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Influences of different nitrate to ammonium ratios on chlorosis, cation concentrations and the binding forms of Mg and Ca in needles of Mg-deficient Norway spruce

B. Mehne-Jakobs and M. Gülpen
Plant and Soil
Vol. 188, No. 2 (January (II) 1997), pp. 267-277
Published by: Springer
Stable URL: http://www.jstor.org/stable/42947934
Page Count: 11
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Influences of different nitrate to ammonium ratios on chlorosis, cation concentrations and the binding forms of Mg and Ca in needles of Mg-deficient Norway spruce
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Abstract

Effects of Mg deficiency and variations of the $NO_3^ - /NH_4^ + $-ratio on chlorophyll, mineral nutrient concentrations and the binding forms of Mg and Ca were investigated in current-year, one-and two-year-old needles of clonal Norway spruce (Picea abies [L.] Karst.). Six-year-old spruce plants were grown for one year in sand culture with circulating nutrient solutions containing sufficient (0.2 mM) or limiting (0.04 mM) concentrations of Mg. The $NO_3^ - /NH_4^ + $-ratio in the nutrient solutions administered to the experimental trees was adjusted to 0.76 in the Mgsufficient treatment and to 1.86,0.76 and 0.035 in Mg-limited treatments. Mg and chlorophyll concentrations, were strongly influenced by the applied nitrogen source in current-year needles and - to a less extent - also in one-year-old needles. $NH_4^ + $-dominated nutrition resulted in decreased height growth and significantly lower Mg and chloropyhll concentrations in current-year and one-year-old needles compared to $NO_3^ - $-dominated nutrition. Decreases in total Mg were linearly correlated to reductions of water-soluble Mg and water-unsoluble Mg not bound to chlorophyll. Mg bound to chlorophyll, however, was only reduced, when total Mg decreased below a physiological threshold value of 2% of the total nitrogen concentration in the respective needles. Total Ca concentrations in the needles, which were reduced by Mg deficiency especially when nutrition was $NH_4^ + $-dominated, were strongly correlated to the portion of Ca bound to oxalate. The amount of water-soluble Ca and pectate-bound Ca remained nearly constant, independent from changes of total Ca concentrations. Negative effects of increasing $NH_4^ + $ supply on concentrations of Mg and other cations in the needles can be attributed to an inhibition of cation uptake induced by ion antagonism and/or reduced root growth.

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