Carbon Balance Variations of C3 and C4 Turfgrasses.

Turfgrasses are ubiquitous and often present as monocultures in the urban landscape. In arid and semiarid metropolitan areas, turfgrass can account for as much as 75 percent of the total household water consumption. Changing climate induced by increasing temperature and drought poses a threat to turfgrass use and to the industry. On the other hand, turfgrasses have the potential to act as a carbon sink in urban ecosystems and sequester as much as 1 kg carbon per ha per year, which is 1.5 to 3 times higher than in agricultural systems. They can also provide localized cooling effects to urban residents. Understanding the relative water and nutrient use efficiencies among different species and cultivars are important for quantifying the role of turf in regional and global changes and developing management practices to improve the production of ecosystem services. In this study, we evaluated the performance of six cool-season (C3) and eleven warm-season (C4) species and cultivars in mono- or polystands based on their carbon balance and water use efficiency. Plots (2m x 3m) with three replications were laid out as sod or plugs in a randomized complete block design in 2008. Beginning in March 2009, ecosystem carbon dioxide and water exchange have been measured using a closed static chamber seated over each plot with an open-path infrared gas exchange analyzer placed inside at two week intervals. From 7 March to 18 April 2009, mean carbon exchange for C3 cultivars decreased from 12.35 µmole CO2 m-2 sec-1 to 11.35 µmole CO2 m-2 sec-1, whereas, the C4 cultivars increased from 6.29 µmole CO2 m-2 sec-1 to 12.06 µmole CO2 m-2 sec-1. Significant differences in carbon balance and water use efficiency were observed over time among cultivars within C3 and C4 species.