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Isoprene is emitted from numerous plant species in response to light and temperature and parameterisations of these relationships, based on observations from a few vascular plant species, have been shown to be broadly applicable to many different vegetation types. Here, we investigate their performance when applied to an ecosystem dominated by bryophytes. Over a six-week period, emissions of isoprene were measured above a Scottish peat bog. The light response derived on the basis of both canopy-scale flux and whole-plant enclosure measurements, deviated from the classical response, showing no sign of saturation within the observed range. We attribute this response to the canopy architecture of moss hummocks, which may attenuate light differently compared to a grass canopy. Both existing big-leaf and canopy-level emission algorithms, developed for vascular plants but commonly used for moorland vegetation, failed to replicate the observed fluxes, overestimating at low light intensities (μmol m−2 s−1 photosynthetically active radiation) and underestimating during daytime clear sky conditions. The light response was optimised for bryophyte-dominated ecosystems using measured fluxes and incorporated into the EMEP4UK chemical transport model and applied exclusively to moorland. The revised parameterisation resulted in a small reduction in the average annual isoprene emissions in the northern latitudes (5%), but peak isoprene emissions and concentrations increased by up to a factor of two. Yet, no significant change in average or maximum surface ozone concentrations was observed, reflecting that the northern latitudes are in a chemical regime that is strongly NOx limited, in part due to the spatial segregation with the urban sources of NO x . We conclude that, the anticipated increase in isoprene emissions from the northern latitudes in response to climate change is unlikely to contribute towards ozone-related air quality issues, as long as NO x pollution does not increase. However, the non-saturating light response may be equally applicable to non-vascular plants elsewhere, including in the tropics.

Peatlands have often been neglected in Earth system models (ESMs). Where they are included, they are usually represented via a separate, prescribed grid cell fraction that is given the physical characteristics of a peat (highly organic) soil. However, in reality soils vary on a spectrum between purely mineral soil (no organic material) and purely organic soil, typically with an organic layer of variable thickness overlying mineral soil below. They are also dynamic, with organic layer thickness and its properties changing over time. Neither the spectrum of soil types nor their dynamic nature can be captured by current ESMs. Here we present a new version of an ESM land surface scheme (Joint UK Land Environment Simulator, JULES) where soil organic matter accumulation – and thus peatland formation, degradation and stability – is integrated in the vertically resolved soil carbon scheme. We also introduce the capacity to track soil carbon age as a function of depth in JULES and compare this to measured peat age–depth profiles. The new scheme is tested and evaluated at northern and temperate sites. This scheme simulates dynamic feedbacks between the soil organic material and its thermal and hydraulic characteristics. We show that draining the peatlands can lead to significant carbon loss, soil compaction and changes in peat properties. However, negative feedbacks can lead to the potential for peatlands to rewet themselves following drainage. These ecohydrological feedbacks can also lead to peatlands maintaining themselves in climates where peat formation would not otherwise initiate in the model, i.e. displaying some degree of resilience. The new model produces similar results to the original model for mineral soils and realistic profiles of soil organic carbon for peatlands. We evaluate the model against typical peat profiles based on 216 northern and temperate sites from a global dataset of peat cores. The root-mean-squared error (RMSE) in the soil carbon profile is reduced by 35 %–80 % in the best-performing JULES-Peat simulations compared with the standard JULES configuration. The RMSE in these JULES-Peat simulations is 7.7–16.7 kg C m−3 depending on climate zone, which is considerably smaller than the soil carbon itself (around 30–60 kg C m−3). The RMSE at mineral soil sites is also reduced in JULES-Peat compared with the original JULES configuration (reduced by ∼ 30 %–50 %). Thus, JULES-Peat can be used as a complete scheme that simulates both organic and mineral soils. It does not require any additional input data and introduces minimal additional variables to the model. This provides a new approach for improving the simulation of organic and peatland soils and associated carbon-cycle feedbacks in ESMs.

The UK proposes additional bioenergy plantations and afforestation as part of measures to meet net-zero greenhouse gas emissions, but species and locations are not yet decided. Different tree species emit varying amounts of isoprene and monoterpene volatile organic compounds that are precursors to ozone and secondary organic aerosol (SOA) formation, the latter of which is a component of PM2.5. The forest canopy also acts as a depositional sink for air pollutants. All these processes are meteorologically influenced. We present here a first step at coupling information on tree species planting suitability and other planting constraints with data on UK-specific BVOC emission rates and tree canopy data to simulate via the WRF-EMEP4UK high spatial resolution atmospheric chemistry transport model the impact on UK air quality of four potential scenarios. Our ‘maximum planting’ scenarios are based on planting areas where yields are predicted to be ≥50 % of the maximum from the Ecological Site Classification Decision Support System (ESC-DSS) for Eucalyptus gunnii, hybrid aspen (Populus tremula), Italian alder (Alnus cordata) and Sitka spruce (Picea sitchensis). The additional areas of forest in our scenarios are 2.0 to 2.7 times current suggestions for new bioenergy and afforestation landcover in the UK. Our planting scenarios increase UK annual mean surface ozone concentrations by 1.0 ppb or 3 % relative to the baseline landcover for the highest BVOC emitting species (e.g., E. gunni). Increases in ozone reach 2 ppb in summer when BVOC emissions are greatest. In contrast, all the additional planting scenarios lead to reductions in UK annual mean PM2.5 – ranging from -0.2 µg m-3 (-3 %) for Sitka spruce to -0.5 µg m-3 (-7 %) for aspen – revealing that PM2.5 deposition to the additional forest canopy area more than offsets additional SOA formation. Relative decreases in annual mean PM2.5 are greater than the relative increases in annual mean ozone. Reductions in PM2.5 are least in summer, coinciding with the period of maximum monoterpene emissions. Although only a first step in evaluating the impact of increased forest plantation on UK air quality, our study demonstrates the need for locally relevant data on landcover suitability, emissions and meteorology in model simulations.

