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Plant-soil-herbivore interactions in a high Arctic wetland - Feedbacks to the carbon cycle

Falk, Julie Maria LU (2014) In Plant-soil-herbivore interactions in a high Arctic wetland- Feedbacks to the carbon cycle
Abstract (Swedish)
Popular Abstract in Danish

Omkring halvdelen af den globale kulstof mængde som findes i jorden, er lagret i de arktiske jorde. Arktiske jorde har været anset for at være vigtige kulstof reservoirs de sidste 10.000 år, hvor der bliver optaget mere kulstof end der frigives. Dette skyldes blandt andet den langsomme omsætning af organiske materiale på grund af de kolde forhold, men også de store mængder kulstof som ligger gemt i permafrosten. Men med klimaændringer er der tegn på at denne balance er ved at ændre sig og flere har observeret at arktiske økosystemer nu frigiver mere kulstof end de optager. En stor del de arktiske økosystemer er påvirket græssende dyr, som også har stor betydning for kulstof balancen. Deres... (More)
Popular Abstract in Danish

Omkring halvdelen af den globale kulstof mængde som findes i jorden, er lagret i de arktiske jorde. Arktiske jorde har været anset for at være vigtige kulstof reservoirs de sidste 10.000 år, hvor der bliver optaget mere kulstof end der frigives. Dette skyldes blandt andet den langsomme omsætning af organiske materiale på grund af de kolde forhold, men også de store mængder kulstof som ligger gemt i permafrosten. Men med klimaændringer er der tegn på at denne balance er ved at ændre sig og flere har observeret at arktiske økosystemer nu frigiver mere kulstof end de optager. En stor del de arktiske økosystemer er påvirket græssende dyr, som også har stor betydning for kulstof balancen. Deres påvirkning er dog sjældent inkluderet i diskussionen omkring kulstof balancen i en natur som står overfor store klimaændringer.

Dette PhD projekt, omhandler netop den interaktion der er mellem planter, jord og moskusokser i et højarktisk vådområde, i Zackenberg Nordøstgrønland. Det er svært at sige hvad der vil ske med moskusokse populationen med klimaændringer, hvor to modsatrettede senarier er sandsynlige. Ved klimaændringer i Nordøstgrønland følger øget snemængder og flere tø-episoder i den ellers kolde vinter; øget snemængde og de islag som dannes ved tø-episoder vil påvirke populationen negativt, da de ikke vil være i stand til finde føde om vinteren. Klimaændringer vil dog også føre til højere temperaturer som vil øge biomasse produktionen, hvilket vil give dem bedre leve vilkår om sommeren, hvilket vil kunne øge populationen af moskusokserne. Konsekvensen for kulstof balancen i de to scenarier, blev gennem tre år studeret i Zackenberg, hvor både vegetationssammensætningen, CO2 udvekslingen og metan frigivelsen blev moniteret i sommer perioden. Til vores store overraskelse så vi at begge scenarier reagerede på samme vis. I det ene projekt blev moskusokserne ekskluderet ved hjælp af store ”udhegninger”, og her så vi efter tre år at antallet af kærplanter havde faldet drastisk, hvilket førte til et fald på 47% af det samlede CO2 optag og et fald på 44% af metan frigivelsen. I det andet scenarie studie, øgede vi græsnings trykket ved at klippe plots to gange om sommeren, som allerede var udsat for moskusokse græsning. Her så vi allerede første år at CO2 optaget faldt drastisk, gennem de tre års målinger faldt CO2 optaget med 35%. Efter et år havde metan udslippet også faldet, for de sidste to år var metan udslippet faldet med 26%. I et tredje projekt fandt vi en tydelig sammenhæng mellem, hvor produktive planterne var, hvor meget CO2 som blev optaget og den mængde metan som blev frigivet. Og herved kan færre kærplanter ved både øget græsning og ingen græsning forklare både et fald i CO2 optag men også udslippet af metan. I et mindre laboratorie forsøg så vi på hvordan kulstoffet blev fordelt i små tørv-plante prøver fra Zackenberg. Her var der flere indikationer af at kulstoffet bliver fordelt anderledes når disse prøver blev udsat for klipning; hvor mere kulstof blev fordelt til vegetationen over jorden.

