Effect of growth temperature on monoterpene emission rates of Acer palmatum.

To understand the effect of increasing atmospheric temperatures on monoterpene emissions from mature trees, we measured the monoterpene emission rate, monoterpene precursor content, and the SPAD value of Acer palmatum, a mature tree grown at three different field sites. The annual mean temperature differed by intervals of 3 °C among the three sites from 10.6 °C to 17.7 °C, depending on the site elevation. The short-term monoterpene emission rate of A. palmatum depended on both the leaf temperature and the light intensity. The growth temperature did not affect the monoterpene emissions in response to short-term variations in temperature and light intensity. The highest standard monoterpene emission rate, M, was observed from July to August, but this rate did not differ among the three sites. The M showed clear seasonal variation, whereas the monoterpene precursor content did not show them. The trend of the M was similar to that of the SPAD, as both values depend on leaf phenology. In A. palmatum, a warming of approximately 3 °C caused the start date of the monoterpene emissions to commence two to three weeks earlier, and end date of the monoterpene emissions to be delayed by two to three weeks. The cumulative temperature method could be used to predict the start and end dates of the monoterpene emissions. To estimate the annual monoterpene emissions, a temperature and light intensity dependent emission model was modified to incorporate the effect of growth temperature on seasonal patterns of M. Annual monoterpene emissions were found to increase linearly with annual mean temperature. For each 1 °C of warming, the annual monoterpene emissions from A. palmatum increased by approximately 15%. Our results suggest that the effect of growth temperature on monoterpene emissions should be considered when predicting monoterpene emissions in response to global warming in the foreseeable future.