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

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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.