Steps to scaling up UK sustainable bioenergy supply

This technical annex was produced to support the Committee on Climate Change’s 2018 report 'Biomass in a low-carbon economy'. The objective was to identify steps to scaling up UK sustainable bioenergy supply, focussing on short to medium term measures that can increase UK production of bioenergy feedstocks whilst delivering social, economic and environmental benefits. The assessment was based on stakeholder workshops held in July 2018 and informs chapter 4 of the report

Solar park microclimate and vegetation management effects on grassland carbon cycling

Increasing energy demands and the drive towards low carbon (C) energy sources has prompted a rapid increase in ground-mounted solar parks across the world. This represents a significant global land use change with implications for the hosting ecosystems that are poorly understood. In order to investigate the effects of a typical solar park on the microclimate and ecosystem processes, we measured soil and air microclimate, vegetation and greenhouse gas emissions for twelve months under photovoltaic (PV) arrays, in gaps between PV arrays and in control areas at a UK solar park sited on species-rich grassland. Our results show that the PV arrays caused seasonal and diurnal variation in air and soil microclimate. Specifically, during the summer we observed cooling, of up to 5.2 °C, and drying under the PV arrays compared with gap and control areas. In contrast, during the winter gap areas were up to 1.7 °C cooler compared with under the PV arrays and control areas. Further, the diurnal variation in both temperature and humidity during the summer was reduced under the PV arrays. We found microclimate and vegetation management explained differences in the above ground plant biomass and species diversity, with both lower under the PV arrays. Photosynthesis and net ecosystem exchange in spring and winter were also lower under the PV arrays, explained by microclimate, soil and vegetation metrics. These data are a starting point to develop understanding of the effects of solar parks in other climates, and provide evidence to support the optimisation of solar park design and management to maximise the delivery of ecosystem services from this growing land use

Biotic and abiotic factors interact to regulate Northern peatland carbon cycling

Understanding the spatio-temporal variability of controls on peatland carbon (C) cycling is essential to project the effects of future environmental change. While there is understanding of individual drivers of C cycling, the effect of multiple drivers, including interactions, remains poorly understood. Using a spatially and temporally explicit sampling framework, we examined the effects of biotic and abiotic controls on key indicators of peatland functioning: ecosystem respiration (R (eco)), photosynthesis (P (cal)), net ecosystem exchange (NEE), methane (CH4) fluxes, and pore water dissolved organic carbon concentration ([DOC]). Measurements were made over 12 months in a blanket peatland hosting a wind farm in Scotland, UK. Overall, we found that (i) season and plant functional type (PFT) explained most variation in R (eco) and P (cal), (ii) PFT and spatial location within the wind farm, which integrates several peat properties, were dominant predictors of CH4 fluxes, and (iii) season and location within the wind farm correlated with pore water [DOC]. Examination of predictors indicated that interactions, between and within biotic and abiotic factors, explained a significant amount of variation in greenhouse gas fluxes and [DOC]. These findings indicate that combinations of biotic and abiotic factors could mediate or exacerbate the effects of future environmental change on peatland C cycling. Given this, studies of C cycling need to capture the spatial and temporal variance of biotic and abiotic factors and their interactions to project the likely impacts of environmental change

Legumes increase grassland productivity with no effect on nitrous oxide emissions

Aims: Grasslands are important agricultural production systems, where ecosystem functioning is affected by land management practices. Grass-legume mixtures are commonly cultivated to increase grassland productivity while reducing the need for nitrogen (N) fertiliser. However, little is known about the effect of this increase in productivity on greenhouse gas (GHG) emissions in grass-legume mixtures. The aim of this study was to investigate interactions between the proportion of legumes in grass-legume mixtures and N-fertiliser addition on productivity and GHG emissions. We tested the hypotheses that an increase in the relative proportion of legumes would increase plant productivity and decrease GHG emissions, and the magnitude of these effects would be reduced by N-fertiliser addition. Methods: This was tested in a controlled environment mesocosm experiment with one grass and one legume species grown in mixtures in different proportions, with or without N-fertiliser. The effects on N cycling processes were assessed by measurement of above- and below-ground biomass, shoot N uptake, soil physico-chemical properties and GHG emissions. Results: Above-ground productivity and shoot N uptake were greater in legume-grass mixtures compared to grass or legume monocultures, in fertilised and unfertilised soils. However, we found no effect of legume proportion on N2O emissions, total soil N or mineral-N in fertilised or unfertilised soils. Conclusions: This study shows that the inclusion of legumes in grass-legume mixtures positively affected productivity, however N cycle were in the short-term unaffected and mainly affected by nitrogen fertilisation. Legumes can be used in grassland management strategies to mitigate climate change by reducing crop demand for N-fertilisers

Microbial carbon mineralization in tropical lowland and montane forest soils of Peru

