Natural 15 N abundance in two nitrogen saturated forest ecosystems
Natural N abundance values were measured in needles, twigs, wood, soil, bulk precipitation, throughfall and soil water in a Douglas fir (Pseudotsuga menziesii (Mirb.) and a Scots pine (Pinus sylvestris L.) stand receiving high loads of nitrogen in throughfall (>50 kg N ha year ). In the Douglas...
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Published in | Oecologia Vol. 111; no. 4; pp. 470 - 480 |
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Main Authors | , , , |
Format | Journal Article |
Language | English |
Published |
Germany
08.08.1997
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Subjects | |
Online Access | Get full text |
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Summary: | Natural
N abundance values were measured in needles, twigs, wood, soil, bulk precipitation, throughfall and soil water in a Douglas fir (Pseudotsuga menziesii (Mirb.) and a Scots pine (Pinus sylvestris L.) stand receiving high loads of nitrogen in throughfall (>50 kg N ha
year
). In the Douglas fir stand δ
N values of the vegetation ranged between -5.7 and -4.2‰ with little variation between different compartments. The vegetation of the Scots pine stand was less depleted in
N and varied from -3.3 to -1.2‰δ
N. At both sites δ
N values increased with soil depth, from -5.7‰ and -1.2‰ in the organic layer to +4.1‰ and +4.7‰ at 70 cm soil depth in the Douglas fir and Scots pine stand, respectively. The δ
N values of inorganic nitrogen in bulk precipitation showed a seasonal variation with a mean in NH
-N of -0.6‰ at the Douglas fir stand and +10.8‰ at the Scots pine stand. In soil water below the organic layer NH
-N was enriched and NO
-N depleted in
N, which was interpreted as being caused by isotope fractionation accompanying high nitrification rates in the organic layers. Mean δ
N values of NH
and NO
were very similar in the drainage water at 90 cm soil depth at both sites (-7.1 to -3.8‰). A dynamic N cycling model was used to test the sensitivity of the natural abundance values for the amount of N deposition, the
N ratio of atmospheric N deposited and for the intrinsic isotope discrimination factors associated with N transformation processes. Simulated δ
N values for the N saturated ecosystems appeared particularly sensitive to the
N ratio of atmospheric N inputs and discrimination factors during nitrification and mineralization. The N-saturated coniferous forest ecosystems studied were not characterized by elevated natural
N abundance values. The results indicated that the natural
N abundance values can only be used as indicators for the stage of nitrogen saturation of an ecosystem if the δ
N values of the deposited N and isotope fractionation factors are taken into consideration. Combining dynamic isotope models and natural
N abundance values seems a promising technique for interpreting natural
N abundance values found in these forest ecosystems. |
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ISSN: | 0029-8549 1432-1939 |
DOI: | 10.1007/s004420050260 |