Plants can modify their environment

In additon to responding to enviromental stimuli such as light and gravity, plants can also modify their environment. For example, turgor pressure in plant roots can crack rocks and damage man-made materials like concrete and asphalt. Plant roots also secrete a variety of organic compuunds that can interact with their environment, including acids that can help solubilize minerals and other materials.

Acid efflux from Arabidopsis roots

This movie shows Arabidopsis seedlings growing on an agar growth medium containing a pH indicator that changes from purple to yellow in response to acidification. The seedlings were placed onto the agar surface immediately before filming began. Acidification of the agar caused by acid efflux from the roots is readily detected by the color change of the agar as the roots elongate. The acidification is most likely due to secretion of malate from the roots. In a natural setting, acidification of the soil water can help solubilize iron into a form that plants can take up and use for growth. The acidification of soil by plants can also contribute the the production of soil in rocky environments by chemically dissolving minerals.