Karlsruhe Institute Of Technology Researchers Discover Biochar Base Drives Plant Response

Phosphorus is one of the most commonly used fertilizers worldwide, with German agriculture alone using 115,000 tons a year. But natural phosphorus deposits are shrinking. An alternative could be biochar, a special biochar that is produced when biomass is burned. However, it was previously unclear how the combination of Biochar and the widespread mycorrhizal fungi affects the plants. Researchers at the Karlsruhe Institute of Technology (KIT) have now shown for the first time using gene expression analysis that the “response” of tomato seedlings to the mycorrhizal symbiosis – and thus their phosphate nutrition – depends on the starting material of the biochar. The results are published in Science of the Total Environment .

Biochar has been intensively researched as a replacement product for phosphate fertilizers for several years. Biochar is a recycling product resulting from the pyrolysis of biomass. Organic starting materials are burned at temperatures between 400 and 700 degrees Celsius without oxygen. The basis of Biochar can be very different: for example, wood residues, chicken manure or leaves can be processed into fertilizer. But research in recent years has shown that plants react differently to Biochar: Some grew better, others reacted as if they were not fertilized, and others were even toxic to the plant.

Now an interdisciplinary KIT team, consisting of researchers from the Joseph Gottlieb Kölreuter Institute for Plant Sciences (JKIP) and the Institute for Technical Chemistry, has found out using the example of tomato seedlings that the origin of the Biochar biomass is decisive for the symbiosis with the naturally occurring soil occurring arbuscular mycorrhizal fungi (AM fungi).

In a first experiment, the team examined the sole effect of Biochar from wheat straw and chicken manure. Chicken manure biochar contained nine times more phosphate than wheat straw biochar. Phosphate is the soluble form of phosphorus combined with oxygen. It is an essential molecule for plant growth. “As expected, the tomato seedlings that we fertilized with chicken manure biochar grew quickly and vigorously,” explains Professor Natalia Requena, an expert in molecular phytopathology at JKIP. “They had a lot of phosphate available that they could process directly.”

Symbiosis with micro-fungus ensures long-term growth of the plant

In the second experiment, the researchers colonized the tomato plants with AM fungi. The micro fungi have existed on earth for more than 400 million years and live in the roots of 80 percent of land plants. They settle in their bark, absorb phosphate and pass it on to the plant. In return, the plant supplies them with sugar and lipids.

By observing selected molecules, the researchers were able to show that the phosphate-rich biochar based on chicken manure impaired this symbiosis between tomato and AM fungi: there was hardly any molecular exchange. The Biochar based on wheat straw did the opposite: plants and micro-fungi developed a lively symbiosis. “In the long term, these plants fertilized with Biochar based on wheat straw are more compatible with other microorganisms and are therefore better protected against pathogens,” explains Requena. “We did not expect such a complex molecular response from the plants.”

Understand cells better – fertilize less in the future

The team was able to demonstrate these results by using gene expression analysis: “This is a complex, expensive method, but it makes it possible to see what is happening in the plant’s genes and which markers are stimulated or not,” says Requena. Further experiments are now necessary to better understand the response of the plants. “If we decode this, we can program plants in the long term so that they need less phosphate and thus less mineral fertilizer,” says Requena.

This research is supported at KIT as a university of excellence project KIT Future Fields “Plants fit for Future” (PffF). In this network, the researchers are looking for ways to make plants fit for a future in which phosphorus fertilizers are scarce and pesticides will be largely banned from our fields.