| Walnut green husk is a major by-product in walnut industry.Its resource utilization is very important.Walnut green husk contains a large amount of cellulose and lignin,which is difficult to be decomposed.Due to its high water content and rich active substance content,it is randomly stacked in the field,which will seriously affect the surrounding ecological environment.At present,there are many studies on the application of extracts of walnut green husk in medicine,food and so on.But only a small part of the walnut green husk can be used for the extraction of active substances,and the extracted walnut green husk has not been effectively treated.Human activities have made soil heavy metal pollution more and more serious.It is of great practical significance to study soil amendments with heavy metal remediation effects.In this paper,the selected lignin and cellulose degrading bacteria were added in the fermentation process of walnut green husk,and the lignin and cellulose were degraded into oligomers or monomer compounds which can be easily utilized by microorganisms,so as to speed up the composting process of green husk.In order to solve the allelopathy of walnut green husk,the degradation methods of juglone,polyphenols and flavonoids were studied.The fermentation product was mixed with biochar to prepare organic fertilizer products,and its promoting effect on the growth of green vegetables was studied.The organic fertilizer products were combined with inorganic phosphorus-solubilizing bacteria and sulfatereducing bacteria to prepare soil modifier,which was used for remediation of heavy metals Pb,Cu and Cd in potted soil.The contents of heavy metals in the aboveground and underground parts of Chinese cabbage and the changes of heavy metal forms in soil were analyzed,and the remediation effect of soil modifier was discussed.The research results are as follows:(1)Two strains of lignin degrading bacteria(M2,M7)and two strains of cellulose degrading bacteria(X1,X2)were screened.M2,M7,X1 and X2 were Enterobacteriaceae,Burkholderia,Aspergillus polymyxa and Beauveria bassiana respectively.It took X1 20 days to disintegrate the filter paper,the degradation rate was 15.24%,and M7’ s degradation rate of alkali lignin was 6.8% in 14 days.The degradation rates of four strains on walnut green husk’s lignin reached more than 50% at 14 d,among which M7 had the highest degradation rate of 61%,and M7 had the best degradation rate of 68% at 21 d.After adding microbial agents,the cellulose content increased in different degrees,with M7 increasing the most,reaching 29.3%.(2)The culture medium using juglone as a single carbon source did not screen out juglone degrading bacteria.Lignin degrading bacteria and cellulose degrading bacteria can degrade juglone,polyphenols and flavonoids.The degradation rate of walnut green husk jugquinone,polyphenols and lei flavonoids by M2 was the highest at 21 d,which were 93.6%,68.9% and81.9%,respectively.(3)By measuring the related enzyme activities of lignin and cellulose degrading enzymes of strain M7,it was found that the lignin enzyme activity of strain M7 was slightly higher than that of strain M2,and the cellulase activity of strain X1 was higher than that of strain X2.The subsequent optimization of culture conditions was only carried out on strain M7 and strain X1.The optimum conditions of M7 enzyme production are: temperature 35℃,pH 6,alkali lignin as carbon source and peptone as nitrogen source.The optimum conditions of enzyme production of X1 are: temperature 30℃,pH 6,carbon source CMC-Na and glucose1:1,nitrogen source peptone.(4)The water content and pH are relatively stable during the fermentation process,and the pH keeps between 4 and 5,and the water content keeps above 85%.The total content of total potassium,total nitrogen and total phosphorus in fermentation products is more than 4%,and the nutrient content and heavy metal content of fermentation products added with four kinds of microbial agents are in line with the current(NY 525—2021)Organic Fertilizer standard.On 21 st day,the GI value of M7 was higher than 75%,which met the standard of organic fertilizer.The GI value of X2 was 10% lower than that of Z group,which could not play a promoting role in the fermentation process.In order to make the pH and water content of fermentation products meet the standard of organic fertilizer,organic fertilizer H was prepared by adding 60% biochar.(5)Compared with organic fertilizer CK,the fresh weight of organic fertilizer H increased by 2.75%,the dry weight increased by 0.77%,and the plant height increased by 1.84%,and the promotion effect was not significant.Compared with CK group,the biomass of green vegetables in XF group has increased in different degrees.There is a significant difference between Cu XF group and Cu CK group.15-3-2 Remediation of Cu pollution is effective.The soil amendments played a certain role in the stabilization of heavy metals.After adding the improver,the contents of heavy metals Pb,Cu,and Cd in the roots of green vegetables were reduced by 82.8%,92.9%,and 72.8% compared with those in the CK group.Compared with the CK group,the contents of heavy metals Pb,Cu,and Cd in the leaves of green cabbage were decreased by 52.2%,34.0%,and 3.30%.After the soil amendments acts,the exchangeable states of Pb,Cu and Cd in potted soil decreased to a certain extent,while the carbonate bound state and residue state increased. |
