DISTINCT INFLUENCE OF ROOT AND SHOOT TEMPERATURE ON NITROGEN-FIXATION BY WHITE CLOVER

White clover (Trifolium repens L.) was grown in controlled environments to determine the distinct effects of root and shoot temperature on the accumulation of total and fixed (15 N dilution) nitrogen at two levels of nitrate (1·0 and 7·5 mM). Nitrogen fixation (BNF) showed a positive response to higher shoot temperature (23 vs. 13 °C day temperature), irrespective of whether or not root temperature was increased in parallel. Low root temperature (5 °C) caused a marked reduction in the accumulation of total nitrogen at both nitrate levels, and led to a lower proportion of N derived from BNF. The temperature response of BNF was attributed for the major part to an adaptation to the demand for fixed N. It is therefore concluded that BNF is not primarily responsible for the reduced clover growth at low temperatures. © 1990 Annals of Botany Company.