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|Koppisch, D; Schulze, ED; Gebauer, G: 15N-labelled ammonium and nitrate uptake by the grass Calamagrostis villosa, Isotopes Environm. Health Studies, 29, 77-84 (1993), doi:10.1080/10256019308046138|
Calamagrostis villosa dominates the understory vegetation in declining spruce forests at higher elevations of the Central European mountain areas which show symptoms of needle yellowing and associated magnesium (Mg) deficiency. It was hypothesized that grasses would preferentially take up nitrate-nitrogen (NO3--N) over ammonium-nitrogen (NH4+-N) which would support the cation balance in Mg deficient soils. In order to test this hypothesis, growth experiments were carried out in the greenhouse using plants which were cultivated in sand for nine weeks with full nutrient solution containing 0.2 or 2 mmol of N with different NH4+ to NO3- ratios (1:0, 0.5:0.5, 0:1). In a short term experiment with labelled (NH4+)-15N and (NO3-)-15N, uptake of NH4+ and NO3- was measured. When NO3- was the only N source it was taken up at similar rate per g dry mass as in the experiment in which NH4+ was the only N source. However, at high supply pure NO3- nutrition resulted in higher biomass. In contrast, supply of only NH4+ caused accumulation of N in the roots but growth remained restricted. If NH4+ and NO3- were supplied at equal amounts, NH4+ was the preferred form for N uptake. Biomass of the plants with mixed supply did not differ from the plants with pure NO3- nutrition.
The results point to an interesting interaction of carbon and nitrogen relation, but they do not support the initial hypothesis that grasses may prefer NO3- over NH4+.