Global atmospheric methane uptake by upland tree woody surfaces.

Methane is an important greenhouse gas1, but the role of trees in the methane budget remains uncertain2. Although it has been shown that wetland and some upland trees can emit soil-derived methane at the stem base3,4, it has also been suggested that upland trees can serve as a net sink for atmospheric methane5,6. Here we examine in situ woody surface methane exchange of upland tropical, temperate and boreal forest trees. We find that methane uptake on woody surfaces, in particular at and above about 2 m above the forest floor, can dominate the net ecosystem contribution of trees, resulting in a net tree methane sink. Stable carbon isotope measurement of methane in woody surface chamber air and process-level investigations on extracted wood cores are consistent with methanotrophy, suggesting a microbially mediated drawdown of methane on and in tree woody surfaces and tissues. By applying terrestrial laser scanning-derived allometry to quantify global forest tree woody surface area, a preliminary first estimate suggests that trees may contribute 24.6-49.9 Tg of atmospheric methane uptake globally. Our findings indicate that the climate benefits of tropical and temperate forest protection and reforestation may be greater than previously assumed.

The potential to increase grassland soil C stocks by extending reseeding intervals is dependent on soil texture and depth.

Grasslands account for ∼30% of global terrestrial carbon (C), of which most is stored in soils and provide important ecosystem services including livestock and forage production. Reseeding of temporary grasslands on a 5-year cycle is a common management practice to rejuvenate sward productivity and reduce soil compaction, but is physically disruptive and may reduce soil organic carbon (SOC) stocks. However, research to date is limited, which impacts on the ability to optimise grassland management for climate change mitigation. To determine whether extending the time interval up to 20 years between grassland reseeding can increase stable SOC stocks, a soil survey was conducted across three UK grassland chrono-sequences comprising 24 fields on contrasting soil types. We found that grassland SOC stocks (39.8-114.8 Mg C ha-1) were higher than co-located fields in arable rotations (29.3-83.2 Mg C ha-1) and the relationship with grassland age followed a curvilinear relationship with rapid SOC stock accumulation in the year following reseeding (2.69-18.3 Mg C ha-1 yr-1) followed by progressively slower SOC accumulation up to 20 years. Contrary to expectation, all grasslands had similar soil bulk densities and sward composition questioning the need for traditional 5-year reseeding cycles. Fractionation of soils into stable mineral associated fractions revealed that coarse textured grassland topsoils (0-15 cm) were near-saturated in C irrespective of grassland age whilst loam soils reached saturation ∼10 years after reseeding. Fine-textured topsoils and subsoils (15-30 cm) of all textures were under saturated and thus appear to hold the most potential to accrue additional stable C. However, the lack of a relationship between C saturation deficit and grassland age in subsoils suggests that more innovative management to promote SOC redistribution to depth, such as a switch to diverse leys or full inversion tillage may be required to maximise subsoil SOC stocks. Taken together our findings suggest that extending the time between grassland reseeding could temporarily increase SOC stocks without compromising sward composition or soil structure. However, detailed monitoring of the trade-offs with grassland productivity are required. Fine textured soils and subsoils (15-30 cm) have the greatest potential to accrue additional stable C due to under saturation of fine mineral pools.

The importance of nitrogen for net carbon sequestration when considering natural climate solutions.

To store substantial amounts of carbon in natural climate solutions the strong interlinkages between carbon and nitrogen cycling must be considered. There are many agricultural management options for increasing soil organic carbon stocks but each approach must be evaluated in context of the full, net greenhouse gas balance. This requires a detailed understanding of the implications of increased nitrogen demand to store organic forms of carbon in soil, on potential nitrous oxide emissions in particular.

Diurnal variability in soil nitrous oxide emissions is a widespread phenomenon.

