Abstract
For the first time in an arctic long-term warming and fertilization experiment, the short-term (days) and longer-term (month and year) nitrogen (N) uptake and allocation in plants, microbes, and soil pools were studied, with 15N-labeling of an organic nitrogen form, glycine. The long-term warming and fertilization had no marked effect on soil inorganic N content, but both dissolved organic N (DON) and plant biomass did increase after fertilization. Soil microbes initially immobilized most of the added 15N, but in the following months, they lost two-thirds, while label concentration in plants increased. After a year, however, the 15N recovered in microbes was still 10-fold higher than that in the plant biomass, showing the high importance of soil microbes in nutrient retention in arctic ecosystems, irrespective of the impact of long-term warming or fertilization. The effects of the treatments on the uptake of label by deciduous shrubs and evergreens paralleled that of their N pool sizes, suggesting that their N uptake potential was unaffected by long-term warming and fertilizer addition. Mosses and herbs had high uptake potential but in fertilized plots they took up less 15N, that is, they were N saturated. The fraction of 15N in microbes tended to decrease after fertilization, but this was an effect of higher N pool dilution after 1 month and a year, and not due to lower initial uptake. Although the concentration of soil inorganic N did not change after fertilization, both increased DON and the results of the 15N label addition showed that the N availability in the ecosystem had increased. By contrast, warming had little effect on soil N pools and microbial 15N uptake, and, hence, had no detectable effects on 15N accumulation.
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Acknowledgments
The authors are grateful for the excellent logistic facilities provided by the Abisko Scientific Research Station. We thank Jane Kongstad Pedersen, Anja Vilsholm, and Vivian Danielsen for help in the field, and Gosha Sylvester and Esben Vedel Nielsen for assistance with laboratory analyses. Dr. Lena Ström from the University of Lund kindly assisted with amino acid analyses. We also thank two anonymous referees for helpful suggestions to improve the paper. This research was funded by The Faculty of Science, University of Copenhagen and the Danish Science Research Council.
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Sorensen, P.L., Michelsen, A. & Jonasson, S. Nitrogen Uptake During One Year in Subarctic Plant Functional Groups and in Microbes After Long-Term Warming and Fertilization. Ecosystems 11, 1223–1233 (2008). https://doi.org/10.1007/s10021-008-9204-6
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DOI: https://doi.org/10.1007/s10021-008-9204-6