The Context of the Research - Many high-profile research papers and syntheses have equated increased vegetation productivity and shifting vegetation types in northern high latitudes with increased net carbon (C) sequestration from the atmosphere. Although logical and intuitive, this largely overlooks the potential fate of pre-existing soil organic carbon (SOC) in these regions. This is a problem because soils at high latitudes are notably C-rich (containing ~570 Pg C in boreal/taiga forest and tundra soils alone; note, 1 Pg (Peta-gram) = 1,000,000,000 tonnes) and this pool is dynamic, intrinsically interacting both with vegetation cover and with climate. Although challenging to investigate, we cannot overlook below-ground processes if we are to understand net C budgets on timescales relevant to the Climate Emergency. Understanding the fundamental mechanisms controlling the accumulation, stability, and loss of soil organic matter (SOM) is as essential for predicting the Earth's future climate as understanding photosynthesis and plant productivity. However, our understanding of, and ability to model, SOM dynamics lags far behind that of primary productivity. Furthermore, rapid warming at high northern latitudes adds urgency to understanding controls on whole-ecosystem C cycling, net fluxes of CO2 between ecosystems and the atmosphere, and the vulnerability of SOM to changes in both climate and management (for example, tree planting for C-sequestration). Aims and Objectives - In MYCONET we focus on the 'mycorrhizosphere' (the soil and organisms directly influenced by roots and their mycorrhizal fungi) of C-rich soils of northern high latitudes and its potential response both to increasing plant productivity and to shifts to woodier shrub and tree communities. We hypothesise that associated changes in the mycorrhizosphere could, paradoxically, result in net losses, rather than gains, of soil C over timescales (i.e. several decades) of relevance to the Climate Emergency. This would represent a 'positive feedback' on climate change (i.e. when the rates of CO2 emission to the atmosphere, due to SOM decomposition, exceed net rates of CO2 uptake via photosynthesis). We will push the frontiers by applying ground-breaking techniques in the use - and innovative experimental deployment - of natural abundance (and depleted) radiocarbon (14C), together with metagenomics, soil and root-tip enzyme assays and SOM chemistry, to quantify and understand the processes and dynamics of the mycorrhizosphere and how these affect SOC stocks. We focus, in detail, on the process of 'priming' (which occurs when material added to soil affects the rate of decomposition of SOM, either positively or negatively), and the specific role of mycorrhizal fungi in this, and related, processes. We will measure these processes both in situ (in the Arctic and the UK uplands) and in controlled experiments (using specific combinations of tree, shrub and mycorrhizal symbionts), as part of an integrated package of mechanistic studies, soil profile analysis and dynamic SOM modelling, to quantify and understand how priming works, and the implications for SOM dynamics, ecosystem C fluxes, and nutrient cycling. Potential applications and benefits - By applying ground-breaking techniques MYCONET will transform our understanding of plant-soil interactions and the role of mycorrhizal fungi in SOM dynamics. The fundamental new knowledge gained will significantly improve regional and global modelling of climate-biogeochemical interactions, with a particular focus on the indirect effects of shifting plant communities. The project has relevance for the pan-Arctic 'shrubification', as well as for ecosystems being managed for C-sequestration or 're-wilding'. This project is especially timely, given the major policy emphasis and public interest in tree planting for C sequestration.

