A model to predict diurnal pollen shed in maize

We have developed a mathematical model to predict the diurnal pattern of maize pollen shed based on local meteorological conditions. Our goal is to improve simulations of maize pollen dispersion, which have typically released pollen at a constant rate in contrast with measurements that show diurnal variation in the rate of shed. Of particular importance is predicting the time when peak shed occurs because pollen released around this peak typically accounts for most of the pollen dispersed during a day.

A model was developed to predict the diurnal pattern of pollen shed as a function of vapor pressure deficit, solar radiation, temperature and the amount of pollen remaining to be shed. The model was derived from measurements of pollen shed and local meteorological variables made during laboratory experiments and a 2004 field experiment. An unexpected result of these experiments was the absence of a relationship between wind speed and pollen shed in our observations. Previous studies have suggested wind as a primary factor in pollen shed, but it appeared that the rate of pollen shed was independent of wind speed as long as sufficient wind existed to dislodge pollen from the anther.

The model was validated ageast independent data by predicting the rate of pollen shed, normalized by the daily total of pollen shed, that occurred hourly for days during a 2003 field study (Avg. RMSE= 0.061 hr-1) and results from van Hout et al. (2008; Avg. RMSE = 0.089 hr-1). The model captured the general trend of pollen shed and predicted the time of peak shed within an hour of the measured peak on most days. The model, however, tended to underpredict the magnitude of the normalized peak rate of shed and did not account for secondary peaks in pollen shed that were occasionally observed. Future model refinements will include identifying additional biological or environmental factors that affect the instantaneous rate of pollen shed.

Reference:

van Hout, R., M. Chamecki, G. Brush, J. Katz and M. B. Parlange. 2008. The influence of local meteorological conditions on the circadian rhythm of corn (Zea mays L.) pollen emission. Agric. For. Meteorol. 148:1078-1092.