To assess the status of and trends in agricultural nitrogen (N) flows and their wider consequences for Bangladesh, in this study, we analyzed data from national and international bodies. The increased rates of N fertilizer applied for increased food production leaves behind a huge amount of unutilized reactive N (Nr). N fertilizer use is the largest in the crop sector, an important sector, where current annual consumption is 1190 Gg. The present combined annual Nr production from crop, fishery, and livestock sectors is ~600 Gg, while emissions of nitrous oxide (N2O), a potent greenhouse gas, are ~200 Gg. Poor N management results in Nr leaking into the environment, which has increased approximately 16-fold since 1961. One potential consequence is the disruption of ecosystem functioning. The balanced tradeoff between food production and reducing Nr input needs to be achieved. One solution to reducing Nr may be a holistic approach that optimizes N application rates and incorporates waste of one subsector as an input to another applying the principle of the circular economy.

Oil palm plantations have rapidly expanded over the last 30 years, and now occupy 10% of the world’s permanent cropland. The growth of one of the world’s most efficient and versatile crop has alleviated poverty and increased food and energy security, but not without side effects. Losses of forest biodiversity hits the news. Although equally important, climate change issues have not reached this limelight. Data on greenhouse gas emissions associated with oil palm production is limited, especially for the potent greenhouse gas nitrous oxide (N2O). This paper provides an overview of the data availability, and identifies knowledge gaps to steer future research to provide the data required for climate change models and more accurate international and national nitrous oxide emission accounting.

Oil palm (OP) plantations have replaced large areas of forest in the tropical landscape of Southeast Asia and are major emitters of greenhouse gases (GHGs). However, within established plantations there are management options which may reduce these emissions, including altered management practices within plantations and restoring forest within the landscape. Managing the vegetation within and around plantations could potentially minimise environmental damage and maximise co-benefits such as soil protection, pest control and support for biodiversity. Such practices include relaxed management, passive restoration, and active restoration. The impact of these management practices is uncertain, and there is a real need for an evidence-base to guide improvements in the environmental sustainability of OP management.Here we present GHG fluxes from two long-term experiments as part of ‘The Biodiversity and Ecosystem Function in Tropical Agriculture’ (BEFTA) Project. The first experiment is investigating the impact of three alternative understory management treatments on biodiversity, ecosystem functioning and yield in Sumatra, Indonesia:Normal biodiversity complexity: standard industry practice, intermediate level of herbicide use in harvest circles around the palms. Reduced biodiversity complexity: spraying/removing all understory vegetation with herbicides. Enhanced biodiversity complexity: reduced-input management with no herbicide application and limited understory cutting. The second experiment focusses on riparian restoration options (‘Riparian Ecosystem Restoration in Tropical Agriculture’ (RERTA) Project). The experimental site began as a mature OP plantation, followed by felling in April 2019 and replanting and riparian restoration in October 2019. Four management strategies were applied on both sides of a river to create 50 m riparian buffers, 400 m in length:A control treatment of no restoration, the removal of mature OP and replanting of young OP to the river margin. Passive restoration: Little to no agricultural management of mature OP. Active restoration A: Clearance of mature OP and enrichment planting with native forest trees. Active restoration B: Little or no agricultural management of mature OP and additional enrichment planting with native forest trees. For both experiments, we measured the GHGs nitrous oxide (N2O), methane (CH4) and ecosystem respiration/carbon dioxide (CO2) from static chambers and analysis by gas chromatography (GC-µECD/FID). Additionally, meteorological and basic soil parameters were measured as potential variables or drivers of measured fluxes that might be greater than any ‘treatment’ or ecological management effect. Measurements were carried out monthly from the understory treatments, taken from 54 static chambers for the duration of one year starting in October 2018. For the riparian restoration project, monthly background measurements were taken between January and April 2019 and then approximately monthly after replanting from 6 chambers in each riparian treatment and 16 in the actual OP plantation resulting in 40 chambers in total.We investigated whether the observed ecological benefits of alternative management and restoration options such as introducing native tree species in riparian buffers and allowing the natural regrowth of understory in plantations may be associated with an additional or reduced GHG burden; thereby assessing the overall environmental impact.

Peatlands have often been neglected in Earth System Models (ESMs). Where they are included, they are usually represented via a separate, prescribed grid cell fraction that is given the physical characteristics of a peat (highly organic) soil. However, in reality soils vary on a spectrum between purely mineral soil (no organic material), and purely organic soil, typically with an organic layer of variable thickness overlying mineral soil below. They are also dynamic, with organic layer thickness and its properties changing over time. Neither the spectrum of soil types nor their dynamic nature can be captured by current ESMs. Here we present a new version of an ESM land surface scheme (Joint UK Land Environment Simulator, JULES) where soil organic matter accumulation - and thus peatland formation, degradation and stability – is integrated in the vertically-resolved soil carbon scheme. We also introduce the capacity to track soil carbon age as a function of depth in JULES, and compare this to measured peat age-depth profiles. This scheme simulates dynamic feedbacks between the soil organic material and its thermal and hydraulic characteristics. We show that draining the peatlands can lead to significant carbon loss along with soil compaction and changes in peat properties. However, negative feedbacks can lead to the potential for peatlands to rewet themselves following drainage. These ecohydrological feedbacks can also lead to peatlands maintaining themselves in climates where peat formation would not otherwise initiate in the model, i.e. displaying some degree of resilience. The new model produces similar results to the original model for mineral soils, and realistic profiles of soil organic carbon for peatlands. In particular the best performing configurations had root mean squared error (RMSE) in carbon density for peat sites of 7.7–16.7 kgC m−3 depending on climate zone, when compared against typical peat profiles based on 216 sites from a global dataset of peat cores. This error is considerably smaller than the soil carbon itself (around 30–60 kgC m−3) and reduced by 35–80 % compared with standard JULES. The RMSE at mineral soil sites is also smaller in JULES-Peat than JULES itself (reduced by ~30–50 %). Thus JULES-Peat can be used as a complete scheme that simulates both organic and mineral soils. It does not require any additional input data and introduces minimal additional variables to the model. This provides a new approach for improving the simulation of organic and peatland soils, and associated carbon-cycle feedbacks in ESMs, which other land surface models could follow.

