The root to stability - the role of plant roots in ecosystem response to climate change

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

Abstract

Climate change is severely affecting the functioning of the Earth's ecosystems. Particularly, drought and increased temperatures affect plant production in grasslands and cropping systems, which might, in the future, lead to lower yields and threaten food production for a growing population. Most people are very familiar with the effects of a dry, hot summer on their garden: the grass turns brown, flowers hang their head, and if you don't water them, they might even die. So, plants are having a hard time, but the effects belowground are even worse. About half of a plant's biomass is hidden belowground, and the soil is inhabited by millions of tiny creatures that we can't see with our bare eyes, such as fungi, bacteria, nematodes (microscopic worms), springtails, and mites. Especially bacteria, which populate the tiniest soil pore with thousands, don't cope very well with drought. Because they have semi-permeable cell walls, drought causes their cells to shrivel and die. After rewetting, they swell up and explode. Fungi, which perform many of the same functions as bacteria in the soil, are better able to cope with extreme drought than bacteria: they have stronger cell walls and are slower-growing than bacteria, which makes them more likely to resist stresses like drought. Warming, in contrast, makes both fungi and bacteria switch to a higher gear - they work harder, and by doing so, they use up more energy, and might be less able to also cope with the effects of drought.

We are now beginning to discover that the belowground responses to climate change are as important as the aboveground responses to drought. Bacteria and fungi break down organic matter and release nutrients for plant growth, and their activities are tightly linked to plants. Like cows and rabbits graze on aboveground plant parts, soil organisms graze on plant roots, but plant roots also release significant amounts of carbon (mostly in the form of sugars) into the soil. One function of root exudates is providing fuel for soil microorganisms, which in turn break down organic matter and release nutrients that are locked up in the soil for plant growth. Recent evidence shows that root exudates play a crucial role in the response of ecosystems to climate change: they can enhance the recovery of soil organisms and communities after drought, potentially also restoring their functions. However, very little is known about how and why plants differ in their root exudates, and how root exudates themselves are affected by drought.

This project aims to investigate how plant roots and their exudates affect the response of ecosystems and their functioning to drought and warming. It will focus on grasslands, which cover a large part of the world, and are crucial for biodiversity and carbon and nitrogen storage. Because so little is known about how and why plants differ in their root exudates, we will first look at how different root systems affect the composition of root exudates, and how roots and root exudates themselves respond to drought and warming. Then, in a combination of laboratory and field experiments, we want to find out how roots and their exudates affect the response of soil bacteria and fungi to drought and warming, and how they might affect longer-term ecosystem response to drought and warming. This research will be done in collaboration with world-leading scientists in the field of plant metabolomics (Roy Goodacre) and plant physiology (Giles Johnson), plant-soil interactions (Richard Bardgett), and microbial ecology (Jim Prosser, the University of Aberdeen). The results of this work might be used to increase the resistance of ecosystems to climate change, for example through sowing specific plant species, or by informing plant breeding programmes.

Technical Summary

Climate change can severely impact on plant production in grasslands and cropping systems, which might, in the future, lead to lower yields and threaten food production for a growing population. Despite many efforts, we still know very little about the factors that determine the response of ecosystems to drought and warming, which are predicted to increase with climate change. This is in part because most research in this area has focussed on aboveground responses of plant communities, whereas evidence is now emerging that belowground components of ecosystems, such as plant roots and soil organisms, are as strongly affected by climate change as aboveground components.

Plant roots release substantial amounts of carbon (C) belowground, which fuel microorganisms to break down organic matter and release nutrients, thus benefitting both soil microbes and plants. These root exudates - complex mixtures of sugars, amino acids, organic acids, and signalling molecules - have been proposed to be the key to increased soil carbon storage, but they can also enhance the recovery of soil communities after drought, thereby potentially also restoring ecosystem functioning. However, we know very little about how plants differ in their root exudates, and even less about how roots and their exudates themselves are affected by climate change.

This project aims to elucidate the mechanisms through which plant roots modify the response of ecosystems to drought and warming, using grassland, which cover a large part of the UK and are crucial for C and nitrogen (N) storage, as a model system. Combining metabolic profiling and next generation sequencing, it will establish how root exudates vary between grassland species, and how these in turn affect plant and microbial community composition and ecosystem functioning under drought and warming. This knowledge might be used to inform future breeding and management strategies to increase the resistance of ecosystems to climate change.

Planned Impact

Who will benefit from this research and how?

