Decoupling Temperature and Light Effects on Terpene Emissions From Subtropical Eucalyptus: Insights From Controlled Field Experiments

Abstract

Emissions of biogenic volatile organic compounds (BVOCs) from plants are significantly influenced by both temperature and light, yet the individual contribution of these factors, particularly for emissions of monoterpenes (MTs) and sesquiterpenes (SQTs) from tropical and subtropical plant species, remain poorly quantified due to their covariant effects. In this study, we conducted in situ and controlled field experiments on subtropical Eucalyptus trees using a portable LI-6800 photosynthesis system to isolate and quantify the temperature and light responses of major MTs. Additionally, we qualitatively assessed the light dependence of minor MTs and SQTs through dynamic chamber measurements. Our results revealed distinct light dependence across different compounds: β-ocimenes were fully light-dependent but exhibited unexpected suppression under high light conditions, whereas α-pinene and 1,8-cineole were light-independent. Temperature response experiments indicated that the temperature sensitivity (β) for light-dependent β-ocimenes (0.095 K⁻¹) and light-independent α-pinene (0.071 K⁻¹) and 1,8-cineole (0.102 K⁻¹) were similar to the model value (0.1 K⁻¹), but significantly lower than previously reported values from uncontrolled tropical measurements (0.2 K⁻¹), suggesting an influence of light on observed temperature sensitivity. Chamber-based results revealed that acyclic MTs and α-phellandrene were fully light-dependent, similar to β-ocimenes, while cyclic MTs and the SQT α-longipinene were light-independent and followed an exponential temperature function. Other SQTs exhibited partial light-dependence and would need a hybrid modeling approach. These results provide valuable insights into the emission mechanisms of various terpene types, with important implications for enhancing predictive models of BVOC emissions.