Weather history-based parameterization of the G-93 isoprene emission formula for the tropical plant Ficus septica

Abstract

The Guenther 1993 (G-93) formula is the most extensively used algorithm for predicting leaf-scale isoprene emissions driven by temperature and light intensity, and has been incorporated into many isoprene emission models. The temperature and light response variables of the G-93 define the rate of increase (ascend) and decrease (descend) of emissions as driven by temperature and light intensity. Our previous study on the tropical tree Ficus septica noted that hot weather in the previous days impacted unevenly the ascend and descend changes of isoprene emission, causing a significant deviation between the G-93 prediction and observations. Separate parameterization of the ascend and the descend phases successfully ameliorated this deviation, however, the relationship between weather history and parameters for individual ascend and descend phase still warrants more detailed studies to inform their reliable use in emission algorithms. We herein further examined the relationship between weather history and G-93 parameters for individual ascending and descending phase responses. We found that among the G-93 parameters, C_T1 and α correlated with cumulative temperature or PPFD, whilst C_T2 essentially remained constant for both the ascending and descending phases. These correlations allowed us to parameterize the G-93 formula based on weather history for the first time, and direct modification of C_T1 and α in terms of cumulative temperature and light intensity captured 96.6% of variation in the ascending and 98.1% in the descending phase in the study period. Separate parameterization of the upward and the downward changes was found to be effective in improving our ability to predict isoprene emission from plants that experienced hot weather in the previous days. More importantly, this result implies that the assumption of a symmetric response of isoprene emission across the maxima temperature and light intensity needs revision especially under circumstances of a warming climate.