The Combined Effects of Arbuscular Mycorrhizal Fungi (AMF) and Lead (Pb) Stress on Pb Accumulation, Plant Growth Parameters, Photosynthesis, and Antioxidant Enzymes in Robinia pseudoacacia L.

Abstract

Arbuscular mycorrhizal fungi (AMF) are considered as a potential biotechnological tool for improving phytostabilization efficiency and plant tolerance to heavy metal-contaminated soils. However, the mechanisms through which AMF help to alleviate metal toxicity in plants are still poorly understood. A greenhouse experiment was conducted to evaluate the effects of two AMF species (Funneliformis mosseae and Rhizophagus intraradices) on the growth, Pb accumulation, photosynthesis and antioxidant enzyme activities of a leguminous tree (Robinia pseudoacacia L.) at Pb addition levels of 0, 500, 1000 and 2000 mg kg-1 soil. AMF symbiosis decreased Pb concentrations in the leaves and promoted the accumulation of biomass as well as photosynthetic pigment contents. Mycorrhizal plants had higher gas exchange capacity, non-photochemistry efficiency, and photochemistry efficiency compared with non-mycorrhizal plants. The enzymatic activities of superoxide dismutase (SOD), ascorbate peroxidases (APX) and glutathione peroxidase (GPX) were enhanced, and hydrogen peroxide (H2O2) and malondialdehyde (MDA) contents were reduced in mycorrhizal plants. These findings suggested that AMF symbiosis could protect plants by alleviating cellular oxidative damage in response to Pb stress. Furthermore, mycorrhizal dependency on plants increased with increasing Pb stress levels, indicating that AMF inoculation likely played a more important role in plant Pb tolerance in heavily contaminated soils. Overall, both F. mosseae and R. intraradices were able to maintain efficient symbiosis with R. pseudoacacia in Pb polluted soils. AMF symbiosis can improve photosynthesis and reactive oxygen species (ROS) scavenging capabilities and decrease Pb concentrations in leaves to alleviate Pb toxicity in R. pseudoacacia. Our results suggest that the application of the two AMF species associated with R. pseudoacacia could be a promising strategy for enhancing the phytostabilization efficiency of Pb contaminated soils.

Comparisons of Soil Properties, Enzyme Activities and Microbial Communities in Heavy Metal Contaminated Bulk and Rhizosphere Soils of Robinia pseudoacacia L. in the Northern Foot of Qinling Mountain

“…Zn is an essential metal for plant growth and plays an important role in photosynthesis and enzyme composition for protein synthesis [46]; however, Pb is a non-essential element and has toxic effects on plant growth (membrane damage and oxidative stress) [47]. Therefore, plants may develop their own strategy to survive in HM polluted soil: reducing availability of toxic HM (Pb) in rhizosphere and preventing the translocation of Pb from soil to the aerial parts of plants, which was consistent with our previous study [24,31]. Various studies have indicated that plant root exudates could react with HM ions and affected metal solubility, mobility and phytoavailability [48].…”

“…The HM polluted area had the same soil type and was divided into polluted levels of light (S1, 33 • Figure S1), according to our previous investigation and the Chinese environmental quality standard (Grade II) for soils (GB 15618-1995) [27,[29][30][31]. In August 2012, four study plots (15 × 15 m) dominated by target tree species (R. pseudoacacia) were identified at each site for soil sampling.…”

Impact of abiotic factors on development of the community of arbuscular mycorrhizal fungi in the soil: a Review

“…Fungal hyphae can also be a barrier for the translocation of heavy-metal ions to the plant aboveground parts as these ions are immobilized in the root (Cd, Ti, Ba, B) with the participation of polyphosphates or specific metalloproteins (Nowak and Kunka, 2009;Turnau et al, 1993;Yang et al, 2015). Soil contamination with zinc is also toxic for plants and, at the same time, antagonistic during phosphorus uptake (Ryan and Graham, 2002).…”

Subcellular Compartmentalization and Chemical Forms of Lead Participate in Lead Tolerance of Robinia pseudoacacia L. with Funneliformis mosseae

“…R. pseudoacacia plants are well grown and commonly colonized by AMF such as F. mosseae in the Qiandongshan lead–zinc polluted area (Yang et al, 2015b,c). Recent studies have shown that photosynthesis and antioxidant enzymes (e.g., superoxide dismutase and ascorbate peroxidases) in the leaves of R. pseudoacacia are enhanced by F. mosseae under Pb stress (Yang et al, 2015a). Additionally, F. mosseae is effective at accumulating Pb in plant root systems (Yang et al, 2015a).…”