A Cr(VI)-tolerant strain, Pisolithus sp1, with a high accumulation capacity of Cr in mycelium and highly efficient assisting Pinus thunbergii for phytoremediation.

Ectomycorrhizal (ECM) fungi can improve the growth of pine trees and enhance their tolerance to heavy metal stress, and may also be useful during the afforestation and phytoremediation of polluted regions with pine trees. Hebeloma vinosophyllum (Cr(VI)-sensitive strain) and Pisolithus sp1 ((Cr(VI)-tolerant strain) were selected through liquid culture experiment, and were used in symbiosis with Japanese black pine (Pinus thunbergii) in pot experiments, to determine their potential for improving phytoremediation of Cr(VI)-contaminated soils. Our results indicated that Pisolithus sp1 also had a significantly higher accumulation of Cr than H. vinosophyllum in mycelium under the same Cr(VI) treatments in liquid culture experiment. The tolerance index of Pisolithus sp1 ECM seedlings' shoots and roots to Cr(VI) were significantly higher than that of H. vinosophyllum ECM and non-ectomycorrhizal (NM) seedlings while the total accumulated Cr per seedling in Pisolithus sp1 ECM seedlings were 1.50-1.96 and 2.83-27.75 fold higher that of H. vinosophyllum ECM and NM seedlings, respectively, within 0-800 mg kg-1 Cr(VI) treatments in pot experiments. In addition, the significant differences ratios of photosynthetic rate, stomatal conductance, transpiration rate and intercellular CO2 concentration between Pisolithus sp1 ECM and NM seedlings were significantly higher than those between H. vinosophyllum ECM and NM seedlings under 400 and 800 mg kg-1 Cr(VI) treatments. Compared with the control (no plant), and planting NM or H. vinosophyllum ECM seedlings, the planting of Pisolithus sp1 ECM seedlings significantly reduced the percentage content of exchangeable Cr in the soil.