| Summary: | 碩士 === 國立臺灣大學 === 森林環境暨資源學研究所 === 104 === Isoprene (2-methyl-1, 3-butadiene), which is known as a volatile organic compound (VOC), has strong impacts on air pollution and global warming. Former studies indicated that plant can emit isoprene for multiple purposes including enhancing thermotolerance and preventing ozone-exposing damages. According to former estimations, the isoprene emission amount from plants was enormous, suggesting the importance of estimating fluxes of isoprene emission from plants. As well, former studies indicated that environmental factors (e.g., leaf temperature, light intensity) and physiological factors (e.g., position in the canopy) can affect isoprene emissions. Previously, several studies proposed models for estimating isoprene emission from plants, yet they did not consider bamboos. Nevertheless, moso bamboo is one of the dominant species in eastern Asia, currently showing rapid expansion and invasion into other forests. Hence, the objectives of this study were 1) to identify the ability of isoprene emission in moso bamboos and then to clarify 2) spatial and 3) temporal variations in isoprene emission in a moso maboo forest. Also, 4) this study developed a model reproducing the temporal changes in isoprene emission from the bamboos based on the measurements. This study conducted isoprene measurements based on a leaf chamber method in a bamboo specimen garden and a bamboo forest in Xitou Experimental Forest, central Taiwan. First, by checking 14 species of bamboo in November and December 2014, this study revealed that B. oldhami, P. Edulis and P. lithophila Hayata had significant isoprene emission which were about 32.02, 23.20 and 38.30 nmol m-2 s-1, respectively. All species of Dendrocalamus and Phyllostachys showed isoprene emission detected, but the isoprene emissions were not detected in C. marmorea cv. Variegata, S. fastuosa, T. siamensis and Yushania niitakayamensis. As the result, this study confirmed significance of isoprene emission in moso bamboos. Second, this study examined the pattern of vertical variations in isoprene emission within canopy under the standardized environmental conditions, and only one individual showed significant difference in isoprene emission rates between canopy top and bottom (P= 0.041) if we test the significance in each individual; however, if we consider total seven individuals measured, that is, canopy top and bottom tended to show higher and lower isoprene emission rates, respectively (P= 0.0052). Third, by measuring isoprene emission rate under fixed light intensity levels, the seasonal variation in isoprene emission during September 2015 to March 2016 increased with light intensity differently between months; where December 2015, January, February and March 2016 have lower emission at the given light level than those of September, October and November 2015. The seasonal variation in isoprene emission rates at the same light intensity (PPFD = 1000 mol m-2 s-1) generally corresponded to that of leaf temperature, although some discrepancy was found in February and March 2016, suggesting that there were other factors affecting the seasonal variation. Fourth, to develop a model, this study considered the effect of leaf temperature and light intensity, and better performances found in using the function based on Gaussian distribution for leaf temperature and the function for light-intensity proposed by Guenther et al. (1993) in the fitness to the measurements. The RMSE of each month in the model were 38.79, 31.26, 86.24, 46.24, 44.16, 60.89 and 62.53 in September 2015 to March 2016, respectively. Overall, this study established a foundation of estimating total amount of canopy-scale isoprene emission in the moso bamboo forest. For precise estimation, an isoprene emission model for annual canopy-scale should consider not only the effect of leaf temperature and light intensity but also variations in potential emission rates within canopy and phenological and physiological effects in spring.
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