Manual measurements of nitrous oxide (N2 O) emissions with static chambers are commonly practised. However, they generally do not consider the diurnal variability of N2 O flux, and little is known about the patterns and drivers of such variability. We systematically reviewed and analysed 286 diurnal data sets of N2 O fluxes from published literature to (i) assess the prevalence and timing (day or night peaking) of diurnal N2 O flux patterns in agricultural and forest soils, (ii) examine the relationship between N2 O flux and soil temperature with different diurnal patterns, (iii) identify whether non-diurnal factors (i.e. land management and soil properties) influence the occurrence of diurnal patterns and (iv) evaluate the accuracy of estimating cumulative N2 O emissions with single-daily flux measurements. Our synthesis demonstrates that diurnal N2 O flux variability is a widespread phenomenon in agricultural and forest soils. Of the 286 data sets analysed, ~80% exhibited diurnal N2 O patterns, with ~60% peaking during the day and ~20% at night. Contrary to many published observations, our analysis only found strong positive correlations (R > 0.7) between N2 O flux and soil temperature in one-third of the data sets. Soil drainage property, soil water-filled pore space (WFPS) level and land use were also found to potentially influence the occurrence of certain diurnal patterns. Our work demonstrated that single-daily flux measurements at mid-morning yielded daily emission estimates with the smallest average bias compared to measurements made at other times of day, however, it could still lead to significant over- or underestimation due to inconsistent diurnal N2 O patterns. This inconsistency also reflects the inaccuracy of using soil temperature to predict the time of daily average N2 O flux. Future research should investigate the relationship between N2 O flux and other diurnal parameters, such as photosynthetically active radiation (PAR) and root exudation, along with the consideration of the effects of soil moisture, drainage and land use on the diurnal patterns of N2 O flux. The information could be incorporated in N2 O emission prediction models to improve accuracy.

Changes in soil organic carbon under perennial crops.

This study evaluates the dynamics of soil organic carbon (SOC) under perennial crops across the globe. It quantifies the effect of change from annual to perennial crops and the subsequent temporal changes in SOC stocks during the perennial crop cycle. It also presents an empirical model to estimate changes in the SOC content under crops as a function of time, land use, and site characteristics. We used a harmonized global dataset containing paired-comparison empirical values of SOC and different types of perennial crops (perennial grasses, palms, and woody plants) with different end uses: bioenergy, food, other bio-products, and short rotation coppice. Salient outcomes include: a 20-year period encompassing a change from annual to perennial crops led to an average 20% increase in SOC at 0-30 cm (6.0 ± 4.6 Mg/ha gain) and a total 10% increase over the 0-100 cm soil profile (5.7 ± 10.9 Mg/ha). A change from natural pasture to perennial crop decreased SOC stocks by 1% over 0-30 cm (-2.5 ± 4.2 Mg/ha) and 10% over 0-100 cm (-13.6 ± 8.9 Mg/ha). The effect of a land use change from forest to perennial crops did not show significant impacts, probably due to the limited number of plots; but the data indicated that while a 2% increase in SOC was observed at 0-30 cm (16.81 ± 55.1 Mg/ha), a decrease in 24% was observed at 30-100 cm (-40.1 ± 16.8 Mg/ha). Perennial crops generally accumulate SOC through time, especially woody crops; and temperature was the main driver explaining differences in SOC dynamics, followed by crop age, soil bulk density, clay content, and depth. We present empirical evidence showing that the FAO perennialization strategy is reasonable, underscoring the role of perennial crops as a useful component of climate change mitigation strategies.

Microbial responses to warming enhance soil carbon loss following translocation across a tropical forest elevation gradient.

