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Linking sequestration of 13 C and 15 N in aggregates in a pasture soil following 8 years of elevated atmospheric CO 2
Author(s) -
VAN GROENIGEN KEESJAN,
HARRIS DAVID,
HORWATH WILLIAM R.,
HARTWIG UELI A.,
VAN KESSEL CHRIS
Publication year - 2002
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.1365-2486.2002.00527.x
Subject(s) - pasture , lolium perenne , chemistry , environmental chemistry , organic matter , fertilizer , nitrogen , zoology , agronomy , poaceae , biology , organic chemistry
The influence of N availability on C sequestration under prolonged elevated CO 2 in terrestrial ecosystems remains unclear. We studied the relationships between C and N dynamics in a pasture seeded to Lolium perenne after 8 years of elevated atmospheric CO 2 concentration (FACE) conditions. Fertilizer‐ 15 N was applied at a rate of 140 and 560 kg N ha 2−1 y 2−1 and depleted 13 C‐CO 2 was used to increase the CO 2 concentration to 60 Pa pCO 2 . The 13 C– 15 N dual isotopic tracer enabled us to study the dynamics of newly sequestered C and N in the soil by aggregate size and fractions of particulate organic matter (POM), made up by intra‐aggregate POM (iPOM) and free light fraction (LF). Eight years of elevated CO 2 did not increase total C content in any of the aggregate classes or POM fractions at both rates of N application. The fraction of new C in the POM fractions also remained largely unaffected by N fertilization. Changes in the fractions of new C and new N (fertilizer‐N) under elevated CO 2 were more pronounced between POM classes than between aggregate size classes. Hence, changes in the dynamics of soil C and N cycling are easier to detect in the POM fractions than in the whole aggregates. Within N treatments, fractions of new C and N in POM classes were highly correlated with more new C and N in large POM fractions and less in the smaller POM fractions. Isotopic data show that the microaggregates were derived from the macro‐aggregates and that the C and N associated with the microaggregates turned over slower than the C and N associated with the macroaggregates. There was also isotopic evidence that N immobilized by soil microorganisms was an important source of N in the iPOM fractions. Under low N availability, 3.04 units of new C per unit of fertilizer N were sequestered in the POM fractions. Under high N availability, the ratio of new C sequestered per unit of fertilizer N was reduced to 1.47. Elevated and ambient CO 2 concentrations lead to similar 15 N enrichments in the iPOM fractions under both low and high N additions, clearly showing that the SOM‐N dynamics were unaffected by prolonged elevated CO 2 concentrations.