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Defoliation, soil grazing legacy, dung and moss cover influence growth and nutrient uptake of the common grass species, Festuca ovina
Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences. (Arcum)
Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences. (Arcum)
Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences. (Arcum)
(English)Manuscript (preprint) (Other academic)
Abstract [en]

Herbivores can strongly influence plant growth directly through defoliation and the return of nutrients in the form of dung and urine but also indirectly by reducing the abundance of neighbouring plants and inducing changes in soil processes. The relative importance of these driving mechanisms of plant response to herbivory are still poorly understood. In a common garden experiment, we studied the aboveground and belowground responses of Festuca ovina, a grazing tolerant grass common in arctic secondary grassland, to defoliation, reindeer dung addition, changes in soil microclimate induced by the presence or the absence of a moss cover, and soil grazing legacy. Defoliation strongly reduced shoot and root growth and plant nutrient uptake. Plants did thus not compensate for the tissue lost due to defoliation, even at a higher nutrient availability. By contrast, defoliation enhanced plant N concentration and decreased plant C to N ratio. Soil from heavily grazed sites and dung addition increased plant production, plant N concentrations and nutrient uptake, although the effects of dung addition were only small. Mosses had a strong negative effect of root biomass and reduced plant compensatory growth after defoliation. Interestingly mosses also had facilitative effects on aboveground plant growth in absence of defoliation and on plant nutrient uptake and N concentrations. Although plants suffered severely from defoliation, they were also strongly favoured by the increased nutrient availability associated with herbivory. After two years, plants produced as much biomass when all positive and negative effects of herbivores were considered (defoliation, soil communities and nutrient availability under heavily grazing, dung addition and no moss cover) as in the ungrazed conditions (no defoliation, soil communities and nutrient availability under lightly grazing, no dung addition, a thick moss cover). This study indicates that graminoids can tolerate high densities of herbivores, although it suffer from defoliation directly, and suggests that changes in plant quality following defoliation and grazing-induced changes in soil processes are two key mechanisms through which herbivores can control plant productivity in arctic secondary grasslands. Plant tolerance to herbivory will depends on how herbivores utilise a pasture area and on the balance between the positive and the negative effects of grazing on plant growth.

Keyword [en]
Arctic tundra, Compensatory growth, Defoliation, Mosses, Plant nutrient uptake, Plant performance, Plant tolerance to herbivory, Reindeer grazing, Soil nutrient availability
National Category
Ecology
Research subject
biology
Identifiers
URN: urn:nbn:se:umu:diva-120189OAI: oai:DiVA.org:umu-120189DiVA: diva2:927065
Available from: 2016-05-10 Created: 2016-05-10 Last updated: 2016-06-30
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.
Keyword
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
Ecology
Research subject
biology, Environmental Science; biology
Identifiers
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)
Opponent
Supervisors
Available from: 2016-05-12 Created: 2016-05-10 Last updated: 2016-06-30Bibliographically approved

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Barthelemy, HélèneDorrepaal, EllenOlofsson, Johan
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