-term wastewater treated soil. Soil was sampled from a plough layer of the Ah horizon of a sandy Haplic Luvisol which was either (1) irrigated with municipal wastewater for almost 100 years, or (2) no more irrigated since 20 years, or (3) never received wastewater. The samples were fractionated by wet sieving to obtain seven size fractions of organic and mineral soil particles, and a separate silt+clay fraction. The individual soil samples contained between 1.2% (never irrigated) and 4.1% (long-term irrigated) organic particles by weight, but these particles harboured up to 47.8% of the total soil carbon and 41.7% of nitrogen, and thus represented an important storage of energy and nutrient for microorganisms. In total, however, the highest C and N amounts were accumulated in the silt+clay fraction, whereas coarser mineral particles which dominanted by weight in the Haplic Luvisol were low in C and N. The highest numbers of bacteria, actinomycetes and fungi per gram of the individual soil fractions were found in organic particles of the long-term irrigated soil. Less nutrient-dependent oligotrophic bacteria were for the most part associated with the silt+clay fraction, irrespective of the soil treatment with wastewater. Similar to microbial counts, also the ATP content, as a measure of active microbial biomass, and the activities of β-glucosidase, β-acetylglucosaminidase, and proteinase were higher in the long-term irrigated soil than in that which was never irrigated. In most cases slightly enhanced values of microbiological and biochemical parameters were still detectable 20 years after the wastewater irrigation was terminated. The values of the individual parameters decreased in all soil samples under testing in general gradually with decrease in size of the organic soil particles. In conclusion, the coarse soil organic particles > 5 mm and the silt+clay fraction < 0.05 mm represent the sites with the highest microbial inhabitance, ATP contents and enzyme activities in the Ah horizon of an Haplic Luvisol. Long-term wastewater irrigation resulted in an increase of microbial counts, total biomass and soil enzyme activities. Verteilung von Mikroorganismen, Biomasse-ATP und Enzymaktivitaten in organischen und mineralischen Partikeln eines langzeitig mit Abwasser berieselten Bodens Die Untersuchungen hatten zum Ziel, den Einfluss einer langzeitigen Abwasserverrieselung auf die raumliche Verteilung der Bodenmikroorganismen und enzymatischer Aktivitaten im Boden zu beleuchten. Es wurden Proben aus dem Oberboden (Ah-Horizont) eines sandigen Haplic Luvisol untersucht. Die einzelnen Bodenstandorte wurden (1) seit ca. 100 Jahren mit mechanisch vorgeklartem Kommunalabwasser berieselt, (2) seit ca. 20 Jahren nicht mehr berieselt, (3) niemals berieselt. Die entnommenen Bodenproben wurden einer Nasssiebung unterzogen. Auf diese Weise konnten sieben Fraktionen von organischen und mineralischen Partikeln unterschiedlicher Grose gewonnen werden. Die Bodenproben enthielten zwischen 1,2% (unberieselt) und 4,1% (ca. 100 Jahre berieselt) organische Partikel nach Gewicht. Jedoch waren in diesen Partikeln bis zu 47,8% des Bodengehalts an Kohlenstoff bzw. 41,7% an Stickstoff und somit auch ein bedeutendes Energie- und Nahrstoffreservoir fur Mikroorganismen enthalten. In absoluten Zahlen waren allerdings die hochsten C- und N-Gehalte in der jeweiligen Schluff+Ton-Fraktion akkumuliert. Die groberen mineralischen Partikel, die ihrem Gewicht nach in den Bodenproben dominierten, enthielten nur kleine Mengen an C und N. Die hochsten Zahlen an Bakterien, Actinomyceten und Pilzen per Gramm der gesiebten Bodenfraktionen wurden in den organischen Partikeln der Bodenproben aus dem langzeitig berieselten Standort festgestellt. Die an Nahrstoffkonzentrationen wenig anspruchsvollen oligotrophischen Bakterien waren uberwiegend mit der Schluff+Ton-Fraktion der jeweiligen Bodenprobe assoziiert. Ahnlich wie die Mikrobenzahlen waren auch der ATP-Gehalt als ein Masstab fur aktive mikrobielle Biomasse und die Aktivitaten von β-Glucosidase, β-Acetylglucosamidase und Protease im berieselten Boden hoher als im Boden des unberieselten Standortes. Etwas abgeschwacht waren die Erhohungen der einzelnen Parameter auch noch 20 Jahre nach der Beendigung der Bodenberieselung feststellbar. Die Werte der einzelnen biologischen und biochemischen Parameter zeigten in den untersuchten Bodenproben fast immer eine mit der sinkenden Grose der organischen Partikel einhergehende rucklaufige Tendenz. Man kann insgesamt feststellen, dass die organischen Partikel > 5 mm und die Schluff+Ton-Partikel < 0,05 mm in den untersuchten Bodenproben aus einem Haplic Luvisol die Mikrohabitate mit der hochsten mikrobiellen Besiedlung, dem hochsten ATP-Gehalt und den hochsten enzymatischen Aktivitaten darstellen. Eine langzeitige Abwasserverrieselung bewirkte deutliche Erhohungen der mikrobiellen Besiedlungsdichte und der biochemischen Aktivitaten des Bodens.

Changes in soil diversity and global activities following invasions of the exotic invasive plant, Amaranthus viridis L., decrease the growth of native sahelian Acacia species

The objectives of this study were to determine whether the invasive plant Amaranthus viridis influenced soil microbial and chemical properties and to assess the consequences of these modifications on native plant growth. The experiment was conducted in Senegal at two sites: one invaded by A. viridis and the other covered by other plant species. Soil nutrient contents as well as microbial community density, diversity and functions were measured. Additionally, five sahelian Acacia species were grown in (1) soil disinfected or not collected from both sites, (2) uninvaded soil exposed to an A. viridis plant aqueous extract and (3) soil collected from invaded and uninvaded sites and inoculated or not with the arbuscular mycorrhizal (AM) fungus Glomus intraradices. The results showed that the invasion of A. viridis increased soil nutrient availability, bacterial abundance and microbial activities. In contrast, AM fungi and rhizobial development and the growth of Acacia species were severely reduced in A. viridis-invaded soil. Amaranthus viridis aqueous extract also exhibited an inhibitory effect on rhizobial growth, indicating an antibacterial activity of this plant extract. However, the inoculation of G. intraradices was highly beneficial to the growth and nodulation of Acacia species. These results highlight the role of AM symbiosis in the processes involved in plant coexistence and in ecosystem management programs that target preservation of native plant diversity.