Effect Of Application Of Pleurotus Ostreatus Mushroom Substrate On Soil Microbial Communities And Crop Growth

Edible fungus cultivation is an important part of agricultural production in our country.As the waste produced in the cultivation of edible fungi,spent mushroom substrate（SMS）is widely considered as an excellent substrate for plant growth and soil improvement.Nitrifying inhibitors are a class of chemicals that inhibit soil microorganisms from converting ammonium nitrogen into nitrate nitrogen,including nitrapyrin（CP）,dicyandiamide（DCD）and pyrazole,3,4-dimethyl-phosphate（DMPP）.This study aimed to analyze the effects of spent mushroom substrate on soil enzyme activities and greenhouse gas emissions under different soil moistures.The effects of spent Pleurotus ostreatus mushroom substrate and nitrification inhibitor on crop yield and quality,soil safety risk and soil environment were investigated by using spent Pleurotus ostreatus mushroom substrate alone or in combination with nitrification inhibitor to plant lettuce and pepper.（1）Soil urease,chitinase andβ-glucosidase activity were positively correlated with the spent mushroom substrate application rates,and the activities were the strongest when the addition level of fungus residue was 10.0%,and there was no significant difference under different water holding capacity.There was a positive correlation between N₂O emission and soil water holding capacity at 2.0%and 0%spent mushroom substrate addition level,while there was no significant difference between N₂O emission and soil water holding capacity at5.0%and 10.0%of spent mushroom substrate addition level,and there was a negative correlation between N₂O emission and spent mushroom substrate addition level at 90%moisture content.（2）Compared with the control,spent mushroom substrate application significantly increased the lettuce biomass,soil enzyme activities and the abundances of chitinase,protease,nitric-oxide reductase,nitrogenase and urease genes.However,the abundances of antibiotic resistance and human-disease genes were also significantly enhanced following the spent mushroom substrate application.Relative to spent mushroom substrate application alone（SAA）,dicyandiamide addition into spent mushroom substrate significantly decreased the soil p H and human-disease gene abundances,and DCD or DMPP addition enhanced the aboveground dry biomass of lettuce by 61.4%and 45.0%,respectively.The human-disease gene abundances were positively correlated with soil p H but were negatively correlated with the Acidobacteria and Streptomyces ratios in soil.spent mushroom substrate application could generate both beneficial and undesirable effects,and the health risk should be considered in the use of spent mushroom substrate in agriculture.Adding dicyandiamide together with SMS could further promote crop growth whilst decreasing the human-disease risks from spent mushroom substrate application.（3）The combined applications of spent mushroom substrate and DCD significantly enhanced the yields of pepper fruit.Compared with the control treatment,the pepper fruit NO₃^--N content decreased by 43.2%,66.8%and 64.4%in the SAA,DCD addition treatments（SDCD）and DMPP addition treatments（SDMPP）,respectively.The combined applications of SMS and nitrification inhibitors significantly enhanced the p H,bacterial community diversity and relative abundances of Bacteroidetes of soil samples.The relative abundances of aerobic chemoheterotrophy in the fruit samples were 0.28,0.17,0.10 and 0.15 for the CK,SAA,SDCD and SDMPP treatments,respectively.The relative abundances of Bacteroidetes and aerobic chemoheterotrophy were significantly and positively correlated with the NO₃^--N contents in the fruit.The accumulation factor of NO₃^--N had significantly negative correlations with soil p H and ammonium content.Apart from increases in fruit yield,the SMS and nitrification inhibitor applications could also decrease the health risk of crop NO₃^--N accumulation by affecting the soil p H,ammonium content and endophytic bacterial community diversity,structures and functions in fruit samples.