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The Role of Carbon-Nitrogen Interactions for Terrestrial Ecosystem Dynamics under Global Change - a modelling perspective

Wårlind, David LU (2013)
Abstract (Swedish)
Popular Abstract in Swedish

Framtida klimatförändringar påverkas till stor del på människans utsläpp av CO2, samt av klimat- och CO2-relaterade återkopplingar genom kolcykeln i både landbaserade ekosystem och hav. Landbaserade ekosystem tar för tillfället upp omkring 25% av de antropogena utsläppen av CO2 från förbränning av fossila bränslen och markanvändning, men att tillskriva vilka mekanismer som står för detta upptag, och de viktigaste områdena där det förekommer, är en utmanande uppgift. På senare tid har forskning börjat fokuseras på om, och hur, interaktioner mellan kol- och kvävecyklerna påverkar framtida kolsänkor. Till relativt nyligen var inte dessa interaktioner representerade i modeller av den globala... (More)
Popular Abstract in Swedish

Framtida klimatförändringar påverkas till stor del på människans utsläpp av CO2, samt av klimat- och CO2-relaterade återkopplingar genom kolcykeln i både landbaserade ekosystem och hav. Landbaserade ekosystem tar för tillfället upp omkring 25% av de antropogena utsläppen av CO2 från förbränning av fossila bränslen och markanvändning, men att tillskriva vilka mekanismer som står för detta upptag, och de viktigaste områdena där det förekommer, är en utmanande uppgift. På senare tid har forskning börjat fokuseras på om, och hur, interaktioner mellan kol- och kvävecyklerna påverkar framtida kolsänkor. Till relativt nyligen var inte dessa interaktioner representerade i modeller av den globala kolcykeln, trots att kväve är en begränsande faktor som kontrollerar vegetationens produktivitet i många ekosystem.

Den dynamiska vegetationsmodellen LPJ-GUESS har utökats med en fullständigt kopplad, dynamisk kol-kvävecykel i vegetation och mark, vilken introducerar kvävebegränsningar för växtproduktion och jordnedbrytning. Med kvävedynamik, simulerar LPJ-GUESS de nuvarande kol- och kvävepoolerna i marken och vegetationen i enlighet med observationer och modellbaserade uppskattningar. Globala simuleringar visar en brantare gradient av produktiviteten från höga till låga breddgrader jämfört med simuleringar som gjorts utan kvävecykeln, vilket ökar förmågan att korrekt återge produktiviteten i boreala och tropiska ekosystem under en utvärdering mot 75 FLUXNET-stationer. Sekundära effekter uppstår också via ekologiska processer, såsom att kol-kväveinteraktioner förändrar konkurrensen mellan olika växttyper, vilket resulterar i en förändring i den modellerade biom-distributionen, t.ex. en sydligare arktisk trädgräns.

Under ett "business-as-usual"-scenario för framtida atmosfärisk CO2, klimat och kvävedeposition, resulterar införandet av kvävedynamik i globalt högre kumulativt kolupptag över perioden 1850-2100 jämfört med simuleringar utan kvävecykeln. Detta resultat står i kontrast mot resultat från tidigare studier, där andra modeller simulerade en framtida progressiv kvävebegränsning. I LPJ-GUESS påverkar ökad kvävemineralisering i ett varmare klimat särskilt kolupptaget på högre breddgrader, där trädens tillväxt ökar, vilket leder till förtätning och expansion av de boreala skogarna. Våra resultat understryker behovet av att ta hänsyn till kol-kväveinteraktioner, inte bara i studier av den globala landbaserade kolcykeln utan även för att förstå de underliggande interaktionerna på regional skala. (Less)
Abstract
The nature of future climate change will depend on anthropogenic emissions of CO2, as well as climate- and CO2-mediated feedbacks through carbon (C) cycling in both terrestrial ecosystems and oceans. Terrestrial ecosystems remove presently about 25% of the anthropogenic CO2 fossil-fuel and land-use change emissions, but to attribute which mechanisms cause this uptake, and the key regions where it occurs, is a challenging task. Considerable attention has focused in recent years on whether, and how, interactions of the C and nitrogen (N) cycles affect the future terrestrial C sink. Until relatively recently these interactions were not considered in models of the global C cycle, although in many ecosystems N is believed to be a limiting... (More)
The nature of future climate change will depend on anthropogenic emissions of CO2, as well as climate- and CO2-mediated feedbacks through carbon (C) cycling in both terrestrial ecosystems and oceans. Terrestrial ecosystems remove presently about 25% of the anthropogenic CO2 fossil-fuel and land-use change emissions, but to attribute which mechanisms cause this uptake, and the key regions where it occurs, is a challenging task. Considerable attention has focused in recent years on whether, and how, interactions of the C and nitrogen (N) cycles affect the future terrestrial C sink. Until relatively recently these interactions were not considered in models of the global C cycle, although in many ecosystems N is believed to be a limiting factor controlling vegetation productivity.