Tropical soils contain huge carbon stocks, which climate warming is projected to reduce by stimulating organic matter decomposition, creating a positive feedback that will promote further warming. Models predict that the loss of carbon from warming soils will be mediated by microbial physiology, but no empirical data are available on the response of soil carbon and microbial physiology to warming in tropical forests, which dominate the terrestrial carbon cycle. Here we show that warming caused a considerable loss of soil carbon that was enhanced by associated changes in microbial physiology. By translocating soils across a 3000 m elevation gradient in tropical forest, equivalent to a temperature change of ± 15 °C, we found that soil carbon declined over 5 years by 4% in response to each 1 °C increase in temperature. The total loss of carbon was related to its original quantity and lability, and was enhanced by changes in microbial physiology including increased microbial carbon-use-efficiency, shifts in community composition towards microbial taxa associated with warmer temperatures, and increased activity of hydrolytic enzymes. These findings suggest that microbial feedbacks will cause considerable loss of carbon from tropical forest soils in response to predicted climatic warming this century.

Zones of influence for soil organic matter dynamics: A conceptual framework for data and models.

Soil organic matter (SOM) is an indicator of sustainable land management as stated in the global indicator framework of the United Nations Sustainable Development Goals (SDG Indicator 15.3.1). Improved forecasting of future changes in SOM is needed to support the development of more sustainable land management under a changing climate. Current models fail to reproduce historical trends in SOM both within and during transition between ecosystems. More realistic spatio-temporal SOM dynamics require inclusion of the recent paradigm shift from SOM recalcitrance as an 'intrinsic property' to SOM persistence as an 'ecosystem interaction'. We present a soil profile, or pedon-explicit, ecosystem-scale framework for data and models of SOM distribution and dynamics which can better represent land use transitions. Ecosystem-scale drivers are integrated with pedon-scale processes in two zones of influence. In the upper vegetation zone, SOM is affected primarily by plant inputs (above- and belowground), climate, microbial activity and physical aggregation and is prone to destabilization. In the lower mineral matrix zone, SOM inputs from the vegetation zone are controlled primarily by mineral phase and chemical interactions, resulting in more favourable conditions for SOM persistence. Vegetation zone boundary conditions vary spatially at landscape scales (vegetation cover) and temporally at decadal scales (climate). Mineral matrix zone boundary conditions vary spatially at landscape scales (geology, topography) but change only slowly. The thicknesses of the two zones and their transport connectivity are dynamic and affected by plant cover, land use practices, climate and feedbacks from current SOM stock in each layer. Using this framework, we identify several areas where greater knowledge is needed to advance the emerging paradigm of SOM dynamics-improved representation of plant-derived carbon inputs, contributions of soil biota to SOM storage and effect of dynamic soil structure on SOM storage-and how this can be combined with robust and efficient soil monitoring.

Extreme rainfall affects assembly of the root-associated fungal community.

Global warming is resulting in increased frequency of weather extremes. Root-associated fungi play important roles in terrestrial biogeochemical cycling processes, but the way in which they are affected by extreme weather is unclear. Here, we performed long-term field monitoring of the root-associated fungus community of a short rotation coppice willow plantation, and compared community dynamics before and after a once in 100 yr rainfall event that occurred in the UK in 2012. Monitoring of the root-associated fungi was performed over a 3-yr period by metabarcoding the fungal internal transcribed spacer (ITS) region. Repeated soil testing and continuous climatic monitoring supplemented community data, and the relative effects of environmental and temporal variation were determined on the root-associated fungal community. Soil saturation and surface water were recorded throughout the early growing season of 2012, following extreme rainfall. This was associated with a crash in the richness and relative abundance of ectomycorrhizal fungi, with each declining by over 50%. Richness and relative abundance of saprophytes and pathogens increased. We conclude that extreme rainfall events may be important yet overlooked determinants of root-associated fungal community assembly. Given the integral role of ectomycorrhizal fungi in biogeochemical cycles, these events may have considerable impacts upon the functioning of terrestrial ecosystems.

Microbes follow Humboldt: temperature drives plant and soil microbial diversity patterns from the Amazon to the Andes.

