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

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 CO 2 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 [CO 2 ] (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 [CO 2 ] 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 CO 2 efflux rates indicate accelerated decay rates in fumigated plots (2001: elevated [CO 2 ]: 10.5±1.2 μmol CO 2 m −2 s −1 vs. ambient: 8.9± 1.0 μmol CO 2 m −2 s −1 ). There were no treatmentbased 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 CO 2 fertilization. In this study, SOM turnover appears to be accelerated under elevated [CO 2 ] 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.

Distinct responses of soil microbial communities to elevated CO2 and O3 in a soybean agro-ecosystem

“…Such differences may be ecosystem-dependent. A previous study showed that as soybean yield and root biomass increased under eCO 2 , soil organic matter turnover was accelerated but soil moisture and nutrients were not limiting factors at the SoyFACE (Peralta and Wander, 2008). Compared with grassland ecosystems, the soybean agro-ecosystem is N-rich and has competive advantages over non-legumious species at eCO 2 by capitializing on eCO 2 benefits (for example, increaseing N fixation) and limiting deleterious eCO 2 effects (Rogers et al, 2009).…”

“…and corn, Zea mays L. for more than 25 years, and the soil at the site is a Drummer fine-silty, mixed, mesic Typic Endoaquoll, typical of wet, dark-colored 'prairie soils' in northern and central Illinois (Pujol Pereira et al, 2011). More soil background properties, including soil pH, moisture, Bray P, K, Ca and Mg were previously documented (Peralta and Wander, 2008). SoyFACE aims to discover the effects of atmospheric change on the agronomy, productivity and ecology of Midwestern agro-ecosystems planted in a typical corn-soy rotation.…”

Experimental Study Of Cements And Stone/shale-brine-co2 Interactions

“…In many natural and semi-natural ecosystems, the CO 2 -induced stimulation of plant growth may not persist because of nutrient limitation [9,39]. In agricultural ecosystems, however, N is typically not a limiting factor for plant growth due to the application of chemical N fertilizers and/or the incorporation of legume plants, and CO 2 -stimulation of biomass production is expected to be sustained [2,31,66]. Therefore, it has been suggested that elevated CO 2 can increase long-term C storage in agroecosystems, particularly in combination with no-tillage management [38,67,68].…”

Aboveground dominant functional group predicts belowground properties in an alpine grassland community of western China

“…Furthermore, increased N contents can boost microbial respiration and population growth, resulting in accelerated N turnover and net mineralization from decomposition of microbial residues (Mengel 1996;Ebersberger et al 2003). The AN may also support root accelerated mineralization of SOM (Peralta and Wander 2008). Moreover, GFG-dominated meadows had lower pH values, which may impact plant rhizosphere secretion, soil acidity, and the organic acids released during the decomposition process.…”