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Even plants can have neighbour trouble

Restoring a natural plant environment on exhausted agricultural lands and in nature areas is difficult. We can speed this up by steering the soils towards the desired situation. This is what Martijn Bezemer, newly appointed Professor of Ecology of Plant-Microbe-Insect interactions at Leiden University’s Institute of Biology Leiden, argues. Inaugural lecture 18 December.

Research on soil life has increased over the past twenty years. ‘From that moment on, the black box was opened, and researchers unravelled the world beneath their feet,’ says Bezemer. ‘Underground soil organisms may look dirty, scary and nasty, but we now know that they are very important for everything that happens above and below ground and thus what they mean to us.’

Neighbour trouble

Together with plants, organic substances, bacteria and fungi, these underground soil organisms form a soil food web. It was hard to imagine that every plant maintains a unique food web in nature where many different plants live together. However, fieldwork showed that all plants in a grassland have their own soil food web, which is different from other plants.

But neighbouring plants do influence the soil food web of an individual plant. ‘You don’t get to pick your neighbours, and underground, too, plants can suffer from the presence of a particular neighbour,’ according to Bezemer.

Insect pest

‘We have been busy for a while now describing the soil and its interactions. The challenge is to find out what we can do with this knowledge,’ Bezemer explains. One example is in horticulture, where growers steam the soil to get rid of the harmful organisms that are present. This steaming also destroys the useful organisms. Recently, Bezemer and his colleagues discovered that, beside this steaming, the addition of other specific soil food webs made the plants more resilient against thrips. Thrips are minute insects that are a major and persistent  problem in horticulture. ‘This discovery opens up many new possibilities for the sector.’

Faecal transplant

Bezemer compares introducing a different soil to change the soil food web with a faecal transplantation. ‘This is a  process by which  a watery faecal solution from a healthy person is introduced into the intestine of a patient with a bowel problem to obtain a healthier gut flora.’

'You can easily insert something new into the steamed soil, because there is no competition. That is much more difficult when there is an existing food web, as in nature areas,’ Bezemer comments. Still, he and his colleagues succeeded in applying this technique on a grassland in the Veluwe. They scattered a few millimetres thick layer of soil of a species- rich grassland and heathland in the new nature area. Vegetation already started growing within a few years with species characteristic for those other locations.

Intervention

With his transplantation research Bezemer does not simply let nature take his course. ‘When the soil is wrong, you get the wrong plants. Those plants will keep stimulating the soil and vice versa, and if you allow that to continue, you will never get the soil and plants you want,’ Bezemer explains. ‘So, we intervene and speed up the soil processes to achieve that species-rich grassland or heathland earlier.’ Meanwhile this technique is now being applied to nature restoration in the Netherlands.

Future

Bezemer wants to exchange the grassland of the Veluwe for the sandy soil of the dunes. Together with the Institute of Environmental Science in Leiden he is setting up a field experiment in the dunes where researchers will compare the effectiveness of different soil transplantations on dune ecosystems. ‘This is also a good platform for students. Nowadays a lot of education and research take place in the laboratory, but it is still important for students to experience fieldwork. This way the generation of the future is working on the soil of the future.’ Bezemer hopes to start the measurements in the spring.

The chair held by Martijn Bezemer at Leiden University is an honorary position; Bezemer also works for NIOO-KNAW. 

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