Spent mushroom substrates affect soil humus composition, microbial biomass and functional diversity in paddy fields

Spent mushroom substrate (SMS) is the residue after mushroom production. The aims of this work were to analyze the effects of continuous application of SMS for nearly 10 years on soil organic carbon (SOC), soil humus composition, microbial biomass and functional diversity in paddy fields and to provide a theoretical basis for scientific application of SMS. A continuous application of SMS from Agaricus bisporus experiment was established in paddy field of southeastern China in 2007. Soils were collected from 6 treatments in 2016. The results showed that application of SMS could significantly increase the contents of SOC, soil total alkali-soluble humic carbon (HEC), humic acid carbon (HAC), especially the treatment of with high quantity of SMS, but not significantly increase the content of fulvic acid carbon (FAC). The microbial biomass carbon and nitrogen contents of MR3 (the amounts of SMS were 9574.5 kg hm(-2), converted to pure nitrogen were 180 kg hm(-2)) were the largest, it illustrated that the amount of SMS was not the more the better. The average well color development (AWCD), the Shannon index, Simpson index and McIntosh index of MR3 treatment were the highest. Microorganisms of MR3 treatment could make better use of carbon sources. Carboxylic acids, carbohydrates and polymers were the main carbon source types. Sufficient but not excessive application of SMS was beneficial to the carbon source utilization of fast-growing microorganisms and was considered to be a good way to improve the productivity of paddy soil.