Photosynthesis and respiration of managed C3 turfgrass fields under various light conditions

摘要

Net ecosystem C0_2 exchange from managed C_3 turfgrass (Kentucky bluegrass, Poa pratensis) fields under various light conditions (irradiance level of100, 60, 49, 20%) was measured with the closed dynamic chamber method from spring to fall. Net ecosystem C0_2 exchange was measured in situ using a 'clear' chamber, and total ecosystem respiration rate was measured using a 'dark' chamber. Both respiration rate and the amount of biomass were smaller in the shaded plots. Ecosystem respiration normalized with respect to soil temperature decreased in summer, coinciding with the seasonal change in plant biomass. The amount and seasonal change of biomass, not temperature, mainly governed the ecosystem respiration of the C_3 turfgrass fields under various light conditions. The light curve of gross photosynthesis, which was calculated by adding the respiration rate to net ecosystem exchange at each measurement time, was compared between plots. There were no obvious differences between plots in the response ofgross photosynthesis to light in spring, and a decline of the maximum photosynthesis at an optimal irradiance was observed in summer, except in the darkest plot.