Altered soil microbial community at elevated CO ₂ leads to loss of soil carbon

Abstract

Increased carbon storage in ecosystems due to elevated CO2 may help stabilize atmospheric CO 2 concentrations and slow global warming. Many field studies have found that elevated CO 2 leads to higher carbon assimilation by plants, and others suggest that this can lead to higher carbon storage in soils, the largest and most stable terrestrial carbon pool. Here we show that 6 years of experimental CO 2 doubling reduced soil carbon in a scrub-oak ecosystem despite higher plant growth, offsetting Ϸ52% of the additional carbon that had accumulated at elevated CO 2 in aboveground and coarse root biomass. The decline in soil carbon was driven by changes in soil microbial composition and activity. Soils exposed to elevated CO 2 had higher relative abundances of fungi and higher activities of a soil carbondegrading enzyme, which led to more rapid rates of soil organic matter degradation than soils exposed to ambient CO 2. The isotopic composition of microbial fatty acids confirmed that elevated CO 2 increased microbial utilization of soil organic matter. These results show how elevated CO 2, by altering soil microbial communities, can cause a potential carbon sink to become a carbon source.carbon cycling ͉ global change ͉ microbes ͉ priming effect

Priming and microbial nutrient limitation in lowland tropical forest soils of contrasting fertility

“…According to this theory, the soil C-specialists increase in abundance by utilizing some of the new labile C and persist to degrade stable soil C when the labile C becomes diminished (Fontaine et al 2003). Supporting evidence for this mechanism is provided by studies that measured prolonged priming after supply of added labile C is exhausted (Fontaine et al 2004), and priming alongside an increased dominance of the microbial community by fungi (Carney et al 2007).…”

“…Priming has been suggested as the cause of reductions in soil C in temperate forest grown under experimentally elevated CO 2 , despite increased inputs of plant-C to soils (Carney et al 2007;Langley et al 2009). The parallel loss of soil C and increase in N mineralization in the study by Langley et al (2009) suggests that priming occurred due to microbial 'co-metabolism' of organic matter to acquire N (Kuzyakov et al 2000), which is often considered the limiting nutrient in temperate forests.…”

“…Priming due to increased abundance of recalcitrant-C degrading microorganisms can be identified by a shift in microbial community composition (e.g. increase in fungal:bacterial ratios; Carney et al 2007), prolonged priming following the exhaustion of the added substrate, and greater priming in low fertility soils (Fontaine et al 2003(Fontaine et al , 2004.…”

Free atmospheric CO<sub>2</sub> enrichment increased above ground biomass but did not affect symbiotic N<sub>2</sub>-fixation and soil carbon dynamics in a mixed deciduous stand in Wales

“…going from a high fertility agricultural soil to a forest soil with a declining soil fertility status Hoosbeek and Scarascia-Mugnozza, 2009). In a scrub-oak ecosystem with higher biomass production under elevated [CO 2 ], Carney et al (2007) observed a decline of soil C due to relative higher abundances of fungi and higher activities of phenol oxidase which is responsible for the degradation of recalcitrant SOM such as lignin. Based on incubation experiments at the Duke FACE experiment, Billings and Ziegler (2008) inferred that increasing N limitation under elevated [CO 2 ] would result in greater turnover rates of relatively stable soil C pools.…”

Warming and nitrogen deposition lessen microbial residue contribution to soil carbon pool

“…To date, the majority of studies on ecosystem C storage response triggered by climate change have been focused on the role of above-ground tissue chemistry and biomass production 12 , the dynamics of total terrestrial C capacity 13 , and more recently in identifying microbial indices of C utilization and activity that lead to trace gas production [14][15][16][17] . However, little is known about the degree to which soil microbialderived C persists in the soil, and contributes to stable C. Microbial production of recalcitrant organic C lies at the root of two issues of global concern-maintaining soil productivity and controlling greenhouse gas levels 7 .…”