Climate warming accelerates CO 2 -release from subsurface carbon in a sub-arctic peatland

Transcription

1 Climate warming accelerates CO 2 -release from subsurface carbon in a sub-arctic peatland Ellen Dorrepaal Sylvia Toet, Richard van Logtestijn, Elferra Swart Marjan van de Weg, Terry Callaghan, Rien Aerts Department of systems ecology

2 Climate change at northern high latitudes IPCC (2007) Global average warming ( ): C Strongest at high northern latitudes Precipitation increase in winter at northern high latitudes Sub-arctic / boreal peatlands 3 % of total land area One-third of world soil carbon pool Climate-carbon cycle feedback poorly predicted because vegetation and soil responses not well understood

3 Climate effects on C-cycling

4 Questions 1) What are the long-term effects of climate change on CO 2 -emission in northern peatlands? 2) What are the sources of increased respired CO 2? Is the cycling of carbon through compartments with different turnover rates equally affected by climate change? 1: vegetation 2: young (i.e. labile/superficial) peat 3: old (i.e. recalcitrant/deeper) peat (How) can we distinguish between different CO 2 sources in situ?

5 Climate change manipulation on Sphagnum fuscum bog N, E

6 Photo: Frank Trosien

7 Spring warming: May Summer warming: June September T air : Spring: C, June-July: C T soil : Spring (-5 to -20 cm): C ( T max : C) Summer (-5 to -20 cm) : C ( T max : C)

8 Winter snow capture : October - April Doubled snow thickness (+ approx. 15 cm) T soil : Winter (-5 to -20 cm): C

9 Climate change effects on total CO 2 -emission Ecosystem respiration (g CO 2 m -2 h -1 ) Spring *** NA Year *** *** Dorrepaal et al. (2009) Nature 460: Ambient Summer warming Summer warming + winter snow addition Summer warming + winter snow addition + spring warming

10 Climate change effects on total CO 2 -emission Ecosystem respiration (g CO 2 m -2 h -1 ) Spring Summer ** *** ** ** Ambient Summer warming Summer warming + winter snow addition ** NA Year *** *** Summer warming + winter snow addition + spring warming Dorrepaal et al. (2009) Nature 460: Short and long-term enhancement of ER

11 Climate change effects on CO 2 -sources Plants: short-term cycle (autotrophic) Soil carbon: longer-term cycle (heterotrophic) Does climate change affect heterotrophic respiration?

12 Climate change effects on components of ER 0.6 ** Dorrepaal et al. (2009) Nature 460: Respiration (g CO 2 m -2 h -1 ) *** *** 0.0 ER R h R a Control Warming Total ER Aboveground vegetation removed R h (heterotrophic) R a (plant-related) Enhancement of both plant and soil respiration

13 Climate change effects on soil CO2-sources Young / high quality Short-term direct responses / T sensitive? Lower δ13c value = less 13C (= depleted) (How) can we distinguish between different CO2 sources in situ? CO2 (atm): -8 Whole plant C (C3): -27 (-20 to -31) Old / low quality Long-lasting responses / T insensitive? CO2 (resp): -? Soil carbon: increasing δ13c

14 Lab-incubation and bulk-c analysis 0 Delta 13 C (permil) Dorrepaal et al. (2009) Nature 460: Depth in soil (cm) Field capacity, 10ºC, 288 days Respired CO 2 Bulk soil C δ 13 C of bulk peat C and respired CO 2 increase with depth in active layer: potential for use as source tracer

15 CO 2 flux [CO2] (ppmv) Determining δ 13 C of CO 2 sources in the field: y = x x R 2 = y = x x R 2 = y = x x R 2 = Time 0.5 (hour) 0.6 Delta 13 C (permil) AA1 WS+1 1V 1AAR 1R Poly. (AA1) Poly. (WS+1) Poly. (1V) Poly. (1AAR) Poly. (1R) Delta 13 C Time (hour) AA1 WS+1 1V 1AAR 1R Keeling plot Delta 13 C (permil) y = x R 2 = y = x R 2 = y = x R 2 = /[CO2] (1/ppm) AA1 WS+1 1V 1AAR 1R Linear (AA1) Linear (WS+1) Linear (1V) Linear (1AAR) Linear (1R)

16 Isotopic signature of respired CO 2 (field) δ 13 C of respired CO 2 ( ) * * * Dorrepaal et al. (2009) Nature 460: A W1 A W1 W7 R h ER Warming treatments increase δ 13 C of soil respiration: Enhanced decomposition of deeper active layer peat

17 Conclusions Spring and summer warming enhance Ecosystem Respiration rates, even after 8 years Spring and summer warming enhance plant-related and heterotrophic respiration rates equally strongly Peat respiration responsible for large part of increase with warming Spring and summer warming increase the δ 13 C value of respired CO 2 Enhanced decay of subsurface peat

18 Many thanks to: Abisko Naturvetenskapliga Station NWO Esther van Munster

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