Greenhouse gas balance of cropland conversion to bioenergy poplar short-rotation coppice

[摘要] The production of bioenergy in Europe is one of the strategies conceived toreduce greenhouse gas (GHG) emissions. The suitability of the land usechange from a cropland (REF site) to a short-rotation coppice plantation ofhybrid poplar (SRC site) was investigated by comparing the GHG budgets ofthese two systems over 24 months in Viterbo, Italy. This period correspondedto a single rotation of the SRC site. The REF site was a crop rotationbetween grassland and winter wheat, i.e. the same management of the SRC sitebefore the conversion to short-rotation coppice. Eddy covariancemeasurements were carried out to quantify the net ecosystem exchange ofCO₂ (F_CO2), whereas chambers were used to measure N₂O andCH₄ emissions from soil. The measurements began 2 years after theconversion of arable land to SRC so that an older poplar plantation wasused to estimate the soil organic carbon (SOC) loss due to SRCestablishment and to estimate SOC recovery over time. Emissions fromtractors and from production and transport of agricultural inputs(F_MAN) were modelled. A GHG emission offset, due to the substitution of natural gas with SRC biomass, was credited to the GHG budget of the SRC site. Emissions generated by the use of biomass (F_EXP) were alsoconsidered. Suitability was finally assessed by comparing the GHG budgets ofthe two sites. CO₂ uptake was 3512 ± 224 g CO₂ m⁻²at the SRC site in 2 years, and 1838 ± 107 g CO₂ m⁻² atthe REF site. F_EXP was equal to 1858 ± 240 g CO₂ m⁻²at the REF site, thus basically compensating for F_CO2, while it was1118 ± 521 g CO₂ m⁻² at the SRC site. The SRC site couldoffset 379.7 ± 175.1 g CO₂eq m⁻² from fossil fueldisplacement. Soil CH₄ and N₂O fluxes were negligible. F_MANmade up 2 and 4 % in the GHG budgets of SRC and REF sitesrespectively, while the SOC loss was 455 ± 524 g CO₂ m⁻²in 2 years. Overall, the REF site was close to neutrality from a GHGperspective (156 ± 264 g CO₂eq m⁻²), while the SRC site wasa net sink of 2202 ± 792 g CO₂eq m⁻². In conclusion theexperiment led to a positive evaluation from a GHG viewpoint of theconversion of cropland to bioenergy SRC.

[学科分类] 地球化学与岩石