The Optimal Concentration of Exogenous Carbon Monoxide Tolerated by Alfalfa

Nitrogen is a key element in living organisms as it is a building block for DNA and protein, but its most abundant form is atmospheric nitrogen (N2), which is unusable by most organisms. To make use of N2, plants known as legumes partake in a mutualistic interaction with bacteria known as rhizobia that convert N2 into usable forms of nitrogen such as nitrate and ammonia in exchange for food and shelter from the plants within root nodules. This interaction is a possible sustainable alternative to the Haber-Bosch process, which utilizes immense amounts of energy to convert N2. Rhizobia’s viability as a sustainable alternative is limited by the presence of carbon monoxide (CO). Within free-living soil bacteria, CO has been shown to inhibit the nitrogenase enzyme responsible for rhizobia’s ability to convert N2. However, CO has also been shown to induce secondary roots, which are rhizobia’s point of entry into the plant to start the mutualistic interaction. With both positive and negative effects for rhizobia, the implications of increasing CO in a legume’s environment were studied, particularly if secondary root growth is induced and whether increased CO would affect rhizobia’s ability to convert N2. For this project, two sets of legumes known as alfalfa were grown for one week before being placed in two separate airtight glass containers in which one received high concentrations of CO gas whereas the other received none as a control. After one week of exposure, plants were removed from the glass containers and observed for noticeable differences. The root and shoot length of each plant was also recorded. The results showed that plants in CO performed worse as they had wilted and had shorter root and shoot growth. Future experiments will lower the CO concentration enough to have no visible effect on the plants. This is when the secondary roots will be examined and the inoculation of these roots with rhizobia will be conducted. Plants in CO are expected to have increased secondary root growth and subsequently increased rhizobia productivity via increased root nodules