Diameter-associated dynamics of multiple metallic elements during the root decomposition of two dominant subalpine trees in southwestern China.

Litter decomposition is a key pathway of metal cycling in terrestrial ecosystems, yet little is known about the dynamics of metals in decomposing roots. A two-year decomposition experiment was conducted to investigate the temporal dynamics of nine metals (Ca, K, Mg, Fe, Al, Mn, Cr, Cu, and Pb) in decomposing roots of three diameter classes (0–2 mm, 2–5 mm, and 5–10 mm) in two subalpine coniferous tree species (Picea asperata and Abies faxoniana) on the eastern Tibetan Plateau of China. Regardless of tree species and root diameters, macro metals (Ca, K, and Mg) and Cu often released over the experimental period and their remaining were 87.7%, 12.5%, 69.4%, and 47.98%, respectively. However, trace metals (Fe, Al, Mn, Cr, and Pb) generally accumulated during the decomposition process and their remaining were 159.6%, 121.5%, 196.4%, 119.6%, and 124.3%, respectively. The concentrations of Ca, K, Mg, Fe, and Al often decreased with increasing root diameters over the experimental period. For Picea asperata, the Ca, K, Fe, and Pb remaining were higher in the 5–10 mm than 0–5 mm roots, but contrasting trends were found for Mg, Mn, Cr, and Cu. For Abies faxoniana, the 5–10 mm roots had lower macronutrients (Ca, K, and Mg) but higher trace metals (Fe, Al, Mn, Cr, Cu, and Pb) remaining compared to 0–5 mm roots. Taken together, root diameter had pronounced influences on metal dynamics, depending on metallic properties, initial root quality, and/or decomposition period. Root initial chemistry (e.g., C, Mn and lignin) were significantly correlated with the metal remaining during the decomposition. Our findings address the importance of root diameter in understanding metal cycling via root decomposition pathways in forest ecosystems. [ABSTRACT FROM AUTHOR]