Plant and Soil

, Volume 303, Issue 1–2, pp 69–81

Soil organic matter dynamics under soybean exposed to elevated [CO2]

Research Article

Abstract

It is unclear how changing atmospheric composition will influence the plant–soil interactions that determine soil organic matter (SOM) levels in fertile agricultural soils. Positive effects of CO2 fertilization on plant productivity and residue returns should increase SOM stocks unless mineralization or biomass removal rates increase in proportion to offset gains. Our objectives were to quantify changes in SOM stocks and labile fractions in prime farmland supporting a conventionally managed corn–soybean system and the seasonal dynamics of labile C and N in soybean in plots exposed to elevated [CO2] (550 ppm) under free-air concentration enrichment (FACE) conditions. Changes in SOM stocks including reduced C/N ratios and labile N stocks suggest that SOM declined slightly and became more decomposed in all plots after 3 years. Plant available N (>273 mg N kg−1) and other nutrients (Bray P, 22–50 ppm; extractable K, 157–237 ppm; Ca, 2,378–2,730 ppm; Mg, 245–317 ppm) were in the high to medium range. Exposure to elevated [CO2] failed to increase particulate organic matter C (POM-C) and increased POM-N concentrations slightly in the surface depth despite known increases (≈30%) in root biomass. This, and elevated CO2 efflux rates indicate accelerated decay rates in fumigated plots (2001: elevated [CO2]: 10.5 ± 1.2 μmol CO2 m−2 s−1 vs. ambient: 8.9 ± 1.0 μmol CO2 m−2 s−1). There were no treatment-based differences in the within-season dynamics of SOM. Soil POM-C and POM-N contents were slightly greater in the surface depth of elevated than ambient plots. Most studies attribute limited ability of fumigated soils to accumulate SOM to N limitation and/or limited plant response to CO2 fertilization. In this study, SOM turnover appears to be accelerated under elevated [CO2] even though soil moisture and nutrients are non-limiting and plant productivity is consistently increased. Accelerated SOM turnover rates may have long-term implications for soil’s productive potential and calls for deeper investigation into C and N dynamics in highly-productive row crop systems.

Keywords

Carbon sequestration Climate change Priming Soil organic matter 

Abbreviations

Db

bulk density

H-CF

coarse heavy fraction

IL-N

Illinois-N test

LF

light fraction

POM

particulate organic matter

SOM

soil organic matter

TOC

total organic carbon

TN

total nitrogen

Copyright information

© Springer Science+Business Media B.V. 2007

Authors and Affiliations

  1. 1.Program in Ecology and Evolutionary BiologyUniversity of Illinois at Urbana–ChampaignUrbanaUSA
  2. 2.Natural Resources and Environmental SciencesUniversity of Illinois at Urbana–ChampaignUrbanaUSA

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