Search

International audience; Despite many studies on the impact of arable land conversion to Short Rotation Coppice (SRC), few studies have been carried out on soil biota. This study aims at assessing biological and physico-chemical soil properties that are affected by SRC compared to forestry, grassland and an agrosystem.All samples were collected in the Aisne valley (France), from the same type of soil, with four land uses, i.e. willow SRC, agrosystem, grassland and alluvial forest, 3 years after SRC was planted. We studied fertility, the biological community (earthworm diversity, density and biomass, bacterial and fungal density and community structures) and biochemical parameters (enzyme activities, basal respiration and nitrification).After 3 years' growth, soil biological parameters (fungal abundance, laccase activity, anecic earthworm proportion and earthworm diversity) and CEC were higher in the SRC than in the agrosystem soil. In parallel, fungal abundance was higher in SRC than in forest and grassland soils.Compared to annual arable crops, SRC promoted biological properties. However, in the short term, the parameters we measured were lower than in the forest and grassland soils. The use of certain parameters as indicators of soil functioning/quality assessment to discriminate the four land uses is discussed.

Some plants are more mycorrhizal than others and mycorrhizal colonisation of plants in extreme environments is frequently additionally reduced due to decreased spore density and/or diversity and therefore frequently overlooked. We analysed two plant species from both metal polluted and saline enriched soils with differing mycorrhizal colonisation levels/status using classical and molecular methods. The selected plant species were Sesleria caerulea (L.) Ard. and Thlaspi praecox Wulfen from a metal polluted site, and Limonium angustifolium (Tausch) Degen [Statice serotina Rchb., L. vulgare Mill. subsp. Serotinum (Rchb.) Gams] and Salicornia europaea L. from the Secovlje salterns in Slovenia. Despite the high mycorrhizal frequencies (F%) observed, the presence of arbuscules (A%) was at best low in S. caerulea and T. praecox, and undetectable in L. angustifolium and S. europaea. Temporal temperature gradient gel electrophoresis (TTGE) was applied to field-collected samples from both burdened environments and proved to be an effective technique for rapid profiling and identification of arbuscular mycorrhizal fungi (AMF). Sequencing and phylogenetic analysis confirmed the association of AMF of the genus Glomus with roots of all four plant species. This is the first report on the identification and profiling of Glomeromycota in the field-collected Cd/Zn metal hyperaccumulator T. praecox growing at a highly metal polluted site, as well as in L. angustifolium and S. europaea collected in a saline environment. The identification of AMF from both ecosystems only partially resembles previous identifications on the basis of spores.

Rhizodegradation of recalcitrant organic pollutants, such as polycyclic aromatic hydrocarbons (PAH), may benefit from the major role that root exudates have on rhizospheric microbial processes. We investigated the influence of the proximity to ryegrass (Lolium perenne L.) roots on microbial populations and their biodegradation of phenanthrene (PHE) using compartmented pots. PAH degrading bacteria, total heterotrophic bacteria and PHE biodegradation were quantified in three consecutive sections at different distance (0–3, 3–6, 6–9 mm) from a mat of actively exuding roots. A bacterial gradient was observed with higher numbers of heterotrophs and PAH degrading bacteria closest to the roots. In parallel, a PHE biodegradation gradient was evident in the presence of roots. The biodegradation reached 86%, 48% and 36% of initially added PHE, respectively, in the layers 0–3 mm, 3–6 and 6–9 mm from the roots. The biodegradation rate was similar throughout the three layers of the non planted control. The present experimental system seems well suited for spatial and dynamic studies of PAH rhizoremediation.

