In order to reveal the effects of biochar addition on soil dissolved organic matter (DOM) and its dynamics in dryland

a located experiment was conducted to investigate the change characteristics of dissolved organic carbon (DOC)

dissolved inorganic carbon (DIC) and fluorescence spectra components of DOM and its UV spectra characteristics in different soils with different biochar additions during 2012 to 2017.The results showed that the application of biochar increased DOC and DIC contents in soil as a whole

and the contents increased with the increasing of the biochar addition amount. In the same amount of biochar treatment

the DOC content decreased significantly with the increasing of application time

while the DIC content increased gradually. The degree of DOM aromatization increase dsignificantly with the extension of application time. After three years of application

the aromatization degree of 3% and 5% addition amount treatments was both significantly lower than that of CK

but there was no significant difference between 1% addition amount treatment and CK.The molecular weight of DOM showed an increasing trend in different application years. With the increasing of the biochar amount

the difference in the molecular weight between different application years gradually decreased. The soil DOM mainly includes four kinds of substances:UVC humic-like (C1)

UVA humic-like (C2)

Soil fulvic acid (C3) and Tryptophan-like (C4)

of which the C1 and C2 components dominated. In general

except for the addition of 1% biochar

the C2 component decreased with the increasing of the application years

the C1 and C2 components in different treatments gradually increased with the increasing of the application years

while the C3 and C4 components decreased significantly. The fluorescence indices of soil revealed that DOM was mainly terrestrially derived rather than microbial derived.The addition of biochar enhanced the bioavailability of DOM to some extent.The long-term application of biochar could result in changes of DOM components in the dryland. The general trend was that macromolecular humic-like substances increased

while small molecular proteins-like substances decreased.