More than 200 years ago, Alexander von Humboldt reported that tropical plant species richness decreased with increasing elevation and decreasing temperature. Surprisingly, coordinated patterns in plant, bacterial, and fungal diversity on tropical mountains have not yet been observed, despite the central role of soil microorganisms in terrestrial biogeochemistry and ecology. We studied an Andean transect traversing 3.5 km in elevation to test whether the species diversity and composition of tropical forest plants, soil bacteria, and fungi follow similar biogeographical patterns with shared environmental drivers. We found coordinated changes with elevation in all three groups: species richness declined as elevation increased, and the compositional dissimilarity among communities increased with increased separation in elevation, although changes in plant diversity were larger than in bacteria and fungi. Temperature was the dominant driver of these diversity gradients, with weak influences of edaphic properties, including soil pH. The gradients in microbial diversity were strongly correlated with the activities of enzymes involved in organic matter cycling, and were accompanied by a transition in microbial traits towards slower-growing, oligotrophic taxa at higher elevations. We provide the first evidence of coordinated temperature-driven patterns in the diversity and distribution of three major biotic groups in tropical ecosystems: soil bacteria, fungi, and plants. These findings suggest that interrelated and fundamental patterns of plant and microbial communities with shared environmental drivers occur across landscape scales. These patterns are revealed where soil pH is relatively constant, and have implications for tropical forest communities under future climate change.

Interactive biotic and abiotic regulators of soil carbon cycling: evidence from controlled climate experiments on peatland and boreal soils.

Partially decomposed plant and animal remains have been accumulating in organic soils (i.e. >40% C content) for millennia, making them the largest terrestrial carbon store. There is growing concern that, in a warming world, soil biotic processing will accelerate and release greenhouse gases that further exacerbate climate change. However, the magnitude of this response remains uncertain as the constraints are abiotic, biotic and interactive. Here, we examined the influence of resource quality and biological activity on the temperature sensitivity of soil respiration under different soil moisture regimes. Organic soils were sampled from 13 boreal and peatland ecosystems located in the United Kingdom, Ireland, Spain, Finland and Sweden, representing a natural resource quality range of C, N and P. They were incubated at four temperatures (4, 10, 15 and 20 °C) at either 60% or 100% water holding capacity (WHC). Our results showed that chemical and biological properties play an important role in determining soil respiration responses to temperature and moisture changes. High soil C : P and C : N ratios were symptomatic of slow C turnover and long-term C accumulation. In boreal soils, low bacterial to fungal ratios were related to greater temperature sensitivity of respiration, which was amplified in drier conditions. This contrasted with peatland soils which were dominated by bacterial communities and enchytraeid grazing, resulting in a more rapid C turnover under warmer and wetter conditions. The unexpected acceleration of C mineralization under high moisture contents was possibly linked to the primarily role of fermented organic matter, instead of oxygen, in mediating microbial decomposition. We conclude that to improve C model simulations of soil respiration, a better resolution of the interactions occurring between climate, resource quality and the decomposer community will be required.

Interactions between climate warming and land management regulate greenhouse gas fluxes in a temperate grassland ecosystem.

Greenhouse gas (GHG) fluxes from grasslands are affected by climate warming and agricultural management practices including nitrogen (N) fertiliser application and grazing. However, the interactive effects of these factors are poorly resolved in field studies. We used a factorial in situ experiment - combining warming, N-fertiliser and above-ground cutting treatments - to explore their individual and interactive effects on plant-soil properties and GHG fluxes in a temperate UK grassland over two years. Our results showed no interactive treatment effects on plant productivity despite individual effects of N-fertiliser and warming on above- and below-ground biomass. There were, however, interactive treatment effects on GHG fluxes that varied across the two years. In year 1, warming and N-fertiliser increased CO2 and reduced N2O fluxes. N-fertilised also interacted with above-ground biomass (AGB) removal increasing N2O fluxes in year one and reducing CO2 fluxes in year two. The grassland was consistently a sink of CH4; N-fertilised increased the sink by 45% (year 1), AGB removal and warming reduced CH4 consumption by 44% and 43%, respectively (year 2). The majority of the variance in CO2 fluxes was explained by above-ground metrics (grassland productivity and leaf dry matter content), with microclimate (air and soil temperature and soil moisture) and below-ground (root N content) metrics also significant. Soil chemistry (soil mineral N and net mineralisation rate), below-ground (specific root length) and microclimate (soil moisture) metrics explained 49% and 24% of the variance in N2O and CH4 fluxes, respectively. Overall, our work demonstrates the importance of interactions between climate and management as determinants of short-term grassland GHG fluxes. These results show that reduced cutting combined with lower inorganic N-fertilisers would constrain grassland C and N cycling and GHG fluxes in warmer climatic conditions. This has implications for strategic grassland management decisions to mitigate GHG fluxes in a warming world.

