Primary Productivity and Water Balance of Grassland Vegetation on Three Soils in a Continuous CO sub(2) Gradient: Initial Results from the Lysimeter CO sub(2) Gradient Experiment

• Published in: Ecosystems (New York) 2009-08, Vol.12 (5), p.699-714
• Main Authors: Fay, Philip A, Kelley, Alexia M, Procter, Andrew C, Hui, Dafeng, Jin, Virginia L, Jackson, Robert B, Johnson, Hyrum B, Polley, HWayne
• Format: Article
• Language: English
• Subjects: Bouteloua curtipendula; Schizachyrium scoparium; Solidago canadensis; Sorghastrum nutans
• ISSN: 1432-9840; 1435-0629
• DOI: 10.1007/s10021-009-9247-3

Field studies of atmospheric CO sub(2) effects on ecosystems usually include few levels of CO sub(2) and a single soil type, making it difficult to ascertain the shape of responses to increasing CO sub(2) or to generalize across soil types. The Lysimeter CO sub(2) Gradient (LYCOG) chambers were constructed to maintain a linear gradient of atmospheric CO sub(2) (~250 to 500kll super(-1)) on grassland vegetation established on intact soil monoliths from three soil series. The chambers maintained a linear daytime CO sub(2) gradient from 263kll super(-1) at the subambient end of the gradient to 502kll super(-1) at the superambient end, as well as a linear nighttime CO sub(2) gradient. Temperature variation within the chambers affected aboveground biomass and evapotranspiration, but the effects of temperature were small compared to the expected effects of CO sub(2). Aboveground biomass on Austin soils was 40% less than on Bastrop and Houston soils. Biomass differences between soils resulted from variation in biomass of Sorghastrum nutans, Bouteloua curtipendula, Schizachyrium scoparium (C sub(4) grasses), and Solidago canadensis (C sub(3) forb), suggesting the CO sub(2) sensitivity of these species may differ among soils. Evapotranspiration did not differ among the soils, but the CO sub(2) sensitivity of leaf-level photosynthesis and water use efficiency in S.canadensis was greater on Houston and Bastrop than on Austin soils, whereas the CO sub(2) sensitivity of soil CO sub(2) efflux was greater on Bastrop soils than on Austin or Houston soils. The effects of soil type on CO sub(2) sensitivity may be smaller for some processes that are tightly coupled to microclimate. LYCOG is useful for discerning the effects of soil type on the CO sub(2) sensitivity of ecosystem function in grasslands.