The dynamic vegetation model LPJ-GUESS has been extended with a fully coupled dynamic C-N cycle in vegetation and soil, introducing N limitations on plant production and soil decomposition. With N dynamics, LPJ-GUESS simulates the present C and N pools in soil, litter and vegetation in agreement with observation-based and model estimates. Global simulations show a steeper gradient of productivity from high to low latitudes compared with the C-only model version, increasing the ability to correctly reproduce productivity in boreal and tropical ecosystems when evaluated against 75 FLUXNET forest sites. Secondary effects emerge also via ecosystem ecological processes, such as C-N interactions altering the competition between plant functional types, resulting in some differences in the modelled biome distribution, e.g. a more southerly arctic treeline when N cycle dynamics are included.

When applying “business-as-usual” scenario of future atmospheric CO2, climate and N deposition, the inclusion of N dynamics results in moderately higher cumulative C sequestration over the period 1850 to 2100 compared to the C-only version of LPJ-GUESS. This result contrasts to some degree with results of earlier studies using other models that are dominated by progressive N limitation in the future at global scale. In LPJ-GUESS, enhanced soil N mineralisation in a warmer climate particularly affects net primary productivity in high-latitudes, enhancing the growth of trees and providing a transient sink of carbon as woody biomass as boreal forests densify and expand. Our results highlight the need to account for C-N interactions not only in studies of global terrestrial C cycling but to understand the underlying interactions on regional scales. (Less)
Please use this url to cite or link to this publication:
author
supervisor
opponent
  • Dr Raupach, Michael, CSIRO, the Commonwealth Scientific and Industrial Research Organisation
organization
publishing date
type
Thesis
publication status
published
subject
keywords
C-N Interactions, Ecosystem Modelling, DGVM, Nitrogen, Carbon, Climate Change
publisher
Department of Physical Geography and Ecosystem Science, Lund University
defense location
Världen, Geocentrum I, Sölvegatan 10, Lund, Sweden
defense date
2013-09-20 10:00
ISBN
978-91-85793-36-5
project
MERGE
BECC
language
English
LU publication?
yes
id
d04214bd-2489-44e4-acec-6edfbab73fe3 (old id 4016133)
date added to LUP
2013-09-10 08:45:51
date last changed
2016-09-19 08:45:09
@phdthesis{d04214bd-2489-44e4-acec-6edfbab73fe3,
  abstract     = {The nature of future climate change will depend on anthropogenic emissions of CO2, as well as climate- and CO2-mediated feedbacks through carbon (C) cycling in both terrestrial ecosystems and oceans. Terrestrial ecosystems remove presently about 25% of the anthropogenic CO2 fossil-fuel and land-use change emissions, but to attribute which mechanisms cause this uptake, and the key regions where it occurs, is a challenging task. Considerable attention has focused in recent years on whether, and how, interactions of the C and nitrogen (N) cycles affect the future terrestrial C sink. Until relatively recently these interactions were not considered in models of the global C cycle, although in many ecosystems N is believed to be a limiting factor controlling vegetation productivity. <br/><br>
The dynamic vegetation model LPJ-GUESS has been extended with a fully coupled dynamic C-N cycle in vegetation and soil, introducing N limitations on plant production and soil decomposition. With N dynamics, LPJ-GUESS simulates the present C and N pools in soil, litter and vegetation in agreement with observation-based and model estimates. Global simulations show a steeper gradient of productivity from high to low latitudes compared with the C-only model version, increasing the ability to correctly reproduce productivity in boreal and tropical ecosystems when evaluated against 75 FLUXNET forest sites. Secondary effects emerge also via ecosystem ecological processes, such as C-N interactions altering the competition between plant functional types, resulting in some differences in the modelled biome distribution, e.g. a more southerly arctic treeline when N cycle dynamics are included. <br/><br>
When applying “business-as-usual” scenario of future atmospheric CO2, climate and N deposition, the inclusion of N dynamics results in moderately higher cumulative C sequestration over the period 1850 to 2100 compared to the C-only version of LPJ-GUESS. This result contrasts to some degree with results of earlier studies using other models that are dominated by progressive N limitation in the future at global scale. In LPJ-GUESS, enhanced soil N mineralisation in a warmer climate particularly affects net primary productivity in high-latitudes, enhancing the growth of trees and providing a transient sink of carbon as woody biomass as boreal forests densify and expand. Our results highlight the need to account for C-N interactions not only in studies of global terrestrial C cycling but to understand the underlying interactions on regional scales.},
  author       = {Wårlind, David},
  isbn         = {978-91-85793-36-5},
  keyword      = {C-N Interactions,Ecosystem Modelling,DGVM,Nitrogen,Carbon,Climate Change},
  language     = {eng},
  publisher    = {Department of Physical Geography and Ecosystem Science, Lund University},
  school       = {Lund University},
  title        = {The Role of Carbon-Nitrogen Interactions for Terrestrial Ecosystem Dynamics under Global Change - a modelling perspective},
  year         = {2013},
}