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Strong Responses of Subarctic Plant Communities to Long-Term Reindeer Feces Manipulation
Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences. (Arcum)
Rovaniemi, Finland.
Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences. (Arcum)
2015 (English)In: Ecosystems (New York. Print), ISSN 1432-9840, E-ISSN 1435-0629, Vol. 18, no 5, 740-751 p.Article in journal (Refereed) Published
Abstract [en]

Deposition of feces is a key mechanism by which herbivores influence soil nutrient cycling and plant production, but the knowledge about its importance for plant production and community structure is still rudimental since experimental evidence is scarce. We thus performed a 7-year long reindeer feces manipulation experiment in two tundra vegetation types with contrasting nutrient availability and analyzed effects on plant community composition and soil nutrient availability. Despite feces being fairly nutrient poor, feces manipulation had strong effect on both the nutrient-poor heath and the nutrient-rich meadow. The strongest effect was detected when feces were added at high density, with a substantial increase in total vascular plant productivity and graminoids in the two communities. Doubling natural deposition of reindeer feces enhanced primary production and the growth of deciduous shrubs in the heath. By contrast, removal of feces decreased only the production of graminoids and deciduous shrubs in the heath. Although the response to feces addition was faster in the nutrient-rich meadow, after 7 years it was more pronounced in the nutrient-poor heath. The effect of feces manipulation on soil nutrient availability was low and temporarily variable. Our study provides experimental evidence for a central role of herbivore feces in regulating primary production when herbivores are abundant enough. Deposition of feces alone does, however, not cause dramatic vegetation shifts; to drive unproductive heath to a productive grass dominated state, herbivore trampling, and grazing are probably also needed.

Place, publisher, year, edition, pages
Springer, 2015. Vol. 18, no 5, 740-751 p.
Keyword [en]
alpine meadow, feces fertilization, forage quality, plant-herbivore interactions, microbial mobilization, plant productivity, reindeer grazing, soil nutrient availability, tundra heath
National Category
Ecology Earth and Related Environmental Sciences
URN: urn:nbn:se:umu:diva-106774DOI: 10.1007/s10021-015-9856-yISI: 000358089100002OAI: diva2:846146
Available from: 2015-08-14 Created: 2015-08-07 Last updated: 2016-05-20Bibliographically approved
In thesis
1. Herbivores influence nutrient cycling and plant nutrient uptake: insights from tundra ecosystems
Open this publication in new window or tab >>Herbivores influence nutrient cycling and plant nutrient uptake: insights from tundra ecosystems
2016 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Reindeer appear to have strong positive effects on plant productivity and nutrient cycling in strongly nutrient-limited ecosystems. While the direct effects of grazing on vegetation composition have been intensively studied, much less is known about the indirect effect of grazing on plant-soil interactions. This thesis investigated the indirect effects of ungulate grazing on arctic plant communities via soil nutrient availability and plant nutrient uptake.

At high density, the deposition of dung alone increased plant productivity both in nutrient rich and nutrient poor tundra habitats without causing major changes in soil possesses. Plant community responses to dung addition was slow, with a delay of at least some years. By contrast, a 15N-urea tracer study revealed that nutrients from reindeer urine could be rapidly incorporated into arctic plant tissues. Soil and microbial N pools only sequestered small proportions of the tracer. This thesis therefore suggests a strong effect of dung and urine on plant productivity by directly providing nutrient-rich resources, rather than by stimulating soil microbial activities, N mineralization and ultimately increasing soil nutrient availability. Further, defoliation alone did not induce compensatory growth, but resulted in plants with higher nutrient contents. This grazing-induced increase in plant quality could drive the high N cycling in arctic secondary grasslands by providing litter of a better quality to the belowground system and thus increase organic matter decomposition and enhance soil nutrient availability. Finally, a 15N natural abundance study revealed that intense reindeer grazing influences how plants are taking up their nutrients and thus decreased plant N partitioning among coexisting plant species.

Taken together these results demonstrate the central role of dung and urine and grazing-induced changes in plant quality for plant productivity. Soil nutrient concentrations alone do not reveal nutrient availability for plants since reindeer have a strong influence on how plants are taking up their nutrients. This thesis highlights that both direct and indirect effects of reindeer grazing are strong determinants of tundra ecosystem functioning. Therefore, their complex influence on the aboveground and belowground linkages should be integrated in future work on tundra ecosystem N dynamic.

Place, publisher, year, edition, pages
Umeå: Umeå University, 2016. 36 p.
Reindeer grazing, large herbivores, nutrient cycling, plant nutrient uptake, soil nutrient availability, arctic plant ecology, soil microbial communities, 15N stable isotopes, plant-soil interactions, plant quality, dung and urine.
National Category
Research subject
biology, Environmental Science; biology
urn:nbn:se:umu:diva-120191 (URN)978-91-7601-456-1 (ISBN)
Public defence
2016-06-03, Lilla Hörsalen, KBC (KB3A9), Umeå, 13:00 (English)
Available from: 2016-05-12 Created: 2016-05-10 Last updated: 2016-06-30Bibliographically approved

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