Eucalyptus gunnii is a fast-growing, cold-tolerant tree species endemic to Tasmania that is suitable for growing as short-rotation coppice (SRC) plantations in the UK. Fast growing eucalypts such as E. gunnii could potentially deliver higher biomass yields with a superior calorific value for the domestic bioenergy market than other SRC plantation species such as willow or poplar. However, eucalypts are known emitters of biogenic volatile organic compounds (BVOC) like isoprene and monoterpenes. These compounds contribute to the formation of atmospheric pollutants such as ozone and secondary organic aerosols. An assessment of the sources of BVOCs during the lifecycle of a UK E. gunnii SRC plantation found the mean standardised emissions of isoprene and total monoterpenes from branches of juvenile foliage to be 7.50 μg C gdw−1 h−1 and 1.30 μg C gdw−1 h−1, respectively. The predominant monoterpene emitted was cis-β-ocimene. Isoprene emissions from the forest floor were extremely low but monoterpene emissions peaked at 50 μg C m−2 h−1. α-Pinene and d-limonene were the major components of the monoterpene emissions, with higher emissions correlated to the abundance of leaf litter. Both the magnitude and composition of monoterpene emissions from the forest floor varied during the SRC plantation life cycle, with the coppiced and regrowth stands of eucalyptus producing less emissions. The woodchip produced at harvesting emitted only trace levels of isoprene but substantial monoterpene emissions, up to 90 μg C m−2 h−1, predominately eucalyptol. Harvesting and resulting biomass chips may provide a short-lived concentrated source of BVOCs in winter at SRC plantations. Modelled annual emissions using MEGAN 2.1 (canopy emissions only) suggest that BVOC emissions from a UK E. gunnii SRC plantation are most abundant in summer, and that modelled annual isoprene and total monoterpenes emissions could be around 6.9 kg C ha−1 and 2.4 kg C ha−1 respectively, for a young plantation. Based on the very limited data, the per-hectare E. gunnii isoprene emissions are smaller than estimates for other SRC/SRF plantation species in the UK; the per-hectare monoterpene emissions are in the span of estimates for other plantation species.

Riparian forests are often kept as buffers between rivers and oil palm plantations. Many benefits of riparian forests, such as increasing biodiversity and providing a travel corridor for wildlife have been documented. Conversely, data on fluxes of the greenhouse gases nitrous oxide (N2O) and methane (CH4) from riparian forests are sparse. Nitrogen (N) from fertilizer applied in the oil palm plantations leached to the adjacent riparian forests, may increase emissions of N2O. Methane (CH4) fluxes might also differ between oil palm plantations and riparian forests due to carbon (C) availability. In this scoping study, we installed transects from three mature oil palm plantations to adjacent riparian forests within the SAFE project landscape in Sabah, Malaysia (https://www.safeproject.net) for measurements of greenhouse gases and associated parameters every 2 months for 13 months. Emissions of N2O were higher from riparian forests with 40.4 [95% confidence intervals (CI): 35.7–44.6] μg N2O-N m–2 h–1 than from an equivalent area of oil palm plantation 27.6 (CI: 23.1–32.3) μg N2O-N m–2 h–1. Methane uptake was significantly higher from the riparian forest with −14.7 (CI: −21.1 to −8.3) μg CH4-C m–2 h–1 compared to slight positive emission in the oil palm plantations of 6.3 (CI: 1.1–11.4) μg CH4-C m–2 h–1. We are contributing urgently needed flux data for less well studied riparian forests in the Tropics, however, additional long-term studies are needed to be able to draw wider conclusions than possible from this scoping study alone.

This study summarizes a large diverse dataset of methane (CH4) fluxes measured from agricultural sites across the British Isles. A total of 53,976 manual static chamber measurements from 27 different sites were investigated to determine the magnitude of CH4 fluxes from a variety of agricultural fields across the UK and Ireland. Our study shows that contrary to some studies, agricultural soils (both arable and grassland) are small net emitters of CH4 rather than sinks. Mean fluxes measured from arable and grassland sites (excluding fertiliser and tillage events) were 0.11 ± 0.06 and 0.19 ± 0.09 nmol m−2 s−1, respectively, and were not found to be significantly different (Welch t‐test, p = 0.17). Using the values reported in this study, we estimate that an annual emission of 0.16 and 0.09 Mt of CO2‐eq is expected from arable and grassland agricultural soils in the UK and Ireland (comparable to 0.3 and 0.7% of the current annual CH4 emission inventories, respectively). Where CH4 uptake occurs in soils, it is negligible compared to expected emissions of the application of animal manures and tillage events, which were both found to significantly increase CH4 emissions in the immediate few days to months after events. Our study highlights that there are significant differences in CH4 uptake and emissions between sites, and that these differences are partially the result of the moisture content of the soil (i.e., the aerobic status of the soil). We expect uptake of CH4 to be more prevalent in drier soils where volumetric water content does not exceed 35% and emissions to be exponentially greater where agricultural fields become waterlogged.

