Arbuscular mycorrhiza alters metal uptake and the physiological response of Coffea arabica seedlings to increasing Zn and Cu concentrations in soil

Studies on mycorrhizal symbiosis effects on metal accumulation and plant tolerance are not common in perennial crops under metal stress. The objective of this study was to evaluate the influence of mycorrhization on coffee seedlings under Cu and Zn stress. Copper (Cu) and zinc (Zn) uptake and some biochemical and physiological traits were studied in thirty-week old Coffea arabica seedlings, in response to the inoculation with arbuscular mycorrhizal fungi (AMF) and to increasing concentrations of Cu or Zn in soil. The experiments were conducted under greenhouse conditions in a 2 × 4 factorial design (inoculation or not with AMF and 0, 50, 150 and 450 mg kg^− 1 Cu or 0, 100, 300 and 900 mg kg^− 1 Zn). Non-mycorrhizal plants maintained a hampered and slow growth even in a soil with appropriate phosphorus (P) levels for this crop. As metal levels increased in soil, a greater proportion of the total absorbed metals were retained by roots. Foliar Cu concentrations increased only in non-mycorrhizal plants, reaching a maximum concentration of 30 mg kg^− 1 at the highest Cu in soil. Mycorrhization prevented the accumulation of Cu in leaves, and mycorrhizal plants showed higher Cu contents in stems, which indicated a differential Cu distribution in AMF-associated or non-associated plants. Zn distribution and concentrations in different plant organs followed a similar pattern independently of mycorrhization. In mycorrhizal plants, only the highest metal concentrations caused a reduction in biomass, leading to significant changes in some biochemical indicators, such as malondialdehyde, proline and amino acid contents in leaves and also in foliar free amino acid composition. Marked differences in these physiological traits were also found due to mycorrhization. In conclusion, AMF protected coffee seedlings against metal toxicity.     

Comparative effects of native filamentous and arbuscular mycorrhizal fungi in the establishment of an autochthonous, leguminous shrub growing in a metal-contaminated soil

The aim of this study was to assess the effectiveness of inoculation with a native arbuscular mycorrhizal (AM) fungus, Glomus mosseae (Nicol. and Gerd.) Gerd. and Trappe, or a filamentous fungus, Penicillium aurantiogriseum Dierckx 1901, on the establishment of Coronilla juncea L. seedlings grown in a polluted, semiarid soil. For that, root and shoot biomass, nutrient uptake, mycorrhizal colonisation and nitrate reductase (NR) and phosphatase activities were analysed. Six months after planting, the shoot biomass of C. juncea was increased only by the inoculation with G. mosseae (by about 62% compared with non-mycorrhizal plants). The shoot NR and root acid phosphatase activities were increased more by inoculation with G. mosseae than with P. aurantiogriseum inoculation. The root NR activity and foliar nutrient contents were increased only by the inoculation with the AM fungus. The root Zn and Cu decreased with the AM fungus. In conclusion, the autochthonous AM fungus was an effective inoculant with regard to stimulating growth and alleviating heavy metal toxicity for plants growing on a soil contaminated by multiple heavy metals. Inoculation with an autochthonous, filamentous fungus does not seem to be a good strategy for phytoremediation of such problematic sites.