Abstract
The success of mine site restoration programs in arid and semi-arid areas poses a significant challenge and requires the use of high-quality seedlings capable of tolerating heavy metal stresses. The effect of ectomycorrhizal fungi on different physiological traits was investigated in Pinus halepensis seedlings grown in soil contaminated with heavy metals (Pb-Zn-Cd). Ectomycorrhizal (M) and non-ectomycorrhizal (NM) seedlings were subjected to heavy metals stress (C: contaminated, NC: control or non-contaminated) soils conditions for 12 months. Gas exchange, chlorophyll fluorescence, water relations parameters derived from pressure–volume curves and electrolyte leakage were evaluated at 4, 8 and 12 months. Ectomycorrhizal symbiosis promoted stronger resistance to heavy metals and improved gas exchange parameters and water-use efficiency compared to the non-ectomycorrhizal seedlings. The decrease in leaf osmotic potentials (Ψπ100: osmotic potential at saturation and Ψπ0: osmotic potential with loss of turgor) was higher for M-C seedling than NM-C ones, indicating that the ectomycorrhizal symbiosis promotes cellular osmotic adjustment and protects leaf membrane cell against leakage induced by Pb, Zn and Cd. Our results suggest that the use of ectomycorrhizal symbiosis is among the promising practices to improve the morphophysiological quality of seedlings produced in forest nurseries, their performance and their tolerance to multi-heavy metal stresses.
Highlights
Mining activities that are conducted in a Mediterranean climate can exert their greatest effects on the environment through water pollution, contamination and alteration of agricultural soil due to the spread of heavy metals [1,2]
The objectives of this study were: (i) to compare gas exchange variables, water use-efficiency (WUE), electrolyte leakage and chlorophyll fluorescence under multiple heavy metal stresses (Pb, Zn and Cd) in ectomycorrhizal and non-ectomycorrhizal Pinus halepensis seedlings; (ii) to determine water relations parameters that were derived from pressure–volume curves (Ψπ 100, Ψπ 0, RWC0, symplastic water content (SWC) and εmax ) of ectomycorrhizal and nonectomycorrhizal seedlings that were grown in the absence and presence of multi-metal stresses; and (iii) to examine whether osmotic adjustment occurs as a result of long-term exposure of ectomycorrhizal seedlings to high levels of heavy metal toxicity
Our previous results [47] showed that after 12 months of growth in contaminated soil (NM-C) with heavy metals (Pb, Zn, and Cd), shoot and root dry masses of P. halepensis seedlings were reduced compared to the control (NM-NC), while no differences were observed for mycorrhizal seedlings (M-C) compared to the control (NM-NC)
Summary
Mining activities that are conducted in a Mediterranean climate can exert their greatest effects on the environment through water pollution, contamination and alteration of agricultural soil due to the spread of heavy metals [1,2]. In North Africa, land losses due to increasingly heavy metal-polluted soils are the highest in the world [1]. Severe environmental stresses and their interactions can negatively affect the survival of forest trees [4,5,6], the sustainability of ecosystems and the success of reforestation programs on abandoned mine sites in the Microorganisms 2022, 10, 57. North Africa (Morocco, Algeria and Tunisia) is recognized as one of the Mediterranean region’s most vulnerable to climate change, given that it is characterized by a significant decrease in precipitation and a significant increase in temperature, which reinforce both the pressures and the phenomena that are associated with ecosystem degradation [5,7]
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