Regional estimates of VOC fluxes focus largely on emissions from the canopy and omit potential contributions from the forest floor including soil, litter and understorey vegetation. Here, we measured monoterpene emissions every 2 months over 2 years from logged tropical forest and oil palm plantation floor in Malaysian Borneo using static flux chambers. The main emitted monoterpenes were α-pinene, β-pinene and d-limonene. The amount of litter present was the strongest indicator for higher monoterpene fluxes. Mean α-pinene fluxes were around 2.5–3.5 μg C m−2 h−1 from the forest floor with occasional fluxes exceeding 100 μg C m−2 h−1. Fluxes from the oil palm plantation, where hardly any litter was present, were lower (on average 0.5–2.9 μg C m−2 h−1) and only higher when litter was present. All other measured monoterpenes were emitted at lower rates. No seasonal trends could be identified for all monoterpenes and mean fluxes from both forest and plantation floor were ~ 100 times smaller than canopy emission rates reported in the literature. Occasional spikes of higher emissions from the forest floor, however, warrant further investigation in terms of underlying processes and their contribution to regional scale atmospheric fluxes.

An expansion of bioenergy has been proposed to help reduce fossil-fuel greenhouse gas emissions, and short-rotation forestry (SRF) can contribute to that expansion. However, SRF plantations could also be sources of biogenic volatile organic compound (BVOC) emissions, which can impact on atmospheric air quality. In this study, emissions of isoprene and 11 monoterpenes from the branches and forest floor of hybrid aspen, Italian alder and Sitka spruce stands in an SRF field trial in central Scotland were measured during two years (2018–2019) and used to derive emission potentials for different seasons. Sitka spruce was included as a comparison as it is the most extensive plantation species in the UK. Winter and spring emissions of isoprene and monoterpenes were small compared to those in summer. Sitka spruce had a standardised average emission rate of 15 μg C g−1 h−1 for isoprene in the dry and warm summer of 2018, more than double the emissions in 2019. However, standardised average isoprene emissions from hybrid aspen were similar across both years, approximately 23 μg C g−1 h−1 and standardised average isoprene emissions from Italian alder were very low. Average standardised total monoterpene emissions for these species followed a similar pattern of higher emissions in the warmer year: Sitka spruce emitting 4.5 μg C g−1 h−1 and 2.3 μg C g−1 h−1 for 2018 and 2019, aspen emitting 0.3 μg C g−1 h−1 and 0.09 μg C g−1 h−1 and Italian alder emitting, 1.5 μg C g−1 h−1 and 0.2 μg C g−1 h−1, respectively. In contrast to these foliage emissions, the forest floor was only a small source of monoterpenes, typically one or two orders of magnitude lower than foliage emissions on a unit ground area basis. Estimates of total annual emissions from each plantation type per hectare were derived using the MEGAN 2.1 model. The modelled total BVOC (isoprene and monoterpenes) emissions of SRF hybrid aspen plantations were approximately half those of Sitka spruce for plantations of the same age. Italian alder SRF emissions were 20 times smaller than from Sitka spruce. The expansion of bioenergy plantations to 0.7 Mha has been suggested for the UK to help achieve net-zero greenhouse gas emissions by 2050. The model estimates show that with such an expansion total UK BVOC emissions would increase between

Oil palm (OP) growers are under pressure to reduce their environmental impact. Ecosystem function and biodiversity are at the forefront of the issue, but what effect do changes in management practices have on greenhouse gas (GHG) fluxes from plantations? The Riparian Ecosystem Restoration in Tropical Agriculture (RERTA) Project is a collaboration between the University of Cambridge and the SMART Research Institute in Riau, Indonesia. This project explores the ecological changes resulting from the restoration of riparian margins between plantations and watercourses. Four management strategies were applied on both sides of a river to create 50m riparian buffers, 400m in length: (1) A control treatment of no restoration, the removal of mature OP and replanting of young OP to the river margin; (2) Little to no agricultural management of mature OP; (3) Clearance of mature OP and enrichment planting with native forest trees; (4) Little or no agricultural management of mature OP and enrichment planting with native forest trees. Here we present a specific objective to investigate the effect of riparian restoration – and related changes in soil characteristics, structure and vegetation cover – on fluxes of N2O, CH4 and CO2 from mineral soils.The experimental site began as a mature OP plantation, with monthly background measurements taken between January and April 2019. Palms were felled in April 2019 and monthly sampling was resumed when replanting and restoration began, in October 2019. We measured GHGs using static chambers; 6 in each riparian treatment and 16 in the actual OP plantation, 40 chambers in total. Samples were analysed using GC-FID/µECD.Background measurements before felling showed high variability, but indicated no difference between the four experimental plots and the rest of the plantation. Fluxes measured following replanting were also highly variable, with no significant differences observed between treatments. N2O fluxes were relatively low before felling as the mature palms were no longer fertilised. Higher emissions were seen in the disturbed immature OP and forest tree treatments following replanting. Though the sites appeared to recover quickly and emission fluxes decreased after a few months, presumably as the soil settled and new vegetation began to grow. CH4 uptake was seen in the immature OP treatment immediately after replanting. In subsequent months no clear trends of CH4 uptake or emission were observed, with the greatest variability generally seen in the forest tree treatment. CH4 emissions increased in October 2020 with the beginning of the rainy season, most notably in mature OP and mature OP with forest tree treatments. Following restoration CO2 emissions were higher in treatments with established plant communities – mature OP and mature OP with forest trees.These results suggest that riparian restoration had no significant effect on GHG fluxes from mineral soils, and would not alter the overall GHG budget of a plantation. If there is no additional GHG burden and riparian restoration results in enhancing biodiversity and ecosystem services as well as improving water quality, it will be a viable management option to improve the environmental impact of an OP plantation.

