Downy Brome Study Shows Weeds Alter Soil

Plant able to increase nutrients it needs then strip those from soil, enhancing its growth, starving other plants.

Published on: Sep 25, 2013

Have you ever been convinced that weeds, especially invasive ones, have an advantage of the desirable crops you are trying to grow?

Now comes scientific evidence that invasive species do indeed have the ability to change the soil so they can gobble up more than their share of soil nutrients and grow faster and stronger.

In an article published in the current issue of Invasive plant Science and Management magazine, the authors undertook a case study of the invasive plant, downy brome, also known as cheatgrass. Cheat is one of the most problematic weeds in North America.

In their experiment, the tested a hypothesis that soil already infested with downy brome would act as a better growth medium for the weed than other soils. They wanted to determine if the weed alters soil to boost its growth potential and maybe even increase its invasiveness.

Authors of an Invasive Plant Science and Management magazine article on downy brome, or cheatgrass, found that after one season, downy brome grown in invaded soil had 250% more biomass and almost twice the root mass of plants grown in the non-invaded soil.
Authors of an Invasive Plant Science and Management magazine article on downy brome, or cheatgrass, found that after one season, downy brome grown in invaded soil had 250% more biomass and almost twice the root mass of plants grown in the non-invaded soil.

Findings on downy brome

The authors compared the plant–soil relationships and growth of downy brome. They grew it in soil from the northern Great Basin of California that had and had not already been invaded by the plant. They then sampled and compared the root mass and soil at three depths and the plant biomass.

After one season, downy brome grown in invaded soil had 250% more biomass and almost twice the root mass of plants grown in the non-invaded soil. By the second growing season, biomass in the invaded soil was still almost double the amount in the non-invaded soil, while root mass had decreased and was similar between invaded and non-invaded soils.

The authors also found that downy brome became more competitive when it received more nutrients, particularly nitrogen, phosphorus, and manganese. They found that the plant increased these nutrients in the soil for its own benefit.

The authors concluded that downy brome actively increases its growth potential. They speculated that the plant can take over areas filled with supposedly resistant plants by increasing and then exhausting the soil nutrients, causing downy brome to thrive and native plants to struggle. Further studies are needed to determine if results are similar for other areas and other plants.