Why do trees in different tropical forests grow at different rates? Why do some trees within a site grow faster than others? At first impression, It seems a reasonable assumption that the 'visible productivity' (e.g. wood production and canopy litterfall) is somehow related to how much carbon and energy the forest or the individual tree captures from photosynthesis, the Gross Primary Productivity (GPP); this assumption is implicit in much of the forest ecology literature, as well as in many biosphere models. When we see explanations as why forests are increasing growth rates in response to global change, or increased productivity after disturbance, we tend to frame these explanations in the context of increased photosynthesis (either because of increased abiotic drivers - e.g. increased light or carbon dioxide, or because of increased photosyntheric capacity, e.g leaf nitrogen content) However, our recent work in Amazonia has indicated that the site-to-site variability in net primary productivity (NPP) in lowland rainforests is not related to how much carbon and energy the forest captures through photosynthesis, but much more determined by how much of that captured carbon used by plants for their internal metabolism (Malhi et al., submitted to Nature), the autotrophic respiration, Ra. This tentative finding has consequences for much of tropical forest research, and global change vegetation models. Moreover, our early results suggest that disturbance is the main determinant of how much an ecosystem allocates to autotrophic respiration, with less autotrophic respiration in disturbed systems. We would now like to explore this topic further in five ways: (i) by exploring in greater detail the spatial and temporal variation of autotrophic respiration; (ii) by greatly increasing the number of sites investigated; (iii) by assessing the extent to which results from Amazonia are generalisable in another biogeographical realm, namely equatorial Africa; (iv) by explicitly exploring how disturbance affects carbon use and allocation by tracking these before and after selective logging; (v) by exploring how much interspecific variation in NPP is determined by autotrophic respiration. The underlying hypotheses we are exploring are that (i) there is no significant site-to-site variation in the GPP of moist tropical lowland forests (within Africa and in comparison to Amazonia), despite variation is soil properties, climate and tree species composition; (ii) there is substantial site-to-site variation in net primary productivity (NPP), and this is mainly driven by shifts in carbon use efficiency (CUE, the proportion of photosynthetic carbon converted to biomass), and (iii) forest CUE increases substantially after disturbance (logging) and subsequently declines over time, and (iv) this shift is driven by differing plastic variation in CUE within surviving individuals, rather than by community replacement. In the process, we will pioneer comprehensive carbon cycle assessment in intact and disturbed African tropical forests, replicated across two contrasting countries, Ghana (West Africa) and Gabon (Central Africa). Our sampling strategy will encompass plots in (i) wet primary forests (2 countries x 2 plots), (ii) moist primary forests (2 countries x 2 plots),(iii) tracking sites before, during and after logging disturbance (2 countries x 2 plots), and (iv) plots recovering from logging disturbance 10, 15 and 20 years ago (2 countries x 2 plots). At all sites we will collect 2.0-2.5 years of data. Our project will provide substantial scientific capacity building in Ghana and Gabon,we will train and utilise 6 student field researchers (3 full time, 3 part-time) in each country, and hold wider-reach training workshops in carbon cycle science in each country at the start and end of the project. this event.

Plants are currently reducing the rate of 21st Century climate change by absorbing a substantial amount of the carbon dioxide that Humankind releases to the atmosphere through the burning of fossil fuels. However, the rate of carbon dioxide production by soils as plant material decomposes (known as soil respiration) increases at higher temperatures. Therefore, as global temperatures rise, it is feared that ecosystems which are currently absorbing carbon dioxide may begin to release it, with models predicting that this could increase the rate of climate change by 40 %. This prediction is based largely on knowledge of how soil respiration responds to short-term changes in temperature. However, in long-term warming experiments, following the initial stimulation of activity, rates of respiration tend to decline back towards pre-warming levels. This has led to the suggestion that the micro-organisms responsible for breaking down organic matter may be acclimating to compensate for the warmer temperatures, and that this phenomenon may preserve carbon stocks in the world's soils. There is an alternative explanation for the patterns observed in long-term warming experiments. The initial stimulation of activity may result in the depletion of soil carbon stores, leaving microbes with less to break down, and so reducing rates of respiration. While acclimation could preserve stocks, the carbon depletion explanation implies that the reduction in respiration rates is simply a consequence of the continuing loss of carbon from soils to the atmosphere. Therefore, it is critical to distinguish between these two possible explanations. Previously, methodological limitations have prevented us from determining which explanation is correct. The problem was that when soils are warmed up, acclimation and carbon loss are both expected to reduce respiration rates, making it impossible to distinguish between them. We have shown that this problem can be overcome by using soil cooling. When soils are cooled, initially activity will decline but if acclimation occurs to compensate for the lowering of temperature, rates of respiration should subsequently increase. On the other hand, as carbon losses continue at the lower temperature, albeit at a reduced rate, they cannot be implicated in any recovery of respiration rates. So carbon loss and thermal acclimation are now working in opposite directions, allowing us to distinguish between them. This logic was applied to determine whether microbial activity in soils taken from arctic Sweden acclimates to changes in temperature. After cooling, respiration rates showed no signs of recovery. Rather, many days after temperatures were reduced, respiration rates in the cooled soils continued to decline steeply, with no such response being observed in soils maintained at a warmer temperature. So the effect of cooling was amplified over time. It appears that the soil microbes were responding to the colder temperatures by further reducing activity. Looking at this in reverse, a more active microbial community survived at higher temperatures; so microbial community responses enhanced the effect of temperature on decomposition rates. This phenomenon has not been observed before, and we do not know how prevalent it might be. By extending our work to soils sampled from different ecosystems and at sites ranging from the high Arctic to the Mediterranean, our grant proposal aims to investigate how important soil microbial community responses to temperature are in controlling decomposition rates in European soils. We will determine whether acclimation occurs or whether microbial community responses generally enhance respiratory responses to temperature. We will also investigate how the overall response is controlled. Our project will improve understanding of how global warming will affect decomposition rates in soils, and allow more accurate predictions of rates of 21st century climate change to be made.

Riparian zones are the dynamic interfaces between terrestrial and aquatic systems, ultimately governing transfers of the macronutrients carbon (C), nitrogen (N) and phosphorus (P) between the land and the oceans, via rivers. The concern is that with a changing climate, the stability of these systems is shifting, and potentially the nutrient cycling rates are accelerating as a consequence. This proposal focuses on our concept of the dynamic riparian reactive interface (RRI) and how it governs the fate of nutrients down the system from the land to the river, perhaps to the atmosphere, and onward to the oceans. The proposal describes an approach that combines data-rich UK research catchments (Scottish Dee, English Eden) with flagship international catchment platforms (in Sweden and Germany). We propose to conduct new biogeochemical research and new modelling across geo-climatic regions to evaluate riparian functions controlling the potential acceleration in nutrient mass transfers across the land to water interface and how these may scale to globally-significant changes in nutrient cycles as our climate changes.

Insect pollination of crops is absolutely critical to food production with an estimated annual global value of $361 billion. Honey bees (Apis mellifera) are undergoing a serious bee health crisis threatening global food security. Huge annual losses of bee colonies in the US (45%, 34%, 40% in 2012/13, 2013/14 and 2015/16) are now being matched by similar losses in Europe. The status of bee health is recognised as critical with unsustainable losses of bees. Though the cause of the bee health crisis is multifactorial, it is generally accepted that the external parasite varroa mite (Varroa destructor) and its transmission of viral pathogens is one of, if not the, major cause of honey bee colony loss. Because of the impact on global food production, varroosis is arguably the most serious disease of livestock in any species. Despite varroa's unquestionable significance, our understanding of its physiology could be considered rudimentary relative to its importance. Progress in varroa research is substantially hampered by the lack an artificial feeding and rearing system which would supply researchers with adequate numbers of consistent varroa year round and provide an ideal experimental system for studying varroa physiology, reproduction, disease transmission and the development and testing of new control strategies. We have recently developed an artificial feeding system for varroa that far exceeds any currently available. Subsequently, we succeeded in inducing varroa in the artificial feeding system to lay eggs by exposing them to the odour cues from either bee larvae or hormone-treated pupae, but not from standard pupae. These eggs hatched and developed through to adult varroa. We now need to capitalize on these initial findings and better understand the fundamentals of varroa reproduction to allow our artificial feeding system to fully evolve into an artificial rearing system. To this end, the overall aim of the project is to understand the control of reproduction in varroa and assess if this information could be utilised as a control measure. By analysing the volatile compounds emanating from cohorts of larvae, pupae and juvenile hormone-treated pupae and applying a differential chemometrics approach, we will chemically characterize components(s) of the "Oviposition Kairomone" (OK). The effect of the larval volatiles or OK on induction of oviposition, the gender of the egg and cessation of egg laying in varroa will be studied by a combination of bioassay and chemical analysis. The role of juvenile hormone in the production of these bioactive volatiles or OK by bee larvae will be elucidated. We will investigate if the varroa detects this odour cue from the bee larvae with its legs and if this signal causes egg laying in varroa through induced sex hormone production (ecdysteroids) via a neuroendocrine factor. The optimum concentration of larval volatiles or OK required to induce varroa egg laying in the artificial rearing system will be determined by chemical analysis and bioassay and then a suitable method for delivery of that concentration range developed. There are strains of bees in France, Sweden and Germany exhibiting a trait termed "Suppressed Mite Reproduction" by which varroa have reduced reproduction. By performing the oviposition bioassay and chemical analysis, we will test the hypothesis that altered levels of larval volatiles or OK are the basis for the reduced varroa reproduction on these bee strains. Finally, we will assess if larval volatiles or OK can induce varroa to lay eggs even when in an inappropriate scenario such as while on adult bees.