In the last six decades, the consumption of reactive nitrogen (Nr) in the form of fertilizer in India has been growing rapidly, whilst the nitrogen use efficiency (NUE) of cropping systems has been decreasing. These trends have led to increasing environmental losses of Nr, threatening the quality of air, soils, and fresh waters, and thereby endangering climate-stability, ecosystems, and human-health. Since it has been suggested that the fertilizer consumption of India may double by 2050, there is an urgent need for scientific research to support better nitrogen management in Indian agriculture. In order to share knowledge and to develop a joint vision, experts from the UK and India came together for a conference and workshop on “Challenges and Opportunities for Agricultural Nitrogen Science in India.” The meeting concluded with three core messages: (1) Soil stewardship is essential and legumes need to be planted in rotation with cereals to increase nitrogen fixation in areas of limited Nr availability. Synthetic symbioses and plastidic nitrogen fixation are possibly disruptive technologies, but their potential and implications must be considered. (2) Genetic diversity of crops and new technologies need to be shared and exploited to reduce N losses and support productive, sustainable agriculture livelihoods. (3) The use of leaf color sensing shows great potential to reduce nitrogen fertilizer use (by 10–15%). This, together with the usage of urease inhibitors in neem-coated urea, and better management of manure, urine, and crop residues, could result in a 20–25% improvement in NUE of India by 2030.

Inland waters are important sources of greenhouse gases and emissions from polluted subtropical systems may be contributing to the observed global increase in atmospheric methane concentrations. Here we detail a scoping study where dissolved concentrations of greenhouse gases methane (CH4), carbon dioxide (CO2) and nitrous oxide (N2O) were measured in two contrasting urban lakes in Bangalore (Bengaluru), Karnataka, India, from June 2018 to February 2020. Bellandur Lake is a severely polluted system whilst Jakkur Lake has been subject to partial restoration via treatment of organic matter inputs. Methane concentrations in Bellandur Lake were three orders of magnitude higher than in Jakkur Lake, with a mean concentration of 3.02 ± 1.57 mg CH4-C L−1 compared to 1.72 ± 1.22 μg CH4-C L−1. At Bellandur Lake, dissolved CO2 concentrations were of the same order of magnitude as for CH4, whereas at Jakkur Lake dissolved CO2 concentrations were two orders of magnitude greater than for CH4. Concentrations of N2O were negligible in both lakes. Extrapolating our data to estimate greenhouse gas fluxes, mean daily methane fluxes from Bellandur Lake were consistently in excess of 1000 mg CH4 m2 d−1, rendering the lake a source of GHGs to the order of 148,350 ± 21,790 ton yr−1 CO2-e yr−1, compared to 100 ± 37 ton CO2-e yr−1 from Jakkur Lake, with CH4 contributing primarily to this difference. We propose that the contribution of severely polluted urban lakes to global CH4 production warrants further investigation, particularly as our evidence suggests that standard secondary wastewater treatment to support restoration of these systems has the potential to significantly reduce CH4 emissions.

Regional estimates of VOC fluxes focus largely on emissions from the canopy and omit potential contributions from the forest floor including soil, litter and understorey vegetation. Here, we measured monoterpene emissions every 2 months over 2 years from logged tropical forest and oil palm plantation floor in Malaysian Borneo using static flux chambers. The main emitted monoterpenes were α-pinene, β-pinene and d-limonene. The amount of litter present was the strongest indicator for higher monoterpene fluxes. Mean α-pinene fluxes were around 2.5-3.5 μg C m

The UK may be required to expand its bioenergy production in order to make a significant contribution towards the delivery of its ‘net zero’ greenhouse gas emissions target by 2050. However, some trees grown for bioenergy are emitters of volatile organic compounds (VOCs), including isoprene and terpenes, precursors in the formation of tropospheric ozone, an atmospheric pollutant, which require assessment to understand any consequent impacts on air quality. In this initial scoping study, VOC emission rates were quantified under UK climate conditions for the first time from four species of eucalypts suitable for growing as short-rotation forest for bioenergy. An additional previously characterised eucalypt species was included for comparison. Measurements were undertaken using a dynamic chamber sampling system on 2-3 year-old trees grown under ambient conditions. Average emission rates for isoprene, normalised to 30 °C and 1000 μmol m−2 s−1 PAR, ranged between 1.3 μg C gdw−1 h−1 to 10 μg C gdw−1 h−1. All the eucalypt species measured were categorised as ‘medium’ isoprene emitters (1–10 μg C gdw−1 h−1). Total normalised monoterpene emission rates were of similar order of magnitude to isoprene or approximately one order of magnitude lower. The composition of the monoterpene emissions differed between the species and major compounds included eucalyptol, α-pinene, limonene and β-cis-ocimene. The emission rates presented here contribute the first data for further studies to quantify the potential impact on UK atmospheric composition, if there were widespread planting of eucalypts in the UK for bioenergy purposes.

Agricultural and forest soils with low organic C content and high alkalinity were studied over 17 days to investigate the potential response of the atmospheric pollutant nitric oxide (NO) and the greenhouse gas nitrous oxide (N2O) on (1) increased N deposition rates to forest soil; (2) different fertilizer types to agricultural soil and (3) a simulated rain event to forest and agricultural soils. Cumulative forest soil NO emissions (148–350 ng NO-N g−1) were ~ 4 times larger than N2O emissions (37–69 ng N2O-N g−1). Contrary, agricultural soil NO emissions (21–376 ng NO-N g−1) were ~ 16 times smaller than N2O emissions (45–8491 ng N2O-N g−1). Increasing N deposition rates 10 fold to 30 kg N ha−1 yr−1, doubled soil NO emissions and NO3− concentrations. As such high N deposition rates are not atypical in China, more attention should be paid on forest soil NO research. Comparing the fertilizers urea, ammonium nitrate, and urea coated with the urease inhibitor ‘Agrotain®,’ demonstrated that the inhibitor significantly reduced NO and N2O emissions. This is an unintended, not well-known benefit, because the primary function of Agrotain® is to reduce emissions of the atmospheric pollutant ammonia. Simulating a climate change event, a large rainfall after drought, increased soil NO and N2O emissions from both agricultural and forest soils. Such pulses of emissions can contribute significantly to annual NO and N2O emissions, but currently do not receive adequate attention amongst the measurement and modeling communities.

