Abstract
The response of the carbon cycle in forests to global warming could lead to a positive climate feedback if warming accelerates the mineralization of soil organic carbon (SOC), thereby causing net emissions of CO2 into the atmosphere. In Europe, carbon-rich alpine forest soils could be particularly affected by global warming, as a greater rise in temperature is expected in this region than the global average. Here we show that nearly two decades of experimental soil warming (+4°C during the snow-free seasons) in a mountain forest in the Northern Limestone Alps significantly (~13% per 1°C warming) and persistently (no change in response over 18 years) increased soil CO2 effluxes. The SOC stocks in the warmed plots decreased compared to controls, yet non-significantly, and quantitatively much less than the surplus carbon outflux from warmed soil suggests. We attribute the increase in soil CO2 efflux primarily to stimulation of root respiration, which was most sensitive to long-term warming. Furthermore, increased root production, faster fine root turnover, and increased root exudation likely not only facilitated autotrophic respiration but also replenished the SOC pool. The radiocarbon age of SOC indicates a rejuvenation of SOC likely by increased input of root carbon into the lower topsoil. Overall, our findings suggest that increased C allocation into the rhizosphere can at least partially compensate for the C loss through increased SOC mineralization with rising temperatures over many years.
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Claims 10
Claim · model-written summary
Long-term soil warming increased soil CO2 efflux by about 13% per degree Celsius.
- Taxon
- foreste1
- Treatment
- soil warming (+4°C during the snow-free seasons)e0
- Outcome
- soil CO2 effluxese0
- Direction
- increasede0
- Value
- ~13% per 1°C warminge0
- Setting
- Northern Limestone Alpse0
Not reportedComparator
Verbatim
e0“nearly two decades of experimental soil warming (+4°C during the snow-free seasons) in a mountain forest in the Northern Limestone Alps significantly (~13% per 1°C warming) and persistently (no change in response over 18 years) increased soil CO2 effluxes”
e1“in a mountain forest in the Northern Limestone Alps”
Claim · model-written summary
The soil efflux warming response did not change over 18 years.
Verbatim
e0“persistently (no change in response over 18 years) increased soil CO2 effluxes”
e1“in a mountain forest in the Northern Limestone Alps”
Claim · model-written summary
SOC stocks decreased nonsignificantly under warming compared with controls.
Verbatim
e0“The SOC stocks in the warmed plots decreased compared to controls, yet non-significantly”
e1“in a mountain forest in the Northern Limestone Alps”
Claim · model-written summary
Root respiration was especially sensitive to long-term warming and is proposed as the primary driver of increased soil CO2 efflux.
Verbatim
e0“We attribute the increase in soil CO2 efflux primarily to stimulation of root respiration, which was most sensitive to long-term warming”
e1“in a mountain forest in the Northern Limestone Alps”
Claim · model-written summary
Root production increased under warming.
Verbatim
e0“increased root production, faster fine root turnover, and increased root exudation”
e1“in a mountain forest in the Northern Limestone Alps”
Claim · model-written summary
Fine root turnover was faster under warming.
Verbatim
e0“increased root production, faster fine root turnover, and increased root exudation”
e1“in a mountain forest in the Northern Limestone Alps”
Claim · model-written summary
Root exudation increased under warming.
Verbatim
e0“increased root production, faster fine root turnover, and increased root exudation”
e1“in a mountain forest in the Northern Limestone Alps”
Claim · model-written summary
SOC radiocarbon age indicated rejuvenation of SOC.
Verbatim
e0“The radiocarbon age of SOC indicates a rejuvenation of SOC likely by increased input of root carbon into the lower topsoil”
e1“in a mountain forest in the Northern Limestone Alps”
Claim · model-written summary
Increased root carbon input is proposed to replenish the SOC pool.
Verbatim
e0“increased root production, faster fine root turnover, and increased root exudation likely not only facilitated autotrophic respiration but also replenished the SOC pool”
e1“in a mountain forest in the Northern Limestone Alps”
Claim · model-written summary
Greater allocation into the rhizosphere may partly compensate for warming-driven SOC mineralization loss.
Verbatim
e0“increased C allocation into the rhizosphere can at least partially compensate for the C loss through increased SOC mineralization”
e1“in a mountain forest in the Northern Limestone Alps”