Vores resultater har vist at moskusokserne har stor betydning for kulstof balancen i et vådt højarktisk økosystem og deres tilstedeværelse er vigtig at holde for øje når man diskuterer fortidens, nutidens men ikke mindst fremtidens kulstof balance. (Less)
Abstract
Arctic ecosystems hold massive amounts of the global carbon in their soils and are of great importance for the global terrestrial exchange of greenhouse gases to the atmosphere. The arctic region has in general been acting as a C sink for the past 10000 years, however with climate change the C balance in some areas is shifting towards becoming a C source. Herbivory are an important part of many ecosystems and have been found to have an important impact on the C balance. This seemingly important aspect of the C balance in arctic ecosystems are however very rarely considered. In this project, the interactions between plants, soil and herbivores have been studied in a high arctic mire in Zackenberg, northeast Greenland. The aim of the project... (More)
Arctic ecosystems hold massive amounts of the global carbon in their soils and are of great importance for the global terrestrial exchange of greenhouse gases to the atmosphere. The arctic region has in general been acting as a C sink for the past 10000 years, however with climate change the C balance in some areas is shifting towards becoming a C source. Herbivory are an important part of many ecosystems and have been found to have an important impact on the C balance. This seemingly important aspect of the C balance in arctic ecosystems are however very rarely considered. In this project, the interactions between plants, soil and herbivores have been studied in a high arctic mire in Zackenberg, northeast Greenland. The aim of the project was to study the impact of the large herbivores muskoxen on the vegetation composition and density, CO2 and CH4 fluxes and substrate availably for CH4 production.

Over a time period of three years three in-situ field studies were conducted. In paper one and two of this thesis treatments were applied that simulate plausible responses of the muskoxen population with climate change. In paper I muskoxen was excluded from part of the Zackenberg mire, thus representing a decrease in the population. In paper II the grazing pressure was increased, by clipping of plots twice each summer. In paper IV the main in-situ drivers of the spatial variability of CH4 flux was studied. Further, a laboratory study (paper III) was conducted to make an in-depth study on the C allocation pattern in the area and the consequences of clipping.

To our surprise, the results from paper I and II showed that the ecosystem responded in similar ways to changes in grazing pressure despite the contrasting treatments. Both increased and decreased grazing resulted in a decrease in the density of vascular plants, in particular of Eriophorum scheuchzeri (Erioph), and in a substantial decrease in CO2 and CH4 fluxes. The third year into the exclusion experiment in paper I the mean Net Ecosystem Exchange (NEE) of CO2 had decrease with 47%, while the CH4 emission had decreased with 44%. In the clipping experiment in paper II NEE decreased already in year one of the experiment and had after three years decreased with on average 35%. A change in CH4 emission was apparent in year two and over the last two years CH4 emission decreased with on average 26%. In the laboratory study, several factors indicated that clipping altered the C allocation pattern and resulted in more C allocation to above ground vegetation and more root exudation. The results from paper IV showed that there is a strong dependence of the spatial variability in CH4 flux on productivity and C input to vegetation and pore water. The main driver of this carbon input is the vegetation composition, with high number of Erioph tillers leading to high input. Consequently, since both decreased and increased grazing pressure resulted in a decrease in Erioph density both these treatments ultimately resulted in lower productivity and decreased CH4 fluxes.

