Aeroponic system for control of root-zone atmosphere

Control of rhizospheric gases can be critical to research. Culturing plants with roots in liquid is a common component of protocols described previously for controlling the root-zone atmosphere, and liquid culture is routine during assays of symbiotic N2 fixation. However, spurious data may result from gases becoming trapped within the boundary layer of solution-cultured roots and nodules. Aeroponics is a viable alternative to other soilless culture systems for maintaining plants with a controlled root-zone atmosphere. We have designed an aeroponic gas-delivery system that allows statistical treatment of individual plants as discrete experimental units when root-zone-targeted treatments are imposed. Roots of intact plants were held in closed 1-L canning jars, with one plant per jar and the stem emerging from a hole drilled in the jar lid. Extra-fine fog nozzles controlled by a programmable timer sprayed roots periodically with nutrient solution. Gases were mixed and delivered to jars at a prescribed rate by using a system of capillary tubes. During a study of O2 effects on formation of root nodules, 100% survival of plants and profuse nodulation resulted after 4 weeks. The pO2 within each jar remained within ±1.0% of its prescribed value, and pre-and post-experimental O2 measurements within individual jars did not differ (P < 0.0001). The system is easy to construct with inexpensive materials, has many applications for rhizosphere biology, and is unique among systems used previously.