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From microcosm to climate change

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They sit invisibly in the soil, on organic material, on roots and plant leaves. Millions of micro-organisms populate every grain of soil and every square millimeter of plant surface. Bacteria, fungi and yeasts are the most important organisms in this microcosm, which is increasingly becoming the focus of research. Because the smallest inhabitants of our planet have an unimaginably large influence, for example on our climate.​

When Dr. Steffen Kolb talks of "sinks and sources", he does not mean the geographical form of the terrain or water sources. According to Kolb, a sink is primarily the place where a substance is stored or consumed – for example carbon dioxide in wetland and forest soils. A source is exactly the opposite. A dairy farm, for example, is a source of methane because large quantities of this gas are produced in the stomachs of cows. It has long been known that methane is driving climate change. It is the second most important greenhouse gas, although it accounts for less than 0.002 percent of the atmosphere. However, the compound are responsible for up to 17 percent of climate change and is thus around 27 times as potent as carbon dioxide. ​


Greenhouse gas and cloudformers

Methane is only one of thousands of so-called trace gases in the atmosphere whose effects on the atmosphere we know little about so far. Some of them stimulate cloud formation, others are involved in the formation of ozone or contribute to climate change. Yet how these gases are produced, how they are converted within substance cycles and broken down again – many of these questions are still unanswered today. So far, only one thing is clear: microorganisms that live in soil and on plants play a central role in these cycles. 

Steffen Kolb takes a closer look at these organisms. He does not regard bacteria and plants as separate systems. For him, they form tight communities that are dependent upon and influence each other. He calls them "symbiomes". While the plant secretes volatile substances through its leaves, the micro- organisms sitting on them use exactly these substances to feed upon. In return, they provide the plant with water and nutrients. 

Kolb and other researchers are certain: Land use by humans significantly influences these communities of plants and microorganisms – and thus also the release of trace gases. Fertilization, tillage, crop rotation, but also the weather or the type of irrigation – there are numerous factors that determine whether the land used is a source or a sink for particular trace gases. "The balance on a field of arable land is different from the one in a forest", says Kolb. A corn monoculture harbors different microorganisms than a beech tree in an intact forest. And even a pine forest cannot be compared to a beech forest when it comes to the balance of trace gases. 

Which gases are formed in which concentrations by different crop plants and their tiny biological partners, Kolb and his team are investigating using cylindrical containers called incubation chambers. Located in the Leibniz Centre for Agricultural Landscape Research‘s (ZALF) own greenhouse, plants are grown individually under controlled conditions in these airtight chambers, where gases can be selectively introduced and removed. This makes it possible to analyze exactly which emissions are generated during the growing phase, for example.

Underestimated partnership

In order to carry out these observations on a larger scale and for entire agro-ecosystems, the researchers work outdoors with so-called gas chambers. The up to four-meter-high devices made of transparent plastic are placed over the crop plants to measure the concentrations of gases inside. In this way, the researchers receive gas flux data over the entire course of the year and can calculate in which season or with which crops a particularly large amount of greenhouse gases such as methane, nitrous oxide or carbon dioxide is produced or stored. 

Kolb and his team not only want to measure, but also understand the biological drivers of these processes – namely those systems that he refers to as "symbiomes": the ecological unity between plant and microorganisms. In doing so, they are faced with an almost inconceivable diversity: "There are at least 20,000 different species of microorganism in one gram of soil", he explains. Molecular biology aids in their analysis: From soil and plant samples, the researchers not only determine which types of bacteria, fungi, yeasts and plants are present. Using sophisticated methods in laboratory experiments, they can also detect which organisms consume or produce which gases and whether stress caused by heat or drought changes the patterns of emissions. 

​ "There are interactions between plants and microorganisms that we underestimate entirely", says Kolb. More research is therefore needed – especially as the delicate balance of the atmosphere is determined by these interdependencies. "We are constantly exerting influences on these systems without knowing exactly what effects it will have", warns the researcher. His "small-scale" research is an important piece of the puzzle for solving big questions. It is so important, in fact, that ZALF has started to build the "House of Agricultural Biome Research" this year in order to foster an even better understanding of the communities of crop plants and microorganisms in the future.


Text: Heike Kampe


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