In conclusion, the results from this thesis clearly show that herbivores are of great importance for the C balance of this wet arctic ecosystem, the driving forces behind this effect being interactions between plants, soil and herbivores. The results from this thesis further points to the importance of considering the impact of herbivory when the past, present or future C balance in the arctic is discussed. (Less)
Please use this url to cite or link to this publication:
author
supervisor
opponent
  • Post, Eric, Penn State University, USA
organization
publishing date
type
Thesis
publication status
published
subject
keywords
Arctic wetlands, carbon balance, herbivory, increased grazing pressure, methane fluxes, muskox exclusion, substrate avalibility, vegetation composition and density
in
Plant-soil-herbivore interactions in a high Arctic wetland- Feedbacks to the carbon cycle
pages
195 pages
publisher
Department of Physical Geography and Ecosystem Science, Lund University
defense location
Pangea auditorium, Sölvegaten 12, Lund
defense date
2014-09-26 10:00
ISBN
978-91-85793-40-2
language
English
LU publication?
yes
id
ad9b2c14-4d42-4b9b-96c8-d1405d7b7be4 (old id 4612142)
date added to LUP
2014-08-29 08:44:54
date last changed
2016-09-19 08:45:11
@misc{ad9b2c14-4d42-4b9b-96c8-d1405d7b7be4,
  abstract     = {Arctic ecosystems hold massive amounts of the global carbon in their soils and are of great importance for the global terrestrial exchange of greenhouse gases to the atmosphere. The arctic region has in general been acting as a C sink for the past 10000 years, however with climate change the C balance in some areas is shifting towards becoming a C source. Herbivory are an important part of many ecosystems and have been found to have an important impact on the C balance. This seemingly important aspect of the C balance in arctic ecosystems are however very rarely considered. In this project, the interactions between plants, soil and herbivores have been studied in a high arctic mire in Zackenberg, northeast Greenland. The aim of the project was to study the impact of the large herbivores muskoxen on the vegetation composition and density, CO2 and CH4 fluxes and substrate availably for CH4 production. <br/><br>
Over a time period of three years three in-situ field studies were conducted. In paper one and two of this thesis treatments were applied that simulate plausible responses of the muskoxen population with climate change. In paper I muskoxen was excluded from part of the Zackenberg mire, thus representing a decrease in the population. In paper II the grazing pressure was increased, by clipping of plots twice each summer. In paper IV the main in-situ drivers of the spatial variability of CH4 flux was studied. Further, a laboratory study (paper III) was conducted to make an in-depth study on the C allocation pattern in the area and the consequences of clipping. <br/><br>
To our surprise, the results from paper I and II showed that the ecosystem responded in similar ways to changes in grazing pressure despite the contrasting treatments. Both increased and decreased grazing resulted in a decrease in the density of vascular plants, in particular of Eriophorum scheuchzeri (Erioph), and in a substantial decrease in CO2 and CH4 fluxes. The third year into the exclusion experiment in paper I the mean Net Ecosystem Exchange (NEE) of CO2 had decrease with 47%, while the CH4 emission had decreased with 44%. In the clipping experiment in paper II NEE decreased already in year one of the experiment and had after three years decreased with on average 35%. A change in CH4 emission was apparent in year two and over the last two years CH4 emission decreased with on average 26%. In the laboratory study, several factors indicated that clipping altered the C allocation pattern and resulted in more C allocation to above ground vegetation and more root exudation. The results from paper IV showed that there is a strong dependence of the spatial variability in CH4 flux on productivity and C input to vegetation and pore water. The main driver of this carbon input is the vegetation composition, with high number of Erioph tillers leading to high input. Consequently, since both decreased and increased grazing pressure resulted in a decrease in Erioph density both these treatments ultimately resulted in lower productivity and decreased CH4 fluxes.<br/><br>
In conclusion, the results from this thesis clearly show that herbivores are of great importance for the C balance of this wet arctic ecosystem, the driving forces behind this effect being interactions between plants, soil and herbivores. The results from this thesis further points to the importance of considering the impact of herbivory when the past, present or future C balance in the arctic is discussed.},
  author       = {Falk, Julie Maria},
  isbn         = {978-91-85793-40-2},
  keyword      = {Arctic wetlands,carbon balance,herbivory,increased grazing pressure,methane fluxes,muskox exclusion,substrate avalibility,vegetation composition and density},
  language     = {eng},
  pages        = {195},
  publisher    = {ARRAY(0x8587ad0)},
  series       = {Plant-soil-herbivore interactions in a high Arctic wetland- Feedbacks to the carbon cycle},
  title        = {Plant-soil-herbivore interactions in a high Arctic wetland - Feedbacks to the carbon cycle},
  year         = {2014},
}