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Carbon‐13 input and turn‐over in a pasture soil exposed to long‐term elevated atmospheric CO 2
Author(s) -
Van Kessel Chris,
Nitschelm Jennifer,
Horwath William R.,
Harris David,
Walley Frances,
Lüscher Andreas,
Hartwig Ueli
Publication year - 2000
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 - 10.1046/j.1365-2486.2000.00287.x
Subject(s) - lolium perenne , trifolium repens , repens , pasture , agronomy , zoology , lolium , soil water , silt , chemistry , environmental science , biology , perennial plant , poaceae , soil science , paleontology
Summary The impact of elevated CO 2 and N‐fertilization on soil C‐cycling in Lolium perenne and Trifolium repens pastures were investigated under Free Air Carbon dioxide Enrichment (FACE) conditions. For six years, swards were exposed to ambient or elevated CO 2 (35 and 60 Pa pCO 2 ) and received a low and high rate of N fertilizer. The CO 2 added in the FACE plots was depleted in 13 C compared to ambient (Δ− 40‰) thus the C inputs could be quantified. On average, 57% of the C associated with the sand fraction of the soil was ‘new’ C. Smaller proportions of the C associated with the silt (18%) and clay fractions (14%) were derived from FACE. Only a small fraction of the total C pool below 10 cm depth was sequestered during the FACE experiment. The annual net input of C in the FACE soil (0–10 cm) was estimated at 4.6 ± 2.2 and 6.3 ± 3.6 (95% confidence interval) Mg ha − 1 for T. repens and L. perenne , respectively. The maximum amount of labile C in the T. repens sward was estimated at 8.3 ± 1.6 Mg ha − 1 and 7.1 ± 1.0 Mg ha − 1 in the L. perenne sward. Mean residence time (MRT) for newly sequestered soil C was estimated at 1.8 years in the T. repens plots and 1.1 years for L. perenne . An average of 18% of total soil C in the 0–10 cm depth in the T. repens sward and 24% in the L. perenne sward was derived from FACE after 6 years exposure. The majority of the change in soil δ 13 C occurred in the first three years of the experiment. No treatment effects on total soil C were detected. The fraction of FACE‐derived C in the L. perenne sward was larger than in the T. repens sward. This suggests a priming effect in the L. perenne sward which led to increased losses of the old C. Although the rate of C cycling was affected by species and elevated CO 2 , the soil in this intensively managed grassland ecosystem did not become a sink for additional new C.