Nitrogen cycling in heathland ecosystems and effects of climate change

Louise Christoffersen Andresen

Nitrogen cycling in heathland ecosystems and effects of climate change

Louise Christoffersen Andresen

Terrestrial Ecology

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Abstract

Over vore terrestriske økosystemer er der til stadighed klimatiske forandringer med øget CO₂, forhøjet temperatur og periodevis forlænget tørke. På tempereret hede i Danmark undersøges de kombinerede effekter af opvarmning, forhøjet CO₂ og forlænget sommer tørke i et unikt fuld faktorielt in situ forsøg (CLIMAITE). Klimabehandlingerne startede i oktober 2005 og består i forhøjet temperatur (T), forlænget sommertørke (D), forhøjet CO₂ og alle kombinationer af disse behandlinger (TD, TCO₂, DCO₂ og TDCO₂).

I dette ph.d arbejde undersøges forandringer i jords uorganiske og organiske næringsstofsammensætning og mikrobiel biomasse efter et års kontinuerlig klimaforandring. Desuden undersøges gennem vinterhalvåret nedbrydningsprocesser i det øverste jordlag som mineralisering, nitrifikation og mikrobiel immobilisering samt nedbrydning af dødt bladmateriale, adskilt for de to dominerende plantearter Calluna vulgaris og Deschampsia flexuosa. Optag af uorganisk og organisk næring undersøges i planter og jordbunds mikroorganismer.

Klimaforandringerne forøgede den mikrobielle biomasse (N, C og P) og blad nedbrydning under Calluna ved forhøjet temperatur, og Deschampsia udviste prematur senescens med mindsket grøn biomasse og øget rod N koncentration. Effekter af opvarmning blev dog ofte modvirket når tørke og CO₂ kombineredes med opvarmning. I jord under Descampsia faldt netto nitrifikations raten efter øget sommer tørke mens den steg i jord under Calluna. Tørke mindskede desuden blad nedbrydningen for begge arter.

I dette ph.d. arbejde undersøges optag af næringsstofferne ammonium og aminosyrer i plante og jordbunds mikroorganismer ved anvendelse af de stabile isotoper ¹⁵N og ¹³C som sporstoffer. Dette vægter korttids konkurrecen på to dværgbusk heder, en med subarktisk klima og en med tempereret klima, tidligt og sent på året. Mikroorgaismer optog den største part af det tilførte nitrogen på begge heder. På begge heder foretrak planter ammonium, dog optages alle kvælstofformer af bade planter og mikroorganismer. På tempereret hede optog mikroorganismerne aminosyrerne glycin, glutamin syre og phenylalanin som hele molekyler og begge dominerende platearter viste tegn på optag af intakt pheylalanin.

Afhandlingen består af en introduktion der samler de fire udarbejdede manuskripter.

Originalsprog	Engelsk

Udgivelsessted	Københavns Universitet
Forlag	Museum Tusculanum
Status	Udgivet - 2008

FN’s Verdensmål

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Andresen thesis 2008Forlagets udgivne version, 1,72 MB

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@phdthesis{8e818790b6f111ddae57000ea68e967b,

title = "Nitrogen cycling in heathland ecosystems and effects of climate change",

abstract = "Terrestrial ecosystems are currently exposed to climatic and air quality changes with increased atmospheric CO2, increased temperature and periodical droughts. At a temperate heath site this was investigated in a unique full factorial in situ experiment (CLIMAITE). The climate change treatments started October 2005 and consisted of increased temperature (T), extended summer drought (D), increased atmospheric CO2 and all combinations of these treatments (TD, TCO2, DCO2 and TDCO2). In this thesis, responses in soil inorganic and microbial nutrient concentration were investigated after one year of climate change treatment. Additionally, top soil net mineralization, immobilization and leaf litter decomposition was investigated through the winter half year separately below Calluna and Deschampsia plants, and acquisition of organic nitrogen in plants and soil microorganisms was assessed.After one year of treatments, warming increased microbial N, C and P and decomposition of leaf litter below Calluna plants. In Deschampsia soil the net nitrification rate decreased significantly in response to drought, by contrast, an increase was observed in Calluna soil. Drought reduced leaf litter decomposition for both species. In warmed plots an early senescence was observed with effects on green Deschampsia biomass, on Deschampsia root nitrogen concentration and on acquisition of 15N from glycine.In this thesis, experiments using the stable isotopes 15N and 13C as tracers of ammonium and amino acid acquisition by plants and soil microorganisms suggest directions of the short term competition at two dwarf shrub heaths, one with sub-arctic climate and one with temperate climate during spring and fall. Soil microorganisms acquired the largest amount of the added nitrogen sources compared to plants at both heath types. At both heaths, plants preferred the inorganic ammonium, yet all nitrogen forms were acquired by both plants and soil microorganisms. At the temperate heath, soil microorganisms acquired the 15N 13C labeled amino acids (glycine, glutamic acid and phenylalanine) as intact compounds, and both dominant plant species showed indications of phenylalanine acquisition as intact compounds. The thesis consists of an introduction collecting the most important findings from the four manuscripts.",

