Magnesium Isotope Variations to Trace Liming Input to Terrestrial Ecosystems: A Case Study in the Vosges Mountains

Abstract

Liming with Ca and Mg carbonates is commonly used to reduce soil and stream acidity and to improve vegetation growth and nutrition in forests. Ten years ago, dolomite lime was experimentally applied to a forest catchment on granite in the Vosges Mountains (northeast France), which is characterized by acid soils and drained by an acid stream. The average Mg isotope composition of the dolomite lime (-1.75‰) was low compared with that of tree foliage (-0.70‰), granite and deep soil layers (-0.40‰), and stream water (-0.80‰) in the control catchment. After liming, the exchangeable Mg concentrations in surface soil layers, which were initially very low, increased, and the Mg isotope composition decreased (up to -0.60‰). The decrease was smaller in deeper layers but not in proportion to the increase in exchangeable Mg content, suggesting contributions from mineralization of organic matter and/or displacement of exchangeable Mg from surface layers. Before application, Mg concentration in beech and fir leaves was low, and that of 1-yr-old fir needles was lower than that in current needles. Internal Mg translocation within fir needles also resulted in a lower δMg of older needles. Three years after dolomite application, the Mg isotope composition of plant leaves was lower than that in the control catchment; this decrease (up to -1.00‰) was attributed to direct uptake of Mg from dissolving dolomite. Liming doubled the concentration of Mg in the stream, whereas the Mg isotope composition decreased correspondingly from -0.80 to -1.20‰, indicating a fast transfer of dolomite Mg to the stream. Our findings indicate that monitoring of δMg may be a promising tool to study the fate of dolomitic inputs in terrestrial and aquatic ecosystems.

Mg isotope composition in beech forest ecosystems and variations induced by liming: insights from four experimental sites in Northern France

“…Because the difference in Mg isotopic signature between carbonate rocks and Mg pools in forest ecosystems is most often sufficiently big, the Mg released from the liming product can be traced in the ecosystem and its contribution to the different pools of Mg in the ecosystem can be quantified. * (Bedel 2015;Bizzarro et al 2005;Bolou-Bi et al 2016;Bolou-Bi et al 2009;Bolou-Bi et al 2012;Brenot et al 2008;De Villiers et al 2005;Kimmig et al 2018;Opfergelt et al 2014;Teng et al 2007;Wiechert & Halliday 2007;Young & Galy 2004).…”

“…In forest ecosystems, the Mg pool in the organic layer originates mostly from leaf litter inputs and atmospheric inputs that are retained on the cationic exchange capacity of the organic layer(van der Heijden et al 2014). The δ 26 Mg values of atmospheric inputs ranges from -1.05 to -0.51‰(Bedel 2015;Bolou-Bi et al 2012;Pogge von Strandmann et al 2008;Tipper et al 2010) and was lower than the δ 26 Mg values of organic layers at all sites (except at Fougères).Furthermore, previous study in forest ecosystems highlight that leaf litter is slightly enriched in24 Mg compared to green leaves due to re-translocation of the foliar Mg during the growing season(Bedel 2015;Black et al 2007;Bolou-Bi et al 2016;Bolou-Bi et al 2012;Kimmig et al 2018;Kraj 2015;Matile 2000;Moynier & Fujii 2017), which would imply that the δ 26 Mg values of leaf litter at our four sites (not measured) was equal or below the measured foliar δ 26 Mg values. It would thus not be possible to obtain the δ 26 Mg values measured in the organic layer from the simple isotopic mixing of these two sources (i.e.…”

“…1), Mg isotope ratios can, under certain conditions, be used to trace ecosystem sources (Bolou-Bi et al, 2012). A sufficient difference of Mg isotopic composition between the liming product and the Mg pools in the forest ecosystem may allow for tracing the fate and distribution of the Mg originating from the dissolution of the liming product, as demonstrated by Bolou-Bi et al (2016) on two paired forest catchments in the Vosges Mountains (one control and one limed).…”

Fractionation and assimilation of Mg isotopes by fungi is species dependent

“…with 7 M HCl) and AG50W‐X12 cation‐exchange resin (to eliminate major cations with 1 M HNO 3 ), as described by Bolou‐Bi and colleagues (2009). The efficiency of Mg separation from interfering cations was improved further by reducing the length of the column and changing both the acid used and its concentration (Bolou‐Bi et al ., ). Depending on the sample (mycelium or mineral substrate) Mg purification was achieved using either two or three purification stages and subsequently checking the molar ratio of the sum of all cations and Mg (Σ[cation]/Σ[Mg]) that was expected to be lower than 0.05 to avoid the effects of matrices and mass bias during the isotope ratio measurement (Galy et al ., ).…”

A century of liming affects the Mg isotopic composition of the soil and crops in a long‐term agricultural field at Berlin‐Dahlem, Germany

“…The only study on agricultural soil so far by Gao et al (2018) reported increasing values of bulk soil δ 26 Mg with soil depth, from −0.85‰ in topsoil to −0.59‰ in soil at 100-cm depth, in a paddy soil developed from a latosol because of the decreasing Mg content retained on exchangeable sites. Similarly, soil management practices such as liming can also lead to differing δ 26 Mg values, particularly if the applied lime contains Mg of a different isotope composition from that found in the bulk soil, such as dolomite (Bolou-Bi et al, 2016). We hypothesize that differing isotope compositions of Mg in topsoil and subsoil can be used to evaluate the effect of soil managements on Mg uptake by crops.…”