Microbes help unlock phosphorus for plant growth

Poplar trees along the Snoqualmie River — Poplar trees such as these along the Snoqualmie River able to thrive on rocky riverbanks, despite low availability of nutrients like phosphorus in their natural habitat. Microbes help these trees capture and use the nutrients they need for growth.

Phosphorus is a necessary nutrient for plants to grow. But when it’s applied to plants as part of a chemical fertilizer, phosphorus can react strongly with minerals in the soil, forming complexes with iron, aluminum and calcium. This locks up the phosphorus, preventing plants from being able to access this crucial nutrient.

To overcome this, farmers often apply an excess of chemical fertilizers to agricultural crops, leading to phosphorus buildup in soils. The application of these fertilizers, which contain chemicals other than just phosphorus, also leads to harmful agricultural runoff that can pollute nearby aquatic ecosystems.

Now a research team led by the University of Washington and Pacific Northwest National Laboratory has shown that microbes taken from trees growing beside pristine mountain-fed streams in Western Washington could make phosphorus trapped in soils more accessible to agricultural crops. The findings were published in October in the journal Frontiers in Plant Science.

Endophytes, which are bacteria or fungi that live inside a plant for at least some of their lifecycle, can be thought of as “probiotics” for plants, said senior author Sharon Doty, a professor in the UW School of Environmental and Forest Sciences. Doty’s lab has shown in previous studies that microbes can help plants survive and even thrive in nutrient-poor environments — and help clean up pollutants.

In this new study, Doty and collaborators found that endophytic microbes isolated from wild-growing plants helped unlock valuable phosphorus from the environment, breaking apart the chemical complexes that had rendered the phosphorus unavailable to plants.

“We’re harnessing a natural plant-microbe partnership,” Doty said. “This can be a tool to advance agriculture because it’s providing this essential nutrient without damaging the environment.”

While previous work in Doty’s lab demonstrated that endophytes can supply nitrogen obtained from the air to plants, such direct evidence of plants using phosphorus dissolved by endophytes was previously unavailable.