Diversity and Ecological Guild Analysis of the Oil Palm Fungal Microbiome Across Root, Rhizosphere, and Soil Compartments.

The rhizosphere microbiome is a major determinant of plant health, which can interact with the host directly and indirectly to promote or suppress productivity. Oil palm is one of the world's most important crops, constituting over a third of global vegetable oil production. Currently there is little understanding of the oil palm microbiome and its contribution to plant health and productivity, with existing knowledge based almost entirely on culture dependent studies. We investigated the diversity and composition of the oil palm fungal microbiome in the bulk soil, rhizosphere soil, and roots of 2-, 18-, and 35-year old plantations in Selangor, Malaysia. The fungal community showed substantial variation between the plantations, accounting for 19.7% of community composition, with compartment (root, rhizosphere soil, and bulk soil), and soil properties (pH, C, N, and P) contributing 6.5 and 7.2% of community variation, respectively. Rhizosphere soil and roots supported distinct communities compared to the bulk soil, with significant enrichment of Agaricomycetes, Glomeromycetes, and Lecanoromycetes in roots. Several putative plant pathogens were abundant in roots in all the plantations, including taxa related to Prospodicola mexicana and Pleurostoma sp. The mycorrhizal status and dependency of oil palm has yet to be established, and using 18S rRNA primers we found considerable between-site variation in Glomeromycotinian community composition, accounting for 31.2% of variation. There was evidence for the selection of Glomeromycotinian communities in oil palm roots in the older plantations but compartment had a weak effect on community composition, accounting for 3.9% of variation, while soil variables accounted for 9% of community variation. While diverse Mucoromycotinian fungi were detected, they showed very low abundance and diversity within roots compared to bulk soil, and were not closely related to taxa which have been linked to fine root endophyte mycorrhizal morphology. Many of the fungal sequences showed low similarity to established genera, indicating the presence of substantial novel diversity with significance for plant health within the oil palm microbiome.

Isoprene-degrading bacteria associated with the phyllosphere of Salix fragilis, a high isoprene-emitting willow of the Northern Hemisphere.

BACKGROUND: Isoprene accounts for about half of total biogenic volatile organic compound emissions globally, and as a climate active gas it plays a significant and varied role in atmospheric chemistry. Terrestrial plants are the largest source of isoprene, with willow (Salix) making up one of the most active groups of isoprene producing trees. Bacteria act as a biological sink for isoprene and those bacteria associated with high isoprene-emitting trees may provide further insight into its biodegradation. RESULTS: A DNA-SIP experiment incubating willow (Salix fragilis) leaves with 13C-labelled isoprene revealed an abundance of Comamonadaceae, Methylobacterium, Mycobacterium and Polaromonas in the isoprene degrading community when analysed by 16S rRNA gene amplicon sequencing. Metagenomic analysis of 13C-enriched samples confirmed the abundance of Comamonadaceae, Acidovorax, Polaromonas, Variovorax and Ramlibacter. Mycobacterium and Methylobacterium were also identified after metagenomic analysis and a Mycobacterium metagenome-assembled genome (MAG) was recovered. This contained two complete isoprene degradation metabolic gene clusters, along with a propane monooxygenase gene cluster. Analysis of the abundance of the alpha subunit of the isoprene monooxygenase, isoA, in unenriched DNA samples revealed that isoprene degraders associated with willow leaves are abundant, making up nearly 0.2% of the natural bacterial community. CONCLUSIONS: Analysis of the isoprene degrading community associated with willow leaves using DNA-SIP and focused metagenomics techniques enabled recovery of the genome of an active isoprene-degrading Mycobacterium species and provided valuable insight into bacteria involved in degradation of isoprene on the leaves of a key species of isoprene-emitting tree in the northern hemisphere.

