Abstract
We investigated the effects of seasonal and interannual fluctuations in gas exchange parameters as well as differences in growth light conditions to estimate leafscale photosynthesis in coolseason (type C3) turfgrass Kentucky bluegrass (Poa pratensis L.) grown under three different light conditions (irradiance: plot A, 100%; plot C, 48%; plot D, 20%). We measured diurnal changes in the leaf-scale net assimilation rate over 2 years and compared observed and simulated values with parameter sets derived from temperature andl ight curves of net assimilation rate. The simulated values using an optimal parameter set derived from spring data, without distinguishing between differences in light conditions or seasonal and interannual fluctuations, roughly reproduced the observed values, although there were overestimates for periods when there was a decline in the normalized maximum carboxylation rate (Vcmax25), particularly during periods of high-irradiance simulation. Our results suggest that seasonal fluctuations in photosynthetic capacity, i. e., the decline in Vcmax25 in winter and after early summer, should be considered to model and estimate leaf photosynthesis for use in the planning and maintenance of turfgrass fields, rather than differences of Vcmax25 between growth light conditions or interannual fluctuations.
