EFFECT OF ROOT AND SHOOT MERISTEM TEMPERATURE ON SHOOT TO ROOT DRY-MATTER PARTITIONING AND THE INTERNAL CONCENTRATIONS OF NITROGEN AND CARBOHYDRATES IN MAIZE AND WHEAT

Maize (Zea mays L.) and spring wheat (Triticum aestivum L.) were grown in nutrient solution at uniformly high air temperature (20 °C), but different root zone temperatures (RZT 20, 16, 12 °C). To manipulate the ratio of shoot activity to root activity, the plants were grown with their shoot base including the apical meristem either above (i, e. at 20 °C) or within the nutrient solution (i.e. at 20, 16 or 12 °C). In wheat, the ratio of shoot: root dry matter partitioning decreased at low RZT, whereas the opposite was true for maize. In both species, dry matter partitioning to the shoot was one-sidedly increased when the shoot base temperature, and thus shoot activity, were increased at low RZT. The concentrations of non-structural carbohydrates (NSC) in the shoots and roots were higher at low in comparison to high RZT in both species, irrespective of the shoot base temperature. The concentrations of nitrogen (N) in the shoot and root fresh matter also increased at low RZT with the exception of maize grown at 12 °C RZT and 20 °C shoot base temperature. The ratio of NSC:N was increased in both species at low RZT. However this ratio was negatively correlated with the ratio of shoot: root dry matter partitioning in wheat, but positively correlated in maize. It is suggested that dry matter partitioning between shoot and roots at low RZT is not causally related to the internal nitrogen or carbohydrate status of the plants. Furthermore, balanced activity between shoot and roots is maintained by adaptations in specific shoot and root activity, rather than by an altered ratio of biomass allocation between shoot and roots. © 1994 Annals of Botany Company.