Photodegradation of Myrigalone A, an Allelochemical from Myrica gale: Photoproducts and Effect of Terpenes

This study investigated the environmental fate of myrigalone A, a light absorbing natural herbicide found on leaves and fruits of Myrica gale. Myrigalone A was irradiated in water and as a dry solid deposit to simulate reactions on leaves, alone and in the presence of the terpenes generated by Myrica gale. The phototransformation was fast ( t_1/2 = 35 min in water). Analyses by liquid chromatography coupled to high resolution orbitrap electrospray mass spectrometry (MS) and gas chromatography-MS revealed the formation of 11 photoproducts in water and solid and 9 in gaseous phase. Some were detected in the leaf glands and oil covering the fruits of Myrica gale, which suggested that photodegradation occurred in the field. Moreover, myrigalone A photoinduced the oxidation of terpenes that in turn protected it against photolysis. This highlights the need for additional research on the effect of terpenes on the photodegradation of pesticides on vegetation.

[High-spectral responses of Myrica rubra seedlings to UV-B radiation stress]

A simulated field experiment with three treatments, i. e., ambient light (control), reduced UV-B radiation, and enhanced UV-B radiation, was conducted to evaluate the effects of solar ultraviolet (UV-B) radiation on the seedlings of Myrica rubra, a typical woody species in subtropical region. The leaf chlorophyll content, spectral reflectance and spectral characteristic parameters were measured and analyzed. As compared with the control, enhanced UV-B radiation decreased the seedling chlorophyll content while reduced UV-B radiation significantly increased the chlorophyll content, and these effects reflected in the spectral reflectance. Under the effects of the three gradients of UV-B radiation, the differences in the reflectance at visible region mainly occurred around the green peak and red edge on the reflectance curve, and the peak wavelength of the red edge shifted to longer wavelength. Enhanced UV-B radiation had an accumulated temporal effect on M. rubra. The inverted-Gaussian model parameters R0, lambda0, lambda(p), Rs, and 6 were the useful guides to reveal the spectral responses of M. rubra seedlings under UV-B radiation stress, among which, Rs performed the best. The differences in the spectral reflectance under different UV-B radiation levels could be effectively distinguished with the vegetation indices composed of the spectral reflectance of narrow wave bands or the reflectance at specific wavelengths.