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Increased belowground biomass and soil CO 2 fluxes after a decade of carbon dioxide enrichment in a warm‐temperate forest
Author(s) -
Jackson Robert B.,
Cook Charles W.,
Pippen Jeffrey S.,
Palmer Sheila M.
Publication year - 2009
Publication title -
ecology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.144
H-Index - 294
eISSN - 1939-9170
pISSN - 0012-9658
DOI - 10.1890/08-1609.1
Subject(s) - biomass (ecology) , carbon dioxide , soil respiration , temperate climate , respiration , environmental science , agronomy , nutrient , carbon dioxide in earth's atmosphere , soil water , temperate forest , soil carbon , chemistry , zoology , environmental chemistry , botany , ecology , soil science , biology
Atmospheric CO 2 concentrations have risen 40% since the start of the industrial revolution. Beginning in 1996, the Duke Free‐Air CO 2 Enrichment experiment has exposed plots in a loblolly pine forest to an additional 200 μL/L CO 2 compared to trees growing in ambient CO 2 . 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 2 concentrations, and soil‐solution chemistry to 2 m depth. On average in elevated CO 2 , fine‐root biomass in the top 15 cm of soil increased by 24%, or 59 g/m 2 (26 g/m 2 C). Coarse‐root biomass sampled in 2008 was twice as great in elevated CO 2 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 CO 2 . 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 2 . In recent years, increases in root biomass and soil respiration grew stronger, averaging ~30% at high CO 2 . Peak changes for root biomass, soil respiration, and other variables typically occurred in midsummer and diminished in winter. Soil CO 2 concentrations between 15 and 100 cm depths increased 36–60% in elevated CO 2 . Differences from 30 cm depth and below were still increasing after 10 years' exposure to elevated CO 2 , with soil CO 2 concentrations >10 000 μL/L higher at 70‐ and 100‐cm depths, potentially influencing soil acidity and rates of weathering. Soil solution Ca 2+ and total base cation concentrations were 140% and 176% greater, respectively, in elevated CO 2 at 200 cm depth. Similar increases were observed for soil‐solution conductivity and alkalinity at 200 cm in elevated CO 2 . Overall, the effect of elevated CO 2 belowground shows no sign of diminishing after more than a decade of CO 2 enrichment.