Controls on the stability of soils and their functioning under land use and climate change

Lead Research Organisation: University of Manchester
Department Name: Earth Atmospheric and Env Sciences


Soils provide many functions for humans, including the storage of carbon and nutrient cycling, which are crucial for the production of food and mitigation of climate change. However, there is much concern that soils, and the functions that they provide, are being threatened by a range of pressures, including intensive farming methods and increased frequency of extreme climatic events, such as drought. Not only do these disturbances pose an immediate threat to the functioning of soils, but they could also impair their ability to resist and recover from further stresses that come in the future.

Our project will tackle this problem by addressing two general questions: first, what makes a soil able to withstand and recover from disturbance events, such as drought, and, second how can we use this knowledge to ensure soils can buffer disturbances in the future? These are questions that have puzzled soil scientists for many years, but so far, remain unresolved. An area that offers much promise, however, in tackling this issue is food web ecology. Food webs are the networks of interactions describing who eats whom amongst the myriad organisms within an ecosystem. And in soil, they are the engine that drives the very processes of nutrient cycling and energy flow on which the functioning of soil and the terrestrial ecosystems they support, depend. It has been proposed for many years, but so far not fully tested in soil, that simple food webs are less able to withstand and recover from disturbance events, such as drought than complex ones. We want to test this theory in soil, which harbours some of the most complex, but also sensitive, food webs on Earth. We test the idea, through experiments and models, that the ability of a soil to withstand, recover and adapt to disturbance events depends on the architecture and diversity of the soil food web, which governs the rate of transfer of nutrients and energy through the plant-soil system. We also propose that soil disturbances associated with intensive land use, such as trampling and fertiliser addition, erode the very food web structures that make the soil system stable, thereby reducing the ability of soil to resist and recover from future disturbances, such as extreme weather events. We will also resolve what makes a food web stable, and test the roles of different types of organisms in soil, such as mycorrhizal fungi, which we believe play a major role. And finally, we will develop new models to help us better predict how soils will respond to future threats and to guide management decisions on sustainable soil management in a rapidly changing world.

These question are at the heart of the NERC Soil Security programme which seeks to resolve what controls the ability of soils and their functions to resist, recover and ultimately adapt, to perturbations, such as those caused by land use and extreme climatic events.

Planned Impact

Who will benefit from our research?

Project beneficiaries will include the bioscience, ecology and wider scientific research community interested in sustainable and productive food production. Key stakeholders include landowners, farmers groups (e.g. NFU, SNFU, NFUW, HCC, EBLEX, QMS, Soil Association), societies (BES, BSSS), conservation bodies (Plant Life, The Grassland Trust, British Grassland Society, Wildlife Trusts) and local and national government departments (Defra; EA) and agencies (SEPA; EA, Natural England; Countryside Council for Wales, Scottish Natural Heritage) who will benefit as science supported policy develops. We will liaise with BSSS and the Global Soil Partnership to ensure our project goals are integrated into the planned activities for International Year of Soils 2015.
Other beneficiaries are commercial organisations involved in habitat restoration, in particular, horticultural businesses that supply native seed and seed mixes. These businesses stand to benefit from our research through learning (via knowledge exchange; KE) how drought, land management and soil conditions influences communities to resist and recover from the effects of climate change. These organisations also have a financial interest in being able to produce seed mixtures that are stress resistant, and that are more likely to result in habitat restoration that remains successful over the long-term.

It will be vital that our findings are communicated to non-academics and non-researchers within the plant breeding community and end-users. Engagement with these groups will be facilitated though two stakeholder workshops, and through interaction with the Cool Farm Alliance, an umbrella organisation that liaises with numerous businesses with interests in agricultural-related matters. We will also showcase our findings and portfolio of expertise through presentations to farmers groups, building on our existing network forums, public talks and online resources (e.g. You Tube).

How will they benefit from our research?
Data generated in this project will have major implications for our potential to alter soil C and N cycling through land management. A key component of the work is the integration of empirical data with predictive models: this opens up opportunities to gain rapid insight into how specific environmental and edaphic contexts may affect the ability of soils to resist, recover and adapt to perturbations such as drought. Our work will open up the possibility for input of our mechanistic framework into farm management systems, aimed at, for example, coupling enhanced/sustained yields (cf food security) with C storage potential and mitigation of greenhouse gas emissions.

Members of the general public will benefit through (i) an enhanced awareness of climate impacts on biodiversity, (ii) increased knowledge of the role of natural ecosystems in providing valuable goods and services to humanity, and (iii) the role of science in improving the conservation and management of grassland ecosystems and in underpinning our understanding of how the landscape can function for our collective benefit.
Description The project began in 2015 and five experiments involving the entire soil security project team have been completed: a pilot study on the impact of drought and flood on soil communities and processes; another pilot study of the flow of 13C through differently structured soil food webs in response to drought; a glasshouse study of the mechanisms controlling soil food web structure and their response to drought; and two field experiments, done over summer 2016 and 2017, looking at the stability of soil food webs subject to drought and land use change. The latter experiments involved a nationwide sampling programme of intensive and extensive grasslands (n = 15 sites, each with paired extensive and intensive fields) subjected to drought or not, followed by intensive sampling of the soil food web over time. One of the pilot experiments have been published in the journal Global Change Biology (Chomel et al. 2019), the other one have been completed and data analyses are underway, and paper writing is currently underway. As for the glasshouse and field experiments, sample analysis is nearly complete and data processing is underway. Our project has generated a number of key findings that are currently being written up for publication in leading journals. Key findings include:

1. Drought modifies C incorporation into the soil food web. In this study (Chomel et al 2019), we investigated how soil food web composition modulates the response of soil functions related to C cycling and the capture and transfer below-ground of recent photosynthate C by plants to drought. For that purpose, we built microcosms containing soil from semi-natural acid grassland, and examined how simplified food webs (with 1, 2, or 3 trophic groups) and drought influence mycorrhizal fungal abundance, decomposition and soil CO2 efflux, and the flux of C from a common temperate grassland plant species, Agrostis capillaris, to soil organisms using 13C stable isotope labelling. Overall, our results show that drought and soil food web composition do not interact to affect C cycling and microbial community composition, but there were independent effects of each factor on C cycling, with an overall stronger effect of drought. Under drought, the net uptake of 13C by plants was reduced and its retention in plant biomass was greater, leading to a strong decrease in carbon transfer below-ground. This study emphasises the sensitivity of critical pathways of C transfer from plants to soil organisms, and predict that below-ground C flow will be lowered with increasing drought predicted with climate change.

2. Soil food web structure mediates stability of soil food webs across UK grasslands. In this study we aimed to relate changes in the soil food web that can result from differences in land management intensity to the resistance and resilience of those food webs, and their functioning, to drought. We identified 15 grassland sites across three regions of the UK (Devon, Yorkshire Dales and Scotland), each site having paired grasslands under intensive and extensive management, which had resulted in differently structured food webs. We measured multiple dimensions of stability of biomass production of entire food webs and their components, in three ways: variation over time, resistance to a drought event, and resilience after the drought event. We mimicked a drought event by subjecting each site to 8 weeks of simulated summer drought using rain shelters. We measured multiple facets of food web structure, including diversity metrics, fungal and bacterial energy channels, asymmetry and flow of energy through the food webs. Initial analysis indicates that abiotic factors such as pH and climate structure the soil food web, and this structure has a mediating effect on the stability of the soil food web over time and in response to drought. Analysis is ongoing and we aim to relate the stability of the food web to its functioning, in terms of carbon dioxide production and plant productivity. As part of this study, we also conducted stable C and N isotope pulse-chase labelling. Results of the labelling indicate that intensive management reduced 13C net transfer to plant roots, mycorrhizal hyphae, soil fungivorous fauna and soil CO2 efflux indicating a reduction of the carbon transfer from the plant to belowground though mycorrhizal pathway with land use intensification. Plant shoot C uptake and transfer to roots are impacted by drought in intensive grassland, but there is no effect in extensive grassland. This could indicate that plant communities are less resistant to drought in intensively managed grassland. Our results indicate that the overall soil activity rely proportionally less on plant-derived carbon in intensively managed grassland

3. Dominant soil microbial taxa are highly resistant and resilient to drought in UK grasslands. We took samples from the above study and sequenced the bacterial and fungal communities, in collaboration with NERC Soil Security project lead Rob Griffiths. We classified resulting microbial taxa as dominant if they were found across all studied regions and represented the top 10% of taxa when organized by their relative abundance. Dominant bacteria represented 84.6% of all bacterial reads, and dominant fungi represented 63.0% of all fungal reads. We found that 88% of dominant bacterial taxa and 86% of dominant fungal taxa were tolerant to drought. In addition, 5% of dominant bacterial taxa and 7% of dominant fungal taxa were opportunistic, increasing in relative abundance in response to drought. Intensive management increased the relative abundance of opportunistic and tolerant taxa, but had no effect on the relative abundance of sensitive taxa. In general, all dominant taxa recovered to control levels after 60 days of recovery from drought, indicating high resilience of these communities. These novel results show that the majority of microbial taxa found in UK grasslands are resistant and resilient to drought, which may help to explain why these taxa dominate bacterial communities. This study will be submitted in a high profile journal in spring 2020.

4. Physical disturbance and nutrient addition alter the structure of the soil food web and its resistance and resilience to drought. We constructed field disturbance matrices - with factorial combinations of two levels each of trampling and fertiliser N additions - in order to analyse the impact of disturbance on soil food web structure. We then collected intact cores from the matrices and subjected them to drought in a controlled glasshouse environment, to quantify the resistance and resilience of the soil food webs and soil functions. Initial results show that trampling decreased plant root biomass and fungal biomass, and N additions decreased fungal biomass. Ongoing analysis will explore the effects of these changes on the soil food web and its functioning, as well as its resistance and resilience to drought in the glasshouse. As part of this study, we conducted stable 13C and 15N isotope pulse-chase labelling, and analysis is ongoing. It is too early to draw firm conclusions from this study as data analysis is ongoing.
Exploitation Route Modellers of nutrient cycles need to consider soil food webs, especially in relation to understanding the effects of drought and other perturbations on ecosystem function
Sectors Agriculture, Food and Drink,Environment

Description We have collaborated with National Trust to develop new ways of designing management incentives for farmers to maximise soil health and ecosystem services
First Year Of Impact 2019
Sector Agriculture, Food and Drink,Environment
Impact Types Societal,Policy & public services

Description Public Talk 
Form Of Engagement Activity A talk or presentation
Part Of Official Scheme? No
Geographic Reach Local
Primary Audience Public/other audiences
Results and Impact Talk to the Cheshire Wildlife Trust on mycorrhizal fungi
Year(s) Of Engagement Activity 2018
Description Science X 
Form Of Engagement Activity Participation in an activity, workshop or similar
Part Of Official Scheme? No
Geographic Reach Regional
Primary Audience Public/other audiences
Results and Impact A free, interactive festival of exploration and experiments and a great chance for kids to discover the fun behind science and engineering!
Year(s) Of Engagement Activity 2019