Submitted to: American Geophysical Union
Publication Type: Abstract Only
Publication Acceptance Date: 11/15/2006
Publication Date: 12/29/2006
Citation: Hui, D., Fay, P.A., Procter, A., Johnson, H.B., Polley, H.W., Jackson, R.B. 2006. Response of soil respiration to a subambient to elevated CO2 gradient in grassland ecosystems. In: Proceedings of the EOS Trans. American Geophysical Union. December 11-15, 2006, San Francisco, CA. Paper No. B53F-01.
Technical Abstract: Despite the importance of soil respiration responses to atmospheric CO2 concentration ([CO2]) for the global carbon cycle and climate change, the relationship between soil respiration and [CO2] has not been well developed, mainly because previous studies included few CO2 levels. We designed a unique Lysimeter CO2 Gradient experimental facility (LYCOG) at the Grassland, Soil & Water Research Laboratory in Temple, Texas to study the effects of subambient to elevated [CO2] on grassland ecosystems. Eighty intact soil monoliths (1m X 1m X 1.5m) representing 3 soil series, Austin (Udorthentic Haplustolls, a mollisol), Bastrop (Udic Paleustalfs, a sandy loam alfisol) and Houston Black (Udic Haplusterts, a vertisol) were vegetated by transplanting 8 native perennial prairie species (5 grasses and 3 forbes) and linearly arranged to be exposed to a 200-560 ppm CO2 gradient. The CO2 treatments started in May, 2006 as part of a long-term experiment. Soil respiration (Re) was measured on April 4, June 26, and August 2, 2006 together with soil temperature and soil water content to 15 cm depth. Diurnal changes of soil respiration were measured on August 2, 2006 at four [CO2]. No significant relationship of soil respiration with [CO2] was found on June 26, but soil respiration increased linearly with [CO2] on August 2 (Re=3.23+0.0062[CO2], r2=0.54, p<0.01). Across all CO2 treatments, Bastrop soil had the highest soil respiration rate (6.21 +/- 0.48 u mol CO2 m-2 s-1) and Houston soil had the lowest value (4.97 +/- 0.41 u mol CO2 m-2 s-1). Soil respiration increased with soil moisture, but decreased at greater soil temperature. Similar diurnal changes were observed on the three soils, with the maximum soil respiration occurring during early morning. Soil respiration at different times during a day was consistently lower at 250 ppm CO2 treatment than at ambient and elevated [CO2]. Our preliminary data demonstrated a linear increase in CO2 emission in grassland ecosystems with [CO2] increase. Considering plant photosynthesis also increases linearly with [CO2] in the grassland, relative changes in the slopes of photosynthesis and respiration with [CO2] could determine whether grassland ecosystems are a carbon sink or source in a future high CO2 world.