Andrea Monti

Land-use change to bioenergy production in Europe: implications for the greenhouse gas balance and soil carbon

Bioenergy from crops is expected to make a considerable contribution to climate change mitigation. However, bioenergy is not necessarily carbon neutral because emissions of CO2, N2O and CH4 during crop production may reduce or completely counterbalance CO2 savings of the substituted fossil fuels. These greenhouse gases (GHGs) need to be included into the carbon footprint calculation of different bioenergy crops under a range of soil conditions and management practices. This review compiles existing knowledge on agronomic and environmental constraints and GHG balances of the major European bioenergy crops, although it focuses on dedicated perennial crops such as Miscanthus and short rotation coppice species. Such second‐generation crops account for only 3% of the current European bioenergy production, but field data suggest they emit 40% to >99% less N2O than conventional annual crops. This is a result of lower fertilizer requirements as well as a higher N‐use efficiency, due to effective N‐recycling. Perennial energy crops have the potential to sequester additional carbon in soil biomass if established on former cropland (0.44 Mg soil C ha−1 yr−1 for poplar and willow and 0.66 Mg soil C ha−1 yr−1 for Miscanthus). However, there was no positive or even negative effects on the C balance if energy crops are established on former grassland. Increased bioenergy production may also result in direct and indirect land‐use changes with potential high C losses when native vegetation is converted to annual crops. Although dedicated perennial energy crops have a high potential to improve the GHG balance of bioenergy production, several agronomic and economic constraints still have to be overcome.

Characterization and antimicrobial activity of essential oils of industrial hemp varieties (Cannabis sativa L.)

The present study focused on inhibitory activity of freshly extracted essential oils from three legal (THC<0.2% w/v) hemp varieties (Carmagnola, Fibranova and Futura) on microbial growth. The effect of different sowing times on oil composition and biological activity was also evaluated. Essential oils were distilled and then characterized through the gas chromatography and gas chromatography-mass spectrometry. Thereafter, the oils were compared to standard reagents on a broad range inhibition of microbial growth via minimum inhibitory concentration (MIC) assay. Microbial strains were divided into three groups: i) Gram (+) bacteria, which regard to food-borne pathogens or gastrointestinal bacteria, ii) Gram (-) bacteria and iii) yeasts, both being involved in plant interactions. The results showed that essential oils of industrial hemp can significantly inhibit the microbial growth, to an extent depending on variety and sowing time. It can be concluded that essential oils of industrial hemp, especially those of Futura, may have interesting applications to control spoilage and food-borne pathogens and phytopathogens microorganisms.

Comparison of the energy performance of fibre sorghum, sweet sorghum and wheat monocultures in northern Italy

Abstract Four monocultures (fibre sorghum, sweet sorghum and wheat at high and low nitrogen doses) were compared at a field-scale over 3 years (1997–1999) in terms of net energy, net energy ratio and energy use efficiency. Two nitrogen fertilisation levels were assessed for wheat (80 and 120 kg ha −1 of N) to evaluate the energy use efficiency of the applications. For all the crops, fuels, lubricants and farm inputs together formed around 92% of the total input, mainly due to nitrogen fertilisation. A year×crop significant interaction was found for all considered parameters. In fact the monoculture did not lower the biomass yield of both sorghum types, while it involved a drop in wheat yield starting from the second year (third considering that wheat was also cultivated in the same field in 1996). The average (1997–1999) net energy supplied by the monoculture of sweet sorghum was 17, 40 and 50% higher than those of fibre sorghum and wheat at high and low nitrogen doses respectively. The energy use efficiency (EUE, i.e. the energy (MJ) requirement to produce a kg of dry matter) ranged from 0.78 to 0.96 for fibre sorghum, from 0.69 to 0.85 for sweet sorghum and from 1.00 to 1.23 and 0.91 to 1.33 for wheat at low and high nitrogen levels respectively. With ethanol as the end-product of the 3-year monoculture of sweet sorghum, the production process would be a bit less favourable in term of energy balance: the net energy yield would be 90% of that obtained by dry matter gasification (with an efficiency of 50%). If straw was not processed, ethanol from wheat was generally unfavourable. On average of the two nitrogen doses, net energy ratios were 0.99, 1.05 and 0.97 in the first second and third year respectively. If bagasse was not considered also sweet sorghum had a very low net energy ratio, but always higher than wheat (1.14, 1.12 and 1.24 over the 3 years).

