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Soils and climate change – warming and drought

Soils and climate change – warming and drought
Hi, I’m Andrew Cole. I’m a PhD student here at Lancaster Environment Centre and also work in collaboration with the Centre for Ecology and Hydrology here at Lancaster. So I study the effects of climate change and particularly drought. And the reason to do this is that predictions for the future suggest that here in the UK our summers will get drier and drier. And not only will the average be drier, but also the extreme droughts, the time when we have no rainfall, they will become more frequent. So I work in the Yorkshire Dales, and that’s where I set up my field experiment.
And this is a national park in the north of England in the UK, and it’s really of interest to me because it has lots of small traditional farm communities and really plant species-rich hay meadows. So the way we study drought is to do it in the field, and this is really important because field experiments give a much more realistic prediction for how these communities will respond to climate change. So in my study, we do this by setting up rain shelters. So these are shelters made of plastic and wooden frames which we put into the field and they stop the rain reaching the grassland and stop it reaching the grasses.
So it cuts out a large percentage of the rain, simulating drought conditions, and we can see how the plants and the soil respond. So the soil where my field experiment is is what we call a “brown earth,” so this is quite a carbon-rich soil which was formed under deciduous forests sometime since the last ice age. And this is important because it’s quite free-draining, so it doesn’t hold the water and it doesn’t get water logged, which means there’s lots of life, lots of earthworms, lots of invertebrates in the soil. So it means that they mix it really well. Where we’re working, the vegetation is a species-rich grassland, and it’s an upland hay meadows, so it’s grown for hay during the summer.
And these species-rich grasslands are becoming increasingly rare. So recent survey suggests that in the Yorkshire Dales National Park only 5% of these species-rich grasslands remain. And this lost can have an effect on other animals and invertebrates. So the first effect of drought on these systems that we see is that soil gets drier and drier. so putting up these rain shelters reduces the soil moisture, so how much water there is in the soil, by about 45%. So the second thing we can measure in these systems is how much carbon dioxide gets cycled by the grassland. So the plants will be photosynthesising and taking out carbon dioxide, and releasing it into the soil just as carbon.
However the plants will also be releasing it back as carbon dioxide through respiration, and so will the soil. The bacteria and fungi and invertebrates will be respiring and releasing CO2 as well. So the effect of drought on this ecosystem is that the plants photosynthesize less, they take up less carbon. That means they also pass less carbon into the soil, microbial, bacterial, and fungi community. This means the soil respires less and releases less CO2. To measure this in the field, we use equipment which measures carbon dioxide in real time. So we plug it into a chamber placed over the grassland, and it tells us how many parts per million of the air is carbon dioxide.
So we can see that when we start it will be about 400 parts per million, but as photosynthesis takes on and takes over, this can decline. And sometimes on a hot summer day this can decline really quickly. So the other great thing about using this measurement of carbon dioxide in real time is that we can cut out photosynthesis and just measure respiration, that coming from the plants and the soil. To do this is really simple. We just place a dark chamber over the community. The plant realises no light, and they quickly shut down photosynthesising. This means we can see the parts per million of carbon dioxide increase as the plants and the soil are responding.
So it’s really interesting and important to understand what’s happening to carbon dioxide in these grasslands. This is because the results from my work shows actually how we manage these grasslands impact both the photosynthesis and the respiration under drought. So if we know what happens when we add fertiliser or change the plant diversity, it can help us with predictions on how these grasslands will respond to change. So when we’re in the field we also collect soil cores. And this is so we can bring the soil back to the lab and do further analysis. So one of these is looking at how much nitrogen is stored in the soil and how this respond to drought.
So my research has shown under drought the amount of inorganic nitrogen in soils, so that’s ammonium or nitrate in the soil, actually is increased. This is important as the build-up of nitrogen in the soil can have big impact. When the drought ends and we get a huge amount of rainfall, this nitrogen could be washed away into rivers or other water bodies, which can then affect their ecology. So overall my research has shown that understanding the soil responses to climate is really important and also quite complex. Particularly what plants are growing on it and how we humans interact with these habitats can have a big effect.
So following my research at this field site in the Yorkshire Dales, we have a good understanding of the effects of drought on the plants and the soils in this upland hay meadow. However, questions still remain to be answer. Do the patterns we see here also happen elsewhere in the UK, or even across the world? Further research is needed to see the global pattern and response to climate change.

Climate change is one of the most widely recognised changes that are happening in our environment at the moment, but what does it mean for soils?

In this short video Andrew Cole, a former PhD student at Lancaster University talks about his research into how warming and drought impact on grassland soils.

What effect would less rainfall have on the habitats where you live?

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Soil Science: Exploring the World Beneath our Feet

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