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Elevated atmospheric CO 2 effects and soil water feedbacks on soil respiration components in a Colorado grassland
Author(s) -
Pendall E.,
Del Grosso S.,
King J. Y.,
LeCain D. R.,
Milchunas D. G.,
Morgan J. A.,
Mosier A. R.,
Ojima D. S.,
Parton W. A.,
Tans P. P.,
White J. W. C.
Publication year - 2003
Publication title -
global biogeochemical cycles
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.512
H-Index - 187
eISSN - 1944-9224
pISSN - 0886-6236
DOI - 10.1029/2001gb001821
Subject(s) - soil respiration , rhizosphere , water content , environmental science , agronomy , growing season , grassland , respiration , biomass (ecology) , organic matter , moisture , soil science , soil organic matter , soil water , bulk soil , steppe , chemistry , ecology , botany , biology , geology , geotechnical engineering , bacteria , genetics , organic chemistry
The shortgrass steppe is a semi‐arid grassland, where elevated CO 2 reduces stomatal conductance and promotes soil moisture storage. Enhanced biomass growth from elevated CO 2 has been attributed in part to soil moisture effects. However, the influence of this soil moisture feedback on C cycling has received little attention. We used open‐top chambers to increase atmospheric CO 2 concentrations to twice‐ambient for four growing seasons. Soil respiration rates and stable C isotopes of soil CO 2 were measured during the third and fourth seasons. Elevated CO 2 increased soil respiration rates by ∼25% in a moist growing season and by ∼85% in a dry season. Stable C isotope partitioning of soil respiration into its components of decomposition and rhizosphere respiration was facilitated on all treatments by a 13 C disequilibrium between currently growing plants and soil organic matter. Decomposition rates were more than doubled by elevated CO 2 , whereas rhizosphere respiration rates were not changed. In general, decomposition rates were most significantly correlated with soil temperature, and rhizosphere respiration rates were best predicted by soil moisture content. Model simulations suggested that soil moisture feedbacks, rather than differences in substrate availability, were primarily responsible for higher total respiration rates under elevated CO 2 . By contrast, modeling demonstrated that substrate availability was at least as important as soil moisture in driving CO 2 treatment differences in soil organic matter decomposition rates.