Plant-soil interactions: the cycle of life

Last spring, I gave a TED talk about plant-soil interactions and their importance in the global carbon cycle at a TEDx event organised by Amsterdam University College. You can watch the video below, but for those of you who rather read (actually, I am one of those people, as I never have the patience to watch a video from beginning to end!) you can also read the full text below.

Do you ever think about soils? Do you ever think about soils, other than, when your boots are muddy, or your vegetables dirty? Well, I’m going to talk about soils.

Soils! Without soils, we would not be here. Soils sustain all life on land. And that is because all energy flows through soils, via photosynthesis and respiration.

Have soils always been here?

No!

Have you ever thought about how soils are formed? Where plants came from? And the tiny invisible microbes that live in the soil?

More than 4.5 billion years ago, there was no soil. There wasn’t even life. There were only oceans. But somewhere between 4.5 and 3.5 billion years ago, the first microorganisms appeared in the oceans. There wasn’t even free oxygen at that time! But then, photosynthesis evolved in bacteria, and cyanobacteria started producing oxygen around 2.7 billion years ago. About 1.5 billion years ago, the first fungi appeared, and much later, around 500 million years ago, the first land plants arose. Probably, photosynthesis in these plants was derived from photosynthetic bacteria inside plant cells (the endosymbiosis theory). Those first land plants – like this little liverwort – had no, or very rudimentary roots (remember, there was no soil that they could grow their root in, only rock!), and were likely helped on land by symbiotic fungi. 

And this is where soil started to form. 

Why are Dutch farmers and builders angry and why have I started tweeting in Dutch? The Dutch nitrogen crisis.

You might have seen it in the news: Dutch farmers ravaging cities with their tractors. But this week also builders, contractors, dredgers, and gardeners have protested in The Hague, where our government is based. They are angry, because a lot of their activities and projects have been halted, and farmers in the vicinity of protected natural (Natura 2000) areas might have to move or be bought out.

Why? Because of the Programma Aanpak Stikstof (PAS), a programme designed to reduce nitrogen deposition in Natura 2000 (a European network of protected natural areas) areas while still allowing economic growth and development. Cleverly, this programme allowed nitrogen-emitting activities in the vicinity of these areas if there were planned compensating measures to reduce future emissions, as well as future measures to reduce the degradation of Natura 2000 areas. So, essentially, taking a mortgage on future compensating measures. But on the 29^thof May 2019, the Council of State judged that the PAS could no longer be used to allow nitrogen-emitting activities, because this is challenging European law.

So now, according to some people, The Netherlands is in lock-down. Building projects have been halted, and Dutch livestock numbers need to be reduced. Of course it is understandable that builders and farmers are upset; they are just trying to protect their livelihood.

What is the current weather doing to our soils?

There has been plenty of media coverage of the current extremely hot and dry weather. The drought is revealing archaeological features, (see also here), and we can even see the browning of our landscape from space. But this drought is not good news for our ecosystems at all, and one example of that are the recent wildfires in the Peak District. These fires are not just bad news for the plants and animals that live there, but also they make large amounts of carbon that have been sequestered over many years go up in the air as CO₂, and this can amplify climate change. Drought also affects our ecosystems more subtly than that, but the long-term consequences might be as severe.

We can all see the effect the drought is having on plants: lawns are turning yellow, corn leaves are rolling, and in extreme cases, trees even lose their leaves. They become inactive, and can even die. This is not just bad news for the plants, it is also bad news for the soil. When plants stop growing, they are not photosynthesing, and when they are not photosynthesising, they are not removing CO₂from the atmosphere. A large part of this photosynthesised CO₂ goes straight into the soil to fuel the activities of microbes, which carry out important functions such as the decomposition of plant litter and the release of nutrients for plant growth.