Climate change is affecting the amount and complexity of plant inputs to tropical forest soils. This is likely to influence the carbon (C) balance of these ecosystems by altering decomposition processes e.g., "positive priming effects" that accelerate soil organic matter mineralization. However, the mechanisms determining the magnitude of priming effects are poorly understood. We investigated potential mechanisms by adding (13)C labeled substrates, as surrogates of plant inputs, to soils from an elevation gradient of tropical lowland and montane forests. We hypothesized that priming effects would increase with elevation due to increasing microbial nitrogen limitation, and that microbial community composition would strongly influence the magnitude of priming effects. Quantifying the sources of respired C (substrate or soil organic matter) in response to substrate addition revealed no consistent patterns in priming effects with elevation. Instead we found that substrate quality (complexity and nitrogen content) was the dominant factor controlling priming effects. For example a nitrogenous substrate induced a large increase in soil organic matter mineralization whilst a complex C substrate caused negligible change. Differences in the functional capacity of specific microbial groups, rather than microbial community composition per se, were responsible for these substrate-driven differences in priming effects. Our findings suggest that the microbial pathways by which plant inputs and soil organic matter are mineralized are determined primarily by the quality of plant inputs and the functional capacity of microbial taxa, rather than the abiotic properties of the soil. Changes in the complexity and stoichiometry of plant inputs to soil in response to climate change may therefore be important in regulating soil C dynamics in tropical forest soils.This study was financed by the UK Natural Environment Research Council (NERC) grant NE/G018278/1 and is a product of the Andes Biodiversity and Ecosystem Research Group consortium (www.andesconservation.org); Patrick Meir was also supported by ARC FT110100457

Deconstructing the microbial necromass continuum to inform soil carbon sequestration

1. Microbial necromass is a large, dynamic and persistent component of soil organic carbon, the dominant terrestrial carbon pool. Quantification of necromass carbon stocks and its susceptibility to global change is becoming standard practice in soil carbon research. However, the typical proxies used for necromass carbon do not reveal the dynamic nature of necromass carbon flows and transformations within soil that ultimately determine necromass persistence. In this review, we define and deconstruct four stages of the necromass continuum: production, recycling, stabilization and destabilization. 2. Current understanding of necromass dynamics is described for each continuum stage. We highlight recent advances, methodological limitations and knowledge gaps which need to be addressed to determine necromass pool sizes and transformations. We discuss the dominant controls on necromass process rates and aspects of soil microscale structure including biofilms and food web interactions. The relative importance of each stage of the continuum is then compared in contrasting ecosystems and for climate change drivers. 3. From the perspective of the continuum, we draw three conclusions to inform future research. First, controls on necromass persistence are more clearly defined when viewed through the lens of the continuum; second, destabilization is the least understood stage of the continuum with recycling also poorly evidenced outside of a few ecosystems; and third, the response of necromass process rates to climate change is unresolved for most continuum stages and ecosystems. 4. Future mechanistic research focused on the role of biotic and abiotic soil microscale structure in determining necromass process rates and the relative importance of organo–mineral and organo–organo interactions can inform necromass persistence in different climate change scenarios. Our review demonstrates that deconstructing the necromass continuum is key to predicting the vulnerability and persistence of necromass carbon in a changing world

Ground-level climate at a peatland wind farm in Scotland is affected by wind turbine operation

The global drive to produce low-carbon energy has resulted in an unprecedented deployment of onshore wind turbines, representing a significant land use change for wind energy generation with uncertain consequences for local climatic conditions and the regulation of ecosystem processes. Here, we present high-resolution data from a wind farm collected during operational and idle periods that shows the wind farm affected several measures of ground-level climate. Specifically, we discovered that operational wind turbines raised air temperature by 0.18 °C and absolute humidity (AH) by 0.03 g m−3 during the night, and increased the variability in air, surface and soil temperature throughout the diurnal cycle. Further, the microclimatic influence of turbines on air temperature and AH decreased logarithmically with distance from the nearest turbine. These effects on ground-level microclimate, including soil temperature, have uncertain implications for biogeochemical processes and ecosystem carbon cycling, including soil carbon stocks. Consequently, understanding needs to be improved to determine the overall carbon balance of wind energy

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

CDK4/6 inhibitors induce replication stress to cause long-term cell cycle withdrawal

CDK4/6 inhibitors arrest the cell cycle in G1‐phase. They are approved to treat breast cancer and are also undergoing clinical trials against a range of other tumour types. To facilitate these efforts, it is important to understand why a cytostatic arrest in G1 causes long‐lasting effects on tumour growth. Here, we demonstrate that a prolonged G1 arrest following CDK4/6 inhibition downregulates replisome components and impairs origin licencing. Upon release from that arrest, many cells fail to complete DNA replication and exit the cell cycle in a p53‐dependent manner. If cells fail to withdraw from the cell cycle following DNA replication problems, they enter mitosis and missegregate chromosomes causing excessive DNA damage, which further limits their proliferative potential. These effects are observed in a range of tumour types, including breast cancer, implying that genotoxic stress is a common outcome of CDK4/6 inhibition. This unanticipated ability of CDK4/6 inhibitors to induce DNA damage now provides a rationale to better predict responsive tumour types and effective combination therapies, as demonstrated by the fact that CDK4/6 inhibition induces sensitivity to chemotherapeutics that also cause replication stress