Vegetation affects the relative abundances of dominant soil bacterial taxa and soil respiration rates in an upland grassland soil.

Plant-derived organic matter inputs are thought to be a key driver of soil bacterial community composition and associated soil processes. We sought to investigate the role of acid grassland vegetation on soil bacterial community structure by assessing bacterial diversity in combination with other soil variables in temporally and spatially distinct samples taken from a field-based plant removal experiment. Removal of aboveground vegetation resulted in reproducible differences in soil properties, soil respiration and bacterial diversity. Vegetated soils had significantly increased carbon and nitrogen concentrations and exhibited higher rates of respiration. Molecular analyses revealed that the soils were broadly dominated by Alphaproteobacterial and Acidobacterial lineages, with increased abundances of Alphaproteobacteria in vegetated soils and more Acidobacteria in bare soils. This field-based study contributes to a growing body of evidence documenting the effect of soil nutrient status on the relative abundances of dominant soil bacterial taxa, with Proteobacterial taxa dominating over Acidobacteria in soils exhibiting higher rates of C turnover. Furthermore, we highlight the role of aboveground vegetation in mediating this effect by demonstrating that plant removal can alter the relative abundances of dominant soil taxa with concomitant changes in soil CO(2)-C efflux.

Litter evenness influences short-term peatland decomposition processes.

There is concern that changes in climate and land use could increase rates of decomposition in peatlands, leading to release of stored C to the atmosphere. Rates of decomposition are driven by abiotic factors such as temperature and moisture, but also by biotic factors such as changes in litter quality resulting from vegetation change. While effects of litter species identity and diversity on decomposition processes are well studied, the impact of changes in relative abundance (evenness) of species has received less attention. In this study we investigated effects of changes in short-term peatland plant species evenness on decomposition in mixed litter assemblages, measured as litter weight loss, respired CO(2) and leachate C and N. We found that over the 307-day incubation period, higher levels of species evenness increased rates of decomposition in mixed litters, measured as weight loss and leachate dissolved organic N. We also found that the identity of the dominant species influenced rates of decomposition, measured as weight loss, CO(2) flux and leachate N. Greatest rates of decomposition were when the dwarf shrub Calluna vulgaris dominated litter mixtures, and lowest rates when the bryophyte Pleurozium schreberi dominated. Interactions between evenness and dominant species identity were also detected for litter weight loss and leachate N. In addition, positive non-additive effects of mixing litter were observed for litter weight loss. Our findings highlight the importance of changes in the evenness of plant community composition for short-term decomposition processes in UK peatlands.

Influence of temperature on the δ13 C values and distribution of methanotroph-related hopanoids in Sphagnum-dominated peat bogs.