In Southeast Asia, oil palm plantations have largely replaced tropical forests. The impact of this shift in land-use on greenhouse gas (GHG) fluxes and soil microbial communities remains highly uncertain, mainly due to a relatively small pool of available data. The aim of this study is to quantify differences of nitrous oxide (N2O) and methane (CH4) fluxes as well as soil carbon dioxide (CO2) respiration rates from logged forests, oil palm plantations of different ages and an adjacent small riparian area. The focus of this study is on N2O fluxes, as these emissions are expected to increase significantly due to the introduction of nitrogen (N) fertiliser application. This study was conducted in the SAFE (Stability of Altered Forest Ecosystems) landscape in Malaysian Borneo (Sabah) with measurements every two months over a two-year period. GHG fluxes were measured by static chambers; at the same time soil samples were collected for analysis of the key soil physicochemical parameters and for analysis of microbial biodiversity using next generation sequencing in dry and wet season. N2O fluxes were highly variable across the different sites, with the highest mean flux from OP (46.2 ± 166 µg m−2 h−1 N2O-N) and riparian (31.8 ± 220 µg m−2 h−1 N2O-N) sites, compared to lower fluxes from logged forest (13.9 ± 171 µg m−2 h−1 N2O-N). Methane fluxes were generally small; −2.6 ± 17.2 µg CH4-C m−2 h−1 for OP and 1.3 ± 12.6 µg CH4-C m−2 h−1 for riparian with the range of measured CH4 fluxes largest in logged forests (2.2 ± 48.3 µg CH4- m−2 h−1). Soil respiration rates were larger from riparian areas (157.7 ± 106 mg m−2 h−1 CO2-C) and logged forests (137.4 ± 95 mg m−2 h−1 CO2-C) than OP plantations (93.3 ± 70 mg m−2 h−1 CO2-C) due to larger amounts of decomposing leaf litter. Microbial communities were distinctly different between the different land-use types and sites, bacterial communities linked to soil pH and fungal and eukaryotic communities to land-use. Despite measuring a number of environmental parameters, mixed models could only explain up to 17 % of the variance of measured fluxes for N2O, 3 % of CH4 and 25 % of soil respiration. Scaling up measured N2O fluxes to Sabah using land areas for forest and OP resulted in emissions increasing from 7.6 Mt (95 % confidence interval, −3.0–22.3 Mt) per year in 1973 to 11.4 Mt (0.2–28.6 Mt) per year in 2015 due to the increasing area of forest converted to OP plantations over the last ~40 years.

Physiological and ecological studies have provided evidence for pH-driven niche specialization of ammonia oxidizers in terrestrial ecosystems. However, the functional stability of ammonia oxidizers following pH change has not been investigated, despite its importance in understanding the maintenance of ecosystem processes following environmental perturbation. This is particularly true after anthropogenic perturbation, such as the conversion of tropical forest to oil palm plantations. This study demonstrated a great impact of land-use conversion on nitrification, which is linked to changes in soil pH due to common agricultural practices (intensive fertilization). In addition, the different communities of ammonia oxidizers were differently affected by short-term pH perturbations, with implications for future land-use conversions but also for increased knowledge of associated global nitrous oxide emissions and current climate change concerns., Rapidly expanding conversion of tropical forests to oil palm plantations in Southeast Asia leads to soil acidification following intensive nitrogen fertilization. Changes in soil pH are predicted to have an impact on archaeal ammonia-oxidizing archaea (AOA), ammonia-oxidizing bacteria (AOB), and complete (comammox) ammonia oxidizers and, consequently, on nitrification. It is therefore critical to determine whether the predicted effects of pH on ammonia oxidizers and nitrification activity apply in tropical soils subjected to various degrees of anthropogenic activity. This was investigated by experimental manipulation of pH in soil microcosms from a land-use gradient (forest, riparian, and oil palm soils). The nitrification rate was greater in forest soils with native neutral pH than in converted acidic oil palm soils. Ammonia oxidizer activity decreased following acidification of the forest soils but increased after liming of the oil palm soils, leading to a trend of a reversed net nitrification rate after pH modification. AOA and AOB nitrification activity was dependent on pH, but AOB were more sensitive to pH modification than AOA, which demonstrates a greater stability of AOA than AOB under conditions of short-term perturbation. In addition, these results predict AOB to be a good bioindicator of nitrification response following pH perturbation during land-use conversion. AOB and/or comammox species were active in all soils along the land-use gradient, even, unexpectedly, under acidic conditions, suggesting their adaptation to native acidic or acidified soils. The present study therefore provided evidence for limited stability of soil ammonia oxidizer activity following intensive anthropogenic activities, which likely aggravates the vulnerability of nitrogen cycle processes to environmental disturbance. IMPORTANCE Physiological and ecological studies have provided evidence for pH-driven niche specialization of ammonia oxidizers in terrestrial ecosystems. However, the functional stability of ammonia oxidizers following pH change has not been investigated, despite its importance in understanding the maintenance of ecosystem processes following environmental perturbation. This is particularly true after anthropogenic perturbation, such as the conversion of tropical forest to oil palm plantations. This study demonstrated a great impact of land-use conversion on nitrification, which is linked to changes in soil pH due to common agricultural practices (intensive fertilization). In addition, the different communities of ammonia oxidizers were differently affected by short-term pH perturbations, with implications for future land-use conversions but also for increased knowledge of associated global nitrous oxide emissions and current climate change concerns.

