Annual Carbon Fluxes and Water Use Efficiency Among C3 and C4 Turfgrasses Under Deficit Irrigation.

Climate change resulting in increased temperatures, longer drought periods, and depleting water resources greatly impacts turfgrass and landscape use. Recently, we measured the carbon fixation potential and water use efficiency (WUE) of cool and warm-season turfgrasses under non-limiting conditions. Understanding that carbon sequestration is dependent on water and nutrient inputs, our research strives to determine which turfgrasses sequester the most carbon with the fewest inputs.  Plots (2m x 3m) with three replications of each species or cultivar were established in 2008. Beginning in May 2011, all turfgrasses were subjected to deficit irrigation (water stress) based on a percentage of the previous week’s reference evapotranspiration (ETo). Hand watering was used to maintain uniform and accurate irrigation distribution. Net ecosystem exchange (NEE) and ecosystem respiration measurements (µmole CO²/mol air) were taken monthly for each cultivar using a closed static chamber seated over each plot with a Li-COR 7500 open-path infrared gas exchange analyzer placed inside. Gross ecosystem productivity (GEP), or the amount of carbon dioxide exchanged between the plant and the atmosphere was calculated using NEE and respiration measurements (µmole CO²-C/m²/sec). The same measurements were taken for two cool-season, and two warm-season species during the course of wetting (irrigation) and dry-down events. Preliminary results indicated that the cool-season and warm-season species required between 75-95% and 55-75% ETo, respectively to maintain acceptable turf under deficit irrigation, depending upon weather conditions. In general, the mean GEP (an indication of overall plant health) of the cool-season turfgrasses was equivalent to or slightly higher than the warm-season species when they were irrigated with 20% more water.