Methane emissions from peat bogs are mitigated by methanotrophs, which live in symbiosis with peat moss (e.g. Sphagnum). Here, we investigate the influence of temperature and resultant changes in methane fluxes on Sphagnum and methanotroph-related biomarkers, evaluating their potential as proxies in ancient bogs. A pulse-chase experiment using 13 C-labelled methane in the field clearly showed label uptake in diploptene, a biomarker for methanotrophs, demonstrating in situ methanotrophic activity in Sphagnum under natural conditions. Peat cores containing live Sphagnum were incubated at 5, 10, 15, 20 and 25°C for two months, causing differences in net methane fluxes. The natural δ13 C values of diploptene extracted from Sphagnum showed a strong correlation with temperature and methane production. The δ13 C values ranged from -34‰ at 5°C to -41‰ at 25°C. These results are best explained by enhanced expression of the methanotrophic enzymatic isotope effect at higher methane concentrations. Hence, δ13 C values of diploptene, or its diagenetic products, potentially provide a useful tool to assess methanotrophic activity in past environments. Increased methane fluxes towards Sphagnum did not affect δ13 C values of bulk Sphagnum and its specific marker, the C23 n-alkane. The concentration of methanotroph-specific bacteriohopanepolyols (BHPs), aminobacteriohopanetetrol (aminotetrol, characteristic for type II and to a lesser extent type I methanotrophs) and aminobacteriohopanepentol (aminopentol, a marker for type I methanotrophs) showed a non-linear response to increased methane fluxes, with relatively high abundances at 25°C compared to those at 20°C or below. Aminotetrol was more abundant than aminopentol, in contrast to similar abundances of aminotetrol and aminopentol in fresh Sphagnum. This probably indicates that type II methanotrophs became prevalent under the experimental conditions relative to type I methanotrophs. Even though BHP concentrations may not directly reflect bacterial activity, they may provide insight into the presence of different types of methanotrophs.

Diversity of isoprene-degrading bacteria in phyllosphere and soil communities from a high isoprene-emitting environment: a Malaysian oil palm plantation.

BACKGROUND: Isoprene is the most abundantly produced biogenic volatile organic compound (BVOC) on Earth, with annual global emissions almost equal to those of methane. Despite its importance in atmospheric chemistry and climate, little is known about the biological degradation of isoprene in the environment. The largest source of isoprene is terrestrial plants, and oil palms, the cultivation of which is expanding rapidly, are among the highest isoprene-producing trees. RESULTS: DNA stable isotope probing (DNA-SIP) to study the microbial isoprene-degrading community associated with oil palm trees revealed novel genera of isoprene-utilising bacteria including Novosphingobium, Pelomonas, Rhodoblastus, Sphingomonas and Zoogloea in both oil palm soils and on leaves. Amplicon sequencing of isoA genes, which encode the α-subunit of the isoprene monooxygenase (IsoMO), a key enzyme in isoprene metabolism, confirmed that oil palm trees harbour a novel diversity of isoA sequences. In addition, metagenome-assembled genomes (MAGs) were reconstructed from oil palm soil and leaf metagenomes and putative isoprene degradation genes were identified. Analysis of unenriched metagenomes showed that isoA-containing bacteria are more abundant in soils than in the oil palm phyllosphere. CONCLUSION: This study greatly expands the known diversity of bacteria that can metabolise isoprene and contributes to a better understanding of the biological degradation of this important but neglected climate-active gas. Video abstract.

Soil & Water Assessment Tool (SWAT) simulated hydrological impacts of land use change from temperate grassland to energy crops: A case study in western UK.

When considering the large-scale deployment of bioenergy crops, it is important to understand the implication for ecosystem hydrological processes and the influences of crop type and location. Based on the potential for future land use change (LUC), the 10,280 km2 West Wales Water Framework Directive River Basin District (UK) was selected as a typical grassland dominated district, and the Soil & Water Assessment Tool (SWAT) hydrology model with a geographic information systems interface was used to investigate implications for different bioenergy deployment scenarios. The study area was delineated into 855 sub-basins and 7,108 hydrological response units based on rivers, soil type, land use, and slope. Changes in hydrological components for two bioenergy crops (Miscanthus and short rotation coppice, SRC) planted on 50% (2,192 km2) or 25% (1,096 km2) of existing improved pasture are quantified. Across the study area as a whole, only surface run-off with SRC planted at the 50% level was significantly impacted, where it was reduced by up to 23% (during April). However, results varied spatially and a comparison of annual means for each sub-basin and scenario revealed surface run-off was significantly decreased and baseflow significantly increased (by a maximum of 40%) with both Miscanthus and SRC. Evapotranspiration was significantly increased with SRC (at both planting levels) and water yield was significantly reduced with SRC (at the 50% level) by up to 5%. Effects on streamflow were limited, varying between -5% and +5% change (compared to baseline) in the majority of sub-basins. The results suggest that for mesic temperate grasslands, adverse effects from the drying of soil and alterations to streamflow may not arise, and with surface run-off reduced and baseflow increased, there could, depending on crop location, be potential benefits for flood and erosion mitigation.

