Effect of Temperature on Nitrogen Fixation Rates in Seven Clover Cultivars

Seven white clover (Trifolium repens L) cultivars were grown in growth rooms at S different temperatures between S and 2S°C. Plant growth and nitrogenase activity (acetylene reduction) were measured. There were significant effects of temperature on total plant ay matter (DM) accumulation and nitrogenase activity. Temperature x cultivar interactions were significant for DM accumulation, nitrogenase activity per pot and nitrogenase activity/g DM. There was a strong correlation between DM increment/°C rise in temperature over the range 10-20°C, and nitrogenase activity/g DM. Three cultivars had maximum nitrogenase activity/g plant DM at 200C and 4 cultivars peaked at 15° C. These differences between cultivars may be related to the rate of change in DM accumulation and hence demand for nitrogen interacting with the supply of mineral nitrogen from the soil. Cultivars with mediterranean parentage exhibiting cool season growth had peak nitrogenase activity per g DM at a lower temperature than cultivars from colder climates.