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Uptake of pulse injected nitrogen by soil microbes and mycorrhizal and non-mycorrhizal plants in a species-diverse subarctic heath ecosystem

Journal article
Authors Louise C. Andresen
S. Jonasson
L. Strom
A. Michelsen
Published in Plant and Soil
Volume 313
Issue 1-2
Pages 283-295
ISSN 0032-079X
Publication year 2008
Published at
Pages 283-295
Language en
Subject categories Terrestrial ecology


(15)N labeled ammonium, glycine or glutamic acid was injected into subarctic heath soil in situ, with the purpose of investigating how the nitrogen added in these pulses was subsequently utilized and cycled in the ecosystem. We analyzed the acquisition of (15)N label in mycorrhizal and non-mycorrhizal plants and in soil microorganisms, in order to reveal probable differences in acquisition patterns between the two functional plant types and between plants and soil microorganisms. Three weeks after the label addition, with the (15)N-forms added with same amount of nitrogen per square meter, we analyzed the (15)N-enrichment in total soil, in soil K(2)SO(4) (0.5 M) extracts and in the microbial biomass after vacuum-incubation of soil in chloroform and subsequent K(2)SO(4) extraction. Furthermore the (15)N-enrichment was analyzed in current years leaves of the dominant plant species sampled three, five and 21 days after label addition. The soil microorganisms had very high (15)N recovery from all the N sources compared to plants. Microorganisms incorporated most (15)N from the glutamic acid source, intermediate amounts of (15)N from the glycine source and least (15)N from the NH(4)(+) source. In contrast to microorganisms, all ten investigated plant species generally acquired more (15)N label from the NH(4)(+) source than from the amino acid sources. Non-mycorrhizal plant species showed higher concentration of (15)N label than mycorrhizal plant species 3 days after labeling, while 21 days after labeling their acquisition of (15)N label from amino acid injection was lower than, and the acquisition of (15)N label from NH(4) injection was similar to that of the mycorrhizal species. We conclude that the soil microorganisms were more efficient than plants in acquiring pulses of nutrients which, under natural conditions, occur after e. g. freeze-thaw and dry rewet events, although of smaller size. It also appears that the mycorrhizal plants in the short term may be less efficient than non-mycorrhizal plants in nitrogen acquisition, but in a longer term show larger nitrogen acquisition than non-mycorrhizal plants. However, the differences in (15)N uptake patterns may also be due to differences in leaf longevity and woodiness between plant functional groups.

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