Tropical oil palm (OP) plantations are major emitters of greenhouse gases (GHGs), but there are management options, which may reduce these emissions, including increasing understory biomass. Managing the vegetation within and around plantations could potentially minimise environmental damage and maximise co-benefits such as soil protection, pest control and diversity. Such practices include creating reserves, buffer strips and management of vegetation in the plantations themselves. The impact of these management practices is uncertain, and there is a real need for an evidence-base to guide improvements in the environmental sustainability of OP management.The timing for research related to management options is critical for influencing current decision-making. In Indonesia, most OP plantations were established in the late 1980s and early 1990s and due to the 25 – 30-year life cycle of OP plantations, nearly half are due to be clear-cut for replanting in the near-future. Hence, it is vital to understand replanting and restoration options which simultaneously allow for high productivity as well as supporting biodiversity and minimising GHG emissions. The scope and specific objectives of our study were:1) To measure GHG emissions under different understory management techniques (with/without vegetation through use of herbicides). 2) To link GHG data to soil data to develop understanding of ecosystem function under different OP plantation management approaches. We will present monthly static chamber measurements of GHG emissions for the duration of one year starting October 2018, established on an existing long-term experiment investigating the impact of diversifying understory vegetation on biodiversity, ecosystem functioning and yield in Sumatra, Indonesia (The Biodiversity and Ecosystem Function in Tropical Agriculture Project (BEFTA)). The three different understory management treatments were:1) Normal biodiversity complexity: standard industry practice, intermediate level of herbicide use in harvest circles. 2) Reduced biodiversity complexity: spraying/removing all understory vegetation with herbicides. 3) Enhanced biodiversity complexity: reduced-input management with no herbicide application and limited understory cutting. We measured the GHG fluxes of nitrous oxide (N2O), methane (CH4) and soil ecosystem respiration/carbon dioxide (CO2) using static chambers and analysis by gas chromatography (GC-µECD/FID).Preliminary results show little difference amongst the different understory treatments in terms of N2O fluxes. Fluxes were generally low (0-0.1 µg m-2 h-1) with high variability. However, there is a trend towards slightly higher emissions during the wetter months (Oct-Dec 2018) of up to 0.2 µg m-2 h-1.Methane (CH4) fluxes were generally small and fluctuated around zero. During the wet months, (Oct to Dec 2018) small emission fluxes up to 3 µg m-2 h-1 were observed; whereas during the dry months uptake of methane, prevailed. No distinctive differences between the different treatments was observed.Due to the age of the plantation and imminent replanting, none of the plots were being fertilised at the time of measurement – greater differences between vegetation treatments may be observed under fertilisation.In conclusion, initial results showed that the presence or absence of understorey did not increase soil emissions of N2O and CH4. This suggests that the within-crop ecological benefits do not result in an increased GHG burden.

Highlights • We compiled datasets of N2O emission factors (EFs) from 21 separate studies. • A Bayesian approach improves uncertainty analysis of EFs. • AN applications were lower for applications to arable fields than to grasslands. • Microbial inhibitors reduce emissions of N2O from mineral fertilisers significantly., In this study, we analysed datasets of N2O emission factors (EFs) from 21 separate studies carried out on arable and managed grasslands across the UK and Ireland over the past 20 years. A total of 641 separate events were collated from 40 experimental field sites. Individual EFs ranged over an order of magnitude (0–12% of applied N) for each fertiliser type, following a log-normal distribution in all cases. Our study shows that a Bayesian approach can provide a robust statistical method that is capable of performing uncertainty analysis on log-normal distributed data in a more defensible manner than conventional statistical methods allow. This method allowed for a national scale comparison of EFs between the most commonly applied mineral fertilisers based solely on previously published data (UK and Ireland in this case). The study shows that ammonium nitrate (AN) and Calcium ammonium nitrate (CAN) are the largest emitting fertiliser types by mass across the British Isles (temperate climate zone), with EFs of 1.1 (1.0–1.2) % and 1.0 (0.7–1.3) % for all recorded events, respectively; however, emissions from AN applications were significantly lower for applications to arable fields (0.6%) than to grasslands (1.3%). EFs associated with urea (CO(NH₂)₂) were significantly lower than AN for grasslands with an EF of 0.6 (0.5–0.7) %, but slightly higher for arable fields with an EF of 0.7 (0.4–1.4) %. The study highlights the potential effectiveness of microbial inhibitors at reducing emissions of N2O from mineral fertilisers, with Dicyandiamide (DCD) treated AN reducing emissions by approximately 28% and urea treated with either DCD or N-(n)-butyl) thiophosphorictriamide (NBTP) reducing emissions by approximately 40%. Although limited by a relatively small sample size (n = 11), urea treated with both DCD and NBPT appeared to have the lowest EF of all treatments at 0.13 (0.08–0.21) %, highlighting the potential to significantly reduce N2O emissions at regional scales if applied instead of conventional nitrogen fertilisers.

Intermittent flooding (IF) of rice has been encouraged as an approach to reduce water use and methane emissions compared with continuous flooding (CF), but may involve trade-offs. This study compared the contrasting effect of IF and CF flooding regimes on emissions of methane (CH4), nitrous oxide (N2O) and ammonia (NH3), nitrogen use efficiency (NUE) and yield. A split plot design was used which assessed the effects of four different fertiliser types. The results suggest that converting from CF to IF irrigation does lower CH4 emissions (by approximately 18%); however, this comes at a cost. IF irrigation resulted in a significant decrease in grain yield, regardless of fertiliser type (6.1% in this study) and also a significant decrease in NUE (a drop of 22.5% when compared to CF). IF irrigation also resulted in a small, but statistically significant (t-test p < 0.01) increase in N2O emissions. Difference in NH3 emission between the flooding regimes was not statistically significant. Our study concludes that conversion from CF to IF irrigation methods may well reduce overall global warming potential of greenhouse gas emissions from rice production; however, yield penalties and nitrogen pollution are likely to increase as a result. Leaf colour chart based application of Neem coated urea may lower the yield scaled GHG emissions under CF irrigation and NH3 loss in IF irrigation.

