Characterization Of Rapeseed Stalks That Distinctively Accumulated Cadmium For High Lignocellulose Saccharification And Bioethanol Production

Over the past years,cadmium（Cd）as a hazardous substance has polluted the partial agricultural lands in China.Phytoremediation is a powerful approach by using crop stalk accumulation of Cd,and then the Cd-accumulated stalk could be processed simultaneously for bioethanol production and Cd release.In this study,we collected mature stalks of two rapeseed cultivars（Tapidor,Wanyou 29）that grew in the soil pots co-supplied with CdCl₂.Meanwhile,we observed rapeseed growth,determined cell wall compositions as well as structural factors of their mature stalks.Furthermore,we determined lignocellulose enzymatic saccharification and bioethanol production under various chemical pretreatments.Finally,this study measured how much Cd could be released during biomass pretreatments.Here are the major results obtained in this study:1.Cd accumulation could largely affect plant growth and development with reduced seed yields in two rapeseed cultivars.After cadmium application,the biomass of Tapidor and Wanyou29 respectively decreased by 25.43% and 24.56%,and seed yield decreased by 43.38% and 44.79% .2.In general,the two rapeseed cultivars could accumulated large amounts of Cd.In particular,the pectin fractions of two mature stalks could contain 33.72% and 22.09% Cd of total,and the soluble Cd covered 41.23% and 54.87% of total in two rapeseed cultivars.3.Due to Cd accumulation,the mature stalks of two rapeseed cultivars showed much reduced lignocellulose levels including cellulose,hemicellulose and lignin,but pectin was much increased in the stalks.Meanwhile,soluble sugars and uronic acids were largely raised in the stalks of two cultivars.Notably,the Cd accumulation led to much reduced cellulose DP in the mature stalks,with significantly increased substitution degree of xylans and biomass porosity in two rapeseed cultivars.4.Compared to the controls（without Cd supplement）,the Cd-accumulated stalks exhibited remarkably enhanced biomass enzymatic saccharification and bioethanol production under various chemical pretreatments in two rapeseed cultivars.5.The mature stalks could release all accumulated Cd by two-step pretreatments（4% NaOH+2% H₂SO₄）,or by one-step pretreatment of 12% H₂SO₄.By comparison,the 4% NaOH pretreatment only released 45% Cd,but the sequential enzymatic hydrolysis could lead to 50% Cd release.6.The optimal two-step pretreatment（4% NaOH+2% H₂SO₄）led to significantly reduced cellulose DP in the mature stalks of two rapeseed cultivars,with relatively increased cellulose CrI.Meanwhile,the xylose level of hemicellulose was significantly reduced,whereas the biomass porosity was largely increased in the two-step pretreated stalks.Taken all together,those lignocellulose feature alteration should be an integrated factor that distinctively affected biomass enzymatic saccharification and bioethanol production in two rapeseed cultivar.