| Rice is the staple food of human beings,and the healthy and rapid growth of its seedlings is the key to high-quality and high-yielding rice.Exploring high-quality rice seedling substrate soil can provide scientific guarantee for the healthy growth of rice seedlings.Edible mushroom bran is the residue of culture medium after edible mushroom cultivation,which contains a lot of rich organic nutrients,and improper treatment will pollute the environment and waste resources.Edible mushroom bran compost fermentation can make the bran get humified and harmless treatment,and the product has the potential of high quality rice seedling substrate soil.Therefore,this study investigates the dynamic change characteristics of physicochemical properties,microbial community structure and soil enzyme activity during the process of edible mushroom bran composting,as well as the effects of different ratios of compost on the growth of rice seedlings,in order to explore high-quality edible mushroom bran composting as a substrate soil for rice seedling cultivation.This study included composting experiments and potting experiments:（1）From July 21 to October 6,2021,composting experiments of edible mushroom bran were conducted in the Agricultural Park of Antu County,Jilin Province,including four treatments,namely:compost base substrate group（containing 8.4 t mushroom bran,3.6 t wet cow dung,30 kg urea,and 1.6 t chopped soybean straw,C4）,compost base substrate+cellulase preparation and organic fertilizer fermentor group（M1）,compost base substrate+cellulase preparation group（E2）,and compost base substrate+organic fertilizer fermentor group（D3）.The nature of the obtained edible mushroom bran compost was studied and comprehensively evaluated by continuously monitoring the physical and chemical properties,changes in soil enzyme activity,changes in the number of culturable microorganisms and changes in the microbial community structure of the compost at the warming stage,high stage and decaying stage.（2）Pot experiment using edible mushroom bran compost as a substrate for rice seedlings in June 2022.Using commercially available organic fertilizer as a reference,rice seedling cultivation experiments were conducted by adding 5%,10%,15%,20%,and 30%ratios（mass ratio）of compost to black soil and alkaline soil,respectively,and by analyzing and measuring biological performance indicators such as biomass,functional traits,photosynthetic pigments,and antioxidant enzyme activities during the development of rice seedlings.The specific results of the study are as follows:1.By analyzing the physicochemical properties and enzyme activities of the composted material during the composting process of edible mushroom bran,a comprehensive comparison showed that the physicochemical properties of the M1 group were better than the other three groups（E2,D3,C4）after composting treatment.Specifically,during the composting process,the temperature in the M1 treatment group rose faster in the warming period compared with the other three groups,and the temperature in the high temperature maintenance stage was higher and more persistent,showing higher decay,and total carbon and total nitrogen contents;meanwhile,the cellulase activity,glucosidase activity and amylase activity in the M1 treatment group were higher than the other three groups;in addition,only the cellulase activity under the M1 composting treatment In addition,there was a significant positive correlation between cellulase activity and temperature only in the M1 compost treatment（p<0.001）.2.The microbial community structure in the composting process of edible mushroom bran was characterized by temporal dynamic changes.For the culturable microorganisms,bacteria showed a tendency to increase during the warming period of the compost,hold briefly during the high temperature period,and decrease during the decay period,while both actinomycetes and fungi showed a tendency to increase during the warming period and start to decrease during the high temperature period;the numbers of culturable fungi,bacteria,and actinomycetes in M1 were larger than those in E2,D3,and C4,and their maximum values reached 14.5 × 107 cfu g-1 soil,54.1 × 107 cfu g-1 soil,and 54.1 × 107 cfu g-1soil,respectively,Further analysis of the microbial community structure during the warming period,high temperature period and decaying period of M1 treatment showed that the microbial community structure changed significantly during the three periods of composting,and for the bacterial community,the dominant species in the warming period was Bacteroidia,with a relative abundance of 26.4%.For the bacterial community,the dominant species was Bacteroidia with a relative abundance of 26.4%in the warming period,Chloroflexia with a relative abundance of 31.1%in the high temperature period,and Bacteroidia with a relative abundance of 20.9%in the decaying period;similarly,the dominant species of fungi also had significant changes,with Trichocomaceae with a relative abundance of 57.3%in the warming period and Agaricaceae with a relative abundance of 20.9%in the high temperature period.The relative abundance of Trichocomaceae in the warming period was 57.3%,that of Agaricaceae in the high temperature period was 27.9%,and that of Pezizacea in the decaying period was 96.8%.3.The results of the study of compost as a substrate for rice seedlings in the M1 treatment group were as follows:（1）The lowest seedling emergence rate of 88%was achieved when 5%of M1 compost was added to black soil,while the seedling emergence rate in alkaline soil could reach the national standard（85%）only when≥20%of M1 compost was added.（2）The growth characteristics of rice seedlings showed that the seedling growth rate was 22.6%higher when 30%M1 compost was added to the alkaline soil than when 30%organic fertilizer was added to the alkaline soil,and the number of seedling root tips was also 17%higher when 30%M1 compost was added than when 30%organic fertilizer was added;and the addition of 30%M1 compost to the alkaline soil resulted in a highly significant（p<0.001）decrease in electrical conductivity after rice seedlings grew.For the black soil,the addition of compost had insignificant effects on the growth rate of rice seedlings,and the addition of 20%M1 compost in the black soil resulted in 34.2%lower conductivity than the addition of 30%M1 compost.The longest leaf length of seedlings was 13.2 cm when 15%M1 compost was added to the black soil,while the widest leaf width was 0.33 cm when 20%M1 compost was added.（3）The compositional analysis of rice seedlings showed that in alkaline soil,the maximum soluble sugar content of 13.3 μg g-1 was found in seedling leaves when 30%M1 compost was added;meanwhile,the MDA content in seedling leaves was significantly reduced by 14.2%（p<0.001）when 30%M1 compost was added compared with the same amount of organic fertilizer,while chlorophyll a content and SOD activity were increased by 43.7%and 41.6%,respectively.For the black soil,the addition of compost had no significant effect on soluble sugar,MDA and SOD in rice seedling leaves,while the maximum chlorophyll a content of seedlings was 5.8 mg L-1 when 30%M1 compost was added;the POD activity in seedling leaves was 46.1%higher when 30%M1 compost was added than when 30%organic fertilizer was added;meanwhile,15%M1 compost was added to The highest CAT content of rice seedling leaves in black soil was 38.3 Umin-1 mg-1 Pr when 15%M1 compost was added.The above results show that the addition of cellulase preparation and organic fertilizer fermenters to edible mushroom bran compost can enrich soil microbial community structure,accelerate compost maturation efficiency,shorten composting cycle,and improve compost quality.The use of edible mushroom bran compost as rice seedling substrate improved the growth traits of rice seedlings,increased seedling biomass,and enhanced seedling resistance performance.The results of this study not only solve the environmental pollution problem of organic waste and improve the utilization rate of organic matter,but also the edible mushroom bran compost product can be used as a substrate for rice seedling cultivation to produce high-quality seedlings compared with commercially available organic fertilizers. |
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