Photodegradation Characteristics of Dissolved Organic Matter (DOM) in Alpine Soils of the Eastern Margin of Tibetan Plateau

The dissolved organic matter (DOM) in alpine soils of the eastern edge of the Qinghai-Tibet Plateau have unique optical properties. Therefore, a thorough understanding of the photodegradation characteristics of DOM helps in revealing regional DOC dynamics and carbon cycle at the water-land interface in alpine soils. Typical soil samples of the subalpine forest and peat wetland were collected and DOM were extracted and cultivated, ultraviolet-visible absorbance and excitation emission matrix fluorescence spectroscopy with two-dimensional correlation spectrum (2D-COS) and fluorescence regional integration (FRI) were used to characterize the environmental behavior responses to light irradiation. The results showed that the first-order decay constants and photodegradation rates of subalpine forest soil and alpine peat wetland soil were 0.0777 d(-1), 0.0907 d(-1) and 42.06%, 45.47%, respectively. The aromaticity and humification degree of CDOM in alpine soils were decreased with increasing exposure time. The FDOM in alpine soil showed four components (C1-C4), all components degraded in different degrees under light. According to the synchronous and asynchronous map, tyrosine- and tryptophan-like FDOM showed higher susceptibility in subalpine forest soil, while fulvic acid-like and humic acid-like FDOM showed higher susceptibility in alpine peat wetland soil. It confirmed that DOM of alpine soils showed good photodegradation characteristics, light might increase the instability of DOM in alpine soils.