Bioenergy from crops is expected to make a considerable contribution to climate change mitigation. However, bioenergy is not necessarily carbon neutral because emissions of CO ₂, N₂O and CH ₄ during crop production may reduce or completely counterbalance CO ₂ 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.

There is a weak evidence base supporting the effective management of riparian ecosystems within tropical agriculture. Policies to protect riparian buffers—strips of non‐cultivated land alongside waterways—are vague and vary greatly between countries. From a rapid evidence appraisal, we find that riparian buffers are beneficial to hydrology, water quality, biodiversity and some ecosystem functions in tropical landscapes. However, effects on connectivity, carbon storage and emissions reduction remain understudied. Riparian functions are mediated by buffer width and habitat quality, but explicit threshold recommendations are rare. Policy implications. A one‐size fits all width criterion, commonly applied, will be insufficient to provide all riparian functions in all circumstances. Context‐specific guidelines for allocating, restoring and managing riparian buffers are necessary to minimise continued degradation of biodiversity and ecosystem functioning in tropical agriculture.

It is important to demonstrate that replacing fossil fuel with bioenergy crops can reduce the national greenhouse gas (GHG) footprint. We compared field emissions of nitrous oxide (N₂O), methane (CH₄) and soil respiration rates from the C₄ grass Miscanthus × giganteus and willow (salix) with emissions from annual arable crops grown for food production. The study was carried out in NE England on adjacent fields of willow, Miscanthus, wheat (Triticum aetivum) and oilseed rape (Brassica napus). N₂O, CH₄ fluxes and soil respiration rates were measured monthly using static chambers from June 2008 to November 2010. Net ecosystem exchange (NEE) of carbon dioxide (CO₂) was measured by eddy covariance on Miscanthus from May 2008 and on willow from October 2009 until November 2010. The N₂O fluxes were significantly smaller from the bioenergy crops than that of the annual crops. Average fluxes were 8 and 32 μg m⁻² h⁻¹ N₂O‐N from wheat and oilseed rape, and 4 and 0.2 μg m⁻² h⁻¹ N₂O‐N from Miscanthus and willow, respectively. Soil CH₄ fluxes were negligible for all crops and soil respiration rates were similar for all crops. NEE of CO₂ was larger for Miscanthus (−770 g C m⁻² h⁻¹) than willow (−602 g C m⁻² h⁻¹) in the growing season of 2010. N₂O emissions from Miscanthus and willow were lower than for the wheat and oilseed rape which is most likely a result of regular fertilizer application and tillage in the annual arable cropping systems. Application of ¹⁵N‐labelled fertilizer to Miscanthus and oil seed rape resulted in a fertilizer‐induced increase in N₂O emission in both crops. Denitrification rates (N₂O + N₂) were similar for soil under Miscanthus and oilseed rape. Thus, perennial bioenergy crops only emit less GHGs than annual crops when they receive no or very low rates of N fertilizer.

Land–atmosphere exchange of carbon dioxide (CO₂) in peatlands exhibits marked seasonal and inter-annual variability, which subsequently affects the carbon (C) sink strength of catchments across multiple temporal scales. Long-term studies are needed to fully capture the natural variability and therefore identify the key hydrometeorological drivers in the net ecosystem exchange (NEE) of CO₂. Since 2002, NEE has been measured continuously by eddy-covariance at Auchencorth Moss, a temperate lowland peatland in central Scotland. Hence this is one of the longest peatland NEE studies to date. For 11 years, the site was a consistent, yet variable, atmospheric CO₂ sink ranging from −5.2 to −135.9 g CO₂-C m⁻² yr⁻¹ (mean of −64.1 ± 33.6 g CO₂-C m⁻² yr⁻¹). Inter-annual variability in NEE was positively correlated to the length of the growing season. Mean winter air temperature explained 87% of the inter-annual variability in the sink strength of the following summer, indicating an effect of winter climate on local phenology. Ecosystem respiration (R_eco) was enhanced by drought, which also depressed gross primary productivity (GPP). The CO₂ uptake rate during the growing season was comparable to three other sites with long-term NEE records; however, the emission rate during the dormant season was significantly higher. To summarise, the NEE of the peatland studied is modulated by two dominant factors: - phenology of the plant community, which is driven by winter air temperature and impacts photosynthetic potential and net CO₂ uptake during the growing season (colder winters are linked to lower summer NEE), - water table level, which enhanced soil respiration and decreased GPP during dry spells. Although summer dry spells were sporadic during the study period, the positive effects of the current climatic trend towards milder winters on the site's CO₂ sink strength could be offset by changes in precipitation patterns especially during the growing season.