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Bacteria in plants produce nitrogen that might reduce commercial fertilizer use

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Environ beat

Often growing along the rocky riverbank, black cottonwood trees thrive in an environment with little to no soil. Unlike many other plants that gain nutrients from the soil, they seem to have another approach to the nutrients they need for survival and growth. 

Led by professor Sharon Doty, the plant microbiology lab at the School of Environmental and Forest Sciences has come up with an explanation on how cottonwood thrives in a seemingly harsh environment. 

Plants need three essential elements to live and grow: nitrogen, phosphorus, and potassium. Most plants can directly get nitrogen from the air and soil and use them. 

The team’s data and study suggest that the nutrients that cottonwood utilizes come from microbes — the tiny bacteria — living inside of the plant.

As the team’s research shows, when there is a lack of nitrogen sources, plants rely on their bacteria neighbors which can convert nitrogen from the air into a form that can be used. In exchange, plants provide sugar to bacteria as food which creates a symbiotic relationship that benefits both.

According to Doty, this symbiotic relationship, more common than initially thought, is especially important for riverside plants such as poplar and willow growing in Washington state. Since the river system is pure and clean, these plants receive little fertilizers from the water and really need nutrients from the work of microbiomes. 

“Human microbiomes are good for our health,” Doty said. “Plant microbiomes are even more important for them because they can’t move. They are stuck into whatever nutrients and conditions they are landed in. Microbes help them to be healthier, grow better, and deal with those conditions.” 

Most plants including the black cottonwood don’t have nodules. The team discovered that the bacteria are in the branches. They anticipated that bacteria might behave and communicate with plants differently when environmental conditions change. 

The team showed that besides nitrogen, microbes also produce phosphorus to support plant growth. 

Nitrogen and phosphorus fertilizer runoffs have caused nutrient pollution which creates harmful algal bloom and other damage to the water body, for example, in the Gulf of Mexico and the Chesapeake Bay. By studying the natural nitrogen and phosphorus fixation of plants, the use of agricultural fertilizers can be reduced.

“[Some] maize that grows in Mexico doesn’t need fertilizers because their natural symbiosis with bacteria,” Doty said. “We can use less chemical fertilizers if we learn from how plants in natural conditions grow.” 

Doty has developed a bioinoculant also known as probiotics to help crops to generate nitrogen. The commercial product called Tiros is released this year and available in the United Kingdom. The inoculant serves as liquid seed coat that grow with and migrates into crops to provide nitrogen in an environmental-healthier way.

As Doty explained, some bacteria in the plants can fight off pathogens. When bacteria are transferred from wild plants to cultivated plants, they increase the drought tolerance of cultivated plants. This is increasingly important as climate change causes frequent drought and higher temperatures. 

Reach reporter Sunny Wang at Twitter: @sunnyqwang64

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