Impact of temperature on the relationship between respiration and nitrogen concentration in roots:: an analysis of scaling relationships, Q10 values and thermal acclimation ratios

The impact of nitrogen (N) supply on the temperature response of root respiratory O-2 uptake (R) was assessed in several herbaceous species grown in solution culture. Warm-grown (25 : 20 degrees C, day:night) plants differing in root N concentration were shifted to 13 : 8 degrees C for 7 d to cold-acclimate. Log-log plots of root R vs root N concentration both showed that R increased with increasing tissue N concentration, irrespective of the growth temperature. Although the regression slopes of the log-log plots did not differ between the warm-grown and cold-acclimated plants, cold-acclimated plants did exhibit a higher y-axis intercept than their warm-grown counterparts. This suggests that cold acclimation of root R is not entirely dependent on cold-induced increases in tissue N concentration and that scaling relationships (i.e. regression equations fitted to the log-log plots) between root R and N concentration are not fixed. No systematic differences were found in the short-term Quo (proportional change in R per 10 degrees C change in temperature), or degree of cold acclimation (as measured by the proportional difference between warm- and cold-acclimated roots) among roots differing in root N concentration. The temperature response of root R is therefore insensitive to tissue N concentration. The insensitivity of Q(10) values and acclimation to tissue N concentration raises the possibility that root R and its temperature sensitivity can be predicted for a range of N supply scenarios.