Manganese deficiency of silver fir trees (Abies alba) at a reforested site in the Jura mountains, Switzerland: aspects of cause and effect

Abstract

We examined manganese uptake and translocation in 30-year-old silver fir trees (Abies alba Mill.) showing severe symptoms of needle chlorosis by analyzing both xylem and phloem sap of shoots and an extract of root sap originating from both xylem and phloem elements. Manganese concentrations in shoot xylem and phloem sap were significantly lower in chlorotic trees than in neighboring healthy trees. The Mn concentration of root sap was also lower in these Mn-deficient trees than in healthy trees, indicating reduced Mn uptake by Mn-deficient trees. Although Mn deficiency had no effect on the Mn concentration of whole roots, separation of root tissue into root cortex and stele (wood) suggested impaired translocation of Mn from the cortex to the stele in Mn-deficient trees. Triphenyltetrazolium chloride (TTC) tests indicated that there was no decrease in reducing capacity of the fine roots (< 1 mm in diameter) of Mn-deficient trees. Fine roots of Mn-deficient trees contained significantly more organic acids than fine roots of healthy trees, including increased concentrations of malic, quinic, trans-acontic and formic acid; however, concentrations of pyruvic and acetic acid were lower than in fine roots of healthy trees. The total amounts of organic acids in the rhizospheric soil were similar for healthy and Mn-deficient trees. Pyruvic acid concentration was significantly increased in the rhizospheric soil of Mn-deficient trees, and concentrations of simple aliphatic acids like formic and acetic acid also tended to be higher in the rhizospheric soil of Mn-deficient trees. Both pH and water content were higher in bulk soil and rhizospheric soil around Mn-deficient trees compared with soil around healthy trees. Although lower concentrations of exchangeable Mn were found in the soil around Mn-deficient trees, the active Mn concentration (sum of exchangeable and reducible Mn) did not differ between healthy and Mn-deficient trees. A considerable proportion of manganese was in an oxidized form in the soil around Mn-deficient trees.