Des ressources végétales endémiques pour optimiser durablement les opérations de réhabilitation du couvert forestier en milieu méditerranéen et tropical : exemple des plantes facilitatrices vectrices de propagation des champignons mycorhiziens

The overexploitation of natural resources, resulting in an increased need for arable lands by local populations, causes a serious dysfunction in the soil's biological functioning (mineral deficiency, salt stress, etc.). This dysfunction, worsened by the climatic conditions (drought), requires the implementation of ecological engineering strategies allowing the rehabilitation of degraded areas through the restoration of essential ecological services. The first symptoms of weathering processes of soil quality in tropical and Mediterranean environments result in an alteration of the plant cover structure with, in particular, the pauperization of plant species diversity and abundance. This degradation is accompanied by a weakening of soils and an increase of the impact of erosion on the surface layer resulting in reduced fertility of soils in terms of their physicochemical characteristics as well as their biological ones (e.g., soil microbes). Among the microbial components particularly sensitive to erosion, symbiotic microorganisms (rhizobia, Frankia, mycorrhizal fungi) are known to be key components in the main terrestrial biogeochemical cycles (C, N and P). Many studies have shown the importance of the management of these symbiotic microorganisms in rehabilitation and revegetation strategies of degraded environments, but also in improving the productivity of agrosystems. In particular, the selection of symbionts and their inoculation into the soil were strongly encouraged in recent decades. These inoculants were selected not only for their impact on the plant, but also for their ability to persist in the soil at the expense of the residual native microflora. The performance of this technique was thus evaluated on the plant cover, but its impact on soil microbial characteristics was totally ignored. The role of microbial diversity on productivity and stability (resistance, resilience, etc.) of eco- and agrosystems has been identified relatively recently and has led to a questioning of the conceptual bases of controlled inoculation in sustainable land management. It has been suggested that the environmental characteristics of the area to rehabilitate should be taken into account, and more particularly its degradation level in relation to the threshold of ecological resilience. This consideration should lead to the optimization of the cultural practices to either (i) restore the original properties of an ecosystem in case of slightly degraded environments or (ii) transform an ecosystem in case of highly degraded soils (e.g., mine soils). In this chapter, we discuss, through various examples of experiments conducted in tropical and Mediterranean areas, the performance of different strategies to manage the microbial potential in soils (inoculation of exotic vs. native species, inoculation or controlled management potential microbial stratum via aboveground vegetation, etc.) based on the level of environmental degradation.     

Molecular phylogeny of <Emphasis Type="Italic">Pisolithus</Emphasis> species from Moroccan forest woodlands

The phylogenetic relationships among 200 Pisolithus basidiomata collected from pine, oak, and eucalypt forests and rockrose scrubs in Morocco were investigated. Using PCR-RFLP analysis of the internal transcribed spacer (ITS) of ribosomal DNA, this collection could be divided into 5 groups, by using PCR-RFLP analysis of the internal transcribed spacer (ITS) of ribosomal DNA. The ITS of a representative basidioma of each group was sequenced, and a phylogenetic analysis was performed. The dendrogram suggests that at least five Pisolithus species are present in Morocco. Pisolithus basidiomata collected in the Pinus and Quercus forests correspond to Pisolithus arrhizus and P. species 4 as previously described by Martin and colleagues in 2002. Those collected from the eucalyptus forests, under E. gomphocephala and E. camaldulensis, correspond to P. albus and P. microcarpus. Basidiomata collected from the rockrose scrubs, under Cistus crispus, C. monspeliensis or C. salviifolius, are all identified as Pisolithus species 3. Phylogenetic analyses showed that our different Pisolithus grouped well with Pisolithus specimens from other geographical origins.     

Monoxenic nodulation process of Acacia mangium (Mimosoideae, Phyllodineae) by Bradyrhizobium sp

Acacia mangium Willd., a native tree in Australia and Papua New Guinea, has been introduced to countries in Asia and South America where plantations have been established that cover several hundred thousand ha. The present study investigated the early stages of the nodulation process in A. mangium using an homologous Australian Bradyrhizobium strain. After optimizing the axenic nodulation, histological and cytological studies were conducted using light and electron microscopy. These documented the proliferation of Bradyrhizobium, the lysis of mucilage at the root surface, root hair deformation and initiation, as well as the development and growth of multiple infection threads. A belt of tannin-filled cells was shown to surround the central nodular fixation zone. The nodules were of the indeterminate type and the bacteroids had a rod shape, without size modification and with few polyhydroxybutyrate (PHB) granules. Several bacteroids can share the same symbiosome. A. mangium exhibits both classical and novel features in its nodulation.     

Effect of Different Amendments on Growing of Canna indica L. Inoculated with AMF on Mining Substrate

Canna indica L. (CiL) was used here in phytoremediation of mining soils. Our work evaluated the effect of AMF (i) on the growth and (ii) on the uptake of heavy metals (HM). The tests were conducted in the greenhouse on mining substrates collected from the Kettara mine (Morocco). The mine soil was amended by different proportions of agricultural soil and compost and then inoculated with two isolates of AMF (IN1) and (IN2) of different origins. After six months of culture, the results show that on mining soils (100%) only AMF (IN2) was able to colonize the roots of CiL with a frequency of 40 ± 7% and an intensity of 6.5 ± 1.5%. Also, the lowest values of shoot and root dry biomass are obtained on these mining soils with respectively 0.30 g and 0.27 g. In contrast, the accumulation of HM was higher and reached more than 50% of that contained in the mining soils, the highest values with 138 mg kg^?1 Cu²⁺, Zn²⁺ 270 mg kg^?1 and 1.38 mg kg^?1 Cd was recorded. These results indicate that the colonization of CiL roots by AMF (IN2) could significantly improve its potential to be used in phytoremediation of polluted soil.