Different Harvesting Events’ Effects on Nitrogenase Activity in Alfalfa Root Nodules
Remy C Sutherland
Committee: Steve Cartier, Alisa Hove, Mark Brenner
Defoliation and harvest of shoots have been shown to negatively affect nitrogenase activity in the root nodules of Medicago sativa plants. When shoots are completely removed it can take more than 20 days for nitrogen fixation rates to return to those prior to harvest. In this experiment different types of harvest were examined in order to observe the variance in the resulting nitrogenase activity. Plants were grown in greenhouse in isolated pots. Four different harvesting events were examined: an unharvested control, in which shoots were not affected, a “graze” treatment, in which leaves were denuded from stalks, a “mow” method, in which shoots were removed at half-height, and a complete harvest control, in which shoots were cut at base. Nitrogenase activity following the harvesting events was analyzed by acetylene reduction assay. The results indicated that the “graze” treatment showed significantly greater nitrogenase activity than the “mow” method. These results perhaps suggest that negative response to shoot harvest in nitrogenase activity is not due to decreases in photosynthesis directly but rather the redistribution of plant carbon resources away from root nodules following shoot damage.