Effects Of Exogenous Nitrogen And Manganese On Decomposition Of Wheat Straw By Aspergillus Niger

The straw is rich in nitrogen,phosphorus,potassium and other nutrients,of which returning decomposition is an essential way to recycle nutrient resources.As the main component of straw,lignocellulose is the key factor of straw decomposition.Lignocellulose can be degraded by microorganisms through secreting enzymes,such as cellulase,xylanase and lignin peroxidase,etc.Therefore,it is an important measure to accelerate straw decomposition by screening microorganisms that can efficiently degrade lignocellulose and improving lignocellulose’s secretase activity by exogenous nutrients（such as nitrogen and manganese）.This study,regarding the decomposed wheat straw as the material,aims at screening the high-efficient decomposition fungus to decompose lignocellulose by employing plate marking method.The experiment is designed to explore the change of high-efficiency decomposition fungus’s enzyme activity and its influence on wheat straw decomposition under different conditions of external Mn²⁺and nitrogen by indoor shaker tests.Through the experiment,the optimal nitrogen source and Mn²⁺concentration for promoting microbial decomposition of straw are determined,providing scientific reference for improving wheat straw decomposition efficiency.The main results are shown as follows:（1）Two fungus with the ability of degrading lignocellulose were isolated from the decomposed wheat straw and identified as Aspergillus niger（A.Niger）and Penicillium citrinum（P.citrinum）respectively.The activities ofβ-glucosidase,acid xylanase,manganese peroxidase and lignin peroxidase secreted by A.niger were 756.33 nmol/min/g,1465.98 nmol/min/g,50.63 nmol/min/g and 17.92 U/g,respectively,which were significantly higher than those of P.citrinum（P<0.05）.Meanwhile,the activities of cellulase,exo-β-1,4-glucanase were 1529.47μg/min and 38.08μg/min,respectively,which had no significant difference with P citrinum（P>0.05）.On the whole,A.niger is more conductive to straw decomposition because its lignocellulase activity is higher than that of P citrinum.（2）The experimental results of exogenous addition of different concentrations of Mn²⁺（0,7.5,15 and 30 mg/L）showed that the residue rate of wheat straw with 7.5 mg/L Mn²⁺was the lowest（82.33%）.At different stages of cultivation,the microbial biomass increased by2.41%～14.16%.Besides,the activities ofβ-glucosidase,acid xylanase,manganese peroxidase and laccase incresed by 1.82%～23.13%,23.20%～186.22%,2.52%～4.33%and 5.00%～78.36%respectively.On the 30th day of cultivation,the residue rate of wheat straw with 30 mg/L Mn²⁺treatment（87.21%）was higher than that with 0 mg/L Mn²⁺treatment（85.56%）.The activities ofβ-glucosidase,acid xylanase,manganese peroxidase and laccase decreased by 12.23%,38.45%,25.06%and 5.22%respectively compared with those in 0 mg/L Mn²⁺treatment.What’s more,the results of structural equation modeling showed that low concentration of Mn²⁺（7.5 mg/L）could not only promote the decomposition of wheat straw（SPC=1.17）directly,but also promote wheat straw decomposition by affecting microbial biomass（SPC=0.61）.Hence,it can be said that low concentration of Mn²⁺（7.5 mg/L）can promote the growth of microorganisms and increase the activity of lignocellulolytic enzymes secreted by microorganisms,especially the activity of acid xylanase,so as to accelerate the decomposition of wheat straw.On the contrary,high concentration of Mn²⁺（30 mg/L）restrains the extracellular enzyme activity of microorganisms which is not beneficial to the decomposition of wheat straw.（3）Exogenous addition of different forms of nitrogen（ammonium sulfate,urea and potassium nitrate）could promote microbial growth and accelerate the decomposition of wheat straw by A.niger.The experiment results showed that the microbial biomass increased by 36.63%～65.16%.Besides,the activities ofβ-glucosidase,acid xylanase,manganese peroxidase and laccase incresed by 10.42%～38.89%,13.28%～58.75%,2.80%～26.60%and 22.86%～44.57%respectively.Among the exogenous addition of different forms of nitrogen,urea and potassium nitrate worked best,followed by ammonium sulfate.Furthermore,the results of structural equation modeling showed that nitrogen could increase the activity of straw decomposition enzymes by affecting microbial biomass（SPC=0.45）,so as to further promote the decomposition of wheat straw.So it can be concluded that urea is an ideal nitrogen resource to accelerate the decomposition of wheat straw by A.niger in terms of input cost and practical application.（4）A.Niger had the best decomposition effect on wheat straw under the interaction of nitrogen and manganese.The experiment showed that the residue rate of wheat straw reached its lowest level under the interaction of nitrogen and manganese（75.14%）.At different stages of cultivation,the microbial biomass increased by 45.82%～86.42%.In addition,the activities ofβ-glucosidase,acid xylanase,manganese peroxidase and laccase incresed by9.33%～39.21%,55.41%～240.27%,5.56%～12.51%and 30.34%～170.74%respectively.Residue rates of wheat straw with urea and Mn²⁺treatment were 77.98%and 85.42%respectively,which were lower than those of single treatment with A.niger（89.09%）.It indicated that both urea and Mn²⁺could promote the decomposition of wheat straw by A.niger,and urea was more effective than Mn²⁺in decomposing wheat straw.In conclusion,A.Niger had the best decomposition effect on wheat straw under the interaction of nitrogen and manganese.