Nitrogen deposition is slowing forest respiration
At Loobos, TER fell while GPP rose over 26 years; acid soils (pH 2.9) and N deposition appear to throttle decomposition.
Source
Declining Ecosystem Respiration Linked to Nitrogen Deposition: Insights From a 26-Year FLUXNET Record
What they did
Authors analyzed 1997–2021 eddy-covariance fluxes at the Loobos Scots pine site in the Netherlands, compared other long FLUXNET forests, inventoried the organic layer, and incubated acidic topsoil with glucose and lime to test substrate and pH limits on CO2 release.
What they found
TER fell from 1350 to 1015 g C m−2 year−1 (1997–2021) while GPP rose from 1567 to 1904. Soil respiration is ~69% of TER. The organic layer doubled in mass (about 4.7 to 9.4 kg C m−2). R10 declined (36% implied TER drop); soil warmed 1.25°C. Incubations showed an active but pH-inhibited microbiome (pH 2.9). N deposition was 38 kg N ha−1 year−1 in 1990 and 21 in 2023.
The limits
What it doesn't show
A second, taller tower after 2021 raised TER estimates, so some instrumental contribution cannot be ruled out. 2024 C and N analyses were incomplete. There is no continuous soil-pH time series. NEE sustainability remains an open ecosystem-health question.
Key terms
- TER
- Total ecosystem respiration: CO2 released by autotrophic plus heterotrophic respiration.
- R10
- Reference respiration rate at 10°C in a Lloyd–Taylor fit; it declined even as soil warmed.
- N deposition
- Atmospheric ammonia and NOx input; still 21 kg N ha−1 year−1 in 2023 after 38 in 1990.
- Soil acidification
- Organic-layer pH near 2.9 at Loobos, attributed to long-term N deposition.
- FLUXNET Loobos (NL-Loo)
- A planted 1911 Pinus sylvestris stand on poor Dutch sand with a long eddy-covariance record.
Flashcards
Research intelligence for this paper
See its role on concept claims, tensions it is part of, placement history, and related discoveries.
Quiz yourself
From 1997 to 2021 at Loobos, TER:
Common questions
Did the forest stop taking up carbon?
No. NEE became more negative because GPP rose while TER fell.
Is the extra sink healthy?
Authors warn it may reflect stalled decomposition in an acidifying organic layer, not a sustainable sink.
What did lime and glucose do in jars?
Each raised CO2; together they added, showing both pH and substrate quality limit microbes.
Is Loobos unique?
Several other mature temperate/boreal FLUXNET sites also show seasonal TER declines.
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