Deciphering Factors Controlling Manganese Concentrations in the Leaves of Silver Birch (<i>Betula pendula</i> Roth) in Relation to Recent Acidification of Mountain Forest Soils

Abstract

Manganese concentrations in silver birch leaves were studied in the Ore Mountains and several reference localities in Czechia, both mountainous (up to 950 m MSL) and lowland (ca. 300 m MSL). The studied mountainous areas have been seriously damaged by acid rains in the last decades and forests there have still not recovered from that crisis. The aim of this study was to identify the major controls on the foliar Mn concentration variability, which was more than one order of magnitude, from 200 mg kg -1 (10th percentile) to 2000 mg kg -1 (90 th percentile) in the mountainous sites, that is, under uniform environmental conditions and for the same emission history of mountainous forests. The foliar Mn concentrations in the highest 5% samples were >3000 mg kg -1 which can be close to toxicity for persistent tree growth and thus indicate actual local geochemical stress in plants. Manganese uptake by plants has been enhanced by acid rain in the last decades, inferred from low foliar Mg (ca. 0.15%) and soil acidity (soil pH down to 4.0 in aqueous extracts). Certain bedrocks in the Ore Mountains, particularly local granitic porphyry and mafic lavas, have elevated Mn concentrations; however, in the mafic lavas, the soil Mn excess is compensated by elevated concentrations of soil Mg and pH. The highest foliar Mn concentrations were found in specimens growing in soils on granitic porphyry and on certain granites. The Mn concentration in birch leaves could be proposed as a proxy for the impact of soil acidification in central European mountain forests.

Factors controlling Mn and Zn contents in leaves of silver and downy birch in acidified soils of Central Europe and Norway

“…Soil acidification enhances Mn uptake by plants through two primary effects: (i) leaching of the nutrient elements calcium (Ca 2+ ) and magnesium (Mg 2+ ) from the soil, leading to their insufficiency in plants, and (ii) mobilisation of Mn species such as Mn 2+ in the soils (Kazda and Zvacek 1989 ; Marschner 1991 ; Heal 2001 ; Reimann et al 2007a ; Begley-Miller et al 2019 ). These processes that lead to high Mn FECs have been found for certain smaller regions and tree species; however, the interpretation of Mn FEC datasets during these preceding studies has thus far been equivocal (Hrdlička and Kula 2004 ; Reimann et al 2007a ; Bílková et al 2023 ), whereas certain studies have found elevated Mn FECs associated with low concentrations of certain nutrients, such as Ca, Mg, and/or phosphorus (P) (Kogelmann and Sharpe 2006 ; Reimann et al 2007a ; Gransee and Führs 2013 ; Lambers et al 2015 , 2021 ; Gilliam et al 2018 ; Zemunik et al 2020 ; De Oliveira and de Andrade 2021 ; Roth et al 2022 ). Lambers et al ( 2015 , 2021 ) interpreted excess Mn FECs as resulting from an enhanced exudation of organic acids.…”

“…The FECs of nutrients are regulated by homeostasis within relatively narrow ranges and are required to produce all essential metalloenzymes at concentrations needed for plant health (White and Brown 2010 ). In contrast, the variability of Mn FECs is considerably larger (Reimann et al 2001 , 2007a ; Gilliam et al 2018 ; Zemunik et al 2020 ; Araminienė et al 2021 ; Kalliola et al 2021 ; Bílková et al 2023 ), ranging from essential concentrations sufficient for their health (in an order of 10 mg kg −1 ; White and Brown 2010 ; Lambers et al 2015 ) up to 10,000 mg kg −1 in certain hyperaccumulating plants (Lambers et al 2015 ). Most common tree species growing in temperate and boreal forests, such as Norway spruce or European beech, typically show Mn FECs in the order of hundreds to a few thousand mg kg −1 (Reimann et al 2001 ; Kogelmann and Sharpe 2006 ; Houle et al 2007 ; Reimann et al 2007a ; Araminienė et al 2021 ).…”

“…Furthermore, certain common European tree species, including the silver birch ( Betula pendula Roth) and downy birch ( B. pubescens Ehrh. ), show Mn FECs exceeding Mn concentrations in soils (Reimann et al 2001 , 2015 , 2018 ; Wildová et al 2021 ; Bílková et al 2023 ) up to levels that are potentially harmful to these species (Hrdlička and Kula 2004 ; Bílková et al 2023 ). However, the reason for this high Mn accumulation in birches is unknown.…”

“…Lambers et al ( 2015 , 2021 ) interpreted excess Mn FECs as resulting from an enhanced exudation of organic acids. Generally, due to the intricate patterns of geological, topographic, climatic, and anthropogenic controlling factors, the mutual inter-element relationships in Mn uptake have rarely been examined in detail; therefore, this topic requires further research (Reimann et al 2007a ; Kalliola et al 2021 ; Araminienė et al 2021 ; Bílková et al 2023 ). Accordingly, Alejandro et al ( 2020 ) and others (Gilliam et al 2018 ; Zemunik et al 2020 ; Bílková et al 2023 ) considered Mn uptake by plants to be understudied.…”

“…Generally, due to the intricate patterns of geological, topographic, climatic, and anthropogenic controlling factors, the mutual inter-element relationships in Mn uptake have rarely been examined in detail; therefore, this topic requires further research (Reimann et al 2007a ; Kalliola et al 2021 ; Araminienė et al 2021 ; Bílková et al 2023 ). Accordingly, Alejandro et al ( 2020 ) and others (Gilliam et al 2018 ; Zemunik et al 2020 ; Bílková et al 2023 ) considered Mn uptake by plants to be understudied. The high tolerance of birch trees to excess Mn (Wildová et al 2021 ) renders them particularly suitable for large-scale studies on factors promoting Mn uptake by plants in nutrient-poor and degraded soils.…”