The beneficial role of indigenous arbuscular mycorrhizal fungi in phytoremediation of wetland plants and tolerance to metal stress

Abstract

The potential of fi ve plants namely Atriplex halimus L., A. canescens (Pursh) Nutt., Suaeda fruticosa (Forssk. ex J.F. Gmel.), Marrubium vulgare L. and Dittrichia viscosa (L.) Greuter from two selected wetlands in northwest Algeria subjected to house and industrial effl uents were examined to assess their arbuscular mycorrhizal fungal (AMF) diversity and colonization, as well as to determine their tolerance and ability in accumulating metallic trace elements (MTEs). The purpose was to investigate whether, or not, these fungi are related to metallic uptake. Arbuscular mycorrhizal association was observed in all plant species, since the dual association between AMF and dark septate endophytes (DSE) was found in roots of 80% plants species. Hence, the decreasing trend of metal accumulation in most plant organs was Zn>Cu>Pb, and the most effi cient species were M. vulgare> S. fruticosa> A. canescens> D. viscosa> A. halimus. The bioaccumulator factors exceeded the critical value (1.0) and the transport factors indicated that all these species were phytoremediators. Pearson correlation showed that Cd bioaccumulation and translocation were inhibited by AMF infection; meanwhile Zn, Pb and Cd accumulation were affected by AMF spore density and species richness, DSE frequency, pH, AMF and plant host. Native halophytes showed a multi-metallic resistance capacity in polluted wetlands. M. vulgare was the most effi cient in metal accumulation and the best host for mycorrhizal fungi. AMF played a major role in metal accumulation and translocation. 104 W. Sidhoum, Z. Fortas for soil remediation engineer to establish a novel ecosystem in polluted soils (Yang et al. 2014). As reported by (Wójcik et al. 2015), the communities of the indigenous metallophyte of abandoned metalliferous waste sites are considered as an important source of species, seed banks and gene pools for the environmental phytotechnologies. Two strategies are probably used by plants in order to use to transact with high metal concentrations in the rhizosphere: exclusion (avoidance) mechanisms, where the uptake and/or root-to-shoot transport of metals are restricted, phytostabilization process (reduction of the mobility, bioavailability and/or toxicity of pollutants in the rhizosphere), or in contrast, sequestration of MTE contaminants by plant roots, and then translocation to their aerial parts internally. Here, the aim of phytoextraction or phytoaccumulation is to increase the accumulation of metal in plant tissues, and thus the mechanisms of internal tolerance could be important (Padmavathiamma and Li 2007). The AMF are ubiquitous soil inhabitants associated symbiotically with most plants roots, and constitute a major component of the soil microbial biomass. They promote the penetration of nutrients in ecosystems, enhance plant establishment and growth, soil aggregation, and mineral uptake (Luginbuehl and Oldroyd 2017). In view of above background, the present study was aimed at to 1) determine the concentrations of Cu, Zn, Pb, Cd, Ni and Cr in some plants growing on contaminated saline wetland soils; 2) evaluate the root colonization by AMF and dark septate endophytes (DSE); 3) examine AMF diversity naturally related with the studied plants; 4) identify the hyperaccumulator plants with several established criteria, and thus assess the feasibility of using these plants for phytoremediation purpose, and 5) highlight principle factors in association with plant rhizosphere, affecting plant metal accumulation. Materials and methods Sampling area The study was undertaken in two wetlands: Telamine Lake (LT) (35°42’50” N; 0° 23’30” W) which is listed under Ramsar convention from 2004, and Dayet Morsli (DM) (35°39’58” N, 0°36’27” W) known as the subject of interest due to its Ramsar classifi cation. Their altitude varies between 50 and 87 m.a.s.l., along with a semi-arid Mediterranean regional climate model, characterized by cold and rainy winters followed by dry summers, lasting for about 4–6 months: with 250 m1 (root accumulation, high effi ciency in phytostabilization) and TF›1 ( high effi ciency for metal translocation used for phytoextraction). The factors are calculated by the following formula: BCF = Croot⁄Csoil BAF = Cleaf⁄Csoil TF = Cleaf⁄Croot Where, Cleaf, Croot, and Csoil are MTE concentrations successively in leaves, in roots, and in soil. Mycorrhizal colonization analysis Young roots of the plant species (with root tips) washed in tap water to remove soil particles and fi xed in FAA (formalin, glacial acetic acid and ethanol) were taken out from the fi xation solution, washed several times in tap water, clarifi ed in 10% (w/v) KOH at 90°C for 1 h, rinsed three times, bleached with fresh alkaline H2O2 solution (10%) for 2 to 3 min, acidifi ed with 10% HCl (1–4 min), and afterwards they were stained with 0.1% Trypan Blue (w/w) in lactophenol according to the modifi ed method of (Phillips and Hayman 1970). For each root system, AMF colonization was examined by optical microscopy (Olympus CX22) for 50 root fragments of roughly 1 cm in length. The mycorrhizal development was evaluated as described by Trouvelot et al. (1986) and expressed as mycorrhizal frequency (F%, percentage of root cortex infected by mycorrhiza), mycorrhizal intensity (amount of root cortex that became mycorrhized and it is referred either to the whole root system (M%) or only to the mycorrhizal root fraction (m%)), arbuscular richness (A%) in the whole root system or in the colonized root fragments (a%). In the case of other endophytes (DSE colonization or other fungal endophytes), the freque