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.

摘要

Effects of Mg deficiency and variations of the NO3-:NH4+ 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).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 NO3-:NH4)>+ ratio in the nutrient solutions was adjusted to 0.76 in theMg-sufficient treatment and to 1.86, 0.76 or 0.035 in Mg-limited treatments. NH4+-dominated nutrition resulted in decreased height growth and significantly lower Mg and chlorophyll concentrations in current-year and one-year-old needles compared with NO3--dominated nutrition. Decreases in total Mg were linearly correlated with reductions of water-soluble Mg and water-insoluble 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 NH4+-dominated, were strongly correlated with the portion of Cabound to oxalate. The amounts of water-soluble Ca and pectate-bound Ca remained nearly constant, independent of changes in total Ca concentrations. It was suggested that negative effects of increasing NH4+ supply on concentrations of Mg and other cationsin the needles could be attributed to an inhibition of cation uptake induced by ion antagonism and/or reduced root growth.