Modification of the isoprene emission model G93 for tropical tree Ficus virgata

This study describes parameterization and modification of G93 model to predict the isoprene emission from a tropical tree Ficus virgata. The optimized parameters of CT for four tropical trees determined by best fit were greater than those of default values for G93, and the temperature response profiles of these tropical trees showed divergence from that predicted by G93 model. Among the tropical trees studied, F. virgata was the highest emitter, and hence chosen as model plant for parameterization and modification of the emission model G93. Functions of factors CT and CL were respectively fitted to the emission data at 11 temperature and 12 light intensities obtained from three replicates obtained from cutting of F. virgata. With respect to CT, parameters determined by best fit were again much larger than those of original G93 suggesting that the temperature response of isoprene emission from F. virgata differs from that predicted by G93 model. Temperature normalization of the emission rate by our optimized CT revealed that the isoprene emission from F. virgata leveled off with increasing light intensities. To incorporate this decline in isoprene emission at high light intensities, the original CL of G93 was combined with a logistic function to produce modified CL. These optimization and modification much improved the model performance to predict the diurnal variation of isoprene emission from F. virgata. The present study thus describes a possible modification of model G93 to maximize its model performance to predict the regional isoprene emission more precisely.