Chapter 2 - Mineral weathering in the rhizosphere of forested soils

Abstract

The rhizosphere is a microenvironment enriched with organic matter and generally more acidic than the bulk soil. The chapter submits that mineral weathering and metal fractionation differ in the rhizosphere compared to the bulk soil, a change that could impact on plant nutrition and element toxicity. The objective of the study is to establish the nature of the effect of roots on mineral weathering in the rhizosphere of forested soils based on differences in (1) mineralogical composition and (2) the chemical forms of metals between the rhizosphere and the bulk soil. The study area was located in Rouyn-Noranda (Canada), where samples were collected under Populus tremuloides growing on Luvisolic soils. X-ray diffraction (XRD), time of flight secondary-ion mass spectroscopy (TOF-SIMS), and X-ray absorption near-edge structure (XANES) analyses were performed. The concentrations of Al, Ca, Cd, Co, Cr, Cu, Fe, Li, Mg, Mn, Ni, Pb, Si, and Zn were obtained from an acid ammonium oxalate (AAO) extraction. The XRD results show differences in mineralogical abundance, particularly of chlorite and amphibole, which is interpreted as an increase in mineral weathering in the rhizosphere. It was suggested in the literature that the higher alteration in the rhizosphere could be related to K uptake by roots.