We used Pisolithus tinctorius and Cenococcum geophilum to determine the copper (Cu) resistance of ectomycorrhizal (ECM) fungi and their potential for improving phytoremediation of Cu-contaminated soil by Chinese red pine (Pinus tabulaeformis). The results showed that nutrient accumulation in C. geophilum mycelium was significantly lower under higher Cu concentrations in the soil, which was not observed in P. tinctorius. Meanwhile, P. tinctorius exhibited greater Cu tolerance than C. geophilum. Inoculation with ECM fungi significantly improved the growth of pine shoots planted in polluted soil in pot experiments (p < 0.01). The total accumulated Cu in pine seedlings planted in Cu-contaminated soil increased by 72.8% and 113.3% when inoculated with P. tinctorius and C. geophilum, respectively, indicating that ECM fungi may help their host to phytoextract heavy metals. Furthermore, the majority of the total absorbed metals remained in the roots, confirming the ability of ECM fungi to promote heavy metal phytostabilization. There were no differences between the effects of the two fungi in helping the host stabilize and absorb Cu, even though they have different Cu tolerances. Inoculation with ECM fungi can benefit plant establishment in polluted environments and assist plants with phytoremediating heavy-metal-contaminated soils.
Chinese Douglas-fir (Pseudotsuga sinensis) is an endangered Pinaceae species found in several isolated regions of China. Although soil spore banks of ectomycorrhizal (ECM) fungi can play an important role in seedling establishment after disturbance, such as in the well-known North American relative (Pseudotsuga menziesii), we have no information about soil spore bank communities in relict forests of Chinese Douglas-fir. We conducted bioassays of 73 soil samples collected from three Chinese Douglas-fir forests, using North American Douglas-fir as bait seedlings, and identified 19 species of ECM fungi. The observed spore bank communities were significantly different from those found in ECM fungi on the roots of resident trees at the same sites (p = 0.02). The levels of potassium (K), nitrogen (N), organic matter, and the pH of soil were the dominant factors shaping spore bank community structure. A new Rhizopogon species was the most dominant species in the spore banks. Specifically, at a site on Sanqing Mountain, 22 of the 57 surviving bioassay seedlings (representing 21 of the 23 soil samples) were colonized by this species. ECM fungal richness significantly affected the growth of bioassay seedlings (R = 0.20, p = 0.007). Growth was significantly improved in seedlings colonized by Rhizopogon or Meliniomyces species compared with uncolonized seedlings. Considering its specificity to Chinese Douglas-fir, predominance in the soil spore banks, and positive effect on host growth, this new Rhizopogon species could play critical roles in seedling establishment and forest regeneration of endangered Chinese Douglas-fir.
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