Nitrous oxide (N2O) is a greenhouse gas produced mainly by the microbial breakdown of agricultural fertilizer. ‘Emission factors’ (EFs, the fraction of nitrogen added that is released as N2O) are based on flux chamber measurements following the application of fertilizer. These measurements are very variable in space and time so that EFs are often uncertain, but this is rarely quantified. We developed a method that simplifies the calculation of EFs, incorporates prior knowledge and quantifies the uncertainty with a Bayesian approach to fit the parameters of a lognormal model. We compared this with the standard method for interpolating, extrapolating and integrating fluxes of N2O (trapezoidal integration). We verified both methods against process-based model output where the true integral was known and against eddy covariance data where the integral was estimated more accurately because of the greater spatial and temporal coverage. We used the process-based model to simulate flux chamber data and added a lognormal spatial distribution to the model output. The lognormal model performed better than the standard method, in terms of estimating the true underlying cumulative flux more accurately. Estimates based on chamber and eddy covariance data were sometimes substantially different, but with no clear systematic bias. The Bayesian approach with the lognormal model enabled us to combine both chamber and eddy covariance data to constrain cumulative fluxes. The standard trapezoidal method typically underestimates emission factors to some extent if fluxes are lognormally distributed in space. The Bayesian approach with the lognormal model is a robust method for quantifying the uncertainty in cumulative fluxes of N2O. Highlights Emission factors for N2O are based on sparse and variable measurements, and so are uncertain. We use a Bayesian approach to simplify the calculation and quantify the uncertainty. No observed systematic difference between eddy covariance and chamber measurement methods. The standard trapezoidal method will typically underestimate emission factors.

Soil greenhouse gas (GHG) fluxes of methane (CH4) and nitrous oxide (N2O) were measured over a 2-year period from several land use systems on adjacent sites under the same soil and climatic conditions to assess the influence of the transition from arable agricultural (barley) and fallow to perennial bioenergy crops short rotation coppice (SRC) willow (Salix spp.) and short rotation forest (SRF) Scots pine (Pinus sylvestris). There were no significant differences between CH4 and N2O fluxes measured from the SRC, SRF and fallow, but the arable agricultural site showed an order of magnitude higher N2O emissions compared with the others. Fertiliser application to the arable crop was the major factor influencing N2O emissions, and both air and soil temperature showed no significant effects on fluxes between the different land use systems. Soil moisture was significantly different from the arable crop, showing a greater range than from SRF and SRC. Hence, these bioenergy crops might be viable options for water-stressed areas.

Subarctic and boreal emissions of CH4 are important contributors to the atmospheric greenhouse gas (GHG) balance and subsequently the global radiative forcing. Whilst N2O emissions may be lower, the much greater radiative forcing they produce justifies their inclusion in GHG studies. In addition to the quantification of flux magnitude, it is essential that we understand the drivers of emissions to be able to accurately predict climate-driven changes and potential feedback mechanisms. Hence this study aims to increase our understanding of what drives fluxes of CH4 and N2O in a subarctic forest/wetland landscape during peak summer conditions and into the shoulder season, exploring both spatial and temporal variability, and uses satellite-derived spectral data to extrapolate from chamber-scale fluxes to a 2 km × 2 km landscape area.From static chamber measurements made during summer and autumn campaigns in 2012 in the Sodankylä region of northern Finland, we concluded that wetlands represent a significant source of CH4 (3.35 ± 0.44 mg C m−2 h−1 during the summer campaign and 0.62 ± 0.09 mg C m−2 h−1 during the autumn campaign), whilst the surrounding forests represent a small sink (−0.06 ±

The effects of atmospheric nitrogen deposition (Ndep) on carbon (C) sequestration in forests have often been assessed by relating differences in productivity to spatial variations of Ndep across a large geographic domain. These correlations generally suffer from covariation of other confounding variables related to climate and other growth-limiting factors, as well as large uncertainties in total (dry + wet) reactive nitrogen (Nr) deposition. We propose a methodology for untangling the effects of Ndep from those of meteorological variables, soil water retention capacity and stand age, using a mechanistic forest growth model in combination with eddy covariance CO2 exchange fluxes from a Europe-wide network of forest flux towers. Total Nr deposition rates were estimated from local measurements as far as possible. The forest data were compared with data from natural or semi-natural, non-woody vegetation sites. The carbon sequestration response of forests to nitrogen deposition (dC / dN) was estimated after accounting for the effects of the co-correlates by means of a meta-modelling standardization procedure, which resulted in a reduction by a factor of about 2 of the uncorrected, apparent dC / dN value. This model-enhanced analysis of the C and Ndep flux observations at the scale of the European network suggests a mean overall dC / dN response of forest lifetime C sequestration to Ndep of the order of 40–50 g (C) g−1 (N), which is slightly larger but not significantly different from the range of estimates published in the most recent reviews. Importantly, patterns of gross primary and net ecosystem productivity versus Ndep were non-linear, with no further responses at high Ndep levels (Ndep > 2.5–3 g (N) m−2 yr−1) partly due to large ecosystem N losses by leaching and gaseous emissions. The reduced increase in productivity per unit N deposited at high Ndep levels implies that the forecast increased Nr emissions and increased Ndep levels in large areas of Asia may not positively impact the continent's forest CO2 sink. The large level of unexplained variability in observed carbon sequestration efficiency (CSE) across sites further adds to the uncertainty in the dC / dN response.