Chemical composition of halophytes from the Neusiedler Lake region in Austria

The ionic relations in halophytes from the region east of Neusiedler Lake in Austria have been investigated. The study encompasses the following compounds: Na, K, Mg, Ca; Cl, SO₄, phosphate, nitrate, and organic acids.The ionic composition varies substantially among the species investigated. Frequently a specific pattern of ion content can be found within a specific taxon. a) Dicotyledons: Extraordinary accumulation of sodium, high intake of inorganic ions (mainly Cl, less SO₄), and regular occurrence of free oxalate, causing low Ca-concentrations, are typical for Chenopodiaceae and Caryophyllaceae (Spergularia media). Lepidium crassifolium shows similar sodium preponderance accompanied by high levels of SO₄, Cl, and organic anions other than oxalate (mainly citrate and malate). The remaining dicotyledons show rather moderate salt content; Asteraceae and Cichoriaceae prefer Cl, and Plantago maritima accumulates high amounts of SO₄ as well as Cl. Malate and citrate are, without exception, the main organic anions. The K:Na ratios in dicotyledons (esp. Chenopodiaceae and Lepidium-Brassicaceae) lie far below unity. b) Monocotyledons: In marked contrast, Poaceae, Cyperaceae, and Juncaceae are characterized by a general low salt status. With few exceptions, Cl is stored as the main inorganic anion, phosphate reaches higher levels than in dicotyledons and in many cases lies in nearly the same concentration range as SO₄. The pattern of organic anions with malate and citrate as the main acids, does not basically differ from nonhalophilous species. In any case, K:Na ratio exceeds unity. Triglochin maritimum is the only monocotyle species exhibiting as high salt content and low K:Na ratios as dicotyledons. Nitrate and phosphate are of minor quantitative importance with regard to their osmotic efficiency; their mEq percentage of the total anion concentration range between 0.03 to 2.6 (NO₃) and 0.5 to 13.6 (phosphate), respectively.The results are discussed from different points of view: on the one hand, the general problems of salt tolerance, on the other hand, the taxonomical and ecological aspects. beneficial to plant growth in view of salt sensitivity of enzymatic reactions. However, low osmotic potential of cell sap, and consequently, the acquisition of water is guaranteed by storing high amounts of sugars: according to our data (Albert and Popp, in preparation) total sugar concentration in halophilous Poaceae, Cyperaceae, and Juncaceae amounts to up to 200 mmol·l^-1 fresh water, whereas in salt rich dicotyle species the sugar content is comparatively low (up to 50 mmol).