Polycyclic aromatic hydrocarbons (PAH) can be degraded in the rhizosphere but may also interact with vegetation by accumulation in plant tissues or adsorption on root surface. Previous studies have shown that arbuscular mycorrhizal (AM) fungi contribute to the establishment and maintenance of plants in a PAH contaminated soil. We investigated the fate of PAH in the rhizosphere and mycorrhizosphere including biodegradation, uptake and adsorption. Experiments were conducted with ryegrass inoculated or not with Glomus mosseae P2 (BEG 69) and cultivated in pots filled with soil spiked with 5 g kg−1 of anthracene or with 1 g kg−1 of a mixture of 8 PAH in a growth chamber. PAH were extracted from root surfaces, root and shoot tissue and rhizosphere soil and were analysed by GC-MS. In both experiments, 0.006 – 0.11‰ of the initial extractable PAH concentration were adsorbed to roots, 0.003 – 0.16‰ were found in root tissue, 0.001‰ in shoot tissue and 36 – 66% were dissipated, suggesting that the major part of PAH dissipation in rhizosphere soil was due to biodegradation or biotransformation. With mycorrhizal plants, anthracene and PAH were less adsorbed to roots and shoot tissue concentrations were lower than with non mycorrhizal plants, which could contribute to explain the beneficial effect of AM fungi on plant survival in PAH contaminated soils.

Experiments with excised mycelium of several Glomus spp. with different histories of exposure to heavy metals were carried out to measure their capacities to bind Cd and Zn. Cd sorption was followed for up to 6 h of incubation to determine its time course relationships. Controls treated with a metabolic inhibitor were included to evaluate whether sorption was due to active uptake or passive adsorption. The effect of ion competition (effects of Ca or Zn on Cd sorption) and general measurements of cation exchange capacity (CEC) of roots and hyphae were also performed. The results showed that AM mycelium has a high metal sorption capacity relative to other microorganisms, and a CEC comparable to other fungi. Metal sorption was rapid (

A Cd-tolerant arbuscular mycorrhizal fungus, Glomus mosseae, isolated from a polluted soil (P2 culture), was compared with a Cd-sensitive reference Glomus mosseae (Gm) for its capacity to colonize maize (Zea mays L.) roots and to affect plant growth and Cd uptake in sand culture at increasing exposure to Cd added with the nutrient solution (0, 0.1, 1, 5 and 10 mg L-1). After eight weeks, mycorrhizal colonization by P2 culture was relatively high (50% of the control without Cd added) up to 5 mg L-1 Cd, whereas colonization by Gm was almost totally suppressed at that Cd level. However, even mycorrhizal colonization by the Cd-tolerant P2 culture appeared more sensitive to Cd than plant growth and was completely suppressed at 10 mg L-1 Cd. AM colonization did not alleviate the negative effect of Cd on plant growth compared to the non-mycorrhizal treatment. On the contrary, at the 5 mg L-1 Cd level non-mycorrhizal plants were greater than mycorrhizal plants with lower Cd concentration.

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.

Spores of arbuscular mycorrhizal (AM) fungi were isolated from two heavy-metal polluted soils in France via trap culture with leek (Allium porrum L.). Preliminary identification showed that the predominant spore type of both cultures (P2 and Cd40) belongs to the Glomus mosseae group. Their sensitivity to cadmium was compared to a laboratory reference strain (G. mosseae) by in vitro germination tests with cadmium nitrate solutions at a range of concentrations (0 to 100 mg L−1) as well as extracts from a metal-polluted and unpolluted soils. Both cultures of AM fungi from heavy-metal polluted soils were more tolerant to cadmium than the G. mosseae reference strain. The graphically estimated EC50 was 0.8 mg L−1 Cd (concentration added to the test device) for G. mosseae and 7 mg L−1 for P2 culture, corresponding to effective Cd concentrations of approximately 50–70 μg L−1 and 200–500 μg L−1, respectively. The extract of the metal-polluted soil P2 decreased germination of spores from the reference G. mosseae but not from P2 culture. However, the extracts of two unpolluted soils with different physico-chemical characteristics did not affect G. mosseae, whereas germination of P2 spores was markedly decreased in the presence of one of the extracts. These results indicate a potential adaptation of AM fungi to elevated metal concentrations in soil. The tested spores may be considered as metal-tolerant ecotypes. Spore germination results in presence of soil extracts show the difficulty of assessing the ecotoxic effect of metals on AM fungi without considering other soil factors that may interfere in spore germination and hyphal extension.