Citation: Müller, B.; Arcoverde Cerveira Sterner, V.; Papp, L.; May, Z.; Orlóci, L.; Gyuricza, C.; Sági, L.; Solti, Á.; Fodor, F. Alkaline Salt Tolerance of the Biomass Plant Arundo donax. Agronomy 2022, 12, 1589. https://doi.org/10.3390/ agronomy12071589 Academic Editors: Monica Boscaiu and Ana Fita Received: 4 June 2022 Accepted: 28 June 2022 Published: 30 June 2022 Publisher’s Note: MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affil- iations. Copyright: © 2022 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https:// creativecommons.org/licenses/by/ 4.0/). agronomy Article Alkaline Salt Tolerance of the Biomass Plant Arundo donax Brigitta Müller 1 , Vitor Arcoverde Cerveira Sterner 1,2 ,László Papp 3 , Zoltán May 4 ,László Orlóci 5 , Csaba Gyuricza 6 ,László Sági 7 , Ádám Solti 1 and Ferenc Fodor 1,6, * 1 Department of Plant Physiology and Molecular Plant Biology, ELTE Eötvös Loránd University, Pázmány Péter Lane 1/c, 1117 Budapest, Hungary; brigitta.lantos@ttk.elte.hu (B.M.); vitor.arcoverde@gmail.com (V.A.C.S.); adam.solti@ttk.elte.hu (Á.S.) 2 Doctoral School of Environmental Sciences, ELTE Eötvös Loránd University, Pázmány Péter Lane 1/a, 1117 Budapest, Hungary 3 Botanical Gardens, ELTE Eötvös Loránd University, Illés Street 25, 1083 Budapest, Hungary; papplaca@gmail.com 4 Institute of Materials and Environmental Chemistry, Research Centre for Natural Sciences, Eötvös Loránd Research Network, Magyar Tudósok Blvd. 2, 1117 Budapest, Hungary; may.zoltan@ttk.mta.hu 5 Research Group of Ornamental Horticulture and Green System, Institute of Landscape Architecture, Urban Planning and Garden Art, Hungarian University of Agriculture and Life Sciences, Villányi Street 29-43, 1118 Budapest, Hungary; orloci.laszlo@uni-mate.hu 6 Institute of Agronomy, Hungarian University of Agriculture and Life Sciences, Páter Károly Street 1, 2100 Gödöll˝ o, Hungary; gyuricza.csaba@uni-mate.hu 7 Centre for Agricultural Research, Eötvös Loránd Research Network, Brunszvik Street 2, 2462 Martonvásár, Hungary; sagi.laszlo@atk.hu * Correspondence: ferenc.fodor@ttk.elte.hu Abstract: Soil alkalinization and salinization have increased worldwide due to extreme and/or prolonged drought periods as well as insufficient irrigation. Since crops generally react to soil salinity and high pH with decreased yield, the cultivation of tolerant biomass plants represents a reasonable alternative. Thus, we aimed to characterize the tolerance of the biomass plant Arundo donax to alkaline salt stress, induced by irrigation water containing NaHCO 3 and Na 2 CO 3 mixture (1:1) at 80 mM and 200 mM of final concentration and pH 10. In terms of physiological parameters such as transpiration, chlorophyll content, photosystem II quantum efficiency, relative water content, and water saturation, the plants were resistant to the stress treatment. The negative impact on the water regime was only measured at 200 mM salt. The K/Na ratio decreased in parallel with Na accumulation. Plants also accumulated Zn, whereas a decrease in the concentration of most other elements (Ca, Cu, K, Mg, Ni, S, Si, and Sr) was detected. Antioxidative defence directed by multiple symplastic enzymes contributed to the high physiological tolerance to the applied stress. In conclusion, the cultivation of Arundo donax as a biomass crop appears to be a feasible alternative in areas affected by salinity or alkaline salt accumulation. Keywords: oxidative stress; photosynthesis; relative water content; salinity; sodicity 1. Introduction Salt stress of land plants can arise upon exposure to an excessive salt accumulation in the soil, which is well-above the concentrations required for optimal growth and devel- opment [1]. Soil salinity is usually associated with high sodium chloride (NaCl) content, but in a non-marine environment (e.g., agroecosystems), it is caused by the combination of sodium, calcium, potassium, magnesium, chlorides, nitrates, sulphates, bicarbonates, and carbonates. Combined with an extreme water regime, sodium-rich deposits often cause an elevated sodium concentration in the upper soil layers. Therefore, in a temperate climate, sodium salinity (sodicity) is one of the most serious factors that limit crop productivity, with adverse effects on seed germination, plant vigour, and crop yield [2–4]. Nearly 1 billion hectares are affected worldwide by high salinity [5] causing reduced soil porosity and Agronomy 2022, 12, 1589. https://doi.org/10.3390/agronomy12071589 https://www.mdpi.com/journal/agronomy