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Indirect effects of soil moisture reverse soil C sequestration responses of a spring wheat agroecosystem to elevated CO 2
Author(s) -
MARHAN SVEN,
KANDELER ELLEN,
REIN STEFANIE,
FANGMEIER ANDREAS,
NIKLAUS PASCAL A.
Publication year - 2010
Publication title -
global change biology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 4.146
H-Index - 255
eISSN - 1365-2486
pISSN - 1354-1013
DOI - 10.1111/j.1365-2486.2009.01949.x
Subject(s) - soil water , agroecosystem , soil carbon , water content , environmental science , moisture , carbon sequestration , organic matter , soil science , chemistry , soil organic matter , agronomy , biomass (ecology) , environmental chemistry , carbon dioxide , ecology , geotechnical engineering , organic chemistry , biology , agriculture , engineering
Increased plant productivity under elevated atmospheric CO 2 concentrations might increase soil carbon (C) inputs and storage, which would constitute an important negative feedback on the ongoing atmospheric CO 2 rise. However, elevated CO 2 often also leads to increased soil moisture, which could accelerate the decomposition of soil organic matter, thus counteracting the positive effects via C cycling. We investigated soil C sequestration responses to 5 years of elevated CO 2 treatment in a temperate spring wheat agroecosystem. The application of 13 C‐depleted CO 2 to the elevated CO 2 plots enabled us to partition soil C into recently fixed C (C new ) and pre‐experimental C (C old ) by 13 C/ 12 C mass balance. Gross C inputs to soils associated with C new accumulation and the decomposition of C old were then simulated using the Rothamsted C model ‘RothC.’ We also ran simulations with a modified RothC version that was driven directly by measured soil moisture and temperature data instead of the original water balance equation that required potential evaporation and precipitation as input. The model accurately reproduced the measured C new in bulk soil and microbial biomass C. Assuming equal soil moisture in both ambient and elevated CO 2 , simulation results indicated that elevated CO 2 soils accumulated an extra ∼40–50 g C m −2 relative to ambient CO 2 soils over the 5 year treatment period. However, when accounting for the increased soil moisture under elevated CO 2 that we observed, a faster decomposition of C old resulted; this extra C loss under elevated CO 2 resulted in a negative net effect on total soil C of ∼30 g C m −2 relative to ambient conditions. The present study therefore demonstrates that positive effects of elevated CO 2 on soil C due to extra soil C inputs can be more than compensated by negative effects of elevated CO 2 via the hydrological cycle.