| Bioenergy undergoes a steady development mainly due to the severe situation that the fossil fuels are going to be exhausted and the environmental pollution is becoming more and more serious. As a model energy crop, switchgrass shows much potential because of its high biomass yield and good biomass quality. Late harvest is advised in the actual production process of switchgrass biomass which renders a large waste of biomass resources caused by the falling off of large quantity of switchgrass seeds and tassels. In this study, the relationships between vegetative growth and reproduction were studied using14switchgrass cultivars. On this basis, tassel removal experiment using Alamo, Cave-in-Rock (CIR) and Forestburg as materials and different light treatments (18h and24h) using Alamo as material was conducted independently. The changes in growth status, photosynthetic physiology, transportation and distribution of photoassimilates, activity of the related enzymes, content of endogenous hormones and aboveground biomass quality of switchgrass were studied in detail aiming at providing the basis for improving biomass production performance. The main conclusions were as follows,(1) There were obvious competitive relationships between underground part and aboveground organs, and between vegetative and sexual reproductive organs in the distribution of dry biomass. More carbon resources were allocated into the asexual reproduction and less were allocated into the vegetative growth and sexual reproduction in switchgrass cultivars which originated from the higher latitude, while the case was contrary in switchgrass cultivars which originated from the lower latitude. Alamo, CIR and Forestburg were selected for the further research considering the differences in the ecotypes and resources allocation into the sexual reproduction.(2) The treatment of tassel removal could significantly (P<0.05) enhance the vegetative growth, improve the photosynthetic efficiency, and prompt more photoassimilates to be allocated into stems, roots, rhizomes and cellulose, lignin as well as non-structural carbohydrates. In tassel removed switchgrass, the tillers with tassel removed provided more (P<0.05) photoassimilates for the intact tillers and unestablished tillers compared with that of tillers in the intact switchgrass. Cytokinin (ZR) and gibberellin (GA) in stems played a major role in the response to tassel removal in switchgrass. All these factors above significantly (P<0.05) increased the aboveground biomass dry weight by16.7%,26.03%and33.05%in Alamo, CIR and Forestburg, respectively. The results about biomass quality of CIR and Alamo indicated that tassel removal significantly (P<0.05) increased the content of cellulose and non-structural carbohydrates, significantly (P<0.05) improved the ratio of Ara/Xyl in hemicellulose, and significantly (P<0.05) decreased the cellulose crystallinity indexes and lignin S/G ration in switchgrass stems which rendered significantly (P<0.05) higher digestbility. While, the significantly (P<0.05) higher content of Nitrogen (N) and Sulphur (S) negatively affected the combustion utilization of switchgrass biomass.(3) Light extending treatments obviously delayed the time of tilling and flowering, enhanced the vegetative growth, abated the sexual reproduction and significantly (P<0.05) improved the photosynthetic efficiency of switchgrass. More (P<0.05) photoassimilates were allocated into the stems and belowground part which rendered that the treatments of18h and24h light significantly (P<0.05) increased the aboveground biomass by19.46%and19.97%, respectively, and significantly (P<0.05) decreased the dry biomass weight of sexual reproductive organs by40.05%and50.87%, respectively. GA played an important role in the response of switchgrass to light extending. The activity of related enzymes was significantly (P<0.05) enhanced which promotes switchgrass to produce, transport and store more photoassimilates. |
