The relative contribution of symbiotic N2 fixation and other nitrogen sources to grassland ecosystems along an altitudinal gradient in the Alps |
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Authors: | Jacot Katja A Lüscher Andreas Nösberger Josef Hartwig Ueli A |
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Institution: | (1) Institute of Plant Sciences, ETH-Zurich, 8092 Zurich, Switzerland;(2) Institute of Plant Sciences, ETH-Zurich, 8092 Zurich, Switzerland |
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Abstract: | The significance of symbiotic N2 fixation in legumes (Trifolium alpinum L., T. nivale Sieber, T. pratense L., T. badium Schreber, T. thalii Vill., T. repens L., Lotus alpinus DC.] Schleicher, L. corniculatus L., Vicia sativa L.) and other N sources for the N budget of grassland ecosystems was studied along an altitudinal gradient in the Swiss Alps.
The total annual symbiotic N2 fixation was compared with other sources of N for plant growth of the total plant community (mineralisation and wet deposition).
The contribution of symbiotically fixed N to total above-ground N yield of the swards decreased from at least 16% to 9% with
increasing altitude where legumes were present. This decrease was due to a decrease in the yield proportion of legumes from
15% at 900 and 1380 m a.s.l. to 5% at 2100 and 2300 m a.s.l. (no legumes were found above 2750 m a.s.l.) and not to a decline
in the activity of symbiotic N2 fixation. With increasing altitude legumes are more patchily distributed. The high symbiotic N2 fixation of individual plants up to their altitudinal limit is not primarily the result of low mineral N availability since
an addition of NH4
+ or NO3
− fertiliser at 2300 m a.s.l. led either to no decrease or only to a minor decrease in symbiotic N2 fixation. At 1380 m a.s.l., N mineralisation (13.45 g N m−2 yr−1) appeared to be the main source of N for growth of the sward; N from symbiosis (at least 1.0 g to 2.6 g N m−2 yr−1) and wet deposition (0.4 g to 0.6 g m−2 yr−1) was not a significant N source for plant growth at this altitude. At 2100 m a.s.l., the combined amounts of N from symbiotic
N2 fixation (at least 0.1 g N m−2 yr−1) and wet deposition (0.3 g N m−2 yr−1) appeared to be similarly important for plant growth as soil N mineralisation (0.47 g N m−2 yr−1). At high altitudes, wet N deposition and symbiotic N2 fixation together represent a significant source of N for the grassland ecosystem while at low altitudes these N inputs appear
to be much less important.
This revised version was published online in June 2006 with corrections to the Cover Date. |
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Keywords: | Alpine ecosystem Lotus N sources rhizobia Trifolium |
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