Carbon Dioxide Exchange of Blue Grama Swards as Influenced by Several Ecological Variables in the Field

Abstract

CO2 exchange for swards of blue grama (Bouteloua gracilis (H.B.K.) Lag.) was measured in situ in the field. The effects of soil water potential, irradiance, temperature and phenological stage (and their interactions) on photosynthetic rates were determined by comparisons between different periods when these variables differed. Net photosynthetic rates as high as 65 mg CO2 dm-2 h-1 were observed under optimum conditions. Increasing soil water stress resulted in significant decreases in photosynthetic rates. Photosynthesis was less during the reproductive stage. Integrated values of gross and net photosynthesis and above ground respiration were reported for various 24 h periods throughout the growing season. Daily net photosynthetic rates between 1.7-14.3 g CH2O m-2 day-1 were recorded. Efficiency of solar energy conversion to plant tissue for the 24 h periods varied from 0.24-1.72%.