The contribution of switchgrass in reducing GHG emissions

The contribution of switchgrass (Panicum virgatum L.), a perennial C4 grass, in reducing greenhouse gas (GHG) emissions was reviewed under three main areas; the impact on carbon dioxide (CO2), nitrous oxide (N2O), and methane emissions (CH4), whilst also taking into account the effects of land conversion to switchgrass. Switchgrass is able to enhance biomass accumulation in a wide range of environmental conditions, which is the premise for considerable carbon assimilation and storage in the belowground organs. The progress in some areas of crop husbandry (e.g., tillage and fertilization) has fostered benefits for carbon storage, while restraining GHG emissions. As root biomass is the main indicator of soil carbon sequestration, switchgrasss dense and deep rooting is a relevant advantage, although uncertainty still exists about the crops belowground biomass accumulation. In agreement with this, most LCA studies addressing CO2 emissions report significant benefits from switchgrass cultivation and processing. Beside CO2, switchgrass performed better than most other biomass crops also in terms of N2O emission. In the case of CH4 emission, it may be argued that switchgrass should act as a moderate sink, i.e., contributing to mitigate CH4 atmospheric concentration, but a substantial lack of information indicates the need for specific research on the topic. Land conversion to switchgrass is the latest issue which needs to be addressed in LCA studies: not surprisingly, the net CO2 abatement appears remarkable if switchgrass is grown in former arable lands, although it is slightly negative to positive if switchgrass replaces permanent grassland. In conclusion, switchgrass could significantly contribute to mitigate GHG emissions, although areas of uncertainty still exist in the assessment of soil carbon storage, N2O and CH4 emissions, and the effects of converting lands to switchgrass. Further improvements must, therefore, be achieved to strengthen the crops remarkable sustainability.

Land use change from C3 grassland to C4 Miscanthus: effects on soil carbon content and estimated mitigation benefit after six years

To date, most Miscanthus trials and commercial fields have been planted on arable land. Energy crops will need to be grown more on lower grade lands unsuitable for arable crops. Grasslands represent a major land resource for energy crops. In grasslands, where soil organic carbon (SOC) levels can be high, there have been concerns that the carbon mitigation benefits of bioenergy from Miscanthus could be offset by losses in SOC associated with land use change. At a site in Wales (UK), we quantified the relatively short‐term impacts (6 years) of four novel Miscanthus hybrids and Miscanthus × giganteus on SOC in improved grassland. After 6 years, using stable carbon isotope ratios (13C/12C), the amount of Miscanthus derived C (C4) in total SOC was considerable (ca. 12%) and positively correlated to belowground biomass of different hybrids. Nevertheless, significant changes in SOC stocks (0–30 cm) were not detected as C4 Miscanthus carbon replaced the initial C3 grassland carbon; however, initial SOC decreased more in the presence of higher belowground biomass. We ascribed this apparently contradictory result to the rhizosphere priming effect triggered by easily available C sources. Observed changes in SOC partitioning were modelled using the RothC soil carbon turnover model and projected for 20 years showing that there is no significant change in SOC throughout the anticipated life of a Miscanthus crop. We interpret our observations to mean that the new labile C from Miscanthus has replaced the labile C from the grassland and, therefore, planting Miscanthus causes an insignificant change in soil organic carbon. The overall C mitigation benefit is therefore not decreased by depletion of soil C and is due to substitution of fossil fuel by the aboveground biomass, in this instance 73–108 Mg C ha−1 for the lowest and highest yielding hybrids, respectively, after 6 years.

The Evolution of Switchgrass as an Energy Crop

This chapter discusses the prehistoric origins of switchgrass, its mid-twentieth century adoption as a crop, and late-twentieth century efforts to develop it into an energy crop. The species probably first appeared about 2 million years ago (MYA) and has continued to evolve since, producing two distinct ecotypes and widely varying ploidy levels. We build the case that all existing switchgrass lineages must be descended from plants that survived the most recent glaciation of North America and then, in just 11,000 years, re-colonized the eastern two-thirds of the continent. Moving to historic times, we discuss how switchgrass was first considered as a crop to be grown in monoculture only in the 1940s. Based on scientific reports indexed in a well-known database, interest in switchgrass grew very slowly from the 1940s until it began being considered by the US department of energy (DOE) as a potential energy crop in the 1980s. The history of how switchgrass became DOE’s ‘model’ herbaceous energy crop species is recounted here. Also chronicled are the early research efforts on switchgrass-for-energy in the US, Canada, and Europe and the explosive growth in the last decade of publications discussing switchgrass as an energy crop. If switchgrass—still very much a ‘wild’ species, especially compared to several domesticated grasses—truly attains global status as a species of choice for bioenergy technologies, it will have been a very remarkable evolution.

