Effects Of Incubation With White Rot Fungi On The Nutritional Value And Microbial Diversity Of Wheat Straw

Wheat straw is an attractive renewable resource for the production of ruminant feeds,but lignin hinders the effective utilization of hemicellulose and cellulose by rumen microbes.Solid state fermentation with white rot fungi has been regarded as an effective method to improve the digestibility of lignocelluloses.This study investigated the effects of incubation with three white rot fungi on the chemical composition and rumen digestibility of wheat straw,developed a method to treat wheat straw under non-sterile conditions,and studied the microbial diversity of the non-sterile straw.The main designs and results are as follows:1.The degrading characteristics of Phanerochaete chrysosporium,Pleurotus ostreatus and Irpex lacteus and their effects on the in vitro rumen digestibility of wheat straw were investigated in this study.Results revealed I.lacteus had stronger ability to degrade acid detergent lignin(ADL)than P.ostreatus and better selectivity than P.chrysosporium.After 28 days of incubation,I.lacteus resulted in moderate losses of dry matter,hemicellulose,and cellulose,but the highest degradation of ADL(P<0.05).After 96 hours of in vitro rumen fermentation,the total volume of gas production(GP)from the straw treated with P.chrysosporium dropped by 24%,but that from the straw treated with I.lacteus increased by 33%.Meanwhile,the straw treated with I.lacteus not only improved the production of volatile fatty acids(VFA),but also lowered the molar ratio of acetic acid and propionic acid significantly(P<0.05).2.The effects of incubation with I.lacteus on the chemical composition and in vitro rumen digestibility of 8 different wheat straw were evaluated in this study.Results showed that after 56 days of fermentation I.lacteus degraded the ADL in the wheat straw by 63%and increased the neutral detergent solubles(NDS)by 32%,averagely.The degradation of ADL by I.lacteus has stronger positive correlation with the ash content in the wheat straw(R2 = 0.59,P = 0.026),but there is no significant correlation between the degradation of ADL and the content of ADL.In rumen fermentation,the GP and VFA of the wheat straw treated with I.lacteus were increased by 33%and 24%,respectively,but the molar ratio of acetic acid and propionic acid was decreased from 3.28 to 2.47.3.The abilities of P.chrysosporium,P.ostreatus and I.lacteus to colonize and degrade lignin in ensiled wheat straw were investigated under non-sterile conditions.The results revealed that I.lacteus could colonize stably in the ensiled wheat straw,and inhibited the growth of aerobic bacteria,lactic acid bacteria and molds.After 56 days of incubation,pH of the straw treated with P.chrysosporium,P.ostreatus and I.lacteus was 7.34,7.92 and 4.86,respectively,and the ADL content was 93.3,114.7 and 50.3 g/kg,respectively.What's more,the in vitro dry matter(DMD)and neutral detergent fiber digestibility(NDFD)of the wheat straw treated with I.lacteus increased by 17%and 40%,respectively.4.The effects of ensiling and incubation with I.lacteus on the chemical composition,in vitro digestibility and microbial diversity of non-sterile wheat straw were studied.Results showed that incubation with I.lacteus significantly decreased the pH of both the untreated(CKI)and ensiled(ENI)wheat straw(P<0.05),but the inhibition of aerobic bacteria and mold was only observed in ENI.After 56 days of incubation,the ADL content of ENI was significantly lower than that of CKI and untreated straw(P<0.05),but the DMD of the former was significantly higher than that of the latters(P<0.05).The results of metagenomics revealed that I.lacteus accounted for 97%of the total fungi in ENI,and the bacteria in ENI were mainly composed of the species that could produce spores,such as Bacillales and Clostridiales.Although,I.lacteus accounted for 79%of the total fungi in CKI,the relative abundances of 3 fungi,Chaetomium,Pseudallescheria and Schizothecium,were also more than 1%,which might have competitive relationships with I.lacteus.What's more,the relative abundance of 13 genus bacteria in CKI were more 1%.They might have complex function in the non-sterile wheat straw,such as degrading lignin,releasing nitrogen,hydrolyzing hemicellulose and cellulose,fixing nitrogen,and decomposing fungal mycelia and extracellular enzymes.