Dynamics of Rare Earths and associated major and trace elements during Douglas-fir (Pseudotsuga menziesii) and European beech (Fagus sylvatica L.) litter degradation

Abstract

Abstract. Given the diverse physico-chemical properties of elements, we hypothesize that their incoherent distribution across the leaf tissues, combined with the distinct resistance to degradation that each tissue exhibits, leads to distinct turnover rates between elements. Moreover, litter layers of different ages produce diverse chemical signatures in solution during the wet degradation. To verify our hypothesis, Na, K, Mg, Mn, Ca, Pb, Al and Fe were analysed together with the Rare Earth Elements (REE) in the solid fractions and in the respective leachates of fresh leaves and different humus layers of two forested soils developed under Pseudotsuga menziesii and Fagus sylvatica L. trees. The results from the leaching experiment were also compared to the in situ REE composition of the soil solutions to clarify the impact that the litter degradation processes may have on soil solution chemical compositions. Our results clearly show that REE, Al, Fe and Pb were preferentially retained in the solid litter material, in comparison to the other cations, and that their concentrations increased over time during the litter degradation. Accordingly, different litter fractions produced different yields of elements and REE patterns in the leachates, indicating that the tree species and the age of the litter play a role in the chemical release during the degradation. In particular, the evolution of the REE patterns according to the age of the litter layers allowed us to deliver new findings on REE fractionation and mobilization during litter degradation. In particular, the LaN/YbN ratio highlights differences in litter degradation intensity between both tree species, which was not shown with major cations. We finally showed the primary control effect that litter degradation can have on the REE composition of the soil solution, which presents a positive Ce anomaly associated with the dissolution and/or transportation of Ce-enriched MnO2 particles accumulated onto the surface of the old litter due to white fungi activity. Similar MREE and HREE enrichments were also found in the leachates and the soil solution, probably due to their higher affinity to the organic acids, which represent the primary products from the organic matter degradation.

Dynamics of trace and rare earth elements during long-term (over 4 years) decomposition in Scots pine and Norway spruce forest stands, Southern Sweden

“…All the REEs showed strong and significant positive increases both in concentration and amount with accumulated mass loss (Figures 4, 6). Few other short-term (Tyler, 2005;Gautam et al, 2020;Montemagno et al, 2021) as well as long-term (Brun et al, 2008) studies have reported an increase in REEs with the progression of decomposition. The increase probably is related to their immobilization and accumulation in the decomposing litter (Laskowski et al, 1995;Lomander and Johansson, 2001).…”

“…Their encumbered behavior followed by enrichment can be related to the build-up of organic matter in the litter bags. A number of studies have linked the REE enrichment of litter to biological, chemical, and/or physical processes (Brun et al, 2008;Gautam et al, 2020;Montemagno et al, 2021). Microbes that contribute to litter decomposition have the capacity to render REEs immobilized in their biomass.…”

“…Release of nutrients from decomposing litter is one of the most important processes in the cycling of elements and biogeochemistry of vegetated ecosystems, including forests (Prescott, 2005;Berg, 2014;Hobbie, 2015;Yue et al, 2019;Montemagno et al, 2021). Knowledge about the decomposition processes has helped us to link primary productivity to soil nutritive capital through litter decomposition (Hobbie, 2015;De Marco et al, 2022) and to recognize its significance to vegetation and soil-inhabiting biota (Hättenschwiler et al, 2005).…”

“…Work on understanding the dynamics of some of the elements in this group, namely, heavy metals, started as early as the 1970s (Rühling and Tyler, 1973) and was later followed by crucial studies giving rare views of their dynamics [Fe, Mn, Zn, Cu, Al, Co, Mo, Ti, V, Zn, Cd, Pb, Ni, Cr, and rare earth elements (REEs)] related to litter decomposition (Laskowski and Berg, 1993;Yue et al, 2019;Kondratova and Bryanin, 2021;Montemagno et al, 2021;De Marco et al, 2022). Still, for most of the ecosystems, for reasons unknown, such studies have not been prioritized for several other trace elements and REEs (Berg and Laskowski, 2005;Brun et al, 2008;Cao et al, 2018;Gautam et al, 2019).…”

“…Still, for most of the ecosystems, for reasons unknown, such studies have not been prioritized for several other trace elements and REEs (Berg and Laskowski, 2005;Brun et al, 2008;Cao et al, 2018;Gautam et al, 2019). In particular, for REEs, despite Tyler's (2005) study and a few follow-up decomposition studies by Brun et al (2008), Gautam et al (2019), and Montemagno et al (2021), the dynamics of REEs during litter decomposition have not received much attention. In contrast to nutrient elements, the bulk of the trace elements and REEs is not required by litter-and soilinhabiting macro-and microbiota involved in the decomposition process.…”