Photosynthetic response of sweet sorghum to drought and re‐watering at different growth stages

Sweet sorghum (Sorghum bicolor) is a C4 drought resistant species with a huge potential for bioenergy. Accentuated reductions in water availability for crop production and altered rainfall distribution patterns, however, will have direct impact on its physiological attributes, metabolic functions and plant growth. The objective of this study was to evaluate the effects of drought and re-watering on the photosynthetic efficiency of sweet sorghum. Durable or short transient drought stress periods were imposed at early and late growth stages and compared with well-watered plants. In spite of very similar drought levels at early and late growth stages (Ψsoil  = -1.6 and -1.7 MPa), the decrements in maximum quantum yield (ϕPo ) and performance index (PI) were about twice at late than at early growth stages. All the PI components, that is, density of active reaction centers (RCs), excitation energy trapping and conversion of excitation energy into electron flow followed a similar decreasing pattern. Upon re-watering and regardless the duration and growth stage of the drought period, all the photosynthetic functions, and particularly those of photosystem II (PSII), fully recovered. Such effective self-regulating functional activity by PSII photochemistry likely contributes to both high drought resistance and photosynthetic recovery capacity of sweet sorghum. At vegetative growth stages, the down regulation of the photochemistry seems to be the main photoprotective/regulative mechanisms, while at late growth stages, the accumulation of compatible solutes likely has a more preponderant role. The observed sugar concentration increments likely contributed to prevent permanent photo-oxidative destruction of the PSII RCs of mature droughted sweet sorghum plants.

Internal conductance under different light conditions along the plant profile of Ethiopian mustard (Brassica carinata A. Brown.)

This study focused on the internal conductance (g(i)) along the plant profile of Ethiopian mustard under two light conditions: (i) light from the top only (I1); (ii) light from the top integrated by supplementary lateral light along the whole plant profile (I2). Lateral light strongly increased the productivity (e.g. +104% of seed oil) and net photosynthesis (A). The latter appeared more driven by g(i) (r=0.78**) than by stomatal conductance (g(s)) (r=0.51*). Importantly, irradiance also considerably shortened the time from leaf appearance to senescence, which means that corresponding leaves in I1 and I2 had different ages. Therefore, since leaf age and irradiance have counteracting effects on g(i), I1 sometimes showed higher g(i) values than I2. With respect to irradiance, leaf age had clearly higher effects on g(i), which radically declined from the top to the basal leaves, even under constant light conditions. The internal conductance caused a significant drawdown of CO(2) from the sub-stomatal cavity (C(i)) to the site of carboxylation (C(c)) that, in turn, led to a substantial underestimation of V(cmax) calculated using the A/C(i) model. Again, the trends of g(i) and g(s) were not consistent along the plant profile, and so the ratio between stomatal and internal limitations to A changed from top to bottom leaves, accordingly. This study suggests that g(i) may be a valuable trait for increasing photosynthetic capacity and productivity; nonetheless, it suggests caution in selecting leaves for high g(i), as the latter can considerably change along the plant profile due to leaf age and irradiance effects.

Perennial Grass Production Opportunities on Marginal Mediterranean Land

An increasing global awareness that the supply and security of petroleum-based materials is diminishing, coupled with environmental concerns related to climate change, water availability, and soil degradation, has increased demand for more renewable, diversified, and sustainable agricultural production systems. The objective of this work was to determine if a biogenic approach, focused on producing perennial grasses on marginal Mediterranean land as feedstock for bioenergy or bio-based products, could reduce greenhouse gas (GHG) emissions without depleting soil nutrients, water supplies, or negatively impacting biological and landscape diversity. This study, funded by European Union (EU), was conducted under project optimization of perennial grasses for biomass production (OPTIMA) using environmental impact assessment (EIA) protocols to quantify local environmental impacts of producing perennial grasses, in the Mediterranean region. Different end uses were investigated and biogenic products were compared with conventional ones. The EIA assessment indicated that the biogenic system had low erodibility potential, reduced disturbance of soil properties, and minimal hydrological impacts. Less tillage and high biomass production supported biological and landscape diversity, but site-specific factors should be used to appropriately match the specific crop and location. We conclude that producing perennial grasses on marginal Mediterranean land is feasible and if appropriately managed will have relatively few environmental side effects.

Bio-remediation of Pb and Cd polluted soils by switchgrass: A case study in India

ABSTRACT Introduction: In the present study bioremediation potential of a high biomass yielding grass, Panicum virgatum (switchgrass), along with plant associated microbes (AM fungi and Azospirillum), was tested against lead and cadmium in pot trials. Methods: A pot trial was set up in order to evaluate bioremediation efficiency of P. virgatum in association with PAMs (Plant Associated Microbes). Growth parameters and bioremediation potential of endomycorrhizal fungi (AMF) and Azospirillum against different concentrations of Pb and Cd were compared. Results: AM fungi and Azospirillum increased the root length, branches, surface area, and root and shoot biomass. The soil pH was found towards neutral with AMF and Azospirillum inoculations. The bioconcentration factor (BCF) for Pb (12 mg kg−1) and Cd (10 mg kg−1) were found to be 0.25 and 0.23 respectively and translocation index (Ti) was 17.8 and 16.7 respectively (approx 45% higher than control). Conclusions: The lower values of BCF and Ti, even at highest concentration of Pb and Cd, revealed the capability of switchgrass of accumulating high concentration of Pb and Cd in the roots, while preventing the translocation of Pb and Cd to aerial biomass.