author = "Andresen, {Louise Christoffersen}",

note = "Academic advisor: Anders Michelsen",

year = "2008",

language = "English",

publisher = "Museum Tusculanum",

}

TY - BOOK

T1 - Nitrogen cycling in heathland ecosystems and effects of climate change

AU - Andresen, Louise Christoffersen

N1 - Academic advisor: Anders Michelsen

PY - 2008

Y1 - 2008

N2 - Terrestrial ecosystems are currently exposed to climatic and air quality changes with increased atmospheric CO2, increased temperature and periodical droughts. At a temperate heath site this was investigated in a unique full factorial in situ experiment (CLIMAITE). The climate change treatments started October 2005 and consisted of increased temperature (T), extended summer drought (D), increased atmospheric CO2 and all combinations of these treatments (TD, TCO2, DCO2 and TDCO2). In this thesis, responses in soil inorganic and microbial nutrient concentration were investigated after one year of climate change treatment. Additionally, top soil net mineralization, immobilization and leaf litter decomposition was investigated through the winter half year separately below Calluna and Deschampsia plants, and acquisition of organic nitrogen in plants and soil microorganisms was assessed.After one year of treatments, warming increased microbial N, C and P and decomposition of leaf litter below Calluna plants. In Deschampsia soil the net nitrification rate decreased significantly in response to drought, by contrast, an increase was observed in Calluna soil. Drought reduced leaf litter decomposition for both species. In warmed plots an early senescence was observed with effects on green Deschampsia biomass, on Deschampsia root nitrogen concentration and on acquisition of 15N from glycine.In this thesis, experiments using the stable isotopes 15N and 13C as tracers of ammonium and amino acid acquisition by plants and soil microorganisms suggest directions of the short term competition at two dwarf shrub heaths, one with sub-arctic climate and one with temperate climate during spring and fall. Soil microorganisms acquired the largest amount of the added nitrogen sources compared to plants at both heath types. At both heaths, plants preferred the inorganic ammonium, yet all nitrogen forms were acquired by both plants and soil microorganisms. At the temperate heath, soil microorganisms acquired the 15N 13C labeled amino acids (glycine, glutamic acid and phenylalanine) as intact compounds, and both dominant plant species showed indications of phenylalanine acquisition as intact compounds. The thesis consists of an introduction collecting the most important findings from the four manuscripts.

AB - Terrestrial ecosystems are currently exposed to climatic and air quality changes with increased atmospheric CO2, increased temperature and periodical droughts. At a temperate heath site this was investigated in a unique full factorial in situ experiment (CLIMAITE). The climate change treatments started October 2005 and consisted of increased temperature (T), extended summer drought (D), increased atmospheric CO2 and all combinations of these treatments (TD, TCO2, DCO2 and TDCO2). In this thesis, responses in soil inorganic and microbial nutrient concentration were investigated after one year of climate change treatment. Additionally, top soil net mineralization, immobilization and leaf litter decomposition was investigated through the winter half year separately below Calluna and Deschampsia plants, and acquisition of organic nitrogen in plants and soil microorganisms was assessed.After one year of treatments, warming increased microbial N, C and P and decomposition of leaf litter below Calluna plants. In Deschampsia soil the net nitrification rate decreased significantly in response to drought, by contrast, an increase was observed in Calluna soil. Drought reduced leaf litter decomposition for both species. In warmed plots an early senescence was observed with effects on green Deschampsia biomass, on Deschampsia root nitrogen concentration and on acquisition of 15N from glycine.In this thesis, experiments using the stable isotopes 15N and 13C as tracers of ammonium and amino acid acquisition by plants and soil microorganisms suggest directions of the short term competition at two dwarf shrub heaths, one with sub-arctic climate and one with temperate climate during spring and fall. Soil microorganisms acquired the largest amount of the added nitrogen sources compared to plants at both heath types. At both heaths, plants preferred the inorganic ammonium, yet all nitrogen forms were acquired by both plants and soil microorganisms. At the temperate heath, soil microorganisms acquired the 15N 13C labeled amino acids (glycine, glutamic acid and phenylalanine) as intact compounds, and both dominant plant species showed indications of phenylalanine acquisition as intact compounds. The thesis consists of an introduction collecting the most important findings from the four manuscripts.

M3 - Ph.D. thesis

BT - Nitrogen cycling in heathland ecosystems and effects of climate change

PB - Museum Tusculanum

CY - Københavns Universitet

ER -

Nitrogen cycling in heathland ecosystems and effects of climate change

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