Long-term effect of heavy metal loads on the mycorrhizal colonization and metal uptake of barley

Abstract

A pot experiment was designed to study the colonization of indigenous arbuscular mycorrhizal fungi (AMF) on barley ( Hordeum vulgare L.) host plant. Soils of the pots were collected from a long-term field microelement loading experiment on calcareous chernozem soil twelve years after 13 heavy metals (Al, As, Ba, Cd, Cr, Cu, Hg, Mo, Ni, Pb, Se, Sr and Zn) were applied once in four doses (0, 30, 90 and 270 mg element·kg -1 d.w.). The biomass production and element accumulation of the host plant, the various colonization values of the arbuscular mycorrhiza fungi (AMF) – such as colonization intensity (M %), arbusculum richness (A %) in the root system and the sporulation intensity (g -1 dry soil) in the rhizosphere – were measured. When considering the twelve-year adaptation process of the AM fungal populations at the various metal loads, a relatively balanced inside mycorrhiza colonization was found, suggesting the potentials for the selection of tolerant fungi in metal contaminated soils. The balanced infection intensity (M %) of the AM fungi and their common strategies with the host plant have resulted a nonsignificant shoot and root biomass production of barley in general. Mycorrhiza sporulation in the root system proved to be much variable and indicated the toxicity of metals and metal rates. Cd, Pb and Sr elements significantly reduced spore numbers, while a value of 34 spores·g -1 soil was counted in the case of Ni in comparison to the control’s 22 spores·g -1 soil value. Stress-defending strategies of the fungal–plant symbiosis, such as the increased arbusculum richness (A %) could be established for the Hg and Pb rates. In the case of Cd an increased root biomass production became a tool for stress alleviation and reduced the metal allocation towards the shoots. Mycorrhiza fungi are part of the common plant–microbe interactions and appropriate defending mechanisms in metal contaminated soils.