分类： 生物学 >> 植物学 >> 植物生态学和植物地理学 提交时间： 2016-05-04
摘要： Second-generation biofuels and bio-based products derived from lignocellulosic biomass are likely to replace current fuels derived from simple sugars and starch because of greater yield potential and less competition with food production. Besides the high aboveground biomass production, these bioenergy grasses also exhibit extensive root systems. The decomposition of root biomass greatly influences nutrient cycling and microbial activity and subsequent accumulation of carbon (C) in the soil. The objective of this research was thus to characterize root morphological and chemical differences in six perennial grass species in order to better understand root decomposition and belowground C cycling of these bioenergy cropping systems. Giant reed (Arundo donax), elephantgrass (Pennisetum purpureum), energycane (Saccharum spp.), sugarcane (Saccharum spp.), sweetcane (Saccharum arundinaceum), and giant miscanthus (Miscanthusgiganteus) were established in Fall 2008 in research plots near Gainesville, Florida. Root decomposition rates were measured insitu from root decomposition bags over 12months along with initial and final root tissue composition. Root potential decomposition rate constant (K) was higher in elephantgrass (3.64gkg1day1) and sweetcane (2.77gkg1day1) than in sugarcane (1.62g kg1day1) and energycane (1.48g kg1day1). Notably, K was positively related to initial root tissue total C (Total C), total fiber glucose (TFG), total fiber xylose (TFX), and total fiber carbohydrate (TFC) concentrations, but negatively related to total fiber arabinose (TFA) and lignin (TL) concentrations and specific root volume (SRV). Among the six species, elephantgrass exhibited root traits most favorable for fast decomposition: high TFG, high TFX, high TFC, high specific root length (SRL), and a low SRV, whereas giant reed, sugarcane, and energycane exhibited slow decomposition rates and the corresponding root traits. Thus, despite similar aboveground biomass yields in many cases, these species are likely to differentially affect soil C accumulation.
分类： 生物学 >> 植物学 >> 植物生态学和植物地理学 提交时间： 2016-05-04
摘要： Elephantgrass (Pennisetum purpureum Schum.) and energycane (Saccharum spp. hybrid) are high-yielding C4 grasses that are attractive biofuel feedstocks in the humid subtropics. Determining appropriate harvest management practices for optimal feedstock chemical composition is an important precursor to their successful use in production systems. In this research, we have investigated the effects of harvest timing and frequency on biomass nutrient, carbohydrate and lignin composition of UF1 and cv. Merkeron elephantgrasses and cv. L 79-1002 energycane. Biomass properties under increased harvest frequency (twice per year) and delayed harvest (once per year after frost) were compared with a control (once per year prior to frost). There were no differences between elephantgrass entries in structural carbohydrates; however, elephantgrasses had greater structural hexose concentration than energycane for single-harvest treatments (avg. 398 vs. 366mgg1), a trait that is preferred for biofuel production. Delayed harvest of energycane decreased structural hexose compared with the control (374 vs. 357mgg1) because nonstructural components accumulated in energycane stem as harvest was delayed. Frequent defoliation (2X) increased N, P, and ash concentrations (75% for N and P and 58% for ash) in harvested biomass compared with single-harvest treatments. We conclude that multiple harvests per year increase the harvest period during which feedstock is available for processing, but they do not result in optimal feedstock composition. In contrast, extending the period of feedstock supply by delaying a single harvest to after first freeze did not negatively affect cell wall constituent properties, while it increased length of the harvest period by ~30days in the southeast USA.
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