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

气候变化正在严重影响地球生态系统的功能。特别是，干旱和气温升高影响了草原和种植系统的植物生产，这可能在未来导致产量下降，并威胁到不断增长的人口的粮食生产。大多数人都非常熟悉干燥炎热的夏天对他们花园的影响：草变成棕色，花垂下头，如果你不给它们浇水，它们甚至可能会死亡。所以，植物的日子不好过，但地下的影响更糟。大约一半的植物生物量隐藏在地下，土壤中生活着数百万我们肉眼看不到的微小生物，比如真菌、细菌、线虫（微小的蠕虫）、弹尾虫和螨虫。尤其是细菌，它们在最小的土壤孔隙中都有成千上万的细菌，它们不能很好地应对干旱。因为它们有半透性的细胞壁，干旱会导致它们的细胞萎缩和死亡。重新湿润后，它们膨胀并爆炸。真菌在土壤中发挥着许多与细菌相同的功能，它们比细菌更能应对极端干旱：它们的细胞壁更坚固，生长速度比细菌慢，这使它们更有可能抵御干旱等压力。相反，气候变暖使真菌和细菌都加快了速度——它们更加努力地工作，因此，它们消耗了更多的能量，可能也无法应对干旱的影响。我们现在开始发现，地下对气候变化的反应与地上对干旱的反应一样重要。细菌和真菌分解有机物并释放植物生长所需的营养物质，它们的活动与植物密切相关。就像奶牛和兔子吃地上的植物一样，土壤生物也吃植物的根，但植物的根也会释放大量的碳（主要是以糖的形式）到土壤中。根系分泌物的一个功能是为土壤微生物提供燃料，而土壤微生物反过来分解有机物，释放出土壤中锁在植物生长所需的营养物质。最近的证据表明，根系分泌物在生态系统对气候变化的响应中起着至关重要的作用：它们可以促进干旱后土壤生物和群落的恢复，也可能恢复其功能。然而，对于植物根系分泌物的差异，以及根系分泌物本身如何受到干旱的影响，人们所知甚少。本项目旨在研究植物根系及其分泌物如何影响生态系统对干旱和变暖的响应及其功能。它将重点关注草原，草原覆盖了世界的很大一部分，对生物多样性和碳氮储存至关重要。由于我们对植物根系分泌物的不同方式和原因知之甚少，我们将首先研究不同的根系系统如何影响根系分泌物的组成，以及根系和根系分泌物本身如何对干旱和变暖做出反应。然后，通过实验室和田间试验相结合，我们希望找出根系及其分泌物如何影响土壤细菌和真菌对干旱和变暖的反应，以及它们如何影响长期生态系统对干旱和变暖的反应。这项研究将与植物代谢组学（Roy Goodacre）和植物生理学（Giles Johnson）、植物-土壤相互作用（Richard Bardgett）和微生物生态学（阿伯丁大学的Jim Prosser）领域的世界领先科学家合作完成。这项工作的结果可能用于增加生态系统对气候变化的抵抗力，例如通过播种特定的植物物种，或通过为植物育种计划提供信息。

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.