Ecology, December 2009, Vol.90(12), pp.3352-3366
Atmospheric CO concentrations have risen 40% since the start of the industrial revolution. Beginning in 1996, the Duke Free‐Air CO Enrichment experiment has exposed plots in a loblolly pine forest to an additional 200 μL/L CO compared to trees growing in ambient CO. This paper presents new belowground data and a synthesis of results through 2008, including root biomass and nutrient concentrations, soil respiration rates, soil pore‐space CO concentrations, and soil‐solution chemistry to 2 m depth. On average in elevated CO, fine‐root biomass in the top 15 cm of soil increased by 24%, or 59 g/m (26 g/m C). Coarse‐root biomass sampled in 2008 was twice as great in elevated CO and suggests a storage of ~20 g C·m·yr. Root C and N concentrations were unchanged, suggesting greater belowground plant demand for N in high CO. 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 CO. In recent years, increases in root biomass and soil respiration grew stronger, averaging ~30% at high CO. Peak changes for root biomass, soil respiration, and other variables typically occurred in midsummer and diminished in winter. Soil CO concentrations between 15 and 100 cm depths increased 36–60% in elevated CO. Differences from 30 cm depth and below were still increasing after 10 years' exposure to elevated CO, with soil CO concentrations 〉10 000 μL/L higher at 70‐ and 100‐cm depths, potentially influencing soil acidity and rates of weathering. Soil solution Ca and total base cation concentrations were 140% and 176% greater, respectively, in elevated CO at 200 cm depth. Similar increases were observed for soil‐solution conductivity and alkalinity at 200 cm in elevated CO. Overall, the effect of elevated CO belowground shows no sign of diminishing after more than a decade of CO enrichment.
Elevated Co 2 ; Loblolly Pine Forest ; Root Biomass ; Root Carbon And Nitrogen ; Soil Pore Space Co 2 ; Soil Respiration