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United States Department of Agriculture

Agricultural Research Service

Title: Photosynthetic water use efficiency and biomass of Sorghastrum nutans (C4) and Solidago canadensis (C3) in three soils along a CO2 concentration gradient

Authors
item Fay, Philip
item Hui, Dafeng - DUKE UNIVERSITY
item Proctor, Andrew - DUKE UNIVERSITY
item Jin, Virginia
item Johnson, Hyrum
item Polley, Wayne
item Jackson, Robert - DUKE UNIVERSITY

Submitted to: European Geophysical Society Meeting
Publication Type: Abstract Only
Publication Acceptance Date: March 19, 2007
Publication Date: June 5, 2007
Citation: Fay, P.A., Hui, D., Proctor, A., Jin, V.L., Johnson, H.B., Polley, H.W., Jackson, R.B. 2007. Photosynthetic water use efficiency and biomass of Sorghastrum nutans (C4) and Solidago canadensis (C3) in three soils along a CO2 concentration gradient. European Geosciences Union General Assembly, April 15-20, 2007, Vienna, Austria. A-04329. CDROM.

Technical Abstract: The water use efficiency (WUE) of leaf photosynthetic carbon uptake is a key regulator of ecosystem carbon cycles, however WUE may differ with soil type because of differences in soil moisture retention and plant uptake efficiency. We measured leaf-level WUE and end-of-season biomass in the C4 grass Sorghastrum nutans and the C3 forb Solidago canadensis in constructed grassland species assemblages growing along a 200 – 560 ppm [CO2] gradient in the LYCOG Experiment, in central Texas, USA. LYCOG consists of eighty intact soil monoliths (1 m x 1 m x 1.5 m) representing 3 soil series, Austin (Udorthentic Haplustolls, a mollisol), Bastrop (Udic Paleustalfs, a sandy loam alfisol) and Houston Black (Udic Haplusterts, a vertisol). The monoliths were vegetated by transplanting 8 native perennial prairie species (5 grasses and 3 forbs), including S. nutans and S. canadensis. Both are abundant and widespread; S. nutans is a dominant species throughout much of North American tallgrass prairie, and S. canadensis is one of the most abundant and widespread forbs in North America. WUE, calculated as the ratio of photosynthesis (ACO2) to transpiration (E), was measured three times during the growing season, volumetric soil water content (SWC, 30 cm depth, %) was measured biweekly with a neutron probe to assess soil moisture availability, and biomass was measured by harvesting all current year growth of these species and drying to constant mass. Soil water content (0 – 30 cm) was lower on the Bastrop than Austin or Houston soils (p < 0.0001). WUE did not differ between soil types for either species, but the biomass of both S. nutans and S. canadensis was 2 to 4- fold higher on Bastrop and Houston than on Austin soils (p </- 0.05). Soil water content was not significantly related to [CO2]. However, photosynthetic WUE increased strongly (p< 0.0001) at higher [CO2], due to a combination of decreasing E (p </- 0.0005) and increasing ACO2 (p = 0.0055). This pattern was the same in both species (species x [CO2] ns). Biomass of S. nutans was unrelated to [CO2] (p >/- 0.19), however biomass of S. canadensis increased strongly at higher [CO2] on Bastrop and Houston soils (soil x [CO2] p = 0.0003). We conclude that 1) [CO2] was the primary control on leaf-level photosynthetic efficiency 2) soil type was the primary control on growth 3) Soil type may mediate changes in the relative abundance of these two widespread and common species under increased atmospheric [CO2].

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