Scientific community:
The project will address novel, unanswered questions about the stability of ecosystems, about the mechanisms that underlie the response of plant and microbial physiology and communities to climate change, and about temporal changes in microbial communities, both under ambient conditions and under drought and warming. These questions will be addressed using, and developing, state-of-the-art techniques, including metabolomics and next-generation sequencing. New discoveries in these areas will benefit the scientific research community, including soil scientists, ecologists, plant physiologists, and microbiologists, but also the wider research community of people interested in sustainable food production and the sustainable management of soils, and in the dissemination of these findings, for example initiatives like the Global Soil Biodiversity Initiative.

Stakeholders:
The proposed research will identify specific grassland species that increase the resistance of communities and ecosystems under climate change, as well as identify root traits that contribute to plant and ecosystem resistance to drought and warming. This will provide tangible management strategies for increasing the resistance of grasslands by promoting or seeding specific plant species, which can be recommended by policy makers and farmer groups, and adopted by growers and landowners. Our research can also be used by crop breeders to promote the identified root traits in grasses and other crops, such as cereals, to increase their resistance to drought.

UK consumers and citizens:
The research will benefit UK consumers and citizens by underpinning future policy and crop breeding strategies for securing sustainable food production in a changing world, and protecting highly valued, biodiverse grasslands. In addition, our science will underpin future policies and incentives for increasing soil carbon storage and mitigating climate change. Together, these outcomes will increase the quality of life of UK citizens.

Staff working on the project:
Finally, all people involved in this project will benefit by being trained in this highly relevant and timely research area, and by gaining transferrable skills that can be used in any employment sector. Any other PhD students working in my group will also benefit from ongoing work within the proposed project, especially from the field experiment, which will offer opportunities to do add-on and linked experiments.
 
Description We have developed an ecologically relevant method for collection root exudates, and we show that this method is more appropriate than previously used methods.
We have characterised the root exudates of >30 grassland species using our new method, and found that the quality and the quantity of root exudation is explained by root traits (the shape and structure of the root system).
We have discovered that root exudates from drought plants increase soil respiration, and that this increase compensates for the loss in respiration as a consequence of the absolute reduction in root exudate production under drought.
Exploitation Route Our findings suggest that plant root exudation can be seen as a root trait, and that plants actively control root exudation in response to changing environmental conditions. These findings pose a large number of follow up questions:
- is this common across all plants?
- which genes are switched on and off in this process?
- what are the implications for subsequent plant growth and community composition?
- what are the implications for soil C storage?

I have been awarded an ERC Starting Grant, in which I will investigate the role of plant root exudation for plant community response to drought, via modifying the composition and activity of the soil microbial community.

I am also applying for a CSC studentship to investigate what the consequences of drought-induced changes in root exudation are for ecosystem C cycling.
Sectors Agriculture, Food and Drink,Environment

 
Title Root exudate extraction 
Description This method allows the extraction of root exudates from undamaged roots that have developed in a normal soil environment, and consists of four steps: 1. Grow plant in soil until desired developmental stage 2. Wash soil off roots 3. Prepare hydroponic solution consisting of soil extract 4. Transfer plant roots into hydroponic solution and leave to grow and recover for 1 week 5. Transfer plant roots into sterile water and leave for 1 hour at 4 degrees C to extract root exudates 
Type Of Material Biological samples 
Provided To Others? No  
Impact The extraction of root exudates from intact plant roots is notoriously difficult and riddled with methodological issues concerning root damage, root-soil-microbe interactions, sterility, link to real world conditions. The method we developed extracts root exudates from undamaged, normally developed roots (in the presence of soil microbial communities) and thus allows linking root exudate profiles to soil conditions and functioning. We are preparing a methods paper for this method. 
 
Description Collaboration with Dr Matthew Wallenstein 
Organisation Colorado State University
Department Department of Ecosystem Science and Sustainability
Country United States 
Sector Academic/University 
PI Contribution I was invitied to write a paper for a special issue of Journal of Ecology and I asked Matt to contribute and write the paper with me together.
Collaborator Contribution Input into the direction and content of the manuscript, writing sections of the manuscript, providing illustrations.
Impact De Vries, F.T. and M.D. Wallenstein (2017) Belowground connections underlying aboveground food production: a framework for optimising ecological connections in the rhizosphere. Journal of Ecology, In press.
Start Year 2016
 
Description Collaboration with Dr Tancredi Caruso 
Organisation Queen's University Belfast
Country United Kingdom 
Sector Academic/University 
PI Contribution I invited Tancredi to co-author a publication with me. I had the initial idea for this paper.
Collaborator Contribution Tancredi helped me model the conceptual model I was proposing.
Impact De Vries, F.T. and T. Caruso (2016) Eating from the same plate? Revisiting the role of labile carbon inputs in the soil food web. Soil Biology & Biochemistry 102:4-9.
Start Year 2016