The minirhizotron camera

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A large fraction of plant-environment interactions occur belowground, in the rhizosphere. (The rhizosphere includes plant roots and the portion of the soil and of soil microbes that are influenced by roots.) Unfortunately, rhizosphere processes are nearly invisible from the surface, and excavating roots for examination or measurement certainly alters the physiological processes of interest. The minirhizotron camera represents an attempt to overcome these hurdles. A transparent plastic tube is permanently buried in the plant's root system. Then, a special digital camera can be periodically brought to the site and lowered into the tube. Pictures taken through the wall of the tube monitor the growth of new roots over time. By comparing the lengths of roots in digital images taken at different times, researchers can obtain a quantitative estimate of a plant's allocation to root biomass over the corresponding time period.

Minirhizotron technology

The main technical component of this project is a state-of-the-art minirhizotron imaging system, which enables us to obtain high-quality digital images of natural phenomena occurring belowground continuously and non-destructively. The minirhizotron camera, built by the Bartz Technology Corporation, is a specialized digital camera that can be lowered into the tube to capture images of the tube-soil interface.

Yes, that 6 foot-long device is the camera! Although rather unwieldy for normal applications, its shape is perfect for capturing underground images. At the top of the device is a ratcheting mechanism, built by the University of California's machine shop, that permits the camera window to be raised or lowered to the desired depth.

This is our field setup. Digital output from the camera is converted to analog in the blue box, which also controls the brightness, focus, and zoom mechanisms. The signal is then send via S-video to the computer's image grabber, where they are saved as bitmap images. Notice the tube lying near the camera; although this particular tube is used to protect the camera chassis, it is a facsimile of the tubes which are buried in the soil.

The camera in use! Santa Cruz graduate Michael Lebeck examines the output of the minirhizotron camera. The Fremontodendron californicum at the right is one of the denizens of the UC Arboretum's California Native Plants area.