Long-Term Effects of Soil Remediation with Willow Short Rotation Coppice on Biogeographic Pattern of Microbial Functional Genes

Short rotation coppice (SRC) is increasingly being adopted for bioenergy production, pollution remediation and land restoration. However, its long-term effects on soil microbial communities are poorly characterized. Here, we studied soil microbial functional genes and their biogeographic pattern under SRC with willow trees as compared to those under permanent grassland (C). GeoChip analysis showed a lower functional gene diversity in SRC than in C soil, whereas microbial ATP and respiration did not change. The SRC soil had lower relative abundances of microbial genes encoding for metal(-oid) resistance, antibiotic resistance and stress-related proteins. This indicates a more benign habitat under SRC for microbial communities after relieving heavy metal stress, consistent with the lower phytoavailability of some metals (i.e., As, Cd, Ni and Zn) and higher total organic carbon, NO3−-N and P concentrations. The microbial taxa–area relationship was valid in both soils, but the space turnover rate was higher under SRC within 0.125 m2, which was possibly linked to a more benign environment under SRC, whereas similar values were reached beyond thisarea. Overall, we concluded that SRC management can be considered as a phytotechnology that ameliorates the habitat for soil microorganisms, owing to TOC and nutrient enrichment on the long-term.

Which Large- and Medium-Sized Mammals Use Commercial Short-Rotation Coppice as Habitat?

We surveyed occurrence and activity of large- and medium-sized mammals on six commercial mini-rotation short-rotation coppice (SRC) plantations in northern Germany by camera trapping in different seasons (winter, late summer). In total, eleven species (6–9 per site) were detected. This corresponds to the majority of mammal species occurring in the study region. Roe deer, wild boar and red fox were found across all sites. All other species were detected on fewer sites and some in only one of the seasons. Roe deer was the most active species both in terms of visit frequency (days with detection) and use intensity (detection numbers). With few exceptions on individual sites, all other species showed significantly lower activity. Number of detected species and activity of most of the species did not differ between seasons. Furthermore, there were no differences between near-edge and central areas of the crops with regard to the activity of the occurring species. Activity of individual species on different sites, however, differed considerably in some cases. Our results show that a wide range of mammal species are basically able to include SRC into their habitat utilisation. However, the sporadic use by most species indicates a rather limited current habitat value of the surveyed plantations. Options to increase the habitat value of SRC for mammals are suggested, but their effectiveness needs to be tested in future studies. Since the spatial and temporal scope of our study was limited and only SRC of a uniform age-class were considered, our results are not immediately applicable to other landscapes, seasons or types and management phases of SRC. Therefore, further research is required that considers these aspects as well as species-specific patterns of habitat selection in comparison to other habitat types.

Acid-Catalyzed Liquefaction of Biomasses from Poplar Clones for Short Rotation Coppice Cultivations

Liquefaction of biomass delivers a liquid bio-oil with relevant chemical and energetic applications. In this study we coupled it with short rotation coppice (SRC) intensively managed poplar cultivations aimed at biomass production while safeguarding environmental principles of soil quality and biodiversity. We carried out acid-catalyzed liquefaction, at 160 °C and atmospheric pressure, with eight poplar clones from SRC cultivations. The bio-oil yields were high, ranging between 70.7 and 81.5%. Average gains of bio-oil, by comparison of raw biomasses, in elementary carbon and hydrogen and high heating, were 25.6, 67, and 74%, respectively. Loss of oxygen and O/C ratios averaged 38 and 51%, respectively. Amounts of elementary carbon, oxygen, and hydrogen in bio-oil were 65, 26, and 8.7%, and HHV averaged 30.5 MJkg−1. Correlation analysis showed the interrelation between elementary carbon with HHV in bio-oil or with oxygen loss. Overall, from 55 correlations, 21 significant and high correlations among a set of 11 variables were found. Among the most relevant ones, the percentage of elementary carbon presented five significant correlations with the percentage of O (−0.980), percentage of C gain (0.902), percentage of O loss (0.973), HHV gain (0.917), and O/C loss (0.943). The amount of carbon is directly correlated with the amount of oxygen, conversely, the decrease in oxygen content increases the elementary carbon and hydrogen concentration, which leads to an improvement in HHV. HHV gain showed a strong positive dependence on the percentage of C (0.917) and percentage of C gain (0.943), while the elementary oxygen (−0.885) and its percentage of O loss (0.978) adversely affect the HHV gain. Consequently, the O/C loss (0.970) increases the HHV positively. van Krevelen’s analysis indicated that bio-oils are chemically compatible with liquid fossil fuels. FTIR-ATR evidenced the presence of derivatives of depolymerization of lignin and cellulose in raw biomasses in bio-oil. TGA/DTG confirmed the bio-oil burning aptitude by the high average 53% mass loss of volatiles associated with lowered peaking decomposition temperatures by 100 °C than raw biomasses. Overall, this research shows the potential of bio-oil from liquefaction of SRC biomasses for the contribution of renewable energy and chemical deliverables, and thereby, to a greener global economy.

Low-Temperature Hydrothermal Treatment (HTT) Improves the Combustion Properties of Short-Rotation Coppice Willow Wood by Reducing Emission Precursors

The worldwide transformation from fossil fuels to sustainable energy sources will increase the demand for biomass. However, the ash content of many available biomass sources exceeds the limits of national standards. In this study, short-rotation coppice willow biomass was hydrothermally treated at 150, 170 and 185 °C. The higher heating value increased by 2.6% from x¯ = 19,279 J × g−1 to x¯ = 19,793 J × g−1 at 185 °C treatment temperature. The mean ash content was reduced by 53% from x¯ = 1.97% to x¯ = 0.93% at 170 °C treatment temperature, which was below the limit for category TW1b of the European pellet standard for thermally treated biomass. The nitrogen, sulfur and cadmium concentrations were reduced below the limits for category TW1b of the European biomass pellet standard (N: from 0.52% to 0.34%, limit at 0.5%; S: from 0.051% to 0.024%, limit at 0.04%; Cd: from 0.83 mg × kg−1 to 0.37 mg × kg−1, limit at 0.5 mg × kg−1). The highest reduction rates were sampled for phosphor (80–84%), potassium (78–90%), chlorine (96–98%) and lithium (96–98%). The reduction behavior of the elements is discussed according to the chemical processes at the onset of hydrothermal carbonization. The results of this study show that HTT has the potential to expand the availability of biomass for the increasing worldwide demand in the future.

Environmental Sustainability of Heat Produced by Poplar Short-Rotation Coppice (SRC) Woody Biomass

As demonstrated for some time, the reduction of greenhouse gases in the atmosphere can also take place using agroforestry biomass. Short-rotation coppice (SRC) is one of the sources of woody biomass production. In our work, the supply of woody biomass was considered by examining four different cutting shifts (2, 3, 4 and 5 years) and, for each, the Global Warming Potential (GWP) was evaluated according to the IPCC 2007 method. Regarding the rotation cycle, four biomass collection systems characterized by different levels of mechanization were analyzed and compared. In this study, it was assumed that the biomass produced by the SRC plantations was burned in a 350 kWt biomass power plant to heat a public building. The environmental impact generated by the production of 1 GJ of thermal energy was assessed for each of the forest plants examined, considering the entire life cycle, from the field phase to the energy production. The results were compared with those obtained to produce the same amount of thermal energy from a diesel boiler. Comparing the two systems analyzed, it was shown that the production and use of wood biomass to obtain thermal energy can lead to a reduction in the Global Warming Potential of over 70% compared to the use of fossil fuel.