| Alfalfa (Medicago sativa L.) has been recognized as one of the potential biofuel crops with high biomass and wild adaptability. The stems of alfalfa would be processed to produce ethanol and the leaves could be served as a livestock feed. In this paper, biofuel traits, stem cell wall polysaccharides content and ethanol yield as well as lignin deposition of stem cell wall in alfalfa were studied. The results were as belows:1. Fifty four alfalfa cultivars with twice cutting treatments under greenhouse cultivation were studied. ANOVA and cluster analysis based on biomass, cell wall component (cellulose, hemicellulose and lignin) content, plant height, number of branches and stem/leaf ratio showed that there were significant differences of all biofuel traits such as biomass and cell wall compositions between 54 alfalfa cultivars (P<0.01), and the variations within-varieties were higher than those among-varieties; the variation coefficients of biomass (42.42%)> content of lignin (17.22%)> content of cellulose (12.74%)> content of hemicellulose (10.04%); the content of hemicellulose was significantly affected by cutting treatment, but not for biomass, content of cellulose and lignin; Cluster analysis based on biofuel traits divided 54 alfalfa cultivars into 5 groups, among which the group II and the group V had the highest biomass production performance, and the latter group showed better regeneration. Eight alfalfa cultivars Gannong NO.3, Huangyangzhen, WL903, Hetian, Sanditi, Pingliang, Dayushan and Italian were selected as potential materials to improve biofuel traits in future breeding programme.2. The biomass production, stem cell wall polysaccharides content and theoretical ethanol yield of cultivar Dayushan, Ladak, Italy, Gannong No.l, Amerigraze, Xiongyue, Huangyanzhen and Jindera were investigated under three harvest treatments (full-bloom, green pod and brown pod stage) in Hexi Corridor. The results showed that there were significant differences of biomass, cellulose yield, hemicellulose yield and ethanol production (P<0.05). The stem biomass, hemicellulose yield and ethanol production were increased with the harvest time delay. The ethanol production at brown pod stage higher 44% and 124% than full-bloom stage and green pod stage, respectively. The highest leaf biomass obtained when alfalfa were harvested at green pod stage. There were significant differences biomass, cellulose yield,hemicellulose yield and ethanol production between 8 alfalfa cultivars (P<.0.01) Cultivar Dayushan and Xiongyue had the highest ethanol production with 3045.76 L/hm2 and 3410.05 L/hm2, respectively. And the leaf biomass of these two cultivars was 5.5 t/hm2 and 4.51 t/hm2, respectively. The ethanol yield was significant correlated with the indexes such as plant height, stem diameter, branch number,5th and 6th internode thick (P<0.01). Furthermore, the internode number showed significant negative correlation with cellulose and ethanol production (P<0.01), while internode number and hemicellulose has significantly positive correlation (P<0.05). The hemicellulose showed significant positive correlation with cellulose (P<0.01), there was no significant correlation between hemicellulose content and ethanol production (P>0.01).3. Cytological observations of lignin deposition pattern in alfalfa cultivar Amerigraze, Jindera and M. truncatula at 7 developmental stage (vegetative growth stage at 15 cm and 30 cm height, bud stage, early flowering and full-bloom stage, green pod and brown pod stage) showed that lignification degree enhanced with the stem development, the main reason was that the ligninfied proportion of secondary xylem and pith parenchyma were increased. Lignin deposition sites were mainly in the primary xylem and secondary xylem, primary phloem and pith parenchyma cells, collenchyma and pectin substance deposition parts of secondary phloem, cambium, pith meristematic tissue and pith parenchyma. It showed that the lignin and pectin deposition had selectived in different tissues of alfalfa stem. The most mature at bottom internode, so it had the most lignin deposition, and the least pectic deposition. There were significant differences of lignin deposition time and range of pith parenchyma cells between 3 alfalfa cultivars. A few peripheral cells of pith meristem of M. truncatula were lignified at brown pod stage, while all pith parenchyma cells of Amerigraze and Jindera had been lignified at brown pod stage. Peripheral cells of pith meristem were surrounded with lignified cells and then expanded gradually. Different lignin monomer deposition started from one specific cell and the lignifications expanded gradually. The deposition of lignin monomer in xylem conduits cells showed less S-lignin deposition but more G-lignin deposition. |
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