Abstract
Abstract. Through increases in net primary production (NPP), elevated CO2 is hypothesized to increase the amount of plant litter entering the soil. The fate of this extra carbon on the forest floor or in mineral soil is currently not clear. Moreover, increased rates of NPP can be maintained only if forests can escape nitrogen limitation. In a Free atmospheric CO2 Enrichment (FACE) experiment near Bangor, Wales, 4 ambient and 4 elevated [CO2] plots were planted with patches of Betula pendula, Alnus glutinosa and Fagus sylvatica on a former arable field. After 4 years, biomass averaged for the 3 species was 5497 (se 270) g m−2 in ambient and 6450 (se 130) g m−2 in elevated [CO2] plots, a significant increase of 17% (P = 0.018). During that time, only a shallow L forest floor litter layer had formed due to intensive bioturbation. Total soil C and N contents increased irrespective of treatment and species as a result of afforestation. We could not detect an additional C sink in the soil, nor were soil C stabilization processes affected by elevated [CO2]. We observed a decrease of leaf N content in Betula and Alnus under elevated [CO2], while the soil C/N ratio decreased regardless of CO2 treatment. The ratio of N taken up from the soil and by N2-fixation in Alnus was not affected by elevated [CO2]. We infer that increased nitrogen use efficiency is the mechanism by which increased NPP is sustained under elevated [CO2] at this site.
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Claims 7
Claim · model-written summary
Elevated CO2 increased mean biomass across three tree species by 17%.
- Taxon
- Betula pendula, Alnus glutinosa and Fagus sylvatica
Betula pendula.jpg?width=60)
Alnus glutinosa
Fagus sylvaticae0t0 - Treatment
- elevated [CO2]e0
- Outcome
- biomasse0
- Direction
- increasee0
- Value
- 17%e0
- Comparator
- ambiente0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
.jpg?width=500)
Verbatim
e0“After 4 years, biomass averaged for the 3 species was 5497 (se 270) g m−2 in ambient and 6450 (se 130) g m−2 in elevated [CO2] plots, a significant increase of 17% (P = 0.018).”
t0“Betula pendula, Alnus glutinosa and Fagus sylvatica”
Claim · model-written summary
Soil carbon and nitrogen contents rose following afforestation regardless of treatment or species.
- Taxon
- Betula pendula, Alnus glutinosa and Fagus sylvaticaBetula pendulaAlnus glutinosaFagus sylvaticat0
- Outcome
- Total soil C and N contentse0
- Direction
- increasede0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“Total soil C and N contents increased irrespective of treatment and species as a result of afforestation.”
t0“Betula pendula, Alnus glutinosa and Fagus sylvatica”
Claim · model-written summary
Elevated CO2 did not add a detectable soil carbon sink or affect soil carbon stabilization.
- Taxon
- Betula pendula, Alnus glutinosa and Fagus sylvaticaBetula pendulaAlnus glutinosaFagus sylvaticat0
- Treatment
- elevated [CO2]e0
- Outcome
- additional C sink in the soile0
- Direction
- could not detecte0
Not reportedComparator
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“We could not detect an additional C sink in the soil, nor were soil C stabilization processes affected by elevated [CO2].”
t0“Betula pendula, Alnus glutinosa and Fagus sylvatica”
Claim · model-written summary
Leaf nitrogen decreased under elevated CO2 in Betula and Alnus.
Betula
AlnusNot reportedComparator
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“We observed a decrease of leaf N content in Betula and Alnus under elevated [CO2]”
Claim · model-written summary
The soil carbon to nitrogen ratio decreased regardless of CO2 treatment.
- Taxon
- Betula pendula, Alnus glutinosa and Fagus sylvaticaBetula pendulaAlnus glutinosaFagus sylvaticat0
- Outcome
- soil C/N ratioe0
- Direction
- decreasede0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“the soil C/N ratio decreased regardless of CO2 treatment”
t0“Betula pendula, Alnus glutinosa and Fagus sylvatica”
Claim · model-written summary
Elevated CO2 did not affect the ratio of soil nitrogen uptake to nitrogen fixation in Alnus.
- Treatment
- elevated [CO2]e0
- Outcome
- ratio of N taken up from the soil and by N2-fixatione0
- Direction
- not affectede0
Not reportedComparator
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“The ratio of N taken up from the soil and by N2-fixation in Alnus was not affected by elevated [CO2].”
Claim · model-written summary
The authors infer that greater nitrogen use efficiency sustains NPP under elevated CO2.
- Taxon
- Betula pendula, Alnus glutinosa and Fagus sylvaticaBetula pendulaAlnus glutinosaFagus sylvaticat0
- Outcome
- increased NPPe0
- Qualifier
- increased nitrogen use efficiencye0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“We infer that increased nitrogen use efficiency is the mechanism by which increased NPP is sustained under elevated [CO2] at this site.”
t0“Betula pendula, Alnus glutinosa and Fagus sylvatica”
The same questions in other papers
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- positive
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See all 6 papers →co2 · growth · Fagus sylvatica (European beech)Positive and negative results
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co2 · nutrient: content · Alnus (alders)Results agree
1 paper in the same direction as this paper
- negative
co2 · growth · Alnus glutinosaResults agree
2 papers in the same direction as this paper
- positive
- positive
Claims are grouped by organism, treatment and what was measured or targeted. A paper counts as positive when any of its claims in the group is positive.