Soil N2O emissions with different reduced tillage methods during the establishment of Miscanthus in temperate grassland.

An increase in renewable energy and the planting of perennial bioenergy crops is expected in order to meet global greenhouse gas (GHG) targets. Nitrous oxide (N2O) is a potent greenhouse gas, and this paper addresses a knowledge gap concerning soil N2O emissions over the possible "hot spot" of land use conversion from established pasture to the biofuel crop Miscanthus. The work aims to quantify the impacts of this land use change on N2O fluxes using three different cultivation methods. Three replicates of four treatments were established: Miscanthus x giganteus (Mxg) planted without tillage; Mxg planted with light tillage; a novel seed-based Miscanthus hybrid planted with light tillage under bio-degradable mulch film; and a control of uncultivated established grass pasture with sheep grazing. Soil N2O fluxes were recorded every 2 weeks using static chambers starting from preconversion in April 2016 and continuing until the end of October 2017. Monthly soil samples were also taken and analysed for nitrate and ammonium. There was no significant difference in N2O emissions between the different cultivation methods. However, in comparison with the uncultivated pasture, N2O emissions from the cultivated Miscanthus plots were 550%-819% higher in the first year (April to December 2016) and 469%-485% higher in the second year (January to October 2017). When added to an estimated carbon cost for production over a 10 year crop lifetime (including crop management, harvest, and transportation), the measured N2O conversion cost of 4.13 Mg CO2-eq./ha represents a 44% increase in emission compared to the base case. This paper clearly shows the need to incorporate N2O fluxes during Miscanthus establishment into assessments of GHG balances and life cycle analysis and provides vital knowledge needed for this process. This work therefore also helps to support policy decisions regarding the costs and benefits of land use change to Miscanthus.

Measured and modelled effect of land-use change from temperate grassland to Miscanthus on soil carbon stocks after 12 years.

Soil organic carbon (SOC) is an important carbon pool susceptible to land-use change (LUC). There are concerns that converting grasslands into the C4 bioenergy crop Miscanthus (to meet demands for renewable energy) could negatively impact SOC, resulting in reductions of greenhouse gas mitigation benefits gained from using Miscanthus as a fuel. This work addresses these concerns by sampling soils (0-30 cm) from a site 12 years (T12) after conversion from marginal agricultural grassland into Miscanthus x giganteus and four other novel Miscanthus hybrids. Soil samples were analysed for changes in below-ground biomass, SOC and Miscanthus contribution to SOC (using a 13C natural abundance approach). Findings are compared to ECOSSE soil carbon model results (run for a LUC from grassland to Miscanthus scenario and continued grassland counterfactual), and wider implications are considered in the context of life cycle assessments based on the heating value of the dry matter (DM) feedstock. The mean T12 SOC stock at the site was 8 (±1 standard error) Mg C/ha lower than baseline time zero stocks (T0), with assessment of the five individual hybrids showing that while all had lower SOC stock than at T0 the difference was only significant for a single hybrid. Over the longer term, new Miscanthus C4 carbon replaces pre-existing C3 carbon, though not at a high enough rate to completely offset losses by the end of year 12. At the end of simulated crop lifetime (15 years), the difference in SOC stocks between the two scenarios was 4 Mg C/ha (5 g CO2-eq/MJ). Including modelled LUC-induced SOC loss, along with carbon costs relating to soil nitrous oxide emissions, doubled the greenhouse gas intensity of Miscanthus to give a total global warming potential of 10 g CO2-eq/MJ (180 kg CO2-eq/Mg DM).