Extreme rainfall: Unravelling the importance of new climate-rhizosphere feedbacks across contrasting land use systems

Terrestrial ecosystems play major roles in determining global climate-ecosystem feedbacks, through exchange of greenhouse gases (GHG), and carbon (C) storage in soil and vegetation. There is mounting evidence that climate change is resulting in increased frequency of extreme weather. Studies of the impacts of extreme weather on climate-ecosystem feedbacks are limited because of their unpredictable nature, and our inability to predict events in space and time. However, evidence is building that climate extremes have significant impacts on a range of vital ecosystem functions.

Plant roots are associated with diverse microbial communities which constitute the rhizosphere 'microbiome', the composition and function of which varies significantly between land uses, reflecting differences in the dominant plant species, the intensity of management practices, and consequent differences in soil physico-chemical characteristics. Almost nothing is known of the way in which extreme weather affects the rhizosphere microbiome, and the consequences for climate-ecosystem feedbacks. Climate change is predicted to increase the frequency of intense rainfall events, which can result in soil saturation via flooding or rise in groundwater, leading to hypoxic or anoxic conditions which promote GHG production, and change microbial communities. We were able to study the effect of a natural extreme rainfall event in 2012, the wettest year since records began, on the rhizosphere microbiome, in the field, for the first time. We revealed that prolonged saturation in an agroforestry system reduced the abundance and diversity of beneficial ectomycorrhizal fungi, while increasing abundance of pathogenic and saprotrophic fungi.

We hypothesise that these effects will have profound and previously unrecognised impacts on climate-ecosystem feedbacks, operating through altered plant-soil C flux, GHG emissions and plant productivity. We anticipate that these feedbacks will depend on the extent and longevity of O2 depletion (reflecting seasonal timing and duration of rainfall) and Interaction with ecosystem parameters, including rhizosphere microbiome composition, which vary according to land use system and management intensity. Here we will unravel these feedbacks and interactions for the first time.

We will set up macrocosms with intact soil cores and vegetation from contrasting land uses on a gley soil in Lincolnshire, where our earlier work was conducted; low management intensity permanent pasture and agroforestry, intermediate management intensity grass-arable, and high management intensity arable. We will simulate growing season and non-growing season saturation typical of long term (4 week) and extreme (8 week) durations. We will investigate the effect of saturation treatments on the response and recovery of GHG emissions and the rhizosphere microbiome. We will focus on the frequency, abundance and connectivity of communities at both taxonomic and functional levels. Importantly we will consider communities in a holistic manner, allowing us to compare responses of eukaryote (eg fungi, protists, nematodes), bacterial and archaeal groups to saturation. In this way we will provide fundamental new understanding of community responses to disturbance events. We will label plants with a stable isotope of C which can be differentiated from background C. This will allow us to investigate the long term effect of saturation on the amount of C which flows from the plant to the soil, the proportion retained as soil C or respired, amounts retained in the microbial biomass, and the effects of saturation on 'priming' of C release form native soil C.

The programme will characterise previously overlooked effects of extreme weather on climate-rhizosphere feedbacks, delivering a step-change in our fundamental understanding of the responses of ecosystems to extreme weather, and the role of land use, including management intensity, in mediating these responses.

This project will deliver improved understanding of rhizosphere-climate change-feedbacks and rhizosphere function. Our research will impact a range of non-academic beneficiaries including policy makers, land managers, the general public and schoolchildren.

The data we generate will prove valuable to policy makers and stakeholders interested in predicting and managing extreme weather events, and policy related to climate change. This includes the Department for Energy and Climate Change, Environment Agency, the Department for Environment, Food and Rural Affairs and the UK Met Office. We will make data available to this group which will be valuable for modelling and predicting climate feedbacks following extreme rainfall events. Ultimately this will improve the evidence base for policy decisions relating to climate change. We will invite modellers involved in the Joint UK Land Environment Simulator (JULES) from the Met Office and Centre for Ecology and Hydrology to our stakeholder workshops at Warwick to stimulate data and knowledge exchange with this group.

Land managers will benefit from this work by providing understanding of the effects of climate change on soil, particularly consequences for GHG emissions, plant growth, and plant health, and the ecosystem properties which control resilience to perturbation from soil saturation. This includes the Forestry Commission and farmers. We anticipate additional interest from land managers and policy makers on issues surrounding restoration of riparian buffer strips and their potential for flood and pollution control, particularly the trade-offs for climate feedbacks.

The PIs have strong working links with key policy stakeholders through previous and current large scale consortium projects, including land managers, industry, farmers, Environment Agency, Forestry commission, DECC and Defra. This existing network and infrastructure will be used in the current project to disseminate project findings, and place the results and significance of the project in a context relevant for stakeholders. We will form a project steering group with industrial and government stakeholders which will advise on knowledge exchange. We will engage with stakeholders through workshops at Warwick in month 20, project newsletters and the project website, which will provide a summary of project progress.

The general public will benefit through increased awareness of the way in which climate change will affect UK and global habitats, and the feedback processes by which extreme weather can exacerbate climate change. We will disseminate research to the wider public through twitter, school events and science festivals

Society will benefit from trained researchers adept at multidisciplinary working using state of the art methodologies to unravel plant-soil-climate feedbacks.