Abstract
Root exudates such as low molecular weight organic acids (e.g. citric acid, malic acid, oxalic acid), phenolic compounds (e.g., flavonoids), and siderophores of microbial or plant origin can alter soil mineralogy in the rhizosphere thereby releasing trace elements in solution, which can act as essential micronutrients or dangerous pollutants for plants. This research assesses the effect of various root exudates (citric acid, malic acid, oxalic acid, genistein, quercetin and siderophores) on the mineralogy of two different soils (an agricultural calcareous soil and an acidic polluted soil) and evaluates possible synergic or competitive behaviors. X-ray diffraction (XRD) coupled with Electron Probe Micro Analysis (EPMA) was used to identify the crystalline and amorphous phases which were subjected to mineral alteration when exposed to the action of root exudates. Solubilization of trace metals such as Cu, Zn, Ni, Cr, Pb, Cd as well as of major elements such as Si, Al, Fe and Mn was assessed by means of Inductively Coupled Plasma Optical Emission Spectroscopy (ICPOES). It was also found that soil microorganisms attenuated mineral weathering by reducing the concentration of active root exudates in solution. This information is an important cornerstone to better understand the biogeochemical processes acting in the rhizosphere which can play an important role in the availability of trace elements (either nutrient or toxic) for plant acquisition. Research supported by MIUR – FIRB “Futuro in ricerca” (RBFR08L2ZT), internal grant of Unibz (TN5031) and Provincia BZ Rhizotyr TN5218.