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Impact of nitrogen deposition on carbon stocks in coniferous forest soils

insights from experiments with low and high nitrogen addition rates

Forsmark, Benjamin (2020). Impact of nitrogen deposition on carbon stocks in coniferous forest soils. Diss. (sammanfattning/summary) Umeå : Sveriges lantbruksuniv., Acta Universitatis Agriculturae Sueciae, 1652-6880 ; 2020:2
ISBN 978-91-7760-522-5
eISBN 978-91-7760-523-2
[Doctoral thesis]

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Abstract

Nutrient limitations constrain the capacity for northern coniferous forests to capture and store carbon (C). Nitrogen (N) deposition may enhance tree productivity in these forests, but it remains uncertain how the storage of C in soils is responding to changes in N availability, and how limitations by other elements, such as phosphorus (P), develop in response to N enrichment. In this thesis, I present results from five studies on C cycling in long-term N addition experiments in a Scots pine forest (study I-III) and a Norway spruce forest (study IV-V) in northern Sweden. In these forests, N has been added at low (≤12.5 kg N ha-1 yr-1 ) and high (50 kg N ha-1 yr-1 ) rates for up to 20 years to simulate N deposition.

In the Scots pine forest, I showed that the highest N addition rate increased soil C stocks in the organic layer by 22.3 kg C kg-1 N added (study I), which supports the view that N enrichment can increase the C sink of northern coniferous forests. In study I and II I showed that N additions increased the input of C by both aboveground litter and fineroot litter, which coupled to a decrease in autotrophic soil respiration contributes to soil C accumulation. Study II and III further showed that the increase in fine-root production occurred without a concomitant increase in tree-root associated microbiota, indicating that N enabled higher retention of C in fine-root biomass production.

In the Norway spruce forest, study IV showed that N decreased the activity of enzymes in the soil involved in the degradation of recalcitrant organic matter, and organic N uptake, and increased the activity of enzymes involved in the degradation of simple carbohydrates, whereas enzyme activity targeting P was unaffected. Study V further showed that N had no effect on the mobilization of P in soil organic matter or on the fungal exploration of P rich apatite minerals in the soil. In both forests, N changed the composition of the microbial community, which is likely to impact soil respiration and decomposition. However, more studies are needed on the links between N availability and soil microbial activity. In conclusion, the result presented in this thesis support the view that N deposition is enhancing the C sink of N poor boreal forests, however at a rate that is too low to make a major contribution to the global land C sink.

Authors/Creators:Forsmark, Benjamin
Title:Impact of nitrogen deposition on carbon stocks in coniferous forest soils
Subtitle:insights from experiments with low and high nitrogen addition rates
Alternative abstract:
LanguageAbstract
UNSPECIFIED

Tillgängligheten av näringsämnen är begränsande för nordliga barrskogarnas förmåga att
lagra kol. Kvävedeposition kan öka produktiviteten i dessa skogar men det är ännu oklart
hur markens kolförråd påverkas av gradvisa förändringar i kvävetillgång, och hur
begränsningar av andra näringsämnen, så som fosfor, påverkar denna respons. I denna
avhandling presenterar jag resultat från fem studier av kolcykeln i långliggande
experiment i tall- och granbestånd i norra Sverige, där kväve tillförts i låga och höga
givor i upp till 20 år för att simulera olika nivåer av kvävedeposition.

I tallbeståndet visade studie I att kvävetillförseln ökade kolförrådet i markens
organiska skikt med 22.3 kg kol kg-1 kväve tillfört, vilket ger stöd för att
kvävedepositionen bidrar till att förstärka kolsänkan i nordliga barrskogar. Studie I och
II visade vidare att denna effekt berodde på en ökad produktion av fall- och rotförna,
tillsammans med minskad markandning. Studie II och III visade att ökningen i
rotförnaproduktion skedde utan en motsvarande ökning i mikrober förknippade med
trädens rötter, vilket tyder på att kvävetillförsel möjliggör en högre fasthållning av
kolföreningar i rötterna.

I granbeståndet visade studie IV att kvävetillförseln minskade aktiviteten av enzymer
som bryter ner komplext och svårnedbrytbart organiskt material, och i upptaget av kväve
i organiska former. Däremot ökade aktiviteten av enzymer involverade i nedbrytningen
av enklare kolhydrater, medan den enzymatiska aktiviteten riktad mot fosfor var
oförändrad. Studie V visade att varken frigörandet av fosfor i markens organiska
material, eller marksvamparnas kolonisering av det fosforrika mineralet apatit
påverkades av kvävetillförseln.

I båda bestånden förändrades sammansättningen av mikrobiella samhällen, vilket
sannolikt bidragit till förändringarna i markandning och nedbrytning. Mer studier behövs
dock för att förstå länkarna mellan kvävetillgång och markens mikrobiologiska aktivitet.
Sammanfattningsvis visar resultaten i den här avhandlingen att kvävedepositionen bidrar
till att förstärka kolsänkan i nordliga barrskogsekosystem, om än på en för låg nivå för
att i sig ha avgörande inflytande på den globala landkolsänkan

Series/Journal:Acta Universitatis Agriculturae Sueciae (1652-6880)
Year of publishing :2020
Number:2020:2
Number of Pages:70
Papers/manuscripts:
NumberReferences
IBenjamin Forsmark*, Annika Nordin, Nadia Maaroufi, Tomas Lundmark, Michael J. Gundale. Low and high nitrogen deposition rates in northern coniferous forests have different impacts on aboveground litter production, soil respiration, and soil carbon stocks (accepted in Ecosystems).
IIBenjamin Forsmark*, Annika Nordin, Nicholas Rosenstock, Håkan Wallander, Michael J. Gundale. High levels of nitrogen enrichment in boreal forests decrease soil respiration by increasing root growth and decreasing the relative transfer of carbon to ectomycorrhizal fungi (manuscript)
IIINadia Maaroufi*, Annika Nordin, Kristin Palmqvist, Niles J. Hasselquist, Benjamin Forsmark, Nicholas P. Rosenstock, Håkan Wallander, Michael J. Gundale, (2019). Anthropogenic nitrogen enrichment enhances soil carbon accumulation by impacting saprotrophs rather than ectomycorrhizal fungal activity (Global Change Biology 25 (9), pp 2900- 2914)
IVBenjamin Forsmark*, Tinkara Bizjak, Nicholas Rosenstock, Håkan Wallander, Annika Nordin, Michael J. Gundale. Impact of low and high nitrogen addition on soil microbial communities and enzyme activities in a boreal forest soil (manuscript).
VBenjamin Forsmark*, Håkan Wallander, Annika Nordin, Michael J. Gundale, 2020, Does long-term nitrogen enrichment increase microbial phosphorus mobilization in soils? (manuscript).
Place of Publication:Umeå
Publisher:Department of Forest Ecology and Management, Swedish University of Agricultural Sciences
ISBN for printed version:978-91-7760-522-5
ISBN for electronic version:978-91-7760-523-2
ISSN:1652-6880
Language:English
Publication Type:Doctoral thesis
Article category:Other scientific
Full Text Status:Public
Subjects:(A) Swedish standard research categories 2011 > 1 Natural sciences > 106 Biological Sciences (Medical to be 3 and Agricultural to be 4) > Microbiology (Microbiology in the medical area to be 30109)
(A) Swedish standard research categories 2011 > 1 Natural sciences > 106 Biological Sciences (Medical to be 3 and Agricultural to be 4) > Ecology
(A) Swedish standard research categories 2011 > 1 Natural sciences > 105 Earth and Related Environmental Sciences > Geology
Keywords:boreal forest, carbon sequestration, climate change, decomposition, ecological stoichiometry, ectomycorrhizal fungi, nitrogen deposition, Picea abies, Pinus sylvestris, soil respiration
URN:NBN:urn:nbn:se:slu:epsilon-p-103932
Permanent URL:
http://urn.kb.se/resolve?urn=urn:nbn:se:slu:epsilon-p-103932
ID Code:16655
Faculty:S - Faculty of Forest Sciences
Department:(S) > Dept. of Forest Ecology and Management
Deposited By: SLUpub Connector
Deposited On:06 Feb 2020 14:14
Metadata Last Modified:06 Feb 2020 14:14

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