SIMULATED IRRADIANCE AND TEMPERATURE ESTIMATES AS A POSSIBLE SOURCE OF BIAS IN THE SIMULATION OF PHOTOSYNTHESIS

Most plant physiological processes are not linearly dependent on the environmental factors temperature and irradiance. This means that process rate estimates based on average values of these factors are usually biased. The distribution of simulated light intensity and temperature values does not necessarily match the real distribution. Hence the use of simulated irradiance and temperature data represents a potential source of bias. In this study, two models that simulate instantaneous values of irradiance, and one model that simulates instantaneous values of temperature are compared with measured data. The simulated irradiance was generated from the total daily radiation, and the simulated temperature used daily minimum and maximum values. Nonlinear functions, which are similar to the response functions of leaf photosynthesis and maintenance respiration, are applied to simulated and measured values of irradiance and temperature. The effect of simulated irradiance and temperature values was less than 3% on photosynthesis estimates and less than 1.5% on respiration estimates. Hourly and daily averages of irradiance and temperature are readily available for a number of weather stations throughout the world. In addition, temporal averages of irradiance and temperature were calculated and photosynthesis estimates using averages and instantaneous measured data were compared. The use of hourly averages instead of sensor readings at 2 min intervals led to a 5% overestimate of photosynthesis of an unshaded leaf.