Fluorescent characteristics of dissolved organic matter released from biochar and paddy soil incorporated with biochar.

Dissolved organic matter (DOM) plays a critical part in many processes of the ecological environment due to its mobility and reactivity in the soil and water interface. In the presented study, excitation-emission matrices (EEM) coupled with parallel factor analyses (PARAFAC) and UV-visible spectroscopy were introduced to investigate the variation of DOM derived from wheat straw biochar produced at different pyrolysis temperatures (300 °C, 500 °C and 700 °C), qualitatively and quantitatively. The dissolved organic matter (DOM) content of 700 °C biochar achieved a maximum of 1.45 g kg, while a minimum of 0.61 g kg was found at 500 °C. Components consisting of protein and tryptophan-like, UVA humic acid-like and UVC humic acid-like substances were extracted from the fluorescence data using PARAFAC. The abundance of fluorescent components predicted that DOM was mainly composed of more aromatic humic materials and litter amino acids with the increase in the pyrolysis temperature. Additionally, a column experiment simulating a paddy field was conducted to evaluate the feasible application of biochar produced at different temperatures, and the results showed that biochar addition enhanced the aromaticity and accelerated the decomposition of DOM released from flooded paddy soil. However, the indices SUVA and SUVA showed increasing tendencies in the soil profile, which may be ascribed to the downward transport of water-soluble DOM during the period of leaching. Briefly, the findings obtained, reinforced by statistical analysis could provide some valuable and distinct optical information of DOM derived from biochar and offer technical guidance when incorporating biochar into paddy soil in agricultural production.