Details

Autor(en) / Beteiligte

• Jackson, Robert B
• Cook, Charles W
• Pippen, Jeffrey S
• Palmer, Sheila M

Titel

Increased belowground biomass and soil CO2 fluxes after a decade of carbon dioxide enrichment in a warm-temperate forest

Ist Teil von

• Ecology (Durham), 2009-12, Vol.90 (12), p.3352-3366

Ort / Verlag

Washington, DC: Ecological Society of America

Erscheinungsjahr

2009

Quelle

MEDLINE

Beschreibungen/Notizen

• Atmospheric CO₂ concentrations have risen 40% since the start of the industrial revolution. Beginning in 1996, the Duke Free-Air CO₂ Enrichment experiment has exposed plots in a loblolly pine forest to an additional 200 μL/L CO₂ compared to trees growing in ambient CO₂. This paper presents new belowground data and a synthesis of results through 2008, including root biomass and nutrient concentrations, soil respiration rates, soil porespace CO₂ concentrations, and soil-solution chemistry to 2 m depth. On average in elevated CO₂, fine-root biomass in the top 15 cm of soil increased by 24%, or 59 g/m² (26 g/m² C). Coarse-root biomass sampled in 2008 was twice as great in elevated CO₂ and suggests a storage of ∼20 g C·m⁻²·yr⁻¹. Root C and N concentrations were unchanged, suggesting greater belowground plant demand for N in high CO₂. Soil respiration was significantly higher by 23% on average as assessed by instantaneous infrared gas analysis and 24-h integrated estimates. N fertilization decreased soil respiration and fine-root biomass by ∼10–20% in both ambient and elevated CO₂. In recent years, increases in root biomass and soil respiration grew stronger, averaging ∼30% at high CO₂. Peak changes for root biomass, soil respiration, and other variables typically occurred in midsummer and diminished in winter. Soil CO₂ concentrations between 15 and 100 cm depths increased 36–60% in elevated CO₂. Differences from 30 cm depth and below were still increasing after 10 years' exposure to elevated CO₂, with soil CO₂ concentrations >10 000 μL/L higher at 70- and 100-cm depths, potentially influencing soil acidity and rates of weathering. Soil solution Ca²⁺ and total base cation concentrations were 140% and 176% greater, respectively, in elevated CO₂ at 200 cm depth. Similar increases were observed for soil-solution conductivity and alkalinity at 200 cm in elevated CO₂. Overall, the effect of elevated CO₂ belowground shows no sign of diminishing after more than a decade of CO₂ enrichment.