Annual Carbon Exchange and Water Use Efficiency Among C3 and C4 Turfgrasses.

Carbon balance and water use efficiency of five cool-season (C3) and eleven warm-season (C4) turfgrass species and cultivars in mono- or polystands were monitored for 12 months in Riverside, CA. Plots (2m x 3m) with three replications were laid out as sod or plugs in a randomized complete block design in 2008 and maintained under non-limiting cultural practices. Beginning in March 2009, ecosystem carbon dioxide (CO₂) and water exchange were measured every two weeks using a closed static chamber seated over each plot with a Li-COR 7500 open-path infrared gas exchange analyzer placed inside. Net ecosystem exchange (NEE), or gas exchange during photosynthesis and respiration in µmol CO₂/mol air was measured. Ecosystem respiration was also measured using a shade cloth that was placed over the closed static chamber. NEE and respiration measurements taken for each plot were used to calculate gross ecosystem productivity (GEP) or the amount of carbon dioxide that is exchanged between turfgrass and the atmosphere (µmole CO₂-C/m²/sec). Water use efficiency (WUE) or the amount of CO₂ taken up by the turf per unit of water lost by evapotranspiration (ET) was also determined for each plot as GEP/ET. From March-October 2009, average WUE of the C3 species was highest for Bayside Blend Kentucky bluegrass /perennial ryegrass (1.23 µmol C/mm H₂O), and lowest for Elite Plus tall fescue/K. bluegrass (0.24 µmol C/mm H₂O). Of the C4 species, WUE was highest for Tifgreen 328 bermudagrass (3.96 µmol C/mm H₂O) and lowest for Excalibre seashore paspalum (1.77 µmol C/mm H₂O). Bayside Blend K. bluegrass/P. ryegrass also had the highest carbon fixation potential of the C3 species at 1.14 (GEP/R_e) with the lowest recorded for Medallion tall fescue at 0.02. St. Augustinegrass had the highest carbon fixation potential of the C4 species at 1.73 while Excalibre seashore paspalum had the lowest potential at 0.56. Annual WUE and carbon fixation potentials under non-limiting conditions will be presented for all species.