Cadmium Stress Impacts On Lignocellulose Composition,Biomass Saccharification And Bioethanol Productivity In Miscanthus

Soil cadmium(Cd)contamination largely affects environmental safety and human health,and plant remediation has thus been proposed as a promising solution by uptaking Cd from soil.Miscanthus is a desirable candidate of bioenergy crops with enormous lignocellulose for biofuels and chemical production.Because Cd could largely accumulate with lignocellulose,it is important to examine Cd effects on plant cell wall composition and biomass enzymatic saccharification.In this study,we collected four typical pairs of Miscanthus samples grown in the soil pots supplied with Cd,and determined their cell wall compositions(cellulose,hemicellulose,lignin and pectin)and major wall polymer features.Meanwhile,we tested Cd biomass enzymatic saccharification and bioethanol productivity under various chemical and physical pretreatments.Finally,we performed correlation analysis in order to identify major wall polymer factors affecting biomass enzymatic saccharification in Miscanthus.The major results were described below:1)Treated with Cd in soil pots,M.sacchariflorus accessions(MS55,MS 108)showed much higher Cd levels than other three Miscanthus species.2)Under Cd supply,four Miscanthus species samples exhibited reduced cellulose levels by 6.4%-12.7%and 9%-15%in leaf and stem tissues,compared to the control samples(without Cd supply).By contrast,hemicellulose levels were respectively increased by 5.6%-18%and 7%-20%in leaf and stem tissues,and pectin contents were largely raised by 13%-45%and 12%-26%.However,all Miscanthus samples did not show significantly altered lignin levels.Notably,all Miscanthus samples had a reduction of either cellulose CrI and DP values or hemicellulose Xyl/Ara ratios from Cd treatments.3)Pectin fraction were determined with large amounts of Cd.In particular,the pectin fraction covered 15.94%?30%of total Cd in the stem tissues,whereas the pectin fraction contained 5.35%?50.26%in the leave tissues.4)Supplied with Cd,all Miscanthus samples showed much higher biomass enzymatic saccharification than that of the control samples after alkali(NaOH)pretreatments.5)Under Cd stress,all Miscanthus samples had relatively lower sugar-ethanol conversion rates than those of the control samples after two alkali(NaOH,CaO)pretreatments.6)Based on correlation analysis,two cellulose features(Crl,DP)were negatively correlated with biomass digestibility,whereas uronic acids of pectin positively affected biomass enzymatic saccharification in all Miscanthus samples.