Ammonium and nitrate uptake rates and rhizosphere pH in non-mycorrhizal roots of Norway spruce [Picea abies (L.) Karst.] |
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Authors: | Horst Marschner Max Häussling Eckhard George |
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Institution: | (1) Institute of Plant Nutrition, University of Hohenheim, P. O. Box 700562, 7000 Stuttgart 70, Federal Republic of Germany |
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Abstract: | Summary Relationships between root zone temperature, concentrations and uptake rates of NH
4
+
and NO
3
–
were studied in non-mycorrhizal roots of 4-year-old Norway spruce under controlled environmental conditions. Additionally, in a forest stand NH
4
+
and NO
3
–
uptake rates along the root axis and changes in the rhizosphere pH were measured. In the concentration (Cmin) range of 100–150 M uptake rates of NH
4
+
were 3–4 times higher than those of NO
3
–
The preference for NH
4
+
uptake was also reflected in the minimum concentration (Cmin) values. Supplying NH4NO3, the rate of NO
3
–
uptake was very low until the NH
4
+
concentrations had fallen below about 100 M. The shift from NH
4
+
to NO
3
–
uptake was correlated with a corresponding shift from net H+ production to net H+ consumption in the external solution. The uptake rates of NH
4
+
were correlated with equimolar net production of H+. With NO
3
–
nutrition net consumption of H+ was approximately twice as high as uptake rates of NO
3
–
In the forest stand the NO
3
–
concentration in the soil solution was more than 10 times higher than the NH
4
+
concentration (<100 M), and the rhizosphere pH of non-mycorrhizal roots considerably higher than the bulk soil pH. The rhizosphere pH increase was particularly evident in apical root zones where the rates of water and NO
3
–
uptake and nitrate reductase activity were also higher. The results are summarized in a model of water and nutrient transport to, and uptake by, non-mycorrhizal roots of Norway spruce in a forest stand. Model calculations indicate that delivery to the roots by mass flow may meet most of the plant demand of nitrogen and calcium, and that non-mycorrhizal root tips have the potential to take up most of the delivered nitrate and calcium. |
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Keywords: | Ammonium Calcium